Crack @ rear lockbolt

[smallpatch]

OK, just got back from the range.  Trying to sight in my Type G smoothie.When I finished up, I realized i had a hairline crack from the rear(top) lock bolt and the barrel channel.  While I realize this is a pretty common problem, it's the first time in the approx. 40 guns that I've built, that I ever had this problem.

Barrel seems to be sitting tight lug to wood @ the breech.  What would cause this???  Maybe that lock bolt is sitting against the bolster??  It is drilled through the bolster.  Maybe I need to relieve that hole a bit???

Also, will need to investigate a little further to see what I need to do to repair it.  Don't want to repair it till I eliminate the problem.

All suggestions welcome.

HELP!!

[JTR]

I'll agree with you and guess that the lock bolt must be in contact with the bolster. I'd also guess that the contact must be at the front of the bolster hole, closest to the barrel. I take it that by bolster, you mean the lower part of the tang where the bolt goes through?
Or possibly, that your inletting of the barrel/tang has a small high point in the area of the crack, and that high point is putting excessive pressure on the wood in the area of the crack.
I assume the crack is running with the grain of the wood, and not accross it?
John

[B.Habermehl]

Your barrel has set back a bit.  The hole in the breech tang is binding on the lock bolt.  Probably driving it rearward on recoil and loading.  This is more than likely the cause of the split. I think vigorous loading practices cause more barrel setback than recoil does.  BJH