Rifling question:

[RecoilRob]

Over on Gunboards, http://www.gunboards.com/forums/topic.asp? a fellow has been going through hell trying to get a Semi PPSH-41 up to speed.

He didn't build it, but the people that did seem to be having problems. The latest barrel attempt is overbore (by a bunch!) with a big chamber and has some strange marks that are shown in the chamber cast picture attatched.

I have seen similar marks in a P-11 KelTec barrel but they were only on the lands and (possibly) attributed to a chattering reamer. These marks are on both lands and grooves. Weird...

The folks over on Gunboards are a good bunch, but I think that THR has a collective Gun IQ unmatched anywhere in the world.

Can anyone explain the marks? Thanks guys!

 

[brickeyee]

Looks like chatter from pulling a rifling button through the barrel.
The marks are rather small, but the size is going to depend at least partly on the gearing being used to drive the button.
If you look at lath machined surfaces at high enough magnification you can see the advance that was used to drive the cutter.
Grinding is about the only way to remove them, and even then much care must be taken to prevent a tool post grinder from leaving marks.

Might be worth a little lapping to see if they will smooth out easily.

 

[Jim K]

The drilling and reaming of the barrel was poorly done with lots of circular tool marks. Then the barrel was hammer forged, which didn't remove the tool marks, only compressed them (note the tool marks in the grooves; a scrape cutter or button rifler would have removed them).

IMHO, a junk barrel that should be sent back to wherever it came from.

Jim

 

[Sunray]

Look like there's a crack too.
"...to get a Semi PPSH-41 up to speed..." What does he expect it to do? Shoot accurately? The real PPSH wasn't made for accuracy. It, like the SKS and AK, was made to be issued to illiterate conscripts who got minimal training before they got put in the line.

 

[RecoilRob]

The answer has been found!

It took a while, but the strange marks were, indeed, caused by the button rifling process. Good call brickeyee!

Seems the rifle manufacturer used a rifled blank to make the barrel and didn't bother to lap the marks out....like everyone in the world does. And, they also omitted the important stress relief process before outside turning it which caused the bore diameter to swell several thousandths into unusefullness.

Just thought everyone who had seen this post back when would like to know the outcome.