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Thread: Can you convert a 2 3/4" to 3" chamber?

  1. #1
    Boolit Master Bazoo's Avatar
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    Can you convert a 2 3/4" to 3" chamber?

    So I have an 870. It's an express magnum 12 gauge.

    I've read on a shotgun forum it's common to take a 2 3/4" gun and put a 3" chambered barrel on it. Some guns need the ejector changed and some don't. And since the saami pressure limit is 11,500 for both it's safe.

    Anywho, So my question. Could I take an older barrel with a 2 3/4" chamber and ream it for 3" shells and use it safely?

    I have a 3" chambered barrel already I'm just curious.

  2. #2
    Boolit Master
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    What is your barrel stamped? If it says 2 3/4" only it sounds like the barrel may have been swapped out at some point.

    Everything I read says your Express Magnum is chambered in 3" and that the Express Super Magnum is chambered in 3 1/2".

    "What is the difference between Remington 870 Express and Magnum?
    Everything made for the last 20+ years have had 3" chambers and are usually refereed to as magnums.

    "The Express is chambered for 2 3/4" and 3" shells. The Super Magnum will shoot 3 1/2" shells. You can shoot 2 3/4", 3", and 3 1/2" shells in the Super, but only 2 3/4" and 3" in the standard Express."

    "I have a Remington 870 Express I bought used in 1969. Been shooting 3" shells ever since"

  3. #3
    Boolit Master Cap'n Morgan's Avatar
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    I once reamed a 870 to 3". The ejector had to be moved 1/4" backwards, and if I recall correctly I also had to mess with the lifter timing or magazine stop or something. I'm pretty sure the only difference in Remington's barrel making procedure is they run the reamer a tad deeper in the mag barrel.
    Cap'n Morgan

  4. #4
    Boolit Grand Master Texas by God's Avatar
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    The 870 Express was introduced in 1987. I'm fairly certain they were 3" chambered from the beginning.

    Sent from my SAMSUNG-SM-G930A using Tapatalk

  5. #5
    Boolit Master

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    I have a Rem. 870 Express that I purchased new in 2008 or 9, and it is marked "12 Ga. 2 3/4, 3", 3 1/2" only with super mag receiver". It's funny, but I'm not too sure if it's got a super mag receiver or not. All I've ever used it for was 2 3/4" shells for informal trap shooting. I'd suggest that you phone Remington and talk to them about it, as no doubt they'll be able to tell you what you've got, and what it can be made to do.

    As for the actual reaming out of a 2 3/4" chamber to 3"-- no problem at all if you've got the proper reamer (expensive) and a depth gauge. Used to be, back before 2 3/4" was standard, 2 1/2" was common. Many of the 2 1/2" chambers were reamed to 2 3/4", and I've done a few myself. It can be done using hand tools only. After your depth gauge tells you that you've reached the desired depth, then you'll need a forcing cone reamer (expensive) to make a smooth transition from the end of the chamber to the bore diameter.

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    Again, I'd discuss it with Remington.

  6. #6
    Boolit Master Bazoo's Avatar
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    I appreciate the replies.

    Let be me more clear.

    I have an 870 express magnum receiver and 3" chambered factory barrel. Both made for 3" or less, so no confusion there.

    If I take an older, 2 3/4" chambered barrel and ream it to accept 3" shells will it be safe? Don't get me wrong I'm not dead set on this or planning on it even, but I've got my eye on a barrel that is marked 2 3/4" only and I'm curious.

  7. #7
    Boolit Buddy Ozark mike's Avatar
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    Yes it can be done but you will have more pressure .25" further foward but should be okay. Remember bbls taper off just ahead of the shell. But should not be a problem. Lots of bbls have been reamed without problems
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  8. #8
    Boolit Master gpidaho's Avatar
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    I'd keep it 2 3/4 chambered. If you have any wish to shoot slugs loaded in 2 3/4 hulls it should be more accurate. 870 barrels are cheap on Ebay. Likely less than having your barrel reamed. Gp

  9. #9
    Boolit Master Bazoo's Avatar
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    Thanks for the reply.

