Pellet velocity variance

by B.B. Pelletier

This question came in last week, and I thought it was too good to pass up. I’ll try to address it in this post, though I think this one could keep us talking for a while.

“For an unregulated PCP, how consistent does it have to be in order to be good enough for FT at 50 yards? (ie: what’s the maximum standard deviation in FPS allowable considering pellet weights are equal?).”

I used to think that way – that pellet velocity was a key to accuracy. Now, I’m not so sure. This reader has also made the assumption that a precharged rifle that doesn’t have a regulator will have a greater velocity variation than one that does. Usually, that’s true…but not always.

A regulator controls the air pressure that goes to the firing valve. It steps down the reservoir pressure to a level at which the valve operates uniformly. A regulated gun has a chamber between the reg and the valve that contains the optimum amount of air at a given pressure (the pressure at which the reg is set). When the valve opens at firing, it always passes the same volume of air at the same pressure. Regulated guns usually keep their shots at a velocity that doesn’t vary by more than 10-15 f.p.s. I’ve heard stories about guns that never vary by even one f.p.s., but I’ve never seen one.

When the reservoir pressure drops below the pressure at which the reg is set, the gun goes “off the reg,” and the velocity varies more and starts dropping. The big advantage of a regulator is not the tight velocity variation; it’s the greater number of shots a gun can get before needing to be topped off.

Let’s take a look at a balanced valve. Actually, all precharged valves are balanced, more or less, against the fill pressure of the gun. Some, like the Career 707 set on high power, drop in velocity from shot to shot, while others, like a Daystate Harrier, can get a number of shots (mine gets 24) with a tight velocity variation (15 f.p.s.) before they need to be topped off. My Harrier has to be filled to only 2,650 psi instead of 3,000, which makes pumping a lot easier.

I believe the best example of a balanced valve is found in Mac-1’s USFT rifle. It has a fill pressure of 1,800 psi and gets 60 shots while using only 400 psi of air. It shoots a 10.6-grain Beeman Kodiak at 900 f.p.s. with a velocity variation of 15 f.p.s. for all 60 shots. You may notice that it has a huge air reservoir. That’s what it takes to get that many shots at that low pressure. This unregulated PCP has competed successfully at the national level. The starting price for one of these limited-production airguns is \$1,800.

The USFT rifle gets a lot of shots with a tight velocity variation on relatively low air pressure.

So, the regulator isn’t needed for shot-to-shot consistency. It’s there to give more shots per charge. However, regulators are failure-prone. It’s not a question of “if” they will fail, but when. If you can get along without one, you’re better off, in my opinion.

Finally I’m getting to the question the reader asked! And the answer is: I don’t really know, but the number is higher than most people think. Remember that Career 707 I mentioned? It might drop 50 f.p.s. in the first 5 shots at high power, but it can still group five Crosman Premiers in half an inch at 50 yards on a perfect day! So is 50 f.p.s. the magic number? Like I said, I don’t know.

I always look for a maximum velocity variation of 20 f.p.s. in a spring gun. If it can do that, I’m happy. Obviously, a spring gun does not have velocity drop-off, but I guess I have transferred that number over to PCPs, as well. I tend to think a PCP that varies by no more than 20 f.p.s. is doing well. When I shoot a PCP to determine the maximum number of shots, I usually make the cutoff at the point where the velocity varies by more than 20 f.p.s. My Harrier is an exception, because it goes crazy after the 24-shot cutoff.

My numbers are arbitrary and mean nothing without shooting the rifle at distance. If you plan to shoot field target, the distance is 55 yards.

I know a field target shooter who was so concerned about velocity variation that he put TWO regulators in his FWB P70 FT rifle! One reg controlled the air for the other! Now that’s as anal as it gets, yet this guy was a nationally ranked shooter. He also mounted a wind gauge on his rifle! I would make fun of him; except that, on my best day, I couldn’t shoot as well as he did on his worst day. On the other hand, there was another man who spent even more money on his gear than Mr. Anal. His custom-made scope rings cost \$500! Yet, I could beat him, sometimes. And that, I think, is the real answer here.

In the final analysis, it isn’t the regulator or your equipment or your barrel’s pedigree that matters. It’s how well you shoot. To win at field target takes a rifle that can compete and a shooter who shoots better than most snipers on municipal SWAT teams. You get there by practice, and practice, alone.

37 thoughts on “Pellet velocity variance”

1. Bob

Luis Armstrong, when asked what brand of trumpet he was playing, reputedly said “It ain’t the horn. It’s the player.”

While it seems that the better the gun, the better your chances of shooting well, but in the end “It ain’t the gun. It’s the shooter.”

2. Terence

BB,
You said that “It’s not a question of if [regulators] will fail, but when” what is / are the main reason(s) for regulators failing? and a supplementary question is it normally a catastrophic or sudden failure, or progressive, or does the gun just become “deregulated”?

3. Terence,

Regulators operate with springs. The ones we are discussing use a special spring that consists of a stack of washers shaped something like hubcaps (in that they have some dimension to them, some width) The are called Belleville washers or Belleville springs, and they are the best part for the job. But over time they lose their resiliency and the regulator suffers by changing the pressure it admits.

