Wednesday, June 08, 2005

More about sighting-in: How to determine the two intersection points

By B.B. Pelletier

The following question was a comment to the June 1 post, At what range should you zero your scope?

Question:
How do you figure out what the two intersections are? Is there a formula?

Just shoot & see
No doubt, a formula could be constructed, but I do it the easy way. Simply aim at a specific point at a known distance, shoot and see where the pellet impacts relative to the aim point. That's where I came up with the distances I gave in my June 1 post.

Each pellet has a different trajectory
My distance figures in that posting were not exact. They change slightly because each type of pellet has a unique ballistic flight. If it has higher drag, it slows down faster and the trajectory is more pronounced. The figures I gave were for a domed pellet, like the Crosman Premier, which is pretty standard for field use.

If you shoot wadcutters or hollowpoints that have a sharp shoulder, such as the RWS Super-H-Point, your trajectory will be more pronounced because the pellet is less aerodynamic. The difference will be small at close range but will increase rapidly as the distance passes 30 yards. That's why wadcutters and hollowpoints are not as good for long-range shooting (unless you take the time to learn their performance characteristics well).

Twenty yards is a common zero distance
The initial point of intersection I gave in the posting (20 yards) is based on seven years of competitive experience shooting field target. I had to learn the performance of a great many pellets (all .177, but that makes little difference to what we are doing). Although there are a LOT of variables, I soon noticed that nearly every shooter had a first zero point of around 20 yards. When I tried it myself, I discovered why.

What a precision target shooter wants is the most forgiving zero possible. One where, if the yardage is not exactly what the shooter estimated, the difference in pellet impact point is very small. If you zero your gun so the first impact point is 20 yards, you'll get another 10 to 20 yards of flat trajectory and any apparent rise or fall of the pellet is less than one pellet diameter. The first intersection is at 20 yards and the second is at 30 yards (a 10-yard flat spot) with a gun shooting around 725-750 f.p.s. When you get it up to 950 f.p.s., the second point will be all the way out to 40 yards. If you go even faster, you'll have a flatter trajectory but also get blown groups and leading. It's not worth it.

You CAN stretch out the first point of intersection to 30 yards, if you like. All it takes is a scope adjustment. BUT, your flat spot will be MUCH shorter than when you were zeroed at 20 yards. It may only be 5 yards long. Zero at 40 yards for the first point, and the flat spot MAY be yards long. Get it?

What's really happening is that the pellet is dropping the moment it leaves the muzzle. You have about 30 to 40 yards to play with before the trajectory is a real downward slide. By zeroing at 20 yards, you get a nice long flat spot and can still adjust your scope or hold-over for distances outside that range.

Will zeroing at 5 feet give me a really long flat trajectory?
At this point you may be wondering why I'm saying 20 yards is a good zero point. Why not zero at 5 FEET and enjoy as much of that flat trajectory as possible? If your scope looked straight through the center of your barrel, you could do that. Because you have to mount your scope high above the barrel, you can't make it work that way. The separation of the scope axis and bore axis introduces parallax that has to be accounted for when you sight-in.

This is already a long post, so I'm going to end it here and continue this discussion on another day. I hope I've answered some of your questions. Please feel free to post comments or additional questions!

At June 10, 2005 12:17 PM,  Anonymous said...

What is the practical range for an airgun.

What is the "effective" range for an airgun used for hunting.

Is twenty or 30 yards what everyone shoots at?

At June 10, 2005 12:33 PM,  B.B. Pelletier said...

Well, your question is a VERY deep one, and I think it deserves a better answer than I can give her.

Watch this week's blog for my answer.

And, thanks,

B.B.

At June 15, 2005 2:49 PM,  Anonymous said...

I'm planning on deer hunting w/a 6 mm PCP loaded w/70gr Hollowpoints. I have accuracy down to a 1/4 inch @ 100 yds.
Am I nuts?

At June 15, 2005 7:38 PM,  B.B. Pelletier said...

