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View Full Version : How much would you expect POI to shift from 32 to 40gr bullets?



SSV1761982
12-27-2007, 01:01 PM
With my 204, changing from 32gr bullets to the 39 or 40gr will change where it hits the target by 2.5" - 3" mostly left to right.
The groups are ok with both bullets.

This seems like a radical change to me, is this normal? I haven't noticed such a drastic change with my 223 or 22-250 or 6 PPC. I realize there will be some change but this seems to be excessive.

By the way, this is with a LRPV.

Waiting for your opinions,
Dave

Larry Elliott
12-27-2007, 03:50 PM
I noticed that when Nosler Ballistic Tip bullets were first introduced that they shot off to one side of where "normal" hollow point bullets did in a .223 and .22-250. They were accurate, but always off to one side. I don't think that it's possible to say what a normal displacement of groups from one bullet type or weight to another would or should be.

If the rifle is accurate with both bullet weights it really doesn't matter unless you want to shoot light and heavy bullets interchangeably. Even if they shot to the same place at 100 yards their points of impact at longer ranges would likely be different though.

VarmintGuy
12-27-2007, 08:09 PM
SSV1761982: I feel somewhat "qualified" to answer the question you pose.
I have now brought online 4 different Varmint Rifles in caliber 204 Ruger. I have shot both 32, 35 and 40 gr. bullets in all three of them.
I broke all four 204's in with 32 gr. Hornady factory ammo - with the first three Rifles there was no factory brass to begin with and I bought a large supply of 32 gr. factory ammo then went to 40 gr. factory ammo then 35 gr. handloads and then to 32 gr. handloads for those 3 Rifles.
My latest 204 Ruger got broke in and initially sighted in with some left over 32 gr. factory ammo then I tried the 40 gr. factory then my 32 gr. Sierra handloads.
So, "I been around" with different bullet weights in the 204 Ruger.
2.5" difference in P.O.I. between bullets that are 20 to 25% different in weights is nothing!
I am going from memory here and visualizing my "official BR targets that I prefer to do all my load testing and sight in's on - and I am sure several of my load changes resulted in P.O.I. shifts where 4" differences were the norm. I also note that these P.O.I. shifts were not just vertical in nature but were horizontal to some lesser extent as well. IIRC. I did not make note of the differences in P.O.I. shift with different bullet weights as I have never felt it important to do so.
Over the past 5 decades of shooting I have shot numerous Rifles that have printed the SAME weight bullet (different manufacturers of bullets and/or slightly different velocities/loadings) that have had far greater dispersals of their P.O.I.'s than you have enumerated!
I would not concern yourself with these small (or any!) differences in P.O.I. between different weights of bullets. Its of no real consequence in real world shooting. Once your Rifle is sighted in with its best (most accurate?) loading/bullet then forget about the P.O.I. of previous loads tested.
A whole HOST of issues determining P.O.I.'s come in to play when you change bullets - things like barrel harmonics, recoil, length of time the bullet is in the barrel etc etc etc.
Frankly I think 2.5" difference in P.O.I. is a rather minor difference in bullets that are 20% different in weight, that have 10%+ differences in velocities and maybe about 10% difference in length.
Anyway glad your 204 is shooting well and I wish you continued good luck with this fine cartridge.
Long live the wonderful 204 Ruger cartridge!
Hold into the wind
VarmintGuy

Wapiti
12-27-2007, 09:20 PM
FWIW- My Hart barrelled .204 puts 32 Gr. Hornadys @4200 1/2 min high and 1/2 min right from my 40 Gr.Nosler @ 3900 zero! Go figure.:D

Good shooting!

sicero
12-27-2007, 09:25 PM
My 204 puts 39 & 32 Sierras in the same hole at 100yd. But it would not suprise me to have them several inches apart either. Kenny

SSV1761982
12-27-2007, 10:34 PM
I have only been shooting decent rifles for a few years. VarmintGuy put some good info in his reply. I didn't think about a 20% difference in weight. That is quite a bit of difference compared to 4% from a 50 to 52 grain bullet. Or even a 50 to 55 would only be 10% in a 22 caliber rifle.

I am still working on finding which will be the best bullet. No clear winner yet due to lack of time and weather.

This rifle drove me nuts until I finally bedded it. I also sanded that black rough textured stock smooth and painted it, followed by some car wax. Now it slides freely on the rest. It is much more consistent than it had been.
I think the average group size has been cut in half. It used to print 2 groups half the time.

Thanks,
Dave

B J Atkinson
01-02-2008, 09:32 AM
I noticed that when Nosler Ballistic Tip bullets were first introduced that they shot off to one side of where "normal" hollow point bullets did in a .223 and .22-250. They were accurate, but always off to one side. I don't think that it's possible to say what a normal displacement of groups from one bullet type or weight to another would or should be.

If the rifle is accurate with both bullet weights it really doesn't matter unless you want to shoot light and heavy bullets interchangeably. Even if they shot to the same place at 100 yards their points of impact at longer ranges would likely be different though.

Funny you should mention that, Larry. For years I have noticed that there is a difference in impact point between boat tail and flat base bullets - even of the same weight. I first noticed this in my 7mm-08 which had one of the original 8 groove Shilen barrels.

I have no explanation as to why this might happen - the boat tails always shot to one side of the flat bases.

J. Valentine
01-03-2008, 05:41 PM
I have a theory. It is only a theory so dont jump down my throat! Please.
Flat based bullets suffer from base edge damage from the lands.
It manifests as slight shards of jacket material hanging of the back of the projectile base. ( Less damage on Moly coated bullets ). This part is a proven fact.
The theory part.
This causes the flat base to suffer more precession or spin drift ( Magnus Effect ) than a boattail because the boattail does not get the base edge damage. Is more aerodynamic and less affected traveling out the muzzel blast . I think the correct term is smaller yaw of response.
I think the flat base is shooting to the side not the boattail.
The flat base is still accurate because the base damage is consistant and can sometimes exibit beter group accuracy at short range than a boattail but the POI is moved away from the boattail .
8 grooves = more little fins to increase precession and drag .