Why is there a difference in AR-15 & bolt action load charts?

[brown3345]

That's a great Idea, I will call them Monday and see what they have to say then I will post the answer here.

[brown3345]

That's a great Idea, I will call them Monday and see what they have to say then I will post the answer here.

Just talked to Customer Service over at Sierra Bullets. He said that they have 2 different loadings because they have had many people call them with gun failures when using full house loads which could have been caused by many things like:

Guns not rated for 5.56

Home assembled guns that were put together by people who didn't know what they were doing.

Full power loads made with a combination of commercial and military brass mixed together.

Or a combination of all the above and more.

He further stated that you can use the Bolt Action load data as long as you use your head and load methodicaly like you should be doing anyway. Nice people over there at Sierra!

[jstevens]

a bolt action rifle is stronger than a semi-auto, so will handle a heavier load. Barrel length has no relation to pressure at all.

[Bimmer]

a bolt action rifle is stronger than a semi-auto, so will handle a heavier load.

Huh? What's your basis for saying this?

You can say that a bolt action design is inherently stronger than a typical semi-auto design, but the SAAMI specs for any given cartridge are the same for all actions that chamber that cartridge — they all have to have the same "strength" to resist the same pressure.

[nemohunter]

i'm a NOOB to the sight but not to guns or reloading. the big reason is the pressure curve the gun is designed around. it is designed to work on a certain time/pressure curve. start jacking around with it too much and you start battering the gun. you CAN load bolt gun loads you just need to compensate for it somehow. stouter spring and or heavier buffer would be a good place to start. you could also use and adjustable gas block. also shoot some plain jane loads in your stock set up and measure how far the cases are flying. then when you dial up the pressure you will have a reference piont to go buy. for instance my new 6.8 tosses then about 7-8 feet at about 4:30 to 5:00 from my position when standing. now if i go a jack around with loads for hunting season like i know i will have a piont of reference. hope that helps.

[shadowalker]

The OP called Sierra, they said as long as you use proper load development you can use their bolt action loads in semi autos.

The powder you select still has to be suitable for gas operated semi autos though.

[jstevens]

bimmer

My basis for saying this is because it is true, a bolt action is stronger than an AR15. Sure SAAMI specs for a .223 are the same for both, but have you ever sent any ammo to SAAMI and had it checked? The margin of errror is greater with a bolt rifle than a semi-auto. Sierra when printing up a loading manual has no idea what the pressure is in YOUR rifle, just what it is in their test rifle, therefore it is up to you to decide what is maximum. If you have no way of testing but a WAG then it is prudent to use a lighter load than you could in a bolt action Rem 700. Does this make sense? I have a pressure trace strain gage system on some of my bolt rifles to check pressure, but this isn't possible on an AR15 (or at least not practical) since the gage is mounted over the chamber, which would be under the handguard. The logistics would be difficult. If there is no way to really check it, it pays to be cautious. Excess pressure will be a lot tougher on a semi-auto than a bolt. From using my pressure trace, I have found a large increase in pressure when you let a cartridge get hot, such as firing several rounds, getting the barrel hot, then letting a cartridge sit in the chamber for a couple minutes, pressure may increase almost 7-8000 psi. I think everyone will agree that it is easier and more common to get a barrel hot to the touch with an AR15 than a 700 HB varmint rifle. Just another reason why an AR15 should be loaded to a lower level than a bolt gun. This is just another variable that SAAMI specs have absolutely no control over. If you throw some of SAAMI's tested ammo of a known pressure on the dashboard of your truck in the summer, the margin of error may be erased completely.. Reloading is just no place to wing it and push the envelope without really understanding it and thinking it through.

[nemohunter]

Proof loads are used to test all firearms these days. a Proof load is a SAAMI max load heated to 160 degrees for an hour. the only rub is we have such good stable powder anymore that this is hard to do. Hogdon extream propellents typicaly vary no more than few FPS up or down from 32 to 100 deg. this is good for us. nice consistant ammo no matter the temp.