odd primer strikes

[9x45]

From a new JRC carbine, 17" CA version. It  runs fine, however, it throws sooty brass and has strange looking primer strikes. Anyone ever seen this before? It also doesn't throw the brass very far. Load was both RP 115 factory and my reloads, 124 Bayou or 124 Black and Blue on top of 4 grains of TiteGroup that makes about 135 PF out of my G17.

 

 

OAL left at 1.130", right at 1.100"

 

Edited February 12, 2017 by 9x45
add info

[ChuckS]

What does the tip of the firing pin look like?

[Steve RA]

Primers look like overpressure, brass looks like possibly underpressure ???

[M1A4ME]

Looks like you've got a really big firing pin hole in the bolt.  That would let some of the primer blow back into the hole after the firing pin set the primer off.

 

The sooty brass does look like the pressure isn't very high.  Higher pressure will seal the brass against the chamber walls better and prevent some of the soot/gas from blowing back around the case walls.

 

High pressure can reduce the rounded edge where the primer meets the primer pocket brass and make the primer look very "flat" from the center all the way to the brass of the primer pocket.

[9x45]

very odd, primers looks nice and round like normal, except for the strike. That is what the firing pin looks like, hard to see in the pic. It's 3/32" diameter, same as the bore thru the bolt face, same as is the strike mark. A small pistol primer is .175" in diameter. There's no soot in the primer pocket. Don't really know what it should look like in the chamber, kinda looks Glock like. But the brass shows no signs of pressure either. Gonna crank it up to 4.5 to 5.0 to 5.5 grains of TG and use small rifle primers because they are harder.  DaGoogle says  a thicker or stronger metal cup small rifle version for use with higher pressure loadings in weapons with heavy firing pin impact. Gonna check with JRC on Monday.

 

 

 

 

 

 

 

Edited February 11, 2017 by 9x45

[Aircooled6racer]

Hello: The soot is normal for a pistol caliber carbine. The primer marks are interesting. Could it be firing slightly out of battery? Thanks, Eric

[GrumpyOne]

It has to be the size of the firing pin hole in the breech face. With a typical small hole in a breech face for the firing pin, it doesn’t get blown back into said hole under normal pressure ( nowhere for the metal in the primer cup to go). However, with a larger hole, the pressure is acting on a larger surface, (same pressure acting on a larger area)  on metal that has already been deformed and weakened by the firing pin.

 

Sounds good, right? In reality,  I have no idea...

[Ming the Merciless]

The AR9 has an inertial firing pin meaning the hammer isn't holding the firing pin against the primer like in a 1911, so the primer can push the firing pin back and flow into the firing pin hole.

[Gcarr]

Is the powder compressed at 4.0 and that length?