Load clean in pistols, dirty in PCC

[GMP]

RMR 124g FMJ

4.2g Sport Pistol

Federal primers in Mixed range brass

OAL 1.110”
 

Same go to load I’ve been running in my CZs for a few years now, accurate, good feel, and clean.  Got a Springfield Saint 9mm PCC, set up with a different comp, Kynshot buffer, JP trigger springs and a little polish work.  Runs 100%, accurate, and reasonable recoil impulse for the investment.  Only odd thing I notice is my cases are sooty and the gun runs generally dirtier than my pistols.  Ejection is fine and the gun locks back consistently.  Only thing I can think of is with the relatively fast powder the pressure drops in the long barrel enough to break the case seal to the chamber.  Thoughts? 

[Sarge]

5 minutes ago, GMP said:

RMR 124g FMJ

4.2g Sport Pistol

Federal primers in Mixed range brass

OAL 1.110”
 

Same go to load I’ve been running in my CZs for a few years now, accurate, good feel, and clean.  Got a Springfield Saint 9mm PCC, set up with a different comp, Kynshot buffer, JP trigger springs and a little polish work.  Runs 100%, accurate, and reasonable recoil impulse for the investment.  Only odd thing I notice is my cases are sooty and the gun runs generally dirtier than my pistols.  Ejection is fine and the gun locks back consistently.  Only thing I can think of is with the relatively fast powder the pressure drops in the long barrel enough to break the case seal to the chamber.  Thoughts? 

What's the PF from PCC?

[xrayfk05]

A blowback PCC will always have sooty(er) cases than guns with a lockup system like most pistols.

In a blowback gun nothing keeps the bolt from moving apart from weight of the bolt, buffer and spring, as soon as you fire  it starts moving.

If you really want cleaner cases you could try a heavier buffer. (assuming it's and AR-like gun)

[perttime]

... Or invest in a PCC with a retarded or even gas operated action.

[zzt]

Chambers in most PCC barrels are looser than pistols.  Even with a retarded operation buffer system, you will still get some soot on the cases.   Long barrel or short, it doesn't seem to make a difference.

[GMP]

11 minutes ago, zzt said:

Chambers in most PCC barrels are looser than pistols.  Even with a retarded operation buffer system, you will still get some soot on the cases.   Long barrel or short, it doesn't seem to make a difference.

I thought this might be the case, makes perfect sense, thanks.  This is not a problem just something I noticed.  The gun runs good for the money and is totally reliable after 400 or so rounds so far.  I'm running the Kynshot heavy damped buffer with the AR10 carbine (orange) spring, so its a fair bit stiffer than stock.

 

I RO at matches and see a good amount of PCC malfunctions, mostly with home builds.  

[texasdawg]

 

On 1/23/2024 at 2:28 AM, xrayfk05 said:

A blowback PCC will always have sooty(er) cases than guns with a lockup system like most pistols.

In a blowback gun nothing keeps the bolt from moving apart from weight of the bolt, buffer and spring, as soon as you fire  it starts moving.

If you really want cleaner cases you could try a heavier buffer. (assuming it's and AR-like gun)

XRAY is correct. The weight of the bolt and buffer system is what keeps the bolt closed long enough for the bullet and most of the gas and unburnt powder to go out the front of the gun in a non-delayed or gas operated gun. Although a gas gun will tend to put some gas back into the bolt area. A roller delayed system or a system like a JP5 keep the bolt mechanically closed for a period of time passed on the way the system is set up and the load used. To get a system to run super clean is very much a balancing act, but very rewarding in less felt recoil and having a gun that runs clean and for a long time between cleanings. A weighted buffer system will always be dirtier unless one goes for a heavy weighted buffer and bolt and suffers the recoil from said system.

[GMP]

Yeah your right I understand all that now.  Being my first PCC I did not think that the timing was such to blow the mass of the bolt back so fast.  I don't care about dirty cases, just something I noticed.  Wasn't sure I'd like this PCC thing so $3K + for a JP5 was a non-starter.  For what I'm doing for now its fine, and way more reliable than more than half of what I see out there.  I bought rather than built this time to avoid those pitfalls, and just shoot.