Pellet head sizes - sharing my spreadsheet

[nervoustrigger]

Hey, thanks Stefan and Chaffyn!  I really appreciate your kind words.

[nervoustrigger]

It seems that the ones that I would guess to be the most accurate are all either the correct size or larger.
The undersize ones are the least accurate.

So far, it has been my experience that what you say is true...that a pellet rifle will tend to be more accurate with pellets whose heads are either the same size or just slightly larger than the barrel.  That helps ensure the pellet stays engaged to the rifling so it can achieve the proper spin stabilization.  And the pellet will tend to emerge from the muzzle as nearly perfectly parallel as possible.

Conversely, it's easy to understand why undersized pellets don't fare so well.  Logically, if you think about the expanding gas pushing the pellet from behind, an undersized head pinballs back and forth against the rifling as it accelerates toward the muzzle.  So it doesn't stay engaged with the rifling and therefore does not spin up properly.  Also, the pinballing behavior means that just as the pellet emerges from the muzzle, it will be slightly tipped in some random direction each time, throwing it off course.

But with that said, every once in a while it seems there is a pellet and barrel combination which defies logic.  Since the previous posting, I found that my Beeman RS2 springer prefers slightly undersized JSB 10.3gr pellets.  Slugging the barrel I got 0.177" across the riflings, whereas the pellets are measuring 0.1755".  So the pellets are a full 1-1/2 thousandths smaller than the barrel, yet they somehow shoot more accurately than anything else I've tried.  Not just 10 or 20 yards but out to 45 yards.   I wish I had an explanation for it but I don't.

[jmcgall1]

been a while since i've been on the blog. What did you use to measure the headsize? i'd think i micrometer would work but only gives one diameter (for instance would not show if a pellet is slightly oval-shaped) I've seen the setup ted (ted's holdover) uses just curious to see how you were getting your measurements.

[jmcgall1]

It seems that the ones that I would guess to be the most accurate are all either the correct size or larger.
The undersize ones are the least accurate.

So far, it has been my experience that what you say is true...that a pellet rifle will tend to be more accurate with pellets whose heads are either the same size or just slightly larger than the barrel.  That helps ensure the pellet stays engaged to the rifling so it can achieve the proper spin stabilization.  And the pellet will tend to emerge from the muzzle as nearly perfectly parallel as possible.

Conversely, it's easy to understand why undersized pellets don't fare so well.  Logically, if you think about the expanding gas pushing the pellet from behind, an undersized head pinballs back and forth against the rifling as it accelerates toward the muzzle.  So it doesn't stay engaged with the rifling and therefore does not spin up properly.  Also, the pinballing behavior means that just as the pellet emerges from the muzzle, it will be slightly tipped in some random direction each time, throwing it off course.

But with that said, every once in a while it seems there is a pellet and barrel combination which defies logic.  Since the previous posting, I found that my Beeman RS2 springer prefers slightly undersized JSB 10.3gr pellets.  Slugging the barrel I got 0.177" across the riflings, whereas the pellets are measuring 0.1755".  So the pellets are a full 1-1/2 thousandths smaller than the barrel, yet they somehow shoot more accurately than anything else I've tried.  Not just 10 or 20 yards but out to 45 yards.   I wish I had an explanation for it but I don't.

That is fascinating. I have no idea why that would happen unless somehow the barrel tightened a little and then in the last half inch or so it expanded again because it wouldn't stand to reason that it would shoot a smaller pellet better.  I had also wondered about creating a device that would pre size pellets. Think of it as a choked push through barrel (unrifled). So if you had a .1770 barrel which preferred .1772 pellets you could push all pellets through the pre barrel giving hopefully giving them a consistent size. (any pellets two small would simply fall through i guess)    just spit-balling ideas. would be neat to see if something like that could work.

[aimsmall]

thanks for sharing. I found it interesting that the crossman measured out at 5.51 while the jsb's were smaller and the JSB's seem to have a better reputation.

[stalwart]

Thanks! I've been hoping to see all this in one place... you've saved a lot of people a lot of homework.

 

[nervoustrigger]

been a while since i've been on the blog. What did you use to measure the headsize? i'd think i micrometer would work but only gives one diameter (for instance would not show if a pellet is slightly oval-shaped) I've seen the setup ted (ted's holdover) uses just curious to see how you were getting your measurements.

I'm using calipers checked against NIST gauge pins of the same nominal diameter as the pellets I'm measuring.  I could probably interpolate in 0.0002" increments but I'm limiting it to a half-thousandth (0.0005").  I wish I had a nice micrometer to get finer resolution but I'm finding that there is enough difference between different makes and types of pellets that the resolution I have is adequate to discern some meaningful differences. 

I don't evaluate roundness, per se, but I take 2 measurements from each pellet approximately 90deg out from each other.  In that way the extreme spread tends to open up if the pellets are out of round by very much. 

[nervoustrigger]

thanks for sharing. I found it interesting that the crossman measured out at 5.51 while the jsb's were smaller and the JSB's seem to have a better reputation.

It's a little early to say but now that I'm tracking standard deviation, it looks like JSB (and H&N, who is also held in pretty high esteem) holds an edge over brands like Crosman and RWS.  And indeed, my experiences with JSB and H&N had been that they yielded more consistent groups day in and day out than other brands in general.  That is, provided the rifle "liked" one of them to begin with.  My first two rifles hated JSB pellets and then my next two just loved them.   Nowadays I cherish the QB79 for its affinity for cheap Crosmans because a steady diet of JSB weighs heavy on the wallet.

[Tater]

First time reading this thread. Thank you for the write-up and chart and that is some fantastic shooting Jason.

[Chaffyn]

but I'm limiting it to a half-thousandth (0.0005").

Okay.  One more WOW headed your direction.  You're the main guy today!!!

I'm still trying to keep my new shooting bench from wobbling back and forth
a few inches with each shot.  Forget 0.0005".  I'll get there.  Just wait.

.
_____________________

[aimsmall]

thanks for sharing. I found it interesting that the crossman measured out at 5.51 while the jsb's were smaller and the JSB's seem to have a better reputation.

It's a little early to say but now that I'm tracking standard deviation, it looks like JSB (and H&N, who is also held in pretty high esteem) holds an edge over brands like Crosman and RWS.  And indeed, my experiences with JSB and H&N had been that they yielded more consistent groups day in and day out than other brands in general.  That is, provided the rifle "liked" one of them to begin with.  My first two rifles hated JSB pellets and then my next two just loved them.   Nowadays I cherish the QB79 for its affinity for cheap Crosmans because a steady diet of JSB weighs heavy on the wallet.

Yes exactly.

[nervoustrigger]

Just made some 0.22 cal updates.  See original post for a summary and downloads.