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Post by mdgroundhogger on Mar 8, 2011 22:23:40 GMT -5
Quick question. Do you have to modify standardized loading data for a semi auto rifle? I'm going to start loading for a DPMS 308lr and I was wondering if the action could handle the pressures like a bolt action. thanks
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Post by mdgroundhogger on Mar 9, 2011 23:57:54 GMT -5
(crickets)............. does anybody know if there is an issue or not? I just heard online that approaching max loads could be detrimental to a semi auto platform. Is this BS or does it hold water?
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Post by youp50 on Mar 10, 2011 4:55:12 GMT -5
I do not know about the pressure in an AR.
I do know that in my Remington auto and Savage lever the brass needs to be resized with a small base die.
I would imagine the rifle would need to be able to function at SAAMI pressures. It would also follow that it may last longer at lower pressures.
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Post by Rifleman on Mar 10, 2011 6:24:42 GMT -5
The thing with loading for semi-autos is that the brass must be resized to factory brass specs. If you measure a factory cartridge before it is fired, you will find it is smaller in many measurements then what a reloading manual calls a minimum spec. For example over all case length in many factory cartridges is shorter then the what the reloading manuals call for as " trim to length". Also you should buy a Redding headspace gauge for your caliber of choice. Drop in a factory Federal unfired cartridge and you will find it drops all the way into the gauge, in other words it is smaller then what you would normally resize too. One would think this would result in cases that are overworked during the firing process as they expand to fit the chamber. But a case that is to big will not chamber either.Really it is a tricky thing to get the headspace just right when reloading for a Semi. One thing you can do to help in this regard is to keep your brass sorted out. When running lots of mixed brass, things get even more sketchy. The way I learned to address this was to buy Redding Small Base resizing dies for all my semi-s in .223, 308, and 30-06. I then took a base line measurement of factory Federal ammo and simply resized and trimmed to those dimensions.I also tried to not mix my brass. I also would shoot factory ammo over a chrony and record the avg velocity. I then chose reloading data that would mimic same, and when developing loads sought to match those numbers. I never had any problems loading for semi-s while using this protocol. One word of caution, often folks will buy mil-surplus ammo to shoot from their semis and then use the brass for reloading. That is fine as long as one remembers that most mil-surplus ammo has thicker case walls with a reduction in case capacity, so charges have to be reduced accordingly. Also the AR platform is no where near as strong as a bolt gun and the margin for error is smaller. I suspect most AR's that are damaged from reloading fall victim to ammo that is over size in some manner rather then charges that are to stiff. A case that is too long pinches the bullet in a rifling and if for some reason the gun does lock into battery and fire, the pressures are driven up exponentially regardless of how "mild" the charge is. IMO reloading for semi's is advanced reloading and one must educate themselves and proceed with intelligence and caution. Do a web search for AR-15's that have been blown apart by reloads, and you will find that quiet a few guns are destroyed by poor reloads. Quite frankly if I had to do it all over again, I would buy good mil surplus ammo and shoot that for practice and fun. When it comes to hunting ammo, I would just load a few for my needs or even by a box or two of factory. Matter of fact, that is what I do now and don't miss the reloading process at all.
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Post by mdgroundhogger on Mar 10, 2011 23:08:46 GMT -5
I appreciate the info.  Everything you've said makes perfect sense. I've been reloading for almost twenty years and I've always checked and double checked. The case length was the furthest from my mind but I can see how that would have more of an effect on pressures than approaching max SAAMI book pressures. That must have been why they stated that standard reloading practices would not work for an AR type rifle, but of course they were very vague with the explanation. I am going to get on line with Midway and get some of those small base dies I've always avoided ;D. Thanks |
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Post by rossman40 on Mar 10, 2011 23:28:38 GMT -5
The main problem you run into with the AR platform is using slower powders (or more) that as a result gives you higher muzzle/bore pressure. Even more so with barrels longer then 20", makers will add length but not extend the gas block farther out as you see on race/space guns. Not so much to the gas system that breaks the operating rod in the M1 and M1A (M14) but in the AR you will unlock the bolt before the pressure in the bore has gone down. As a result you see ballooned or ruptured cases, cracked/chipped bolt lugs and the bolt can get slammed back harder then the buffer spring and the little bit of rubber on the end of the buffer can handle. Guys that shoot hot loads in a AR will have a adjustable gas block and will add a weight to the bolt carrier to slow it down. More mass on the bolt carrier means slower opening. Your carrier moving back unlocks the bolt so by adding weight you slow it down a few micro seconds.
Full length resize and watching your case dimensions as Rifleman said insures operation and other related problems
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Post by Rifleman on Mar 11, 2011 7:02:13 GMT -5
Rossman gives some really good insight, I always just used propellants that were similar to what is loaded in Mil spec ammo and never had those problems as a result.
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Post by mdgroundhogger on Mar 11, 2011 22:37:40 GMT -5
Thanks guys. More indepth than I thought. Still worth the extra trouble though. IMO ;D
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Post by mdgroundhogger on Mar 13, 2011 19:35:04 GMT -5
Well I've got my first batch loaded up. I went and bought a box of Hornady SST's just to get some headspace measurements with my Stoney Pt gauge. Set up the full length die for the same measurements and I think we're good to go. I set the C.O.L. to .010" below the listed C.O.L. in my manuals to be on the safe side of the bullet seating. I'm going to be trying 155gr Nosler Custom HPBT's and 165gr Sierra HPBT's with Varget powder (starting at 42gr and working up to 44gr). This should do the trick now I just need some time off w/o rain to get to the range.  |
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Post by rossman40 on Mar 18, 2011 21:54:42 GMT -5
The "jump", from the loaded length to engaging the lands, is probly the hardest thing to get a grip on. The optimum jump will be different with every barrel and even change as the barrel wears not to mention different bullets and powders. But that is what makes the game fun!
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Post by whyohe on Mar 19, 2011 3:38:27 GMT -5
+1 on what Rossman posted. I have a M1 Garand and was told that you should not use factory 06 ammo un less it is specified fro the M1 cause you can damage the acuating rod. Factory ammo was to "HOT" for a semi auto M1 and created too much pressure. if i was to reload for it that i should get a manual that had loads for the M1 wich specified for military brass and standard brass.
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Post by muznut on Jan 31, 2012 16:38:34 GMT -5
In my rem 7400 308 I stay 2 or 3grs from max in my win 300mag super x, same as the new b.a.r. I load right to the max and it tack drives, now the ar that's a different story don't listen to me.
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Everything you've said makes perfect sense. I've been reloading for almost twenty years and I've always checked and double checked. The case length was the furthest from my mind but I can see how that would have more of an effect on pressures than approaching max SAAMI book pressures. That must have been why they stated that standard reloading practices would not work for an AR type rifle, but of course they were very vague with the explanation. I am going to get on line with Midway and get some of those small base dies I've always avoided ;D.
