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Are these tumbling? 225 gr Hornady BTHP's in 300 WM

 
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  #1  
Old 05-13-2013, 02:00 PM
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Are these tumbling? 225 gr Hornady BTHP's in 300 WM

Hi Fellas,

Finally got out to shoot my new to me Browning A-Bolt in 300 Win Mag. I had hopes of making this a good, light weight, mid to long range hunting rifle so when I found a screaming deal on some 225 gr Hornady BTHP's I jumped on them and loaded them over 75, 76 and 77 gr of Retumbo and headed out to test them out. COAL was 3.461" average and they were loaded in 1x W-W Super cases w/WLR primers.

I was shooting at the lower left target (8.5x11 paper each) and you can see what appears to be impact from debris (first shot was a big puff of dirt in front of the target) and then two long holes in each of the right targets. Are these tumbling and not stabilizing? I only shot the 3x of 75 gr given what I saw on target.

The only other load I a had on hand was a 150 SGK over a light load of 760 just to sight with. They printed normally and in about a 2" group.

Thanks for the help as always and God bless you all,

Adam

Here are some photos:





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Old 05-13-2013, 02:30 PM
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Re: Are these tumbling? 225 gr Hornady BTHP's in 300 WM

What is your barrel length, and the barrel twist rate? I would think a 26 inch barrel with a twist rate of 1:10 should be good enough. Might be smart to shoot one shot at 25 and another at 50 yards to look at the angle of the impact.
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Old 05-13-2013, 02:31 PM
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Re: Are these tumbling? 225 gr Hornady BTHP's in 300 WM

If you have a hole...thats anything but ROUND.....you have some amount of tumbling!
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Old 05-13-2013, 03:50 PM
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Re: Are these tumbling? 225 gr Hornady BTHP's in 300 WM

22" barrel and 1:10" twist.

I did not shoot the 6 rounds I loaded heavier, but how will driving them faster or slower affect stabilization?
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Old 05-13-2013, 05:51 PM
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Re: Are these tumbling? 225 gr Hornady BTHP's in 300 WM

Stability is RPM dependent. The actual RPM's can be achieved by various means, such as shooting at a lower speed through a faster twist rate, or a higher speed through a slower twist rate.

For a given twist rate, a higher MV will provide increased stability. The Berger stability calculator will show that. However, the difference between a 20" barrel and a 28" barrel should not make that much practical difference to stability, although it will make a difference to downrange energy.

For grins, I ran some numbers on the Berger stability calculator. Hornady does not state the bullet length, nor do they recommend a twist rate (kinda hard to believe from a premier bullet maker), so I looked up the length of a Berger target bullet of a similar weight (1.6"). I then ran the calc as follows:
Caliber 308
Weight 225gr
bullet length 1.6"
Barrel twist 10
Muzzle Velocity 2500fps
Temperature 20F
altitude 0feet

The calculated SG was 1.34 , for 60F and 1000ft it was 1.5 1.5 is "comfortable stability" and you should really do better than 2400fps unless you are being handicapped by that short barrel.

"corrected base cartridge"
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Old 05-13-2013, 06:20 PM
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Re: Are these tumbling? 225 gr Hornady BTHP's in 300 WM

I'll try the Berger calculator w/ my variables, I've never tried it. But I have no experience w/ bullets this long either.

Here are the impact holes, you can see the 2" group w/the 150s in the first also:



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Old 05-13-2013, 06:27 PM
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Re: Are these tumbling? 225 gr Hornady BTHP's in 300 WM

Caliber 308
Weight 225gr
bullet length 1.6"
Barrel twist 10
Muzzle Velocity 2500fps
Temperature 70F
altitude 8000 feet

I get a SG of exactly 2 with those inputs, so not sure what is off. . .
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