Auto-5 Light Twenty Belgium w/3" Chamber

Another possibility is that this barrel was simply mis-marked. Chamber length is stamped twice, once in inches and once in millimeters. The millimeter stamp is part of the proof marks and is much less likely to be wrong. Unfortunately I can’t make it out in the pictures, but it should be in read 20-75 for a magnum chamber and 20-70 for a Light Twelve.

Let’s hope. I was pretty certain I’d see some obvious differences in a magnum barrel. I seem to remember a spring loaded ejector, but there’s nothing out of the ordinary that I can see.

If it works, I’m going to conclude that it was mis-marked, not that a 3” barrel will work on a 2 3/4” gun.

Yes, it is marked 20-70. I haven't fired it but I did drop a 3" shell into the breech end and it bottomed our on the rim of the shell. Would that not indicate it is a 3" chamber, which is what is marked on the barrel?

I did. Sending pics shortly. Thanks.

Pics sent. Thank you.

Chamber length accommodates the fired length of the shell. A 3” shell isn’t 3” until the crimp unfolds.

I measured the length of an unfired 3" shell and it mic'd at 2.66" so a "3" unfired shell would fit in a 2.75" chamber. I'm about convinced that based on that test and the information posted in this thread it seems reasonable that what I have is a mis-marked barrel as to the chamber.

This isn’t the first time I’d seen this issue with 20 gauge barrels, but I’d forgotten about it.

https://www.shotgunworld.com/threads/belgian-auto5-magnum-twenty-with-questions.514050/#post-4329802