Got gas in my eye, hacksaw time!

[Karre]

So I shot my pcc without glasses for the first time today and got gas in my eye, more then I think it should be. I'm still playing around with buffers and so on, but now I want to start with deciding how long my barrel should be. It's 16 inch now and I can cut it as mush as I want. But it could be good with 16 with a "pinned" comp, if there isn't any benefit on going shorter. 

 

But what is the "perfect" length with a comp? I use the gun for IPSC and Steel challenge.

 

It's a QC10 receiver, barrel and bolt(without the extra weight in it) and a JP Enhanced silent capture (2 tungsten, 3 steel). So either it's more buffer weight/more spring pressure or a shorter barrel to start with. Looking on super slow mo it seems to recoil hard with 124gr ammo (160pf).

 

I like to have my hand stretched so a 12 inch handguard is probably the shortest I will accept.

 

Thanks!

[Bwillis]

If youre getting gas in your eye the lockup time isn’t long enough. Try with 5 tungsten weights and see if the helps. 

 

Barrel length is user preference but max leograndis and Scott Greene seem to be extremely dominate with a 10.5” barrel 6” comp. 

you want to keep your hand extended to 12” then 14.5 barrel with a 2” comp. 

[Karre]

But with a shorter barrel the bullet will leave the mussle sooner and lock time could be shorter.
QC10 recommend lighter buffer with shorter barrel.
With 10 inch barrel I would like to think it's a noticeable difference.

[Bwillis]

If you’re shooting 160pf you want the heaviest buffer setup you can. Even if you cut the barrel down to 10” you will be around 145-150pf. With the buffer setup you have now, you’re not  getting enough lockup time, that’s why you are getting gas in your face. I’ll also take a wild guess you have a lot of unburnt powder in the receiver. You want to think along the lines mp5 roller lock or cmmg guard with ar15 delay lug lock. The goal is to add milliseconds of bolt lockup to force the most amount gas down the barrel as possible. 

 

Qc10 also thinks a floating ejector is a good idea...it’s not at all 

Edited July 25, 2019 by Bwillis

[Karre]

I think I understand the physics. But the needed lockup time is depending on how long the bullet is in the barrel, pressure will drop quick when it leaves. But maybe I need a 8 inch barrel to notice the difference in lockup time.

 

JP tungsten weights are more expensive than gold here. And if I going to cut the barrel I can start with that to see how the lockup time changes.

Edited July 25, 2019 by Karre

[vgdvc]

What trigger assembly do you have? Something that may be able to help lock/dwell time a little bit longer is a Hiperfire 24c with the heaviest toggle springs.Puts a lot more hammer resistance on a bolt coming out of battery than your average AR hammer spring keeping the bolt closed slightly longer. You also get about a 2 lb trigger pull just keep some extra firing pins as some have claimed the increased hammer force can damage tips or mushroom strike point at the rear.

13 hours ago, Karre said:

So I shot my pcc without glasses for the first time today and got gas in my eye, more then I think it should be. I'm still playing around with buffers and so on, but now I want to start with deciding how long my barrel should be. It's 16 inch now and I can cut it as mush as I want. But it could be good with 16 with a "pinned" comp, if there isn't any benefit on going shorter. 

 

But what is the "perfect" length with a comp? I use the gun for IPSC and Steel challenge.

 

It's a QC10 receiver, barrel and bolt(without the extra weight in it) and a JP Enhanced silent capture (2 tungsten, 3 steel). So either it's more buffer weight/more spring pressure or a shorter barrel to start with. Looking on super slow mo it seems to recoil hard with 124gr ammo (160pf).

 

I like to have my hand stretched so a 12 inch handguard is probably the shortest I will accept.

 

Thanks!

 

[Karre]

I have a 24c. Dont remember what springs are in it. Have to check. I know hammer springs make a difference. But since I'm cutting the barrel at least 2,5 inch I'm going to start with that.

My barrel are thicker (for comp support) at 14,5-16 and 8-10 inch. But maybe my gunsmith can add some material at 12 inch. Its 16mm or 19mm in diameter.

[Darqusoull13]

3 hours ago, Karre said:

I have a 24c. Dont remember what springs are in it. Have to check. I know hammer springs make a difference. But since I'm cutting the barrel at least 2,5 inch I'm going to start with that.

My barrel are thicker (for comp support) at 14,5-16 and 8-10 inch. But maybe my gunsmith can add some material at 12 inch. Its 16mm or 19mm in diameter.

If you're going with a 12" hand guard you will probably to stay around 13-14" barrel. I have a relatively large wingspan at 6'7" and still prefer a 9" hand guard with a 10" barrel. 

Is the 160 PF ammo a factory ammo? If you're not reloading I would also suggest either 5 tungsten or 4 tungsten 1 steel set up in the Short Stroke configuration. If I understand you are running JPSCS2-9-5H2? If so, I would order JPSCS2-MAINT-K15 and convert your "Enhanced" 9mm SCS to a Short Stroke and swap tungsten weights until you find a good balance. 

[Karre]

Maybe I could accept a shorter hand guard. But I haven't tried anything that short. But a friend has a 10 inch barrel so I will test his upper on my lower some time.

It's geco 124gr factory ammo that give 160pf. I would like to find some less powerful but Geco isn't known to be "hot". 

 

My scs is already short stroke. So I have to try some tungsten weights.

 

Don't you think a shorter barrel will effect needed lockup time?

 

And I haven't noticed anything with glasses so I don't think it's much gas slipping by.

[rishii]

I had the same problem and solved it by using a milspec upper with a cmmg 9mm dust cover kit with blast defector

https://www.cmmginc.com/product/ejection-port-cover-kit-with-gas-deflector/

[Darqusoull13]

4 hours ago, Karre said:

Maybe I could accept a shorter hand guard. But I haven't tried anything that short. But a friend has a 10 inch barrel so I will test his upper on my lower some time.

It's geco 124gr factory ammo that give 160pf. I would like to find some less powerful but Geco isn't known to be "hot". 

 

My scs is already short stroke. So I have to try some tungsten weights.

 

Don't you think a shorter barrel will effect needed lockup time?

 

And I haven't noticed anything with glasses so I don't think it's much gas slipping by.

I figured it was Geco.  It's not that it's hot, just a longer barrel than typical 9mm (pistols). I like how Geco shoots in my shorty.  My 10.5" barrels shoot better compared to longer barrels  with lighter bullets more because the gas works the comp better the shorter the barrel to a point. 

There's no real "lock" with blow back designs. The increased mass from the tungsten weights will slow the bolt from moving rearward more and should keep less gas from escaping through the chamber. 

[Karre]

Maybe a sloppy grip on this clip. http://cloud.tapatalk.com/s/5d3ad9d9b63ea/20190724_202752_002.mp4