Ballistic coefficient: What is it? Part 1

by Tom Gaylord, a.k.a. B.B. Pelletier

I’m still out of state, caring for my sister who had several operations last week. This report is a 2-parter that generated a lot of interest in 2014 and 2015.

This report addresses:

• Definition of ballistic coefficient (BC).
• How are BCs determined?
• Bullets and pellets have an additional factor.
• BCs are not constants.
• BC is an expression of how much velocity is lost in flight.
• How to cheat the BC numbers.

If ever there was an elephant in a room full of airgunners — this is it! Ballistic coefficient. It seems like everybody talks about it, but what does it mean?

Definition
Ballistic coefficient (BC) is the measure of a ballistic projectile’s ability to overcome air resistance in flight. It’s stated as a decimal fraction smaller than one. When diabolo pellets are discussed, the BCs are very low numbers in the 0.010 to 0.045 range because diabolos are purposely designed to slow down in the air. Their wasp waists, flared skirts and hollow tails all contribute to very high drag that rapidly slows them down — much like a badminton birdie. Lead bullets, in contrast, have BCs between 0.150 and 0.450.

lead bullet comparison
The long lead bullet on the right has a higher BC than the short fat bullet on the left. When they’re both fired at the same speed, the bullet on the right will not slow down as fast as the bullet on the left.

How is it determined?
To physicists, BC is a function of mass, diameter and drag coefficient. This set of parameters seems simple until you examine it closer. A round ball made of pure lead should always weigh the same, as long as the diameter is the same. But a diabolo pellet is conical in shape and can be much longer than the diameter of a round ball of the same caliber. Depending on how the pellet is designed (i.e., how hollow or solid it is), it can also be much heavier because it contains more lead than the ball.

Bullets and pellets have an additional factor
For pellets and bullets, there’s an additional factor to consider — shape. For that reason, there’s a separate definition for the ballistic coefficient of bullets that takes into account the sectional density dictated by the form or shape of the projectile.

I’m purposely avoiding any discussion of BC that includes formulas. Stated simply, a pellet or bullet with a high BC (a large number) will continue to fly much longer than a pellet or bullet with a low BC: A high BC means the pellet will fly farther!

BCs are not constants
Okay, you say, that’s exactly what I want! Give me only those pellets that have high BC numbers.

Not so fast! However, as the velocity of a projectile changes, so does the projectile’s BC. BCs are not constants. There’s no such thing as a pellet with a BC of 0.035. But there are plenty of pellets that will achieve a BC of 0.035 at a certain velocity. When a BC is given, it means something only if the velocity at which that BC was obtained is given with it.

This could get confusing, couldn’t it? Yes, it can be confusing if you try to force numbers onto pellets when they don’t apply. But when you understand that the BC of a pellet is actually a sliding scale, you begin to understand the ballistics of airguns.

BC chart
The ballistic coefficient of a single pellet can change this much with velocity changes.

Who cares?
So what? Who cares about all this sliding scale stuff? You do, and I’ll tell you why. Let’s say there’s a pellet with a BC of 0.042. Wow! That’s a very high number for a diabolo pellet! I’m gonna get me some of them!

Hold on, pardner. What if I told you that pellet was the JSB Exact King in .25 caliber, and that it has that BC only when it’s moving at 1,250 f.p.s.?

BUMMER! You don’t own an air rifle that will propel a .25-caliber JSB exact King up to 1,250 f.p.s. In fact, almost no one does. Therefore, the fact that the pellet has that high a BC at that particular velocity does nobody any good.

If you think about this for a moment, it’ll dawn on you that a particular BC relates to the airgun being used, almost as much as it does to the pellet. Your rifle may only be able to launch the .25-caliber JSB Exact King out the muzzle at 760 f.p.s. At that speed, the BC of the pellet might be 0.033 (these are not the actual numbers, but they’re very close). By the time the pellet has gone 25 yards from the rifle, its velocity has dropped to 635 f.p.s. and the BC is down to 0.030.

