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Trying to find load data for subsonic 308 rounds that will cycle semiautomatic


Lattin1

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So I've got A-Max 208gr. bullets and Burger 220 gr. bullets. Figure thats enough mass to create the back pressure needed to cycle the carrier. Now I just need to know what powder and how much. Also, what primers to use and OAL. Anybody know this stuff or have a link to this kind of info?

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Look up the thread " Forbidden Knowledge about Handloading" in the reloading section. It has links and is a good starting point. You will have to experiment with your loadings to get to a safe load anyway.

Edited by Dane Armory
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This is a 950-1,000 fps .30 caliber rifle... what's the difference between it and the 300Blk? Besides cosmetics, isn't this just a subsonic .30cal and a subsonic .30cal?

Since this is in a .308, why not load up some 240gr or 250gr, get a 1:8 or 1:9 twist barrel, and fling some extra heavy lead.

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COAL will be the issue. You'd get the best results if your rifle used G3 metal mags. Metal mags in general will grant you a fraction more length than the popular polymer models.

What is a G3?A fraction more in lenth. Can you be more specific as to how much more?

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  What rifle ?  

These are Subsonic , so stabilization , I would not think would be an issue , but too many factors involved to make a determination with out more info . You may have to do more than just adj. your loads to get them to function semi auto , hard to tell with out knowing the platform your using & the components its made up with .

 

  Primers , well that would be determined by the powder used & charge weight . You can use Magnum Primers if low volume loading powder & std Primers for a more case filling powder loading . There may be quite a bit of R&D to make the rifle function reliably with the wide range of 308 sub or super sonic loads .

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What is a G3?

The HK G3. There are a few 308AR's that were built to use this magazine. It is designed for the .308 cartridge, but I think intended to regularly shoot heavier 175gr ammo (I believe U.S. Military rifles were originally loaded to shoot 150gr) . Thus the little extra length. There was a company about 5 years ago (Fidelis Arms) claiming they had a 12g prototype that used G3 mags to load 2-3/4" shells.

A fraction more in lenth. Can you be more specific as to how much more?

The polymer PMAG has issues loading heavy loads. The polymer walls are a LOT thicker than the steel walls. Outside dimensions are identical, but internal dimensions are slightly larger in steel mags. PMAG's are stereotypically maxed at 175gr, and even not all 175's are created equal.

I know little to nothing about reloading. If you plan on making a "heavy" load that'll chamber reliably, I think your bigger issues will be magazine related vs gas related. Gas and barrel can be easily figured out.

I still think, if this is going to be attempted, you should go as heavy as possible. I know the .300WM can be loaded up to 250gr. I wouldn't waste my time with the 200-220 gr, as that really wouldn't be any different than a .300Blk (unless you were making a supersonic round)

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1-8" twist barrel will be nessisary.

Those bullets are really long. I have loaded some 190gr at 2.815" big projos.

 

This. Especially if it's subsonic since the bullets will be spinning slower for any given speed. You'll end up keyholeing with a long projectile if it doesn't stabilize properly.

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This. Especially if it's subsonic since the bullets will be spinning slower for any given speed. You'll end up keyholeing with a long projectile if it doesn't stabilize properly.

 

 

  Barrel length probably has a lot to do with it , shorter barrels will enhance Bullet stability problems.

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