    I watch them on ebay and I rarely see one go for less than 100. I don't know how much it costs to have a barrel reamed.

  10. #10
    Boolit Master
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    Buy the 3" barrel & sell the 2 3/4". This is what I did when I wanted a Remington 1100 barrel with choke tubes. I bought a new barrel & off set the cost by selling my plain 28" barrel.

  11. #11
    Boolit Master

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    Quote Originally Posted by Bazoo View Post
    I appreciate the replies.

    Let be me more clear.

    I have an 870 express magnum receiver and 3" chambered factory barrel. Both made for 3" or less, so no confusion there.

    If I take an older, 2 3/4" chambered barrel and ream it to accept 3" shells will it be safe? Don't get me wrong I'm not dead set on this or planning on it even, but I've got my eye on a barrel that is marked 2 3/4" only and I'm curious.
    Yes, this can be done, and it will be safe, but you will have to ream the forcing cone to get decent patterns.

  12. #12
    Boolit Master danski26's Avatar
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    Yes it can be done and it will be safe. Ejector needs to be changed also. If youd like to borrow the ejector staking tools i have them.
    Semper Fi

  13. #13
    Boolit Master danski26's Avatar
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    Now that I'm thinking about this more....my memory is a bit fuzzy. I went to Remington armorers school about 15 years ago. I think i remember Lyle, the instructor from Remington, saying the only difference in those barrels WAS the ejector. Measure your 2 3/4 inch barrel and see how long the chamber is. I bet a nickle it's long enough for 3". Only a nickle though, memory is fuzzy.
    Semper Fi

  14. #14
    Boolit Master
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    Ive considered doing the same thing, but in the end I picked up a used barrel on gunbroker for about the same price as doing the 3" conversion. I was quoted $75 to do the conversion, and then shipping both ways on top of that. Shipping is the deal breaker!

  15. #15
    Boolit Master
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    I really doubt that this sort of conversion is worth the trouble unless you are trying to get more choke options. There has to be a motive for going to all this trouble to buy another barrel and rechamber it. It is probably about a trade off with buying another complete used shotgun.
    EDG

  16. #16
    Boolit Master Bazoo's Avatar
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    My original post is somewhat unclear. I'm not seeking advice on the financial wisdom of gunsmithing work vs acquire more firearms.

    I'm just curious if an older barrel with 2 3/4" chamber can be reamed for 3" safely.

    I have only one shotgun, a 12 gauge Remington 870 express with 3" chambered barrel.

    I'm purchasing an older barrel that is 2 3/4" chambered, to cut for a riot barrel. I do not intend to shoot 3" shells in this barrel. If I am able at some point to borrow the reamer and hone, I'd rechambered it for the experience.

    My question is in regards to safety. Is there enough meat on the barrel to facilitate this or is the barrel, because it is a 2 3/4" chambered barrel, going to be too thin at the end of the chamber? Is it a barrel by barrel case or is it a general rule that all are safe or unsafe if reamed to 3"?
    Last edited by Bazoo; 06-30-2020 at 04:33 AM.

  17. #17
    Boolit Master Shawlerbrook's Avatar
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    Yes, the barrel can be reamed out to 3”. And there were older 870 Express models that were
    2 3/4” only. I had one.

  18. #18
    Boolit Master Bazoo's Avatar
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    Thanks for the info. I didn't know there was any 2 3/4" only express models. Mine was made in 96.

  19. #19
    Boolit Master

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    I have an 870 express from the mid 80s. It is marked 2 and 3/4 inch. However, I measured the camber and it is parallel to past the 3" mark. I have shot hundreds of 3" shells through it duck hunting. Only issue is that the ejector is slightly short, but I very rarely had a failure to eject.

    Why dont you measure the parallel section of the chamber before you do anything. I figured they reamed it 3" but since it went on a 2 3/4" receiver it got stamped 2 3/4". Worth checking before you source a reamer for nothing. Brad

  20. #20
    Boolit Master


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    I would not ream an older Remington barrel to 3". Remington had a lawsuit over its shotgun barrels.

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