BC is an expression of how much velocity a pellet loses in flight
We know that pellets slow down rapidly after leaving the muzzle. Pellets with higher BCs retain their velocities longer than pellets with lower BCs. A pellet with a BC of 0.040 at 900 f.p.s is going to go farther than a pellet with a BC of 0.020 at 900 f.p.s. Both pellets will change their BCs in flight, but the pellet that has the higher BC will never drop below the pellet with the lower BC at the same distance.

Range equals velocity — how to cheat!
I think most shooters know that the velocity of a pellet starts to decrease the moment it leaves the muzzle of the gun. And the BC is a measure of how much velocity a pellet loses in flight. If I want to get higher BCs, I can get them by measuring velocity closer to the muzzle, where the velocity loss will be less than when the pellet has traveled farther. For example, if I were to measure the BC of a pellet by comparing its muzzle velocity to the velocity at 10 meters, the BC would be higher than if I were to compare the muzzle velocity of the same pellet to its velocity at 25 meters.

I can cheat the numbers by measuring velocity loss at a very close range. The pellet that gives me a BC of 0.033 at 25 meters might give me a BC of 0.040 if I measure the velocity loss at just 10 meters. Standards are needed to make sense of these numbers.

Sometimes, people don’t WANT to make sense! Sometimes, people just want to report a high number because the folks reading the numbers think they mean something good.

In that respect, the discussion of BC among those who don’t really understand what it means is not unlike the discussion of muzzle velocity among new airgunners. Some airgun manufacturers proudly advertise their air rifles can achieve 1,300-1,600 f.p.s. People who are new to airgunning think that’s a good thing. We know it isn’t. We know that to achieve such high velocities requires the use of trick pellets no one would ever use in the field because they’re hopelessly inaccurate.

Next time
There’s a whole lot more to this topic. For example, as the velocity of diabolo pellets rises up into the transsonic region, the BC often starts dropping, again. At supersonic speeds, the pellets are very negatively affected.

We’ll also look at the pellet’s shape, for shape is what makes the BC of bullets and pellets different from other BC numbers. Technically, it’s called “form,” but the term shape is clear enough for everyone to understand.

65 thoughts on “Ballistic coefficient: What is it? Part 1

  1. Yes, this is a massive can of worms, I discovered some years ago that the H&N FTT’s were retaining 20% more energy at 30 yards than the JSB Exacts were out of my HW77, despite having a 5% lower muzzle energy.
    The groups I was getting with the JSB’s over that distance was 15% smaller but the H&N was still acceptable at just over half inch, and became my go to hunting pellet despite giving me a marginally inferior muzzle energy and group size!.
    As BB says, your mileage may vary with the velocity your rifle is capable of, it’s never a constant, so published drag coefficients are almost meaningless without a velocity graph.
    There’s a great YouTube of a young British lady testing this with a brace of HW100:’s out there you can view, I’ve never revisited my testing having shot my Chrony to an early grave at 50 yards 🙂


  2. Hi BB,

    Hope your Sis is OK. Recovery sucks anytime be it must be almost unbearable for folks that don’t have friend or family member to help out. My wife is taking care of me today after a lithotripsy procedure to bust up a large stone in my kidney. Could I have taken care of myself ? Probably, but its still nice to just be responsible for getting well while she takes care of everything else for a day or two. you’re a good brother.

    Will you be reposting the other chapters of these “Blasts From The Past” or should I just look them up in their original form ? Do we as airgunners really need to concern ourselves with BC beyond, “Wadcutters loose velocity quickly and domed pellets are generally faster and more accurate at range and pointed pellets are hard to stabilize” ?


    • Halfstep,

      Many of us will unconsciously deal with BC when we go out and try various pellets at various ranges to determine the best performing pellet for that particular air rifle. We usually find that a particular pellet does well at one range, but not so well at another. What most of us end up doing is as Dom pointed out above, we end up compromising and choosing one that gives us the best overall performance unless we are looking for very specific performance at a very specific range such as ten meter competition.



