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Old December 22, 2009, 12:34 PM   #1
(Long Action 86)
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pressure problems 270

I recently purchased a rem 7400 off a man needing some money. I normally don't go for autos bc of accuracy but this gun hadn't had a box ran through it and purchased for 150. Couldn't pass it up. Well anyways I started working up a load bought some 130 hornady sst s using h4831 and some ol win primers I had laying around. I strarted 1 gr over starting load out of my hodgens book. I got heavy cratering. I'm down to 46 gr witch is 4 gr below startin and primers are still flating out preety good. I'm afraid of wearing the gun out with hot loads but I'm not getting near the speeds of a factory load. About 250 ft slower. Any tips or advise welolmed. Note I am crimping shells.
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Old December 22, 2009, 06:40 PM   #2
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Are the factory loads causing primer cratering?

If not, I suspect you are actually seeing an under-pressure problem. Self-loaders are different from bolt guns in that the mechanism can bounce around a bit if you have inadequate pressure. That may account for the apparent cratering? Gas guns have a pressure band that should be neither exceeded nor under done. They typically like powders on the faster end of the normal range for the cartridge. I think IMR 4831 is pushing the slow end of the envelope in a .270 gas gun. Given the bullet is a little smaller than a .308 you might be OK with IMR 4350, but if it were mine I would be trying IMR 4064. Lyman runs IMR 4064 at 44.5 to 49.5 grains, and it's bulky enough for its speed that it is filling the case over 90% at the high end of that range. It will almost certainly have good compatibility with the gas mechanism.

Gas guns are critical as to head space and case sizing, too. Full length resize-only and preferably with rounds that were originally fired in that same chamber when new.
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Last edited by Unclenick; December 22, 2009 at 08:37 PM.
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Old December 22, 2009, 09:32 PM   #3
(Long Action 86)
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Thank for the advise I just so happen to have 4064 ill try here in the next few day post results. And ill get some unfired brass and FL em. It didn't even cross my mind that my brass out of my bolt action may have cause this. And once again thanks for the tips.
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Old December 22, 2009, 10:15 PM   #4
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Let us know how it works out? There is a good section on gas gun loading in Sierra's manual. It is geared toward service rifle match military guns, but some good general information is in there if you get a chance to read it? 15 pages or so as I recall, so it isn't a long read.
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Old December 22, 2009, 10:24 PM   #5
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Try some factory loads first to see if it is still doing that before you invest more time making more loads......if it is, it might be something else that needs investigating....
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Old December 23, 2009, 04:30 PM   #6
(Long Action 86)
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Worked flawlessly I used 45 gr of imr 4064 gettin around 2900 ft. As of right now having some speed varance of about 50 feet witch I'm comfortable with in just a hunting rifle and getting 1.5in moa 5 shots groups. That's also fine with me was expecting lot worse. And best of all preassure sign on primers is little to none . Idk if it was the unfired FL ed brass or the powder change that corrected the problem but I'm happy with the results. Note any load over 45.5 resulted in flattening. I'm at the speed I wanted so that's all that matter. Thanks so much for the advise. Seasons greeting.
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Old December 24, 2009, 02:42 PM   #7
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Good deal. As an experiment, dry seating the primers a little more firmly than normal and see if that cuts ES any? Also, you've got some extra powder room in there. Try tipping the muzzle down before every shot and see what velocity and ES that gives? Then reverse the process and tip the muzzle up to put the powder over the flash hole before every shot. See what that does? The old M72 load for the Garand (46.5 grains of IMR 4895 under the 173 grain FMJ BT) would vary 80 fps for me from doing that. It also went from rounded primers (muzzle down) to flat primers (muzzle up). Never affected its target accuracy much, though, either way.
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Old December 24, 2009, 03:36 PM   #8
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I use IMR 4350 in a bolt rifle, but in a gas operated rifle, IMR 4064 is the slowest you should go.

If you are getting good results with IMR 4064, then stick with it.

Keep your chamber clean and the rifle lubricated.
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