doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Beretta hammer gun

I have a Beretta SXS hammer gun probably made in the late 70's. The bbl flats are stamped 28 cal. chokes are stamped 13.5 in both bbls.
The owner wants the chokes opened and a firing pin and bushing made , (both are missing). I made a new bushing based on the dimensions of the existing bushing,
but it is too small on the thread diameter. The existing thread is .285 diam x 32 tpi. which should convert to 7mm x .8. I have not determined what the other bushing thread is.
When checking the bore diameter it only measures .531" while a 28 ga should be .550. Could it be that these bbls are actually a 32 ga and only the chambers were opened at the factory
but not the bores? Any constructive input would be appreciated

lou, what you say makes sense...

It sounds as though the existing bushing you used to make a replacement may also be an undersized and incorrect replacement. Measuring female threads is never as easy as male threads. I have had some success by making an undersized slightly tapered dowel out of soft wood like balsa or pine, and then wrapping it counter-clockwise with several layers of aluminum foil. For small threaded holes, you can sand down a wooden match stick to make the tapered dowel. Then screw the foil wrapped tapered dowel into the female threads until it is snug enough to get a good thread impression. Then carefully unscrew it and try to get an accurate measurement of the impression with thread gauges, calipers, etc. At one point in time, I had daily access to an optical comparator which made this kind of size determination much easier. Many well equipped machine shops have one, and a comparator may be the most accurate means of determining exactly what is the thread type, diameter, pitch, etc., short of getting the information from a factory blueprint.

I have also heard of using Cerrosafe to pour a cast of internal threads, which can then be removed and measured. Of course, you would have to use clay or something to dam the open backside, and also pour extra into a nut or something on the breech face to have a means to remove the cast. Cerrosafe shrinks a small amount several minutes after casting, but I'd probably want to lightly coat the threads and breech face with a little graphite lube to ensure easy removal.

I don't know why Beretta would stamp a gun as 28 ga., but have the bores .019" under nominal bore size. But it seems better than finding out a gun is oversized because it has been honed to death.

It's common for European bores to be on the "tight" side and I'm not surprised that you measured the bores at .531".

The 13.5mm stamp was the bore diameter when the gun was proofed and they are the same today - 13.5/25.4=.531".

At one time I had a 12 bore chambered English shotgun with 13 bore barrels and have seen them with 14 bore barrels.

are the chambers in fact 28 ga? or are they 32 ga?

and 32 ga is .526...close to .531...

in any event sounds like a cool little gun...

The 13.5 is referring to the choke, which is .531 and is marked that way on the bbl flats. That would make it full choke for a 28ga.
but the bore also being .531 doesn't allow me any material to remove. A 28 ga shell fits in tightly in the chamber and the owner tells me they are
hard to remove after firing. But this could be because he is using 2 3/4 " shells in a 2.5" chamber.

If the bore is .531 and the "choke" is .531 then the gun is cylinder choke - there is no choke to open.

On Italian guns the choke may be indicated by a series of asterisks.

* Full
** 3/4
*** 1/2
**** 1/4

(Approximately)

Does it have any of these?

Fly is correct
13.5 would be marked at the time of proof and is the bore, not the choke = 31 gauge. 32 gauge is .526"
The breech end of the chamber for 32g is .574" tapering to .562"
28g is .626" tapering to .614"
http://www.dave-cushman.net/shot/shotshellloads.html
What does the chamber measure?

Yes, Beretta did do a 32 ga hammer gun.

John
Arrieta