      • Hi B.B
        My prayers for your sister Sir, that she would quickly recover & completely. It’s really great of you to rush to her when in need. What a wonderful brother, despite having just had surgery yourself. You are a good man Sir, with qualities rare in today’s world. Take good care of your eye till it’s healed fully. God bless
        Errol


    • Halfstep,

      I had lithotripsy last year. It took 5 hospital visits and two trips to the emergency room after the operation to get me right. When the stone breaks up but is still in pieces too big to pass is when the trouble comes. You take care!

      B.B.


  3. BB,

    We hope your sister is doing better. Do try to relax and not concern yourself with us.

    This is one of those subjects that I find very interesting, however it has not been until recently that I had the equipment to even begin to explore such. What I lack now is the time to intentionally delve into this myself, though I do such unconsciously when I experiment with various pellets at various ranges to determine which pellet provides me with the best overall performance with a particular air rifle.

    When I start to consider doing this type of experimentation I come to the realization that it has already been done by others, therefore would be a tremendous waste of my time. I then decide to just go out and shoot and have fun. Do not get me wrong. I do indeed appreciate all the effort others have put into this as their efforts have made my shooting more enjoyable. I also enjoy reading about such topics in this blog and truly appreciate the fact that you are not desiring to go too deeply into this so as to not give everyone headaches trying to grasp the various formulas, etc. and bore us silly. One day I hope to have the time for these things, but for now I will just have to shoot. 😉


  4. B.B.,

    Best wishes for your sister. A quick prayer and a nod and a wink to the “Big Guy” for ya both.

    Good article/topic,.. one that could be delved into for eternity. First thought is to run to the “bullet shaped” pellets,.. but I think that falls apart with the difference in muzzle velocity and rifling twist rate. Big bores on other hand do shoot bullet shaped pellets, or actual lead bullets, yet at relatively low velocities. I suppose that begs the question of what a .50 Diabolo shaped pellet may do. Do they even exist? Has it been tried? If so, how did they do in comparison? If they did worse, then why is a bullet shaped projectile better for a big bore, while a Diabolo shaped pellet is almost a prerequisite for a small caliber air rifle?

    (None of the above is meant to be answered by you B.B.). Just food for thought for the rest of the “crew” here on the blog. You know that when you bring up a topic like this that we can keep ourselves occupied for days on end! 😉

    Chris


  5. B.B.,

    Thanks for the simple explanation. The graphics helped. A question though; does Chairgunner calculate the BC, or how do we get a number to plug in?

    My prayers for your sister’s full and speedy recovery.

    Jim M.



    • Jim,

      I have just started working with Chairgun and have been using it to determine the optimum range to zero the rifle for the kill-zone I prefer.

      When you select a pellet and specify your velocity Chairgun will draw the trajectory curve so it must be using a BC to do so.

      I printed out the compensation tables for one of my rifles and will be checking the table against targets to see if they agree. I’ll post my findings on the blog.

      The pellet database in Chairgun looks to be customizable (haven’t explored that yet) so if theory and practice don’t match I will likely be defining a new pellet from the data I get from testing.

      Think the Chairgun program is worth spending some time to learn.

      Fun stuff, all I need is some decent weather to get some shooting done – had to scrape 1/4 inch of ice off of the car this morning 🙁

      Have a great day!

      Hank


      • Hank,

        I did a test awhile back shooting at 5 yard increments out to about 40 yds and compared to chairgun pro. My results were good but I think could have been better I was shooting across a swale so the middle distances were shooting down hill quite a bit. I was planning to repeat the tests again with the targets along the horizontal axis but still have not.

        I will be interested in your results.

        Don


        • Don,

          Nice test, Shooting id the way to go. Chairgun is great and gets you in the ballpark and what to expect. I have been very happy with it.

          As for up or down, both have an effect of less gravity influence and thus requires less holdover. I think that this might play more into the scenario of shooting down a steep hill or up a tree,… both situations that might be encountered more in hunting, not target shooting.