There is no catastrophic failure, the reg just starts changing without any external adjustments, and the washers must be replaced.

To quote you, the gun becomes deregulated.

B.B.

4. Anonymous

BB,

On a non related note; I was browsing the Pyramid site and noticed that Gamo has what looks like full shrouded barrels on the hunter pro. Is it anything functional or just for looks?

dsw

5. dsw,

Looks.

It’s just an elongated muzzle bake, set back on the barrel.

Besides, a silencer on the spring rifle doesn’t have much to do.

B.B.

6. Anonymous

BB,

Yeah, I know spring rifles don’t “silence” but I was just wondering if this was something Gamo was using for looks and marketing, and also if there was some other advantage.

Looks cool, gotta give it to Gamo on that. Though they seem to be over priced at the \$250 and up range.

I can’t hit squat with my CFx anymore!!! Having to resight a scope two or three times everytime you take it out takes the fun out of it. I missed a perfect head shot on a raven at 18yds this morning, so today I look at my CFx and frown!!!

Tomorrow I will resight scope again.

dsw

7. dsw,

It sounds like you have a dirty barrel. Sudden inaccuracy after the gun has performed accurately is the clue.

Try the JB paste method. Yes you will have to go in from the muzzle so cock the gun, rotate the breech open and clean it using a solid rod. The get rid of all the compound and try your luck again.

This is not an easy thing to do, but your CF-X shoots at a velocity that will cause a dirty barrel – expecially with any Crosman pellets or synthetics.

B.B.

B.B.

8. Anonymous

BB

Thanks, I’ll give it a go. I haven’t cleaned it yet and have shot atleast 1000 pellets.

I been trying to get a clean shot on this bird for weeks now. We are beginning to know each others moves too. Usually the bird will stay out at 30yds where I’m ineffective with the CFx.

Wait til my AR6 arrives. Ha hahahaha!

dsw

9. BB,

I was just wondering your opinion on which gun i should get, im looking for a .22 cal hunting rifle for squirrels to rabbits, and wanting to spend around \$300 tops, i was looking at the B40, it looks pretty nice and your review was wonderful by the way. i also want multi or single pump. what rifle would suit my needs?

10. B.B.

oh i forgot, would a .22 or .25 be more suitable for rabbits? i was looking at the webley stingray, is that a good choice for hunting rabbits? this is also the only .25 i could afford, or would there be a nicer .22 i could afford to do the job?

11. StiCkY,

A .22 is great for rabbits and the B40 is one of the best spring rifles. A Stingray is nice, but the B40 will outshoot it.

You mentioned a multi or single pump. A good multi-pump pneumatic is the Benjamin 392. There are no single stroke pneumatics with enough power for hunting.

B.B.

12. BB,

thanks a million! also, ive been seeing a lot of people arguing over what pellets is supreme for hunting, crow magnums, predator, domed *diff brands*,crosman superior hollowpoints and field points… which one would you personally use if u were using a B40 and hunting rabbits?

13. Anonymous

to sticky

i just got the benjamin 392 and it is a great gun. i think you should reconsider. also the lack of recoil (none) is amazing

14. 392,

well thanks for your suggestion! i already have a 392, but in .177
great chipmunk gun, but tired of going after squirrels and feeling bad for shooting them in shoulder and not dying *quite sad really*, did you get yours in .22 , and in .22 does the 392 have enuf oomph to take down a rabbit *i live in AZ, BIG jackrabbits*

15. Bryan

can you comment on the Beeman SS1000?

ooo and I live in AZ too (southern) It just started snowing in the mountians over here!

16. BB,

Since most of my shots would be anywhere from 30 to 50 Yds, im thinkin that the 392*.22cal*wouldnt have enough power at that range to take down a good size rabbit, would the B40 even have enough power?

17. Terence

BB.
Thanks for your earlier answer. I hail from the UK (although I am in China at the moment). As you know in the UK airguns have a legal limit of 12ftlbs (over that we need an FC).
If the regulator fails it sounds as if the gun should remain within the legal limit; since the muzzle velocity is influenced mostly by the balance between the hammer assembly and the valve.

Is this correct?

18. Anonymous

Would a .17 bore snake with a bronze brush be ok for cleaning a gamo recon

19. Out of thw RWS 34, Sheridan 392, and the BAM B40, which one would be the best for all around bang for the buck, and for hunting squirrels to rabbits? really like the BAM B40, i think it suits what i need, but is a bit pricy, but is it worth it?

20. StiCkY,

I read all your comments. If you want to shoot Jacks at 30-50 yards, the B40 is the LEAST gun to get. You really need a Talon.

For squirrels, the B40 is superior. If you can keep the shots confined to 30 yards, the 392 will get ‘er done.

My pellet of choice in .22 for hunting is the JSB Exact Jumbo domed pellet.

B.B.

21. StiCkY,

One last comment. You mentioned that you have a 392, but in .177. However, in .177 the model designation is 397.

I mention that because I try very hard to be specific when I give answers. Some guns like the B40 do exist in both calibers, but others don’t. So when I recommended a 392, it was a .22 caliber rifle, only.