For deer I like to see 500 foot-pounds on target and no .243 air rifle I know of comes close to that.

B.B.

At June 15, 2005 11:37 PM,  Anonymous said...

I'm thinking thats NO problem, I forget all the stats on what he told me. I do know I shot duck decoys @ 200 to 250 yds w/it.(Rangefinder said 250, guy w/scope said parallex was 225)Either way w/the accuracy & what it does to smaller targets.....I say it'll drop a deer in its tracks.

I'll check w/manufacturer on the ft/pounds, but I've seen some amazing results w/these things......They are handmade by a very talented machinist friend of a friend.

The 30 caliber goes through 2 by 4's sideways. I realize this shot was at an unmeasured distance but, its probably 75 yards.
When I get the ft/# numbers I'll get back to you.
Thanks

At February 10, 2006 9:19 PM,  Anonymous said...

I have never tried a scope of any kind, but am interested in trying one on a pistol. What is the difference between a pistol scope and a rifle scope? Can a rifle scope be used on a pistol? I am assuming a scope marketed specifically as a pistol scope is meant to be viewed at arms length, but can't imagine what that must be like.

At February 15, 2006 8:13 AM,  B.B. Pelletier said...

The main difference between pistol and rifle scopes is the eye relief. You have about 20 inches with a pistol scope but around three with a rifle scope. That allows you to extend your arms.

Pistol scopes are lower powered and they tend to cost about twice what comparable rifle scope do.

B.B.

At May 19, 2007 1:35 PM,  Anonymous said...

if i sight my springer (Crosman Storm Xt) at about 35 feet how much further can i still hit targets accuratly ??

At May 19, 2007 2:52 PM,  B.B. Pelletier said...

35 feet is 12 yards. That's a poor distance at which to sight in, but I hear this kind of question all the time because that's all the distance you have where it is convenient to shoot. So this is what you do. Sight in to strike one inch BELOW your aim point at 35 feet. That should put you very close to dead on at 20-30 yards. If you sight in at 35 feet, you will be off at most other distances.

B.B.

At May 22, 2007 3:47 PM,  Anonymous said...

so if i sight at 35 ft and follow your directions i should be pretty close on target at 20 to 30 yards, but if i shoot a target at 35 feet it will mean that i will shoot and hit 1 inch lower right????

At May 22, 2007 5:04 PM,  B.B. Pelletier said...

That's correct. Now you may be off by half an inch, but it should be pretty close if yoiu do it this way.

B.B.

At May 27, 2007 5:46 PM,  Anonymous said...

thank you for your advice. one question can u use remington oil or reel magic to lube springers breech???

At May 28, 2007 5:56 AM,  B.B. Pelletier said...

Rem Oil contains mineral spirits and is therefore not to be used in compression chambers. I cannot find technical information about Reel Magic and therefore cannot recommend its use in compression chambers.

B.B.

At June 14, 2007 4:54 PM,  Anonymous said...

i finally measured the space i have and it is actually 50-55 feet so should i still do the same as if i have 30-35 feet??

At June 14, 2007 7:00 PM,  B.B. Pelletier said...

No. The difference in distance at this range is critical. So use 30 feet and you're done.

B.B.

At July 08, 2007 6:56 PM,  Anonymous said...

i used rem oil on my gun what should i do ( it's compression chambered

At July 09, 2007 6:36 AM,  B.B. Pelletier said...

I don't understand your question. What does "compression chambered" mean and how does that relate to Rem Oil?

B.B.

At July 09, 2007 11:35 PM,  Anonymous said...

i used oil for pumps and put some in the compressing chamber of my air rifle will this affect it .. the oil is Bell and Gossett pump lubricant...

At July 10, 2007 6:03 AM,  B.B. Pelletier said...

You didn't mention what rifle you shoot and it makes a difference. A Benjamin 392 probably won't mind, but I wouldn't use a non-airgun oil in a Air Arms S410 or a Career 707.

B.B.