        • Don,

          I was pretty well planning the same sort of 5 yard increment test though I’d like to try longer ranges just to see what I can do way out there 🙂

          Hadn’t thought about the angle – good point. I’ll level the rifle on the rest and use it as a transit to set up the targets. I can use a step-ladder to mount the targets at the correct height.

          Weather is supposed to improve (wind, rain, snow and ice in MAY is not normal) so I am looking forward to getting some quality trigger time.

          Cheers!
          Hank


        • Don
          I do something similar with my guns. Only I go every 10 yards out to a hundred yards. It does help. But​ haven’t compared it to Chairgun on the Maximus or my.25 Marauder. I guess I should run the numbers on Chairgun just to see how it compares.


      • Hank,

        I think Gunfun1 would be the one to talk to on Chairgun. On BC, I believe you can put in the (exact) data if you know it. As in, put your chrony downrange and compare that to a near muzzle velocity. But, as B.B. mentioned, that BC is dependent on where that downrange data was taken. Fun,… ehh? 😉


    • Jim

      The version I have actually even has a fair sized list of popular pellets that you can pick from a dropdown menu. Then you supply the muzzle velocity and other data and it gives the yardages (near and far )for scope zero.( along with a zillion other calculations )


    • Jim M
      Chairgun has a drop down that you can pick a pellet from. It will give that pellets CD. But you can change the different things in the program that you like including that predetermined CD of that pellet that Chairgun has stored in it’s memory.

      So basically you can input different values and see on the graph how it changes the pellets flight path in relation to what your​ scope see’s at different distances.

      You can even input certian types of scopes and get a scope view with the different holds needed for different distances.

      But remember Chairgun is a reference tool. Actual shooting at different distances will give your true impact points for your hold. But all in all I do like messing with Chairgun and changing the combination of variables around.

      I guess the Hawke scope website still offers the free download for different applications???


  6. “I’m still out of state, caring for my sister who had several operations last week.”

    B.B., that’s way cool of you, but hardly surprising; I pray all goes well with her.


  7. “I’m still out of state, caring for my sister who had several operations last week.”

    B.B., that’s way cool of you, but hardly surprising; I pray all goes well with her.


  8. I have seen Ross on American airgunner tv use the different bc’s to pick a pellet for the gun he is showing. He has a chrony at the muzzel and at 25 yards, the pellet that retains the most energy is the one that “this gun likes”. How credible this test is for picking an accurate pellet, I have much doubt.


  9. Off-topic, but I’ve been studying the Air Venturi Power Booster. It’s a good move in the right direction, by which I mean a truly affordable HPA compressor. At first I thought it was THE one, until I discovered the hidden cost, a shop compressor with more power than the typical one everybody has in his garage. A quick look at Home Depot’s site informed me that a compressor barely adequate for that application would be $300.

    The latest Shoebox plus shop compressor is about the same as the all-in-one Air Venturi compressor at $1300, and the Air Venturi Booster plus an adequate shop compressor is about $1000.

    So things are getting closer each year. Maybe in a couple years a Maximus and HPA compressor bundle at P.A. will run $999.99 (“Excluded from coupons”).

    Michael



      • B.B.,

        I hope that shop compressor you bought to use with the Booster is not oil-lubricated. I’m no engineer or mechanic, but Gunfun1 has warned me oil might still pass through and make one’s air gun unsafe if he fills it with the Air Venturi Booster. Also, is your all-in-one Air Venturi compressor oil-less? If not, you should know it could be unsafe and proceed with caution.

        Michael



          • B.B.,

            Thanks for chiming in.

            My little $100 shop compressor is oil-lubricated, and the handful of times I’ve used it, it worked like a champ, even doing jobs such as blowing water out of looooong hoses and water pipe systems during winterizations. The first time I did it I didn’t expect such a powerful result and the water shot out of the other end hard and far.

            I will check out its specs later today. It might actually just barely meet the minimum requirements of the Air Venturi Booster. If it does, that would go a long way towards making me desire the Booster.

            I guess I got a bit freaked out at the idea of oil in an HPA reservoir going BOOM.

            Michael


            • Michael,

              GF1 is correct in saying that vaporized oil does get into the compressed air from an oil-type compressor. But the Power Booster is in line between the compressor and the gun or tank, and I imagine it takes care of that.

              I am starting the Power Booster report tomorrow.

              B.B.


    • Michael,

      One of the shop compressors that is listed as large enough for the booster is the Harbor Freight 21 gal, 125psi compressor at about $170. They run it on sale all the time for about $140. They also recommend another HF compressor that lists for $140 and may be cheaper on sale.


      • Halfstep,

        I brought up the Booster as a sign of good times being just around the corner, mighty good to see, not a criticism. I still feel that way, but it’s not likely to lure me into a purchase anytime soon. Two or three years, I figure, although the PCP industry has been advancing at a very fast pace in the last year, so who knows?

        According to the description for the Power Booster and Tyler’s answers to questions about it, one of the approved compressors, the Cal. Air Tools one, is borderline too powerful/high output for the Booster and three of the others are borderline not high enough volume. Two of the lesser volume ones are very inexpensive, I’ll admit.

        Frankly, to me there is a kind of “farting around” aspect to the Shoebox and Booster. Were I to buy something to fill PCPs with it would be something like the impressive Air Venturi all-in-one, but not at $1300. I think I might sell my two (basically brand new) four year old Marauders over this summer and wait for a compressor comparable to the Air Venturi with a price of $700 or so. Then I can buy one and a Maximus or other high-quality $300 PCP of the future and not shell out more than my $1000 max figure.

        Originally, in 2012 or 2013, I banked on spending $400 for a Marauder and $300-$350 for a Benjamin Turbo Aire pump, an outlay of $700-$750 total. I have since relented quite a bit, adjusting the total acceptable expenditure upward at least one third, a significant percentage. If that seems unrealistic, consider that for almost exactly $1000 one can buy a brand new TX200 and twenty-five thousand (!) Crosman Premier Lights (in the box).

        Of course, I’d take a bath on the Marauders, but to me it’s really about the principle of the thing. I’ve considered selling off or trading off every airgun I own with “Crosman” or “Benjamin” on it simply out of principle. What’s kept me back once or twice are my two CK92 pistols. They, my Umarex/S&W 586-8, and my S&W 78G are still the best CO2 air guns I own.

        Michael


    • Michael
      Here is something I think is being missed.

      Shoe box still offers a base model that now costs around $650.

      Pyramyd AIr sells only the most expensive model Shoe box.

      You could get the base model Shoe box and a Home Depot small $90 shop compressor for a bit more than what they want for just the Air Venturi booster pump.

      Trust me the base model Shoe box is what I have used with a small Husky shop compressor from Home Depot for about 5-1/2 years now. It works is all I can say. And it is misleading that the high cost Shoe box is the only one available from that company that makes them.


      • Gunfun1,

        For me any Shoebox model is out of the question. I have a perfectly fine light duty, small shop compressor with few hours on it, but it is oil lubricated. I wouldn’t be able to stomach buying a second one just because the Shoebox is limited.

        Michael


        • Michael
          Don’t know if I’m getting what you said right.

          But it sounds like you said you wouldn’t get a Shoe box because it’s limited to a oil-less compressor.

          If that’s what you mean then I think your idea should apply to the Air Venturi booster pump and the big compressor they have. Why would they even think about introducing petroleum based oil into a pumping device that fills a high pressure air resivoir.

          Everything I been taught says that’s a bad idea.

          And here I go again. Well???


          • Gunfun1,

            Two of the Booster-approved shop compressors are oil lubed, and the description and questions/answers sections for the booster clearly states that oil is prevented from entering the reservoir by a filter. Same for the Air Venturi all-in-one compressor.

            Michael


            • Michael
              I think you mean the the Air Venturi HPA compressor’s. Not Air Venturi shop compressor’s. Shop compressor’s is what you can buy at Home Depot and such. Low pressure basically. Like is what is needed for the first stage feed pressure for a Shoe box or Air Venturi booster pump.

