30 Carbine shaving copper jackets

[docsleepy]

Anyone ever had a 30 Carbine (M1) shave near perfect circles of copper off FMJ bullets?

Jams every 2nd or 3rd round.

Commercial rounds (I think they are amscor) that appear to be BRASS jacketed -- .308 - work fine. No shavings, no jams.

Handloaded rounds Hornady FMJ (exposed lead at base) .308 110 grain, loaded to max COAL per caliber, 4227 powder, mid range charge, carefully beveled, trimmed cases, NOT crimped......full circles of copper rings show up in the chamber and prevent further cases from chambering properly, bolt will not close.

Anyone ever had that happen before?

 

[rcmodel]

I haven't.
But a buddy did with a .30 Carbine Ruger Blackhawk revolver.

One chamber out of the six would do it every time with reloads, or GI surplus ammo.

Turned out, it wasn't from the bullet jacket at all.
It was a thin ring breaking off the case mouth and lodging in the chamber.

You simply couldn't load it again until you used a bronze bore brush to grab the ring out!

He had a nice collection of 'little brass rings'!
But neither one of use could ever figure out what was different about that one chamber that caused it.

I polished the chamber, twice, and broke the sharp edge of the headspace step, etc.

Never did figure it out before he finally gave up and traded it off.

Bottom line?
Measure the fired cases and see if it is case brass rings shortening the cases, or bullet jacket rings shaving off the bullets?

rc

 

[docsleepy]

good information

the ring ends up in the dia of the case mouth, and apparently lodges in that area, but the color of the material (multiple observations) indicates clearly it is copper rather than brass.

I think it gets shaved off, blown backwards by gases as the spent casing is ejected, or maybe as the accelerating bullet obturates the transitions between the throat and the rifling, it gets deposited.

Doesn't happen at all with brass-jacketed ammo. I scratched the unusally colored (brass-colored) ammo and the color is not just paint or plate -- really is brass jacket.

Copper jacketed hornady is where I have the problem.

The ring is not a complete solid thing, it is sort of as if frangible stuff had been compacted -- makes me think it is shavings.

I'll try measuring the cases, but as uneven expansion is the rule of the day, not sure I will be able to prove anything. However, they should not SHRINK, and the bevel I put on them should be intact -- I can look for those as confirmatory that it isn't the case.

thanks

 

[carbine85]

I've seen it before. I always thought it was from not having enough bevel on the case and it was shaving the bullet.

 

[docsleepy]

wish it were that simple! I beveled and even smoothed with steel wool. Adjusted seater to JUST take out the mouth expansion done by the powder die, and no more. Still shaves. Got to be the chamber/throat somehow.