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9mm AR - soot on my shoulder?

V

vanfunk

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Joined
Jan 9, 2003
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The widening gyre
Hi All:

So I was shooting my “new” old Colt 9mm AR carbine the other day; what fun blasting 1/2 size steel silhouettes at 50 and 100 yards with open sights and a bunch of 32 round magazines. It’s just so restful and satisfying, ‘specially with a Lula loader for those long sticks. Anyway, after ai had gone through about 200 rounds I noticed black soot on my shoulder. Presumably, gunpowder residue is blowing out through the drainhole in the stock (it’s an A1 rifle stock from the factory) and stsining my shirt. I guess ai usually wear black shirts to the range and had’t noticed before. I know these guns are dirty, but THAT dirty? Is there anything to be done about it? What if I happen to wear my ‘78 white polyester suit to the range next time? :)
 
vanfunk said:
I know these guns are dirty, but THAT dirty?
Click to expand...
Blowback action PCCs will produce a lot of soot, based on ammunition and firearm/bolt/buffer weight and recoil spring rate. As soon as bolt/buffer starts to move back, high pressure gas/soot will BLOW EVERYWHERE. Just like blowback action semi-auto 22LR.

vanfunk said:
Is there anything to be done about it?
Click to expand...
If shooting factory ammunition, try different brands/weights and see if there is difference in soot amount.

If you reload, I found faster burning powders tend to expand case mouth/neck faster to seal with chamber and burn more efficiently to maintain chamber pressure before bolt/buffer move back and start leaking gas/soot to produce "cleaner" less soot on case.

So in my experience with 9mm 115/124 gr bullets, faster burning than W231/HP-38 produced "cleaner" less sooty cases than WSF/BE-86 with faster burning Promo (Same burn rate as Red Dot) producing slightly smaller groups than W231/HP-38 loads at 50-100 yards.
 
Thanks! Makes sense. There *could* be a lot of soot in the buffer tube from ages past (the carbine was built in ‘93. I’ll try giving it a good cleaning first to see if that helps. I don’t currently reload for 9mm but this is a good reason to start! The $.02 solution is to cram an earplug into the recessed space for the stock screw and call it a day, I suppose :)
 
I wouldn't think that would happen since there is no gas tube sending all the nasty back like on a "normal" AR.
 
FL-NC said:
I wouldn't think that would happen since there is no gas tube sending all the nasty back like on a "normal" AR.
Click to expand...
Unlike locked breech action of gas-operated AR, blowback action Pistol Caliber Carbine (Like blowback action 22LR) depends on bolt/buffer weight and recoil spring tension to hold pistol case mouth against chamber but as soon as bolt/buffer starts moving back, high pressure gas will leak all around the case mouth/neck and starts dropping chamber pressure causing less efficient powder burn (Remember, powder "burns" relatively slow around burn rate of match head) hence why so much soot is produced on the outside of case fired in PCC.

In locked breech action AR, powder burn occurs while the case is "locked" and chamber pressure maintained while bullet travels down the bore and high pressure gas is "delayed" in reaching the gas block to travel back through gas tube to bolt carrier group to dissipate burnt gas. Soot from "burnt" gas is less than soot produced on pistol cases and surrounding action of PCC.

Faster burning powders (Faster than W231/HP-38) in my experience produces less soot on case likely from faster "burning" of powder before bolt/buffer start moving back and gas leak/pressure drop starts. I have noticed progressively faster burning powders producing less soot on cases where W231/HP-38 produces less soot than WSF/BE-86 and Promo/Titegroup producing less soot than W231/HP-38.

Of course, due to many reloading variables, YMMV.
 
MarshallDodge said:
I rarely shoot USPSA, and load for reliability in a variety of pistols.
Click to expand...
Believe me, 3-gun match shooters have just about milked, poked and examined everything regarding enhancing reliability, accuracy and flat shooting aspects (To not move front sight for faster follow up shots) of PCC on forums like Brian Enos.

Their combined work past 10-15 years has invaluably improved the entire industry and technological development to benefit down to casual plinkers like us.

Initially thinking was due to longer 16" barrel, relatively slower burning powders maybe better suited and around WSF burn rate powders (A popular match powder I used and also for loading duplicate practice JHP loads like Gold Dot/Golden Saber) were utilized. But like my own PCC load development testing found, faster burning than W231/HP-38 produced smaller groups than slower powders like BE-86 and I ended up designating fast burning Promo as my reference PCC powders.

By the time USPSA PCC division survey was published, general consensus confirmed use of faster burning powders.
 
HSO: nope, the firing shoulder. The only way it can get there, I imagine, is to be blown out through the drain hole in the stock screw, unless there’s another explanation. Weird.
 
IME fast burning powder is cleaner than factory 9mm in a carbine.
I use Bullseye, W231 and Power Pistol in my carbine loads, all very clean burning in my blow back Ruger.
Power Pistol is the accuracy champ.
 
Pat Riot said:
I will try some Power Pistol out one day soon.
Click to expand...
Keep in mind that Power Pistol can produce large fireball at muzzle, around volleyball to basketball size depending on caliber/charge that could be distracting shooting indoors. BE-86 is similar in burn rate but without the large muzzle flash (No, BE-86 is not Power Pistol with flash suppressant).

FYI, BE-86 produced around 3" muzzle flash (Compared to 2" muzzle flash of W231/HP-38) in low light/night vision testing out of Glock 22 with KKM conversion barrel - https://www.thehighroad.org/index.php?threads/need-low-flash-9mm-powder.809859/page-2#post-10357740

BTW, if you are shooting PCC in low light or with night vision, Promo produced smallest, almost non-detectable to shooter muzzle flash. (You know, it's good to know these stuff. ;))

Oh, did I mention that Promo produced smaller 50/100 yard groups than W231/HP-38/BE-86? - https://www.thehighroad.org/index.p...-and-discussions.778197/page-11#post-12415502

index.php


Promo 100 yard group

index.php
 
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