              And yes even though Air Venturi says that no oil is introduced​ into the pumps I will have to say I disagree. We have those types of systems at work too. And believe me over time components fail and oil can pass by. So hopefully Air Venturi has came up with a maintenance routine that should be followed for their pumps.

              Not to say anything bad would happen. But that would be a heck of big grenade or bomb if the petroleum was introduced to the high pressure cylinders in one way or another. You never know ya know.


              • Gunfun, I did not mention Air Venturi shop compressors. Do they even make shop compressors?

                No, I’ll repeat what I wrote above, explaining that while the Shoebox is limited to oil-less shop compressors, the Air Venturi HPA compressors are not limited in that respect.

                Two of the Booster-approved shop compressors are oil lubed, and the description and questions/answers sections for the booster clearly states that oil is prevented from entering the reservoir by a filter. Same for the Air Venturi all-in-one compressor.

                Michael


                • Michael
                  Well yes you did. Here look.

                  “Michael
                  May 9, 2017 at 9:48 pm
                  Gunfun1,

                  ((Two of the Booster-approved shop compressors are oil lubed,)) and the description and questions/answers sections for the booster clearly states that oil is prevented from entering the reservoir by a filter. Same for the Air Venturi all-in-one compressor.

                  Michael”


                  • No, I did not mention that Air Venturi made shop compressors. I wrote, “Two of the Booster-approved shop compressors are oil lubed, and the description and questions/answers sections for the booster clearly states that oil is prevented from entering the reservoir by a filter. Same for the Air Venturi all-in-one compressor.”

                    What part of that says Air Venturi makes shop compressors?

                    Michael


              • Gunfun1,

                I forgot to address your concern about oil getting past the filter. Air Venturi (I presume from his use of “we” that Tyler is a rep of Air Venturi) claims many hours of heavy use without maintenance or rebuilding required. Now, they might be wrong, but if so, Pyramyd Air should stop selling them until Air Venturi rectifies the design flaw or alters their instructions to stipulate that only oil-less shop compressors drive the booster.

                Does BB know his Air Venturi compressor and the booster he has used are unsafe? Seriously. I simply trusted the ad copy.

                Michael


                • Michael
                  One thing you learn when you mess with cars or things in the machining business is you never assume anything when safety is concerned.

                  And probably the system they use on the the booster pump is ok. I don’t remember off hand what the big Air Venturi pump uses. But I will say this. When I watched the video of the Air Venturi booster pump I gasped when they showed the oil added into the system.

                  Again what I was taught is petroleum based oil is (not) suppose to be introduced into a high pressure air situation.


                  • Gunfun1,

                    Well, machinists know their stuff; I’ve always had the utmost respect for them. Besides, I barely know the difference between a crescent wrench and Liquid Wrench! For what it’s worth, I warned B.B. above that these products might be unsafe.

                    Michael


                    • Michael
                      I just don’t know.

                      All I know is it usually doesn’t work out to be very pretty after something goes boom.

                      Maybe the oil system is ok. But then again maybe t ain’t. I hate to be negative about a product. But…..


                  • Gunfun1,

                    You have hammered the final nail in the coffin for me and PCPs. Even my Hill hand pump uses a lubricant, so even that is introducing grease into the reservoir. How are these air guns even allowed on the market?

                    I imagine SCUBA and SCBA compressors somehow use no lubrication because that air is OK to BREATHE. I stopped putting Vick’s Vaporub on my chest at night when I have a cold because the petrolatum fumes should not be breathed in any quantity.

                    All of this has been quite a revelation for me.

                    Michael



                    • Michael,

                      The compressor that the local dive shop uses is oil lubed with a special (and very expensive) synthetic oil. The machine requires overhaul at regular intervals along with oil changes. It has sensors to detect it oil is contaminating the air. In 30+ years of diving, I’ve got bad air once (not in the states). Knew it as soon as I took the first breath – you can taste and smell it.

                      BTW, I got to see that compressor torn down and overhauled. You don’t want to know hat they were using for air filters.