At July 10, 2007 2:49 PM,  Anonymous said...

i am having some troubles when sighting in. i get close grouping for about 3 to 4 shots and then they start to wander off is it the gun or the scope??

At July 10, 2007 2:59 PM,  B.B. Pelletier said...

can you tell me a little more? Like gun, scope, mount, range at which this is happening? What pellet are you using? Is the scope adjusted to the limit of either knob?

Are you using the artillery hold?

B.B.

At July 10, 2007 4:52 PM,  Anonymous said...

gun is crosman quest ammo is crosman pointed the range is 50 feet i get it to sight in small groups and then they just go all over the place i'm getting frustrated and the scope is a powerline 3-9x32 scope...

At July 10, 2007 5:05 PM,  B.B. Pelletier said...

Hang in there!

Is the scope adjusted to the limit either to the right or up high?

Are you holding the rifle on the open flat of your hand - not touching the stock with your fingertips? Are you holding the stock just forward of the triggerguard? Do you allow the rifle to recoil as much as it can?

Are you breathing and relaxing before you align the crosshairs? By aligning them before you relax you are sertting the rifle up to throw the shots high and to the right, if you are right-handed.

It is very frustrating to learn to shoot a breakbarrel air rifle. But the technique I just described is the only way. Shooting off cloth or sandbags is a recipe for failure.

B.B.

At July 10, 2007 7:57 PM,  Anonymous said...

i leave the stock on a pillow to stability....i let the gun recoil as if i am shooting it normally. so i should not use a pillow or anything right??????i tend to shoot more to the left..

At July 10, 2007 8:22 PM,  Anonymous said...

I AM SHOOTING TO MUCH TO THE LEFT..I AM HOLDING THE STOCK WITH MY HAND AND FINGERS AROUND THE STOCK... I DONT LET THE GUN RECOIL AS MUCH AS IT CAN.... AND I HAVE BEEN RESTING MY HAND ON A LPILLOW FOR STABILITY... I AM SUPPOSED TO USE A PILLOW OR SOMTHING TO HELP WITH SHAKING?????I GET ALOT OF SCATTERD SHOTS AND THEN I GET A CLOSE SHOT AND THEN THEY SCATTER AGAIN I AM ABOUT TO GIVE UP BECAUSE IT MIGHT BE THE GUN OR SCOPE.......

At July 11, 2007 5:47 AM,  B.B. Pelletier said...

You need to learn the artillery hold for AN Y spring piston air rifle. They all require it. And breakbarrels are the worst.

The shakinjg is something you need to deal with. It's one of the things shooters nbeed to overcome.

Cloth will not help you. You have to rest a recoiling spring rifle on the FLAY of your open palm.

I can't find any blogs I have done on this hold, so I will do a new one for you. Tomorrow.

B.B.

At July 11, 2007 2:49 PM,  Anonymous said...

i really think that it is not the way i hold the gun because i can get the gun shooting where i want it and then it shoots all over the place i am probaly gonna stick with my open sights.......or buy a new scope for the third time the gun itself shoots okay bu not the best when shooting with open sights...

At January 14, 2008 1:17 PM,  Anonymous said...

B.B,

If i zero my scope at 20 yards,about how many inches under will a pellet hit its target at 100yards (shooting at 900 fps).
Is there any formula?

At January 14, 2008 2:50 PM,  B.B. Pelletier said...

You'll hit about 3-4 feet low at 100 yards. Try it on a large piece of cardboard, knowing the pellet will drop.

B.B.

At January 14, 2008 3:23 PM,  Anonymous said...

Wow..it's about 1 meter...that is big...more than i expected really lol
In the rotating elevation adjustment ,it is said : 1 click,1/4'' at 100 yards....what does that mean?
About how many clicks will i have to turn to get my shots higher to zero at 100 yards?...is it about 160 clicks? Lets say for every click,the shot will go up 1/4 inch for 100 yard distance(0.6 centimeters)....I have about 1 meter to catch up(100 centimeters).Then for 100 centimeters,it will be 100/0.6=166 clicks....
Is that correct? Does the rotating adjustment rotate that many??

