M4 - Stripped recoil tube receptacle

[Knoob07]

First - i need to go on record as an idiot - I grievously mis-installed an OEM 3-position recoil tube and ended up pretty badly mangling the threads on the body of the fun (horror show photos attached)….

Any suggestions?  Otherwise I’m going to go down on bended knee and ask Benelli if they can repair…

PS i have already beaten myself up pretty hard over this stupidity - but feel free to unload some more on me as appropriate.

[NineInchNails]

I don't see how it could harm anything by cleaning it up using an appropriate thread tap.

[xblax619]

2 hours ago, NineInchNails said:

I don't see how it could harm anything by cleaning it up using an appropriate thread tap.

i agree. i would try this before sending it out to the manufacturer. 

[RxArms]

Yes I would consider using a tap to try and clean up the threads, make sure you use oil.

as long as the recoil tube will thread in and be secure, you can load it with a ton of red loctite when you do the install, and it should be okay.  But it does need to hold torque, so you’ll have to be the judge of that.

the receiver is threaded M21x1, but feel free to confirm with Benelli first.  Further, I would find a local gunsmith to do this imo.

also I don’t see how Benelli can fix the threads, other than using a tap like you may do.  They may just say you need a new receiver instead of attempting to service it at all.

I am curious how this happened, Did you force a cross threaded tube in the whole way?  Did you over torque and is the threads stripped?

 

Edited November 12, 2023 by RxArms

[StrangerDanger]

Yikes. Sorry to see that happen to you. Looks like you used brute force on the extension and stripped the receiver threads?

It appears a lot of the aluminum was stripped away. So while using a large expensive tap to correct the threads, I doubt it is going to have the strength you'll want to secure the extension. Plus getting the tap going thru that much damage is not going to be fun.

Benelli might have a receiver they'd be willing to sell you to fix this. I'd give them a call before any Bubba attempts. Basically you'd have to epoxy or JB weld the extension into the receiver and hope for the best.

[EzGoingKev]

The first thing I would do is check with Benelli to see if they will sell you a replacement receiver. 

If they will not I would find a really good machinist that could make and install a custom insert to restore the threads.

[Knoob07]

All, thank you for the thoughtful responses.

Yes this was the result of over-torquing during an install that went wrong.  I’m not certain but i suspect my tube wasn’t aligned right and i know I mis-interpreted resistance as “wow I’m really feeling that loctite even when it’s wet!”.  Don’t try this at home is good advice for a hack like me, i just don’t always listen to it.

Doing some research online most suggest the thread pitch is 21 x 1 or 18 x 1.   I’ll double check at a hardware store with the tube thread.

Thanks again - I’ll report back.

[M2_shootr]

Wow……that’s a lot of missing material. I would reach out to Benelli. A tap will clean threads, but half are missing. I wouldn’t trust that and shoot it. 

[StrangerDanger]

Were you using a oem 3 position extension or an aftermarket one when the install failed?

[Knoob07]

I was replacing an OEM 1-position with an OEM 3-position.  The M4 came with the “1 position” (not sure what it’s actually called) and i replaced it with a 3-position from beneliiparts.

[Knoob07]

All, i wanted to just follow up on my results here for posterity on the off chance that google brings some other lost soul to this thread in the future.

I was able to buy an M21x1 tap and with it I was able to “restore” sufficient thread for a good solid fit.  I did slather it up with loctite and i let it cure for 24 hