My Remington 550 end receiver threads are messed up - how to fix?

Maxim · Nov 6, 2022

I got a Remington 550 semi auto a long time ago and finally got around to trying it out. It sat in someone's closet for way too long.
The problem I found is the threads on the end of the reciever are messed up, I'm guessing someone cross threaded them a few times in the past. The threads on the end cap are fine.
When you try to shoot it the end cap pops off. I measured the threads at the end cap I believe they are 3/4 x 20. The end of the receiver hole is about 0.775, you can still see a little threads left over.
The cap kinda screws in but without any real force to hold it.

How would I go about fixing this? I don't think there is enough metal to simply run a tap and I would guess the receiver is hardened alloy steel so you can't just weld on some metal and bore/thread.'
I didn't see a 3/4x20 helicoil listed anywhere.

I don't want to throw the thing away either, other then the finish looking like a civil war pickup it seems to function fine.

trevj · Nov 6, 2022

Got a lathe?
First, the receiver is not liable to be very hard. If the threads are munged, you can cut larger threads, possibly even picking up the same pitch, and go until they are cleaned up.
Then make a new rear plug.

Or, bore out the threads, and make a threaded insert, to line the inside of the action. Install with Permanent thread locker, or solder. Then the original plug can be left untouched, the fix should be essentially invisible. This is easier.

If you do not have a lathe, it would probably be better handed to someone that does. Short of cross pinning the plug in place, I cannot see any real non-lathe fix.

Maxim · Nov 6, 2022

I have a lathe, I don't see any standard 3/4-20 inserts. The plug itself is a special piece and looks fine. Do you think I can weld metal on it without messing it up? I have a tig welder.

Maxim · Nov 6, 2022

I found a 1/2 compression nut which are 3/4-20 and the plug doesnt fit its actually a .795 X 20 TPI. I can get a ccp grade tap and die for 3/4x20 on ebay.
Would tig welding a little material in there and then tapping and threading to match work? I'm worried I'd screw up the receiver welding on it. The other option recommened on another forum is to
cross tap 3 small screws into the plug

I can't tap it on the lathe because the through bore is too small, the ring holding the tube offsets the barrel from the center.

trevj · Nov 7, 2022

Am not surprised that they used an odd thread, they only had to make the parts fit each other, and not please someone trying to fit the parts elsewhere.

Not surprised at the lack of inserts, either, though, if they were available, I think they would be a poor choice.

If you are not capable and confident, cutting internal threads on your lathe, it may be a job to farm out. Or it may be th ejob that pushes you to practice the needed skills.
What I had in mind, was to use a boring bar to remove the threads from the action, plus a little bit more. Then make a threaded bushing to fit in the space those threads were removed from. Fix in place with solder, or permanent thread locker (LocTite Bearing Retainer compound).

I think the heat from welding would almost certainly cause the requirement to refinish the action, Even if you did weld up the threaded area, you are stuck cutting the thread in the lathe, unless you can find a custom Tap of the correct size.

Drilling and tapping for screws is always an alternative, though kludgy and permanent.

GGaskill · Nov 7, 2022

I am assuming what you are calling the "end cap" is part #46. This looks like an easily made piece. Why not make a replacement with a 13/16-20 thread? Taps are available to alter the receiver tube.

Maxim · Nov 8, 2022

GGaskill, the receiver tube threads are the problem, the cap #46 is in good shape. I think someone loosened the cap and it beat itself over the years.

jmm03 · Nov 8, 2022

I wonder if this could be fixed by using a Devcon product if machining is not feasible? Using one of the metal based epoxies, coat the receiver inside where the damaged threads are, use mold release on the cap and thread it in place. I think it would be strong enough as long as it does not work as a lug. Jim

72bwhite · Nov 8, 2022

Maxim said:
GGaskill, the receiver tube threads are the problem, the cap #46 is in good shape. I think someone loosened the cap and it beat itself over the years.

You missed the point
use 13/16 20 tap to retread the end of receiver
no need to add material

should be plenty meat on the receiver
then you can either build up the threaded portion of the cap
and make it 13/16 20
nice round part much easier to chuck in your lathe

If you just absolutely have to try retreading in the lathe simple
make a jig to hold the receiver and use your 4 jaw

cyanidekid · Nov 8, 2022

hey Maxim, I'd listen to GG. the guy knows a thing or two, but you should know that if you've been around since '05, yes?

being where it is, it looks like it's holding the guts from smacking you in the face. if so, I'd personally prefer to (or have) the receiver retapped, and a new "breech cap" made, and not rely on any additional parts that could separate.
certainly wouldn't rely on anything that says Devcon on it!
seems it would be more trouble to "build up" and rethread the cap than turn a new one, but I love to contour turn freehand, so your preferences may differ.
forget TIg build up on the internal thread. that would be a mess. :ack2:

jmm03 · Nov 8, 2022

I agree that a machined solution would be the best, but since it appeared that the cap was holding with damaged threads, an industrial epoxy suitable for the pressures involved might be a solution if properly prepared and applied. Something like this: https://itwperformancepolymers.com/products/devcon/corrosion-erosion-repair/devcon-titanium-putty/ We used that product to build up the threads on multi stage valves that were subjected to 4800 psi water pressure and they held up surprisingly well. I don't know if it would work in this application, I was just looking for another possible solution.

john.k · Nov 8, 2022

Bubba would drill a hole crosswise through cap and reciever tube,hammer in a tight fitting bolt,cut off the excess ,and call it good.

GGaskill · Nov 8, 2022

Yeah, I was thinking I would fix the receiver threads with the tap and turn a new receiver plug with 13/16-20 threads to match the rethreaded receiver. A new plug would be a simple part to make. You wouldn't even need to make it exactly the same shape as the original.

wesg · Nov 8, 2022

Devcon Titanium? You could buy 2 new rifles for what a kit of that costs :-)

72bwhite · Nov 8, 2022

Not knowing what the receiver is made from I wouldn’t try and build it up
with welding.
best fix is probably tap to 13/16 20 and make a new cap
second choice would be what John said cross drill and tap
a slightly more elegant version of the bubba fix
could use 2 screws one on either side drilled and taped in to the cap

john.k · Nov 9, 2022

Funny you should mention Devcon........when I was working ,one of the bosses got a Devcon rep round to look at an erosion issue.......the result was a delivery of a vanload of cartons of Devcon containers..........the "engineer" took over and applied 1/2 ton of Devcon .....it was all gone in a week ......just as I had predicted ........and then the bill came for all the Devcon !...........was about $50,000.!.

jmm03 · Nov 9, 2022

I should have known pricewise it would not have been practical.

wesg · Nov 9, 2022

If it were mine ...

I'd bore it out and put in an insert matching the original thread. If it wouldn't fit in the spindle with all the attachments, I'd pull the barrel.

Solder, or Loctite? I'd probably thread the receiver with a fine pitch and Loctite.

Dependent on wall thickness.

akajun · Nov 9, 2022

I’m familiar with that gun
The easiest solution would be to chuck the receiver in a lathe and clean up the damaged threads , then make a new endcap with oversized threads to fit. Anothe option would be to cut off the old threads on the cap , weld up, and recut oversize threads on the original cap

john.k · Nov 9, 2022

Its quite likely a repair could be made by inserting a piece of thin soft aluminium ,such as a butter tub seal,in the thread and screwing in the cap...........this was a repair used more than once to fix stripped sparkplugs in ally heads.

My Remington 550 end receiver threads are messed up - how to fix?

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