Thanx for clearing things :)

At January 14, 2008 5:36 PM,  B.B. Pelletier said...

The scope marking mean what you think they mean.

Most scopes have not enough vertical adjustment to shoot 100 yards. You need an adjustable scope mount for the rest.

But instead of talking about it, why not test it yourself? Make an aim point about 3 feet above a large piece of cardboard and see where the pellet hits. If you hit the cardboard (it should be a piece at least a meter square) mark your hit and see how far the pellet dropped.

Guessing, which is what I am doing, only goes so far.

Count the clicks in your scope. That's what I do and they vary widely.

B.B.

At January 15, 2008 7:55 AM,  Anonymous said...

B.B,

Yes i will try it myself of course,but right now the scope i bought was broke(i told you about it).And it is under repair.The guy said he will make it stronger from the inside so that the crosshair wont rotate anymore...and ALSO this time i will buy a scope stop that has a recoil absorber and i will buy a double mount system so that i can fit the scope stop in between those 2 mounts.
Do you think this will prevent my scope (Gamo sporter 3-9x 40) from breaking again?

Thanx,and sorry for asking that many questions,but i hope you dont't mind ...

At January 15, 2008 8:49 AM,  B.B. Pelletier said...

That's a question I can't answer. It depends on what the rebuilder does. But since he says he can do it, it sounds like he knows what he's doing. Many scope repair places don't even acknowledge the difference between airgun stresses and those from firearms.

B.B.

At January 15, 2008 4:52 PM,  Anonymous said...

B.B,

I hope the Recoil absorber of the stop scope will greatly reduce the recoil on the scope....

At July 04, 2008 10:03 PM,  Anonymous said...

Hi,
I recently purchased my first air rifle, a Gamo Big Cat 1200. I followed your tips for sighting in at 35 ft, using Gamo PBA Raptor pellets. I then decided to see how other pellets performed and my problems began. I tried RWS Superpoint Field Line 8.2 grains, RWS Superdome 8.3 gr and RWS Wad cutters and all hit from four to six inches lower than the Raptors and I ran out of clicks on my scope before I got close to the center. Is there something wrong with my initial sighting in? What do you recommend?
Thanks,
Ed

At July 05, 2008 6:58 AM,  B.B. Pelletier said...

Ed,

You have barrel droop. Have you read our discussions abut it? It's very common on breakbarrels.

To correct your scope you either need to shim under the rear ring or you need to use an adjustable mount.

The Raptors hit higher because they are going so much faster. But you will want to use the other pellet because they are more accurate, so you do have to correct the scope.

B.B.

At July 07, 2008 7:52 PM,  Anonymous said...

Thanks for the quick reply. I've quickly read a few of your discussions and did add the 35mm piece "shim" in the rear of the scope mount. I was able to bring down the number of clicks on my scope and got the RWS Superdomes on target at 20 yds. That is ½ “ high at 20 yds. However, when shooting at 15 and 10 yds things got very confusing, and really need your help. I don’t wish to clog up this forum with my problems, so if you wish to write me privately my email address is eforteza@prtc.net. So you know, I’m new at air rifles but been shooting all my life from mortars, M-14, M16 to bows, so I know a little about shooting. However, this really has me scratching my head. As I mentioned before, I’m shooting a Gamo Big Cat with two different pellets, Gamo PBS Raptors and RWS Superdomes. Here were the results with the Superdomes and I did it twice just to make sure. The RWS Superdomes; at 20 yds were hitting ½ high at 20 yds from aim point. When I moved to 15 yds. they were hitting down ½ “ and right 1 ½” from center. When I moved in to 10 yds. they were hitting down 2” and to the right ½”. It doesn’t make sense to me how they went to the right and down, and looped around from 3:30 o'clock to 5:30 o'clock as I got closer. Hope all this makes sense to you. I contacted Gamo and they're willing to check it out under warranty, but I wanted to see if I can figure it out first before spending on shipping charges. Thanks again, Ed from Puerto Rico

At July 08, 2008 8:48 AM,  B.B. Pelletier said...

