I'm asking for a friend who just bought a Model 12 in 20 gauge. He's wondering if it has the 2 1/2" chamber. It was made in 1922. I told him there's a good chance that it is 2 1/2". I've not looked at it. I told him if he could measure it with a short ruler or something. Any help is appreciated. Thanks

Made in 22 should be 2 1/2". I think they changed in 1926.

That's not good. I'll tell him. I think you can still get 2.5" ammo but, it's probably expensive. Thanks

I know Rst made it at one point. Not sure who else. I had one of the early 20s but it had the ejection port enlarged

See if it can be reamed to 2-3/4

The problem isn't lengthening the chamber to 2 3/4 it is that the ejection port has to be opened up as well. If he just wants to shoot it once in a while, buy a box of the RST shells. If he wants a shooter 20 ga there are lots of options out there more practical than butchering a 100 year old winchester.

Been a while since I looked but Precision Reloading did have 2 1/2" hulls listed on their site. I believe MEC offers the 2 1/2" dies sets. Might be an easier and more efficient option to just reload the 2 1/2" shells on a MEC jr.

Die sets 2 1/2" ? You adjust the staff height.or add a short kit.

It should say on the side of the barrel if it is 2 1/2 or 2 3/4. I have an early m12 20 gauge that was made in 1920 according to the sn 24277x and it is marked 2 3/4 full on the side of the barrel. That is all I've ever shot through it with no issues.

I got it from my uncle who bought it new and the sn is stamped on the bottom of the receiver and on the lower part of the magazine tube and they match, so I know that the barrel and magazine and receiver were as issued.

You buy a 100 year old house most likely you will have to fix it so you can live in it. But you would be butchering a Model 12, by making it more easily usable???? One way or the other it isn't a collector piece.

The change from 2 1/2" to 2 3/4" was implemented around 1926. To be more precise, read it's between the 485795 – 487982 serial number range.

Earliest 2 3/4" guns were stamped at bottom of receiver, near the SN. Later on stamp was on the barrel.

2 1/2" guns were not stamped for chamber length.

Many short chamber small frame M-12s had chamber and/or port lengthening done post-market.

A sufficient number of folks have shot factory 2 3/4" shells through unaltered guns to convince me a few rounds chasing grouse won't hurt anything. M-12s do not have abrupt forcing cones, and Sherman Bell debunked blanket proscription of the practice.

Range gun? Yeah, maybe modify it, unless you're a collector, and/or you have something really special - like a single digit SN.

I thought that I might have misread the sn or the 2 3/4 Full on the barrel and double checked. Nope, sn24277x and Googled to a 1920 mfg date. Everything I can find does say that the 2 3/4" chamber 20 gauge m12 was introduced in 1926 when 2 3/4" 20 gauge shotgun shells were loaded.. The only thing I can figure was that Uncle Jack was quite a pheasant hunter and that he got a new barrel and magazine set and had it roll stamped with the same early sn that was on the receiver. I did read where another guy had a similar 20 gauge m12 with a 1920 mfg sn close to mine and his was also marked 2 3/4" and it was suggested that he got a new barrel set.

Making 2 1/2" 20 gauge ammo is far easier than many realize , and there is lots of data out there for 2 1/2" loads.
Cat

I used to load a 12 gauge 2 9/16” gun by cutting down shells to appropriate length and adjusting mec press to crimp properly. Pretty simple process.