Reloading for suppressed rifle

[Old Stony]

I've been playing around with an Ar-15 lately shooting factory ammo, and decided to go ahead and reload some of the brass I've been collecting.
The factory brass comes out pretty black and nasty, and I just figure that's a result of running a suppressor on the barrel...causing it to blow back more gasses into the chamber. I loaded 10 cartridges today just to try them and see how they grouped compared to the factory, and the brass was just as nasty as the factory ammo was.
My loads should be within a reasonable pressure range for the rifle, but I noticed some flattening of the primers and was wondering if the back pressure as a result of the muffler could be causing some of the primer pressure signs?
Any thoughts from suppressor guys on this situation?

 

[Mobuck]

"I noticed some flattening of the primers and was wondering if the back pressure as a result of the muffler could be causing some of the primer pressure signs?"
Not likely. The bore pressure at the point where the muffler is located is far lower than the chamber pressure at the moment of firing.
If you want to cut the "black and nasty" a little, use a faster powder. This builds pressure quicker and hopefully, lowers port pressure and DI system fouling.

 

[Unclenick]

The blackening is, as Mobuck suggested, incompletely burned powder. The slower a powder is, the higher the pressure needs to be to burn it cleanly. The primer can also be flattened somewhat by marginal pressure from a slow powder, though it doesn't look exactly like high pressure flattening. It happens because there is enough headspace that the primer backs out a little. That's normal. But in a load that reaches peak pressure quickly, the case sticks to the chamber and the pressure ring starts to stretch and the head moves back to reseat the primer right away. But if the pressure builds slowly, the primer sticks out for a longer time and that allows pressure more time to flow back through the flash hole to inflate the cup a little before the pressure needed to back the head up is reached. As a result, when it does back up, it squashes the inflated part of the primer, making it flat. Primers that get flat from excess pressure are flattened after the head has backed up. Generally, that makes for a sharper corners at the perimeter.

 

[zeke]

If I am loading max loads for the 223/308, am now in practice of backing them off a tad if they are intended to be used with suppressor. Am of belief use of suppressor slightly increases pressure/velocity.

 

[Mobuck]

We shoot factory loads through suppressed AR rifles all winter w/o any issue what so ever and those are at the top end of the loading scale.
The only thing a suppressor affects is the residual gas in the bore after the bullet is past the muzzle. This "back-pressure" in the bore and muffler body is what blows crud through the DI gas system and past the fired brass as it's being extracted. It's NOT so much the residual pressure, it's the VOLUME of the residual gas in the muffler looking for someplace to vent.

 

[243winxb]

the gun is still in the process or firing while it’s trying to extract the cartridge case.

Hornady Support info - https://www.hornady.com/support/superformance-in-gas-operated-firearms

I watched a guy shoot a suppressed Ar15 with factory ammo. Very dirty.

How about using an adjustable gas port?

 

[zeke]

Generally shooting semi's suppressed is very dirty, and the adjustable gas ports on the firearms owned are significant benefit in reducing gas blowback and stress on operating parts. However am of the belief do not reduce the chamber pressure. The increase in pressure it is just an opinion, based on looking at slight increase of velocity when attaching a can to the rifle I recorded the velocitys on. And no did not do a several hundred round test sample. :>)

 

[Mobuck]

Adjustable gas block doesn't help (much) with the fouling in the action/magazine. Has nothing to do with chamber pressure. Chamber pressure has already peaked and dropped by the time the bullet passes the gas port otherwise bad stuff would happen inside the receiver. A piston op will reduce the fouling inside a center fire semi-auto but not entirely.
Shooting ANYTHING suppressed is going to generate more fouling than w/o since part of what the suppressor does is catch and dissipate the muzzle gasses. Doing this causes that gas(and the fouling it usually carries out the muzzle) to look for someplace to go. All the crud that builds up in a rimfire can didn't just appear by magic, it was being blown out the muzzle with every shot. The muffler catches that gas/carbon/melted bullet lube/lead dust and it settles in the can. Similarly, the powder fouling/bits of unburned powder/particles of bullet jacket generated by firing a center fire cartridge are slowed/redirected/contained within the bore and operating system of the rifle and try to exit anyplace there's a gap(and there are lots of gaps in a DI system like the AR).

 

[jmorris]

I don’t do anything different, I shoot the same loads suppressed or not.

That said I don’t try and make a 22-250 out of a .223. Or for that matter a .22 LR out of one loading subsonic rounds either.

 

[Unclenick]

The increase in velocity is due to the can preventing gas from expanding laterally as fast as it does from a plain muzzle. As a result, post-exit bullet acceleration by muzzle blast goes on a bit longer. The same lack of rapid expansion that maintains pressure behind the bullet reduces the rate at which gas blows out of the bore, so it doesn't sweep fouling out as effectively as with a plain muzzle. This is expected to be true for any gun, semi-auto or not.