Ed,

There are two possibilities here, a scope that's grossly out of alignment or a spiraling pellet. I suspect the latter, because as you go farther from the muzzle, the dispersion changes.

Spiraling pellets are due to gross instability. That pellet, the RWS Superdome, is wrong for your rifle. If you plot all the hits on a single piece of paper you will see the spiral. From that, you can even predict where the pellet will strike at a different range.

Don't expect a Raptor to be accurate at any range.

The Superdome is too narrow for your bore. You need a fatter pellet. Try some Gamo pellets and try some Crosman Premiers.

Incidentally, centerfire bullets also spiral, though they do it over much longer distances.

By the way, I was a 4.2" mortar platoon leader, so we share some common experiences.

B.B.

At July 08, 2008 12:38 PM,  Anonymous said...

B.B.;
81 MM, PLT-SGT 0369, 3rdMarDiv, Okinawa, 1973.
Are you suggesting the Crosman Premiers 7.9 gr dome lights? You mentioned as I go farther from the muzzle, the dispersion changes. What do you mean? In my case the groups move as I get closer. Haven’t tried it longer, until I get it correct from 20 on in. I noticed the information did not type correctly in my previous comment, so to confirm, at 20 yds the hits are half inch high, at 15 yds the group moves right two inches and down one inch; and at 10 yds the group is half inch right and two inches low. At 15 way right and at 10 way low.
I will contact Pyramyd about ordering the pellets and hopefully get on target.
ED

At July 08, 2008 1:53 PM,  B.B. Pelletier said...

Ed,

Mortar platoon leader and later company commander of Combat Support Company, 2nd Battalion, 81st Armor, 1st Armored Division, Erlangen, Germany, 1974-1977.

You hadn't mentioned the caliber of your rifle before, so I couldn't be specific, but now that I know, also get some 10.2-grain JSB Exact pellets. I think among all of those I have mentioned this spiraling tendency will go away.

As for the dispersion, I have actually watched spiraling pellets out to 50 yards and they don't disperse all the time. Sometimes they just rotate around a center at the same distance all the way. Other times they do disperse. You should be able to put a target at 18 yards and predict where it will be hit, based on the other targets.

B.B.

At July 08, 2008 3:24 PM,  Anonymous said...

Waiting list until November for these :(

At July 08, 2008 4:43 PM,  B.B. Pelletier said...

Yes, and when they arrive they will evaporate in two weeks.

B.B.

At July 27, 2008 8:41 PM,  Anonymous said...

Hi B.B.:
Follow up to our last. I ordered a box of Crosman Premiers 7.9 (JSB were on back order) and the results are better. I set my zero at 12 yds and my groups at 10 yds are 1/2 low and at 20 yds 1/2 high, but they are vertical. Need to see how the group does at longer distances. Semper Fi!

At January 01, 2009 11:47 AM,  Anonymous said...

i know this dont really go with this forum but i got a beeman rs2 sportsman series break barrel for christmas.when i took it out i mounted the scope and sighted it in at 15 yards,but it was shooting 2 in. groups?so i started playing wit it and after about 200 rounds i was hitting pepsi bottles at 85 yards aiming at the top of the bottle and my groups improved at 20 yards i was hitting the same hole.after about 600 rounds i oiled it and was shooting fine for 50 or so rounds and then it just started goin crazy. i went from shooting half inch 3 shot groups at 15 yd. to 3 in. groups using same pellet (crosman premiers)at same distance and its getting aggravating,please help!

At January 01, 2009 1:57 PM,  B.B. Pelletier said...

I think I know what's wrong. You are shooting Crosman Premiers, which are wonderfully accurate, BUT, they do lead the barrel.