B.B.

22. Beeman SS1000,

Beeman buys their less-expensive rifles from Spain and China. I don’t know where the SS1000 is made, but it’s a sharp looking air rifle.

These days there are a double handfull of inexpensive spring rifles in the same class. Most of the Gamos, the Remingtons, Crosmans, Daisys and Beemans are quite similar in performance. I haven’t tested every one so there may be a surprise or two, but most of them perform about the same.

They are fairly accurate, reasonably powerful, and in the case of this one, good looking. If you want one, go for it!

B.B.

23. The .17 bore snake will work, but it’s VERY slow. A solid rod is always best if you can get access to the barrel to run it through.

Also, unless you are cleaning with JB Bore Compound (a one-time deal) there is NO reason to ever clean the bore of an air rifle. They don’t get dirty like firearm barrels do.

B.B.

24. Terence,

I can’t say yes for sure. If a reg fails, it could allow air at higher pressure to pass through. The firing chamber will never increase in size, but if the air pressure inside it rises, the muzzle energy will, too. The difference might not be a lot, but in the UK you have to be careful.

B.B.

25. Bryan

thanks for the recommendation, the reason why is I want a nice looking wood, and a decent shooting (also powerful) rifle, as all I have now is a IZH61 953targetpro and a Airmaster 77 (all synthetic/ plastic)

26. Anonymous

BB,

I was looking for your article on the cleaning with JB Paste and came up skunk.

can you post the link? Gotta get the ol’ CFx dialed in. thx

dsw

also, I noticed that your post today on the Master Sniper does not have a blog link. good post btw. I’ve seen that rifle and wondered ’bout it myself.

27. Anonymous

to sticky

i dont know if the 392 could take down a rabit that big but i believe it does great with squirls

28. BB,

oops, i meant to say 397 when i was talking bout already having one < my mistake. Thanks for answering all my questions, im sort of new to the world or air gunning, but it is something that i think i will definately be into for a long long time, i have a full collection of firearms, and have been shooting since i was 7, and never really gave thought about a pellet rifle until recently. I love to shoot, and i cant exactly take out my winchester 30-30 model 94 and go plinkin in my back yard 🙂 , srry if i was asking too many qeustions, but i just want to make sure if im spending that kind of money that im going to be getting every penny's worth!!! also i may have been overly thinkin when i said rabbits from 30-50 yds, i went rabbit huntin today, and got within about 15 yds, i could have hit it in the head with a rock! lol, well the fact is, i LOVE my benji, its a good rock solid gun, and i just want something for the occasional hunter, nothing for like SERIOUS hunting trips, do you think that the 392 could bring a cottontail down from 15-25 yds? i also just ordered a cf-x for plinkin, i love the tactical look of the gun! I tihnk i might just save the money a lil longer to get the B40, the problem is, is that you NEED a scope... which is MORE money. Is the B40 really all its cracked up to be? i mean does it perform even near the tx200? On ur poost for the B40, you said it out shot the tx200 on that day, that amazed me, the tx200 is one of my dream pellet rifles, and the B40 even though its a replica, it looks, and if it performs like the tx200, i dont see a reason to spend the extra \$250 on it? Is the B40 really worth the money? Thanks very very much. And i also think it is fair to say that you are the bext blogger and the most knowledgable *pelletier* i have come across, and i really appreciate your help! thanks!

29. Anonymous

Hi B.B.
Wanted to comment about the UTG sniper, but couldn’t find the link to post comments in for today’s blog. My roommate owns that rifle and it is a very accurate rifle for a pretty good price.

I was also wondering if you will do a post on classic army’s version of the rifle?

I own a classic army M4 AEG and find that classic army guns are very good, so I’m pretty curious about their sniper rifle and how they perform.

Thanks

30. The Classic Army M24 I tested was modified, so I can’t say how good the basic gun is. It had a tight barrel (6.04mm) and a 190 mainspring. It could shoot 1/2″ at 10 yards. It shot 0.20 BBs at 500 f.p.s.

B.B.

31. ok, for the B40 *.22cal* A.G.E. Rocktite 2-piece Medium Scope Rings 1″ x 11mm rings, and the leapers 6×32 bug buster scope, the total would be \$365.89, would this be a good set up, if not what would you change? *dont want to spend more than \$80 for the scope, would this be the best scope for the price im looking for? ANYONE HAVE ANY SUGGESTIONS?

32. StiCkY,

Because of where the scope stop has to be(and therefore the rear ring), the eye relief of the Bug Buster isn’t long enougn to reach your eye. I recommend a full-sized scope.

B.B.

33. Anonymous

BB,

I meant that the comments llink was nowhere to be seen, but now I see you fixed it.

dsw

34. Anonymous

Oh and thanks for the cleaning link!

dsw

35. Chris posted this and it went to spam and was deleted.

We made a rifle that shoots clay pellets. the reservoir has a capacity of 1.5 liters, barrel length of 27 inches, cal 25. it’s filling point is only 765 psi, but it can shoot up to 80+ shots. I can’t measure the velocity but i can hear a ‘whipcrack’ every time i shoot,the one that sounds like an overtuned spring piston air rifle.

Chris