Grendel and silencer troubles

[Mossyoakman3006]

So I’m in a bit of a quandary trying to get my rifle to cycle properly with my silencer. First things first my rifle is has a 20” Tbox barrel, superlative arms gas block, rifle length gas, jp full mass bcg, aac 7.62sd silencer and I’m shooting hornady black ammo, think that covers the details. So here’s my issues the rifle functions perfectly without the can but when I put it on I’m getting pretty severe ejector and extractor marks on the brass. I’ll add pics but I’m getting burrs from the ejector. So I think we’ll i got an adjustable gas block turn it down and bingo no more problems. Well not quite if I turn it down enough not to get the pressure issues solved the rifle won’t function properly failure to feed I mean. I have a jp scs on the way to try that angle with heavier buffer weight and maybe stiffer springs will improve the situation. Just wondering if you guys think I’m headed the right direction or if I’m chasing my tail. Thanks

[Bigs28]

Did you get the jpscs h2?

[Klem]

Hi Mossyoak,

Using an adjustable gas is a good idea.

The energy for loading the next round comes from the compressed spring, not the gas. Turning down the gas will only affect the loading part of the cycle and empty-mag lock-back if the BCG doesn't travel all the way to the rear. The gas pushes against the spring and stores energy in it but once that has dropped below the springs energy the spring takes over and it's all up to the spring. So, if you can turn down that gas to just when the spring is fully compressed but no more...perfect!

[Texas]

You need an adjustable gas block. When we were making piston uppers, there were two notches on the front of the piston, one was for normal use and the other was suppressed which reduced the gas. There was actually a third notch to turn it into a hand operation.

[Mossyoakman3006]

I do have a adjustable gas block my problem is that to get rid of the pressure signs I have to have the gas adjusted to only one rotation from the completely closed position (full gas is 7from closed I believe). When I close it off that much I don’t have enough gas to push the bcg back enough to feed the next round. It’s like this super fine line that I can’t seem to find he happy median it’s either to much or not enough. And yes I have the h2 with the spring kit coming. Also if someone could confirm my understing of the reason I’m getting pressure signs is because the bolt is starting to unlock before the chamber pressure has dropped enough and the brass is still pressing hard against the bolt face is this correct? Thanks for the help this is my first Grendel I’ve built several rifle and never had to deal with the pressure issues like this before just trying to wrap my head around how these rifle operate.

[Mad Charlie]

It seems that I have read numerous threads or posts regarding pressure signs with Hornady Black.
That particular ammo might be higher pressure in general. Might be worth trying different factory ammo to see if those pressure signs persist.

[CaptnC]

I use a lot of range brass in my Grendel's so I see a lot of brass fired from other guns. I'm assuming, it's Hornady Black because I too have read that many guys see brass that is roughed up...that is a factory loaded ammo.

I have limited experience with piston system an my can is still a few months away from being released from jail. But the Osprey system does recommend a lighter spring.

I've never heard of BCG timing being a cause of pressure signs on a case head.

[CaptnC]

OMT on case head pressure signs. I reload an I try to load to "book velocity" to avoid going over the pressure limits of the AR platform. I never see case heads that look like Hornady Black ammo.

I had bought two boxes of Black for break in an brass in my first Grendel. I seen a little signs on the case head, but not like I see from some rifles.

I like the idea of trying another ammo with your gas block opened up a bit.

DNS (Dirty Nasty Spy) runs the same piston system. That system runs great in his videos.

[Bigs28]

With your superlative gas block are you using the blow off feature or the choke gas down feature?

[A5BLASTER]

OP. Double check to see if the gas block is in the correct position over the gas port, before you do anything else.

[Matt.Cross]

Hornady Black runs rather tamely in my Grendel build. Aero upper/lower, Ballistic Advantage 18" barrel w/ rifle gas, and SLR Sentry titanium AGB. I'm also shooting suppressed, with an Ops Inc 12th .30 Cal suppressor.

[snarkscarbine]

H2 buffer and a new spring will probably take care of you. It’ll help keep the bolt closed longer until chamber pressure has subsided more.

Extractor marks can also come from a 556 extractor being used on a Grendel.