                      The compressors that scare me are gas or diesel powered compressors for scuba. Think CO.

                      Jim


                  • Gunfun1,

                    “Well then what two booster pumps we’re you talking about? :0”

                    I’m writing about just one booster, the Air Venturi Booster. Like the Shoebox it requires a shop compressor , purchased separately, for a first stage. Unlike the Shoebox the Air Venturi Booster, so the maker claims, can have an oil-lubed shop compressor as its first stage. Furthermore, two of the five Booster-approved shop compressors with links on the Pyramyd Air site are oil-lubed.

                    Michael



  10. B.B.
    Glad you could be with your sister, best wishes to her and a complete recovery.

    These old blogs are good to reread as I forget about them and then follow the back trail and rediscover many other things I have also forgot about. You have picked some good ones.

    I had not realized that the ballistic coefficient varied so much more for a diabolo shape than a bullet at normal distances for each. I just had not thought about it much and figured it would be consistent enough for most pellets over the distance and time they normally travel. That is another reason why long range shooting with pellets is so challenging.

    I had a similar discussion with a friend about holdover when shooting up or downhill. He was telling me that as long as you used the horizontal distance it did not matter what the angle was. He read it on the internet. I finally convinced him it did. For relatively short distances with high velocity bullets like he shoots it does not make much difference. I set up targets on a hillside at about 30 degrees and about 30 yards and shot targets with my pellet gun don’t remember which one but I ended up showing him it does matter. I also got plenty of exercise that day, he was very hard to convince, even with the targets in front of him.

    Take care,
    Don


    • Don
      Yes the angle you shoot at up or down does make a difference.

      I learned that when I was like 10 years old when me and my buddies would shoot our pellet guns. We lived in the country. You should of seen us when we found out how that worked. We was happy campers when we started hitting things we shot at. 🙂


  11. Best wishes for your sister and yourself, B.B. I take it that in the graph, the ballistic coefficient is the y axis. This reminds me of a couple of incidents at my most recent range trip. I tried shooting my .357 magnum along with my .45ACP and 9mmm at 50 yards. There was no mistaking the .357 holes which were so clean that they looked like they had been made with a paper puncher. In comparison, the holes from the other guns had tears and powder stains. I also noticed a particularly large brass case on the ground, but when I read the case head stamp, it said 7 mm Remington magnum!? I can’t imagine what the big Weatherby magnums look like.

    ChrisUSA, thanks for your good wishes. The problem with my M1 situation is that I seem to be outside of the realm for research. If there was any documentation of my problem, I would have found it and sent the rifle to the appropriate export. But my rifle is the product of a single inventor who is no longer available. I’ve been wondering about the relationship between the amount of gas and the dispersion of a group. Perhaps there is some logic to it. The elevation of a bullet depends on its velocity. When it’s high, the bullet goes up, and when it’s low the bullet goes down in flight. Given this relation, it’s not hard to see how insufficient gas would decrease bullet performance and appear in the vertical dimension. There might even be confirming evidence in front of us. When a pcp loses gas pressure, it will lose accuracy and this theory predicts that the dispersion should be vertical. However, all of our tests of gas pressure focus on the variation in velocity, not group size. Besides the situations are slightly different. The pressure for a pcp will continue to go down which means the pellet’s impact should too with successive shots. If the M1 has inadequate gas, it should remain within a band of performance rather than getting progressively worse. Nevertheless, insufficient gas means fluctuation which should still take place in the vertical dimension. As to why excess guess leads to horizontal stringing…could it be that it’s because more gas is the opposite of less gas? 🙂 No idea.

    Mike, I think you’re right that the problem is not the gas system but something more fundamental. While looking over the tests from the original gunsmith, I see that the gas system easily handled both surplus and a high pressure handload without any problem. If it did that, it beggars the imagination that the system would break down with a low pressure handload using the same bullet weight and powder type that the gun was first adjusted for. Now, I’m wondering if it’s worth even having one more session of banging around the gun’s action when it is not working properly. But it probably is worth it to gather as much information about the gun as possible before sending it out, and that includes ruling out the gas system as the source of the problem. On the bright side, assuming that there is a rational cause for my jams which is not a gremlin and which is fixable, I’ll get the gun back in working condition and then be able to adjust the gas system as it was meant to be. So, I’ll come out ahead.

