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

[lattin1]

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?

[Clint]

I believe this is what you're looking for...

http://300aacblackout.com

[waveslayer]

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?

the question is what powder do you have access to? if you can find the unicorn named Accurate 1680 then there are a lot of loads that will work with that powder. but if you are like the common man, good luck finding it! I have a sweet little load using Norma 200. I use CCI Small pistol primers Sierra 220gr. SMK's. loaded to mag length. now the amount of powder will depend on your barrel length, where your gun shoots at subsonic velocity, and whether or not it will keyhole. you have to do some testing for keyholing or you will get a baffle strike!

[Onyx Z]

the question is what powder do you have access to? if you can find the unicorn named Accurate 1680 then there are a lot of loads that will work with that powder. but if you are like the common man, good luck finding it! I have a sweet little load using Norma 200. I use CCI Small pistol primers Sierra 220gr. SMK's. loaded to mag length. now the amount of powder will depend on your barrel length, where your gun shoots at subsonic velocity, and whether or not it will keyhole. you have to do some testing for keyholing or you will get a baffle strike!

I believe the OP is referring to 308 Win, not 300BLK.

I've seen a lot of people using Trail Boss for subsonic 308 Win. The Hodgdon website lists Titegroup and Clays for 168gr SMK's as well. Be aware that you NEED a chronograph for working up subsonic loads.

[waveslayer]

I believe the OP is referring to 308 Win, not 300BLK.

I've seen a lot of people using Trail Boss for subsonic 308 Win. The Hodgdon website lists Titegroup and Clays for 168gr SMK's as well. Be aware that you NEED a chronograph for working up subsonic loads.

you are correct, small over look.

[lattin1]

As far as powders go all I have is Hodgon h110, IMR 4198, Accurate 2495, and Reloadr 7. I did pick of a chronograph the other day by chance so atleast I got that out of the way. Only thing that worries me is I have a 14.5" barrel with 1:10 twist so it might be pretty tough to get these loads to stabilize. Thanks for the help

[waveslayer]

trail boss is what you will want to use. their is a great video in line that show a good way to grease the bullets too. basically I resorted to loafing subsonic. 308 wasn't worth it. that's why I got a .300 blackout

[mic2377]

Unfortunately I am sure that the goal of a subsonic 308 Win that cycles will ultimately be fruitless. If you have played around with 300 BLK subsonics, you would see that they provide VERY little energy to cycle, even for a AR-15 action. The 308 AR platform has a significantly stronger action spring, much heavier BCG, and requires much more force to strip rounds from the magazine, all of which make it impossible to cycle with subsonics. I am sure that you could mod a 308 AR to cycle, somehow, with an ultra short gas system and large gas port to do so. But it would beat itself to death with any sort of full-power rounds.

The powders you have will not provide enough case fill or the correct burn rate for subsonic 308 Win. Trailboss (or SR 4579?) are your options. They will be quiet but won't even make the BCG move. I have also used Red Dot under a 168 SMK for some ultra-quiet sub loads but I would be VERY careful with such a fast burning powder.

Take this advice from someone who has experimented...