Pellet speed vs accuracy questions

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lamarkeiko

Member
Jun 22, 2017
129
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Oregon, United States
I'm fairly new in the air gun world to understanding the relationship in velocity of different caliber and weights of pellets and how they effect accuracy. I've only owned my first PCP air rifle for 3 months where it is possible to change the hammer spring pressure, which will effect velocity. My pcp rifle is a Hatsan AT44S-10 QE .22 cal. So far I have adjusted the hammer spring until it has bottomed out, giving me the lightest spring and the lowest velocity. I arrived at this point because I had the lowest ES with a 20 shot string. At this setting, I've shot about a dozen different pellets at 50 yd to test for accuracy. I eliminated about half of those pellets for my gun when they grouped 3+ inches. My best accuracy pellets have ranged from 14.3 gr Crosman Premier @ ave 949 fps to H & N Baracuda Match 22.14 gr @ ave 840 fps and a couple pellets about 18 gr that ave about 875 fps.
My question is, what will happen to the accuracy of these pellets as I increase hammer spring tension and velocity? I have heard mention of a pellet hitting the sound barrier. Besides noise, does this effect accuracy? Is there a maximum velocity for a pellet in a specific gun that accuracy will go down, and is it possible for accuracy to get better as velocity is increased. Also, is there any possibility that the pellets I eliminated when their group was over 3" could get better with more hammer spring and velocity.
My ultimate goal is to get at least one 10 shot clip to be accurate near 1" c-c with the most power/velocity at 50 yd. I like the idea of having a light pellet that's accurate for its flat trajectory, and also the heavier pellet for the better wind handling.
Lamar

 
Welcome to the question that haunts every one of us! Congratulations, this begins your endless journey trying to find the best combination of rifle, pellet, weight, and speed.

I'l be brief but, I'm sure others will weigh in on this with their experiences. 
If you break the sound barrier, your pellet will destabilize in flight. 
"Is there a maximum velocity for a pellet in a specific gun that accuracy will go down, and is it possible for accuracy to get better as velocity is increased. Also, is there any possibility that the pellets I eliminated when their group was over 3″ could get better with more hammer spring and velocity." - yes and yes. 
I hope you are able to reach your goal! :) You've got the right idea about the weight, flat trajectory, and ability to buck the wind. Keep up the good work and you'll get your tight groups. :)
Tom
 
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I am in no way any kind of expert. My often flawed understadning is thus: Speed of sound varies due to temp, barometric pressure an humidity. Generally speaking around 1180-1200 FPS is where I consider the speed of sound. Pellets are drag stabilized rather than spin stabilized as bullets are. Yes, pellets do have a slow spin but they are effected more by drag than spin.

​The issues arrise at the trans-sonic stage, where the sound barrier and shock waves travel with the pellet. Buffeting from the shock wave can cause issues and destabilize the pellet in flight. Generally below 970 fps is where you want .22 pellets to fly. The heavier pellets will hold velocity better down range than the lighter pellets will.

​Welcome to the AGN - there is a lot of good information here. Good luck to ya'.
 
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Thanks guys for the replies back. I'm sure I don't have to worry about my gun shooting over the sound barrier. I had my 14.3 gr Crosman Premiers shooting at 1000 psi at one time when I first got the gun. I guess my next step is to increase my hammer spring a little at a time and keep shooting all the pellets again while keeping tract of the velocity and accuracy. Accuracy is by far the most important quality. How many shots in a group do most of you do for your accuracy test, and how many fliers is acceptable in a shot string?
 
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What I really want to understand about fliers is what is normal to be expected from a can of pellets that generally shoots good a high percentage of the time. For example, I may be shooting at 50 yd, and all my shots are 1" c-c or less with 5 or 6 shots, but one shot is several inches away from the group. I know my hold was good. I always inspect the pellets looking for obvious deformations prior to loading. Is the quality control of manufacturing not good enough to eliminate all defective pellets, thus causing you to have an occasional flyer? Are there certain brands of pellets that have a better quality control?
 