    On another upbeat note, I finally got a brief report from my uncle as well as pictures of his new customized Corvette C7. He’s certainly enjoying his investment. It looks like the color he has selected is a very dark maroon. The sound of the 465 horsepower is quite invigorating to him. And he is continuing to learn about the features which include a g-meter for measuring how many g’s he is pulling in a turn. I told him to be careful if he ever got up to 9 because that is where F16 pilots black out.

    Matt61


    • Matt61
      Your not going to believe this. My modified .25 Marauder starts shooting to the left as velocity gets lower. Actually that’s how I determine my low fill. I start seeing a left hand shift in my impact. And yes the pellet does start dropping also.

      I have not seen the left hand shift with other PCP guns I had​ overtime. Put I have seen the side shift in groups with Co2 guns towards the end of the cartridge fill.

      I’ll do this in reverse here if you will. I believe that when power increases of course velocity goes up. I think when velocity goes up and not talking about pcp fill pressure or Co2 cartridge fill pressure. But actual velocity of the pellet or projectile be it a air gun or firearm. I think the impact raises and also goes more to the side towards what way the rifling is in the barrel. Left hand or right hand.

      Now back the other way. Power drops and the projectiles velocity is lower. So now the impacts starts dropping and moving to the side in a opposite direction of the rifling in the barrel.

      That’s pretty much what I have seen though so far.

      Oh and I even went as far as drilling a much bigger hole in the top and bottom of the piece that goes on the end of the barrel of my .25 Marauder that centers the barrel in the shroud as well as holds the baffles in place. I did find that if I rotated that piece and made the big holes point at a different position I was able to change the amount of side movement I had as pressure and velocity decreased. I believe the big holes are at the 2:00 and 8:00 position. So that basically kept pressure relieved better at higher pressures and does not make as much difference at lower pressures. All I know is it helped. I think it’s working kind of like how a air stripper works with lower pressures that air guns make. Now air stripper on a firearm is another story. They make a lot more pressure than a air gun does for the most part. Well excluding the new big, big bore air guns. Now they are making firearm pressures I’m sure.

      From what I’m thinking though. I bet if a air stripper was put on a air gun. Especially the bigger caliber higher power pcp’s that impact could be redirected by rotating the opening of the air stripper to different positions.



  12. Matt61—–In the 25+ years that I shot in rifle matches, I never saw an M1 with the problems that you are having with your M1. Have you tried replacing your gas cylinder and operating rod and other parts with standard as issued parts? I have seen many M1,s that shot consistent 1 1/2 -2″ groups at 100 yards. These were unmodified rifles. The match conditioned ones shot even tighter groups, all with the gas system as designed by Garand. Of course there were rifles that had problems. Welded receivers, worn , rusted parts, guns assembled from surplus parts , often malfunctioned. Sometimes the fault was in the ammo. I once saw a good M1 malfunction. The shooter was using a mixture of 1906 ball and M1 and M2 ammo , Some of his rounds had WW1 dates ! But no one used these rifles and old ammo in target matches. Your rifle should be free of these defects. I wish that we lived near each other so that I could help you.——Ed


  13. G’day BB,
    Can a lead BB going through rifling have the same accuracy as a diablo pellet? Does a lead BB have a higher ballistic coefficient than a diablo?
    Those “squirrel gun” rifled muskets shot pretty accurately a long way out.
    Cheers Bob


    • Bob,

      Your question is really whether round lead balls can be accurate when shot from a rifled barrel. And we know from shooting blackpowder guns they can — to an extent. They are accurate to a limited distance. In larger calibers it’s around 100 yards, with reasonable accuracy (animal-killing) out a little farther. In BB calibers is 10-25 yards.

      B.B.


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