Crowning on a breech?

[Scooter]

I've been shooting my 34 a lot lately and notice that the "breech" where the pellet fits is a little off-center and unevenly crowned.  Gun shoots accurate enough for me, but I was just curious if anyone has ever modified the crown on the breech end of the barrel. (?)

Just thinking of fluid dynamics and how much energy might be wasted on the mismatch.

[SDale]

I really wouldn't worry about the breach end very much. But if it bothers you, then you can crown it the same as the muzzle. The only thing it would do is help ease pellet insertion.  I've done it on a few of my rifles and it makes loading a bit easier. No change in accuracy.

[leftcoast1]

As long as it's not leaking at the breech your fine. your alignment is not off that bad. I've seen a lot of 34 with the same problem lately

[davee1]

My Diana 350Ms and P5have that off center breech also. And I've read about others wondering about what effect this has on their Diana models. Apparently, many models of Diana's line have that. As long as the pellet isn't getting clipped when you close the breech, or the seal leaking,I think you are ok. That was the consensus elsewhere where I was reading too. It was also mentioned that most folks couldn't understand how Diana screwed that one up...given their usual German qualty and engineering.

I've done a little deburring/crown on my Gamo shadow's transfer port, because it was chewing up the breech seal. I would also note that the chewed up breech seal had no negative effect on the velocity and was not leaking...this iscommonwith Shadow breech seals...but I saw a possible way to stop it, because I hate that. I took a drill bit that was very sharp and brand new and several sizes bigger than the port hole, and turned it by hand against the port, which shaved off a very small amount of metal, and left a rough crown behind. Then I took some valve grinding compound and put it on the port, ballistol for the polishing fluid, and used ahigh quality1/4"ball bearing to roll around on the port with my thumb, polishing the rough crown. After a few mintutes of me rolling the bearing around on the port, it was nice and polished. Then I completely washed everything to remove all traces of the grinding compound. No more chewed up seal.

[Scooter]

Thank you for the answers!

[tjk]

Hey Scot,...that looks like my 34!!! Beauty's ain't they. Like stated before,...accuracy won't improve much at all,...but crowning will make pellet insertion easier and avoid 'skirt pinch'. But you can also try different pellets and avoid all the hassle. Have you tried the JSB's?? They all seem to have a thinner skirt, and seat better in the breeches of most guns. I think this is because of the softer lead that they are made of. One tip that might help in pellet placement, is to stick the pellet into the breech untill the skirt is flush with the top-side of the breech,..then "roll' your thumb nail downwards to bring the exposed side of the pellet flush with the bottom of the breech hole. This seems to work for me,...and JSB's are the easiest to seat this way for me. Good Luck with whatever you decide to do!!! tjk

[kiwi]

In all guns i have seen the port hole is a lot smaller than the barrel
so the chance of the offset barrel bore closing of a section of the
 port and restricting air flow is very low unless the hole is a lot
more offset then what you have.
As for the crown at the breech end after you have inserted the pellet
it is past the uneven crown so it will no longer have any effect on the pellet.

[leftcoast1]

After asking the same question about my new B-28 I found out it's not a flaw it's built that way because of the way the gun closes. All the current RWS break barrels have it. I would leave it alone. Same kinda of thing Theoben dose with their breech seals. They puta cut in itat the factory.