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Using my 22 marauder, with MM barrel, I shot two groups at 50 yards yesterday, 10 rounds each, 980 to 925 fps, non reg gun, both groups nice and tight, would all easily fit under a dime. (No fliers).

I dont inspect my pellets, I normally use a small sharp pointer to seat 3 or 4 pellets per mag. So sizing skirt issues in every mag. 

I had had no fliers. I attribute fliers to either me, gun (poor barrel), wind, or really bad pellets. 

While I haven’t narrowed things down too much, if you have a good barrel, paramount, and the gun is operating correctly, no sig leaks etc. then it is you, environment/wind or really bad pellet. 

One flier is is too much, but I can almost tolerate one every 40 or 50 shots. 
 
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I have an unregulated rifle (Hatsan Nova in .22). I found that my rifle likes the JSB Diabolo Exact 18.13g with head size of 5.55mm. The problem is that this pellet is sold as 5.52mm only, thus I have only been able to find a few tins with 5.55mm head size. The difference between 5.55mm and 5.52mm is typically 1/2" group versus 1" or more at 50 yards. 

Would I be able to get the same accuracy with the 5.52mm head size by decreasing/increasing the power?
 
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That is what I'm in process of doing now. I'm slowly increasing spring pressure on my Hatsan AT44-10 and shooting groups from 10 different pellets, then recording the results to see if I can see changes in their grouping. For some reason, the pellet that Cokemaster mentions, JSB Diabolo Exact 18.13 gr is the worst shooting pellet I have had in my arsenal for my rifle, and that has been very disappointing to me, since that pellet seems to be one of the best shooting pellets for most people. My gun shoots that pellet like a shotgun. I took 50 shoots at 25 yd, and the pellets are scattered all over over 6" c-c. This is hard for me to understand why they shoot so bad. The pellets look very good in the tin. With a group like this, I don't think this pellet would shoot good in my gun at and velocity.
 
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Originally my rifle shoot around 930 FPS, so I reduced the speed to 880 FPS. This had no effects, and the results where the same as previously with JSB 18.13 (5.55mm versus 5.52mm). Then I reduced the speed to 820 FPS. This time the 5.52mm performed even worse than before, > 2". However, the 5.55mm seems to be a little tighter than before (I only shot two set of 6 shots, and both where within 1/2" @50 yards). 
 
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Unfortunately, or fortunately if you like to do lots of testing, you'll need to start with the hammer spring all the way out (lightest) and test EACH PELLET BRAND AND WEIGHT by doing 5, five shot groups and take the average CTC of those groups. Then again with a few turns in, again with a few more turns in, etc. till you're all the way in (heaviest). Now you'll know what speed your gun shoots THAT BRAND AND THAT WEIGHT PELLET at for best accuracy. Now again with the next brand or weight of pellet. It's fun! Let us know what you find. My first PCP was an AT44S-10. Great rifle! Have fun with it.

BTW, if you want more accuracy out of it, there's a guy on the forum, Baltwan sp? I believe, that tunes Hatsan rifles. May want to check him out at some point. Think he also has y-tube videos as well. Others chime in if I'm not correct. 
 
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I've started the testing almost as chasdicapua suggested, except I'm not doing 5 five shot groups of each pellet and spring adjustment. I've been doing 6 shot groups, for each different pellet at each hammer spring adjustment. I started at the lowest hammer spring, and have been increasing the spring tension 1/2 turn at a time for each 6 shot group for all my pellets. So far most pellets seem about the same, but some do show improvement, and one pellet is getting drastically worse in grouping. From 3" c-c to 6" c-c. I may just eliminate that pellet from my testing. When I've gone through to the maximum spring tension, I'll just eliminate the pellets that are way off the accuracy scale for me, and do a retest of the pellets that seem to have some potential.
 
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