Here is what I want you to do. I want you to clean your barrel. I really want you to use a new brass brush loaded with JB Non-Embedding Bore Cleaning Compound. Please read this report and clean your gun exactly as I describe there:

http://www.pyramydair.com/blog/2005/11/is-your-airgun-barrel-really-clean.html

I have talked hundreds of shooters through a similar problem and I'm pretty sure it will work for you. You can buy the JB compound at a good gun store if you want to speed up the process. Don't use Hoppes No. 9 or any other solvent cleaners -- only use JB paste that most benchrest shooter clean their barrels with.

Then get back to me on the current day's blog (whenever that is) and tell me your results. I will then tell you how to continue to keep shooting the same pellets and not have to clean the barrel again.

http://www.pyramydair.com/blog/

B.B.

At January 13, 2009 1:54 PM,  Anonymous said...

thank you for the information,it helped ALOT.i went back to shooting 3 shot one hole groups at 20 yards!

At January 13, 2009 1:59 PM,  kevin said...

Anonymous,

Great news that your barrel cleaning improved accuracy!

Here is a link to take you to current/active dialogue:

http://www.pyramydair.com/blog/

Look forward to hearing from you.

kevin

At January 13, 2009 1:59 PM,  B.B. Pelletier said...

You can do me a favor in return. Would you mind commenting about your accuracy problem on the current day's blog and tell them what you did to fix it? A lot of people don't yet believe this works.

B.B.

At April 21, 2009 12:17 AM,  Anonymous said...

B.B.

I'm a 34yr old pilot that hasn't fired a rifle down range since my 10th grade JROTC class. I recently purchased a Crosman Quest 1000 to take me back to the happy place I recall the range was for me. Many things you talked about helped me thru the 1st 50rds I've fire, is their any advice for do's and don'ts with my new rifle.

Thanks,
Wings.

At April 21, 2009 5:42 AM,  Mr B. said...

Hi Wings,

Welcome to the wonderful world of air guns. You posted to a blog that was written in 2005. Come join us at http://pyramydair.com/blog/ and ask your question on our current blog.

There's a group of folks there that will be happy to answer your questions.

Mr B.

At April 21, 2009 7:23 AM,  Anonymous said...

Tom am I missing something? It seems to me that the separation distance between bore and scope has to come into play here. For example on my condor with rings and a tri-rail there's quite a gap there, meaning I have to point the scope looking more down to get on-sight at 20 yards. With that much of an "X" (the difference of the scope looking down, or the bore pointing up) and assuming 950 fps using 21.1 Gr. .22 Cal. Beeman Kodiaks. Do I still want to use 20 yards? I'm looking for no more than 1/2 an inch above line of sight. Thanks From SavageSam

At April 21, 2009 7:47 AM,  B.B. Pelletier said...

SavageSam,

Keep the 20 yards! It's too handy not to use.

The scope separation will THEN affect where the SECOND impact point is - and that you determine on the range.

In other words, don't think about it too much. But if you DON'T use the 20 yards with normal velocities (800-950 f.p.s.) you will have a screwy setup.

B.B.

At April 21, 2009 8:48 AM,  Anonymous said...

Thank you VERY MUCH for the quick reply. I'm hopeing to get out today before it gets too hot. From SavageSam.

At July 04, 2009 10:40 AM,  Anonymous said...

I think this discussion is all about scope on a rifle which is at least 1 inch above .
If I use default factory open sight , do I still need to follow this sight-in procedure ?
thanks !

At July 04, 2009 1:34 PM,  B.B. Pelletier said...

Here is an easy way to understand this problem and to answer your question with any gun. If you put a target against the muzzle and sighted on the same target with the sight, where would you hit, relative to where the sights are looking?

You would hit below the point of aim, of course.

The discussion in this report is the range at which you want the aim point and the impact point to coincide. And it works for open sights as well as scopes.

As you point out, scopes will always be higher than open sights, but both are higher than the bore.

B.B.