Overgassed or Undergassed? Or just right?

[DefenderAO]

Report
I took the SBR to the range today to check how its gassed. Ejection patterns were consistently at the 1/1:30. Bolt locks back on empty mag 100% of the time. From this, I thought "overgassed." However, randomly watching a video today I saw brass hitting the deflector which had a very similar sent-casing angle as I saw at the range today. Two other issues: 1. I do not have a spent casing picture to determine indentations or markings. 2. I never did check to see if the spent casing was hitting the deflector or going to 1/130 on its own (obvious).

Overgassed or undergassed? Or simply gtg?

Details:

- 11.5" barrel
- carbine gas system
- suppressed, Griffin Armament can
- gas port .48...made for suppressed only shooting. Yes, it's small.
- FA carrier; LMT bolt, no special extractor
- JP Rifles H2 buffer/sprong combo
- ammo - M193 Federal 55 gr

The only tell I have is this picture of the deflector. Apparently it is a common marking, but is this indicative of over or undergassing? I was going to upgrade to an H3 JPR system, but if the brass is hitting the deflector, I may need to go H system or lighter.

[Artos]

Ya know, I'm the last guy that should pipe up on the technical stuff with all the other sperts here knowing much more than me...if I'm running like a sewing machine & dumping brass at 1-2 ejection, I'm happy.


Welcome to the Forum!!

[Clint]

The brass always his the deflector.

It's just a matter of where and at what angle.

Hitting that inside edge and ejecting to 1:00 would seem to indicate over gassing.

How big is that gas port again?

[DefenderAO]

The brass always his the deflector.

It's just a matter of where and at what angle.

Hitting that inside edge and ejecting to 1:00 would seem to indicate over gassing.

How big is that gas port again?

.48. Will not cycle without a can. I'm pretty shocked with a JP Enterprise H2 spring/buffer, a .48 gas port, and a FA vs SA carrier I found a way to be overgassed. And I was not aware the casings always hit the deflector? So on an ideally gassed AR the hit the deflector and bounce to 4 o'clock?

[scooter22]

.48. Will not cycle without a can. I'm pretty shocked with a JP Enterprise H2 spring/buffer, a .48 gas port, and a FA vs SA carrier I found a way to be overgassed. And I was not aware the casings always hit the deflector? So on an ideally gassed AR the hit the deflector and bounce to 4 o'clock?

It’s not 0.48”. More like 0.048”.

Triarc’s 11.5” suppressed only barrel is 0.045” last I checked.

Locking back on an empty mag with suppressor attached shooting XM193 is appropriate.

Don’t overthink it.

Sent from my iPhone using Tapatalk

[DefenderAO]

It’s not 0.48”. More like 0.048”.

Triarc’s 11.5” suppressed only barrel is 0.045” last I checked.

Locking back on an empty mag with suppressor attached shooting XM193 is appropriate.

Don’t overthink it.

Sent from my iPhone using Tapatalk

.048 yes. I have read Triarc is .046 to .048. Either way I have not read of a smaller port size. BCM is something like .076, DD .069. I’m concerned parts may wear faster than needed and, when they do, best case is bad ejection become more pronounced and worst case, failures.

[scooter22]

.048 yes. I have read Triarc is .046 to .048. Either way I have not read of a smaller port size. BCM is something like .076, DD .069. I’m concerned parts may wear faster than needed and, when they do, best case is bad ejection become more pronounced and worst case, failures.

Triarc told me themselves that it is 0.045. Perhaps that has changed. Parts would wear leas quickly with a properly or conservatively ported barrel such as yours. Your rifle seems to be functioning fine.


Sent from my iPhone using Tapatalk

[1168]

Which Griffin can?

[MikhailBarracuda91]

My LMT (non enhanced) BCG does the exact same thing. It ejects spent cases to 1:30, when I switch it out to a BCM BCG it throws the cases to 4:30.

Chris Bartocci form Small Arms Solutions says LMT designs their weapons like that. In my experience it's the BCG's

Sent from my SM-G970U using Tapatalk

[georgeib]

I've read here that a forward ejection pattern can sometimes be caused by the extractor spring. Do you have another spring, or bolt to try?