View Full Version : 2.75" barrel on a 3" chamber

March 26, 2002, 04:46 AM
If a guy had a 870 12ga 3" express magnum (factory), and later bought a used police 18" barrel that said 2.75" on it; which would take precedence?
With the 18" 2.75-chambered BARREL on a (formerly?) 3" receiver, can it fire 3" shells or is it limited to 2.75" shells?

Dave McC
March 26, 2002, 05:07 AM
Do NOT fire 3" or longer shells in a bbl marked for 2 3/4" shells only.Pressures will be excessive,patterns poor, kick terrific, and sooner or later there'll be a catastrophic failure.

March 26, 2002, 09:16 AM
Dave, I dont understand that. I've had it explained to me that the receiver is the critical issue, that the barrels are virtually the same.

While my SG is non magnum receiver, my original barrel says 2 3/4" only (even though a 3" will fit in it), I've never shot a 3" in it because you just never know about secondhand information, plus with my 2 3/4" receiver, it wouldnt eject properly.

Shotgun shells headspace on the extractor, correct? How could it go to high pressures if the barrels are the same?

I dont think you're wrong, I just dont understand why. My newish barrel for it says 2 3/4" or 3" shells in guns marked magnum. 2 3/4" in all other guns.

I've got enough confidence in 2 3/4" shells, that I'm not interested in shooting 3" shells anyway, just academic question for me. Thanks

Cpeliri, I just bought an 18" blue barrel with bead sight (blue 98%) Cyl. bore that takes 3" shells also, that I'll never shoot 3"ers in, due to my receiver. Pay shipping for both barrels, and flip me $20 and I'll swap ya' Just a thought, tryin' to help.:)

March 26, 2002, 01:25 PM
Dave right....as usual.
Not a headspace factor. The chamber is in the barrel, the chamber is larger than the bore by about the thickness of the shell casing. A chamber marked for 2 3/4 shells will be a little longer than that to allow space for the crimp to expand. Using a three incher in the shorter chamber will not allow room for the crimp to fully expand, hence restricting the bore and raising pressures.

Shotshells headspace off the rim, space between bolt or breech face and barrel face with the rim trapped in between. Extractor is not a factor in shotgun headspace.

Hence, barrel marking has precedence.


March 26, 2002, 05:43 PM
Thanks Sam. That makes sense.

March 30, 2002, 10:53 PM
If you hace a 3"inch reciever you might want to take your barrel to the gunsmith to let him ream it out. Around here it only costs about 20 bucks.

CR Sam is right, since the chamber is in the barrel, its a simple proccess of lenthening the chamber and pushing the forcing cone back.

Its not a good thing to have barrels and recievers mismatched. Its just an accident waiting to happen.You might be aware of it but someone else might not. Thats the main reason that all of my shotguns have 3" barrels and recievers.

March 31, 2002, 12:31 AM
Watchman is right Sam too, I bought a police barrel and had the chamber reamed , but also smoothed it out so no ridge, it seems to kick less,and I paid $30. no ridge means the contour is a smooth no 3 in" ridge.

March 31, 2002, 07:39 AM
Actually 2 private messages, from me.