I picked up a 28" Mod. Barrel for my 1950's vintage Model 12,12ga.
I can 't get the new barrel on,i can t get it to twist on the last little bit,i have the barrel take up ring backed off to the last notches,it still won 't go on. The new /used barrel assembly i got looks to be much older than the one i have,has an older style of writting on it.Is there something i m missing ? Thanks.

I've got a few model 12s but have never changed out barrels on any of mine. There's a member on here Bobmar, might try sending him a pm. He's pretty knowledgeable about model 12s.

You need to loosen the adjusting sleeve.
Start at 2:00.

Pretty sure model 12 barrels are hand fitted one at a time.

Thanks for answering,i have the adjusting sleeve backed off,counter clockwise tightens the barrel fit,clockwise loosens it,i have it turned all the way in,still won t fit,too tight.

I've heard there were various thickness barrel sleeves....you might need a thinner one to make it work. Apparently old M12 smiths stocked the various thickness sleeves.

I ll try that ,if i can find one ,thanks.

Just looked at Midwest Gunworks and they have adjusting sleeves. Not sure which you might need, but you can call and ask them.

https://www.midwestgunworks.com/winchester-model-12/adjusting-sleeve.html

Thanks for the info,i'll give that a try.
It is the adj. sleeve,i removed the set screw,and pushed the locking piece up,i turned the adj. Sleeve all the way in past the locking threads,and tried it,it went right together,question is ,which adj.sleeve is the one that gives the least clearance ? I ll call Mid west on mon. and see if they can help.
Thanks for all the answers,it is much appreciated.

As I recall, there were over a dozen different sleeves available and picking the right one was sometimes a matter of trial and error, until the right fit for that gun was made. A gunsmith familiar with Model 12’s could tell pretty quickly which sleeve was required.

Also wanted to add that headspace is another issue all together.