need help cycling " bunny fart" loads though an AR

M

MRTJBIGA

New member
i have a SBR with a Griffen GP7 toob. 9inch 300blk barrel ,with a riflespeed gas block

and LWRC Ultra Compact (UCIW) Stock Assembly (with buffer weights removed)

ive loaded a few rounds with 4.2 gr of trail boss and sirrea 30 cal 168 gr gas

setting fully opened and weights out of my buffer . it will not eject the rounds

is it possable to get my rile set up to cycle quiet like rounds with trail boss .

how much at one time do i add more trail boss i dont want to grenade my rifle

the sierra bullets are just what i had laying around. gonna switch to lead cast coated

later for plinking any ideal gr weight for queit rounds ? or it is mainly the type of

powder you use
 
Trail Boss load has low energy. I would probably try the following.

Light weight skeleton bcg.

Lighter weight spring but still able to store enough energy to feed and chamber.

Heavier bullet and higher power charge (safe working up of course) to increase chamber pressure.

Crimping the bullet to promote better gas sealing of the brass on chamber wall.

Enlarge the gas port.

Pistol length gas system (requires new barrel).

-TL

Sent from my SM-N960U using Tapatalk
 
Ive never gotten Trailboss to cycle any of my AR’s in 300blk. Its a super quiet powder for use in my boltguns, just not enough gas volume to move a BCG.
 
Accept the fact that "bunny fart" loads don't have enough "poop" to cycle the semi auto action.

You can play all kinds of games, changing all kinds of parts, to try and get this to work, and maybe it will, or maybe it won't. Parts changed to cycle really light loads must be changed back to original spec before shooting full power ammo, or you're risking damage.

Easiest and simplest thing is just to run the super light loads and manually cycling the action.
 
The problem is Trail Boss is a fast powder, so it burns up and makes its peak pressure before the bullet has moved very far, and that, in turn, means it peaked in a small volume and didn't make much gas relative to what you would get from a powder that lets the bullet move forward a couple of inches before it peaks. If you loaded, say. 4227 to the same velocity, you might get twice the gas port pressure, though a lot of the powder would blow out of the barrel unburned, making a heck of a fireball if you don't have a really good flash suppressor.

Try this experiment. QuickLOAD shows 4.2 grains of Trail Boss, giving you a velocity of 785 fps from a 9" barrel. Safely subsonic, even in 0°F weather, would be 1050 fps. If you fill the case just short of starting to compress the load (to be avoided with Trail Boss), which should be about 6 grains, you are still sub-sonic and at modest pressure. If that doesn't cycle the gun, it is time to switch to something rather slower that wastes some powder and makes a muzzle flash. 11 grains of H or IMR 4227 should roughly double gas port pressure, though a lot will go out of the barrel as muzzle flash and waste or as a means of plugging up your suppressor. You might want to use the hottest magnum primer you can find to minimize the waste aspect of it.
 
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