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Posted: 2/19/2012 7:52:42 AM EDT
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ok
M2 ball loaded with 44gr IMR4895 in LC brass. win primers. GTG point of aim point of impact now some thing different 7.62x54r 147gr projos pulled and resized. caliper measures them at .307. loaded with 40gr of 4895 since the projos are longer. same brass and primers. shot at 100 yds...no keyholing but dispersion all over. cqb range wouldnt group like the previous load. im thinking i dont have enough powder in the case therefore causing inconsistent burn or the projos just suck thoughts? |
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Any time you change a component or powder charge you can have an affect on accuracy and POI.
loaded with 40gr of 4895 since the projos are longer
I agree that one should start low and work back up when changing any component, but what does bullet length have to do with the reduced powder charge? |
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For longer bullets and the same COAL (2.80 in this situation, I presume), the shank of the longer bullet takes up powder space in the cartridge assembly. It then is similar to peak pressure changes between .mil cases and comm'l cases for the .308 / 7.62. However, I would agree that phenom is secondary to bullet weight. Going up in bullet weight for the same powder charge definitely does increase peak pressure.
As far as stabilization in flight from rotation, the formula is definitely related to bullet length and not so much bullet weight. So, as far as the OPs question, I would say a little bit of both...low charge and lesser quality bullets. And, please let us know if going up in charge helps solve the scatter problem. |
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Quoted: ok M2 ball loaded with 44gr IMR4895 in LC brass. win primers. GTG point of aim point of impact now some thing different 7.62x54r 147gr projos pulled and resized. caliper measures them at .307. loaded with 40gr of 4895 since the projos are longer. same brass and primers. shot at 100 yds...no keyholing but dispersion all over. cqb range wouldnt group like the previous load. im thinking i dont have enough powder in the case therefore causing inconsistent burn or the projos just suck thoughts? Teh russian bullets weren't intended to go in 308. |
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Quoted:
Quoted:
ok M2 ball loaded with 44gr IMR4895 in LC brass. win primers. GTG point of aim point of impact now some thing different 7.62x54r 147gr projos pulled and resized. caliper measures them at .307. loaded with 40gr of 4895 since the projos are longer. same brass and primers. shot at 100 yds...no keyholing but dispersion all over. cqb range wouldnt group like the previous load. im thinking i dont have enough powder in the case therefore causing inconsistent burn or the projos just suck thoughts? Teh russian bullets weren't intended to go in 308. i know sold as resized for blasting foder just trying to get something workable |
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Quoted:
For longer bullets and the same COAL (2.80 in this situation, I presume), the shank of the longer bullet takes up powder space in the cartridge assembly. It then is similar to peak pressure changes between .mil cases and comm'l cases for the .308 / 7.62. However, . Reducing OAL in a bottle necked rifle round does not increase pressure. In fact, just the opposite is true, it reduces pressure. |
I think I know what you are basing that statement on. However in this situation, the .311 R bullet is resized to .308 which would make a longer bullet. The "jump" distance would not necessarily change, for a longer shank in the case. It would be similar to this:
The most important thing to remember about military brass is that the internal capacity will probably be less than commercial .308 Win brass, because military brass often has thicker webs or casewalls. Montana Marine reports his fire-formed milsurp cases hold 56 grains of H20 on average compared to 58 grains for fire-formed Winchester. Given the reduced capacity of military brass, you should reduce posted max loads by 1.5 grains when loading with Lake City or most other milsurp brass. However, the IMI MATCH brass is closer to commercial brass in internal case capacity (ICC). Kevin Beggs reports: "Fired, my IMI Match brass runs with an ICC of 55.0gr and bumping the shoulder back .001" will net me an ICC average of 54.0gr. LAPUA runs an average of 54.4gr and Federal runs an average of 54.3gr ICC."
––www.6mmbr.com When commercial cases were substituted for the military LC cases using the Key load, both velocities and pressures were significantly lower. The three different commercial cases (Federal Winchester and Remington) all gave substantially the same results. As has been pointed out before in the American Rifleman and other NRA publicsations, the cubic capacity of the commercial .308 Win case is greater than that of the 7.62 NATO military cases , and the lower velicities and pressures produced in the commercial cases are the expected consequence of the differences in case capacity.
–– p.30, Semi-Auto Rifles Data & Comment, R.W. Hunnicutt, 1988 Military cases are often thicker than commercial ones and have less case capacity. Reduce charges developed in commercial cases at least 5% when loading military brass.
––p. 277 Speer Reloading Manual #13, 2005 Military cases are generally thicker than those made for the civilian market. This slight reduction in internal capacity can raise pressures. –– ABCs of Reloading Ed. 7 & 8 , p. 34 first para. |
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Bumping bullets up in size is usually not a problem, but sizing them down can be.
The jackets have a certain amount of spring back while the lead core doesn't. When you size them down the jacket can separate and cause accuracy issues such as you are describing. I have not personally sized down any rifle bullets but I have some handgun and the accuracy was abysmal. |
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You changed bullets and accuracy went south. Head back north to the original bullets you were using. The Russian .310 bullets are not known for great accuracy before they were sized down. ive reloaded all my M2 ball the russian i bought in 08 when components were rare and costly. picked up 2k. so i would like to use them. not expecting much more than blasting ammo but would like something bettter than Minute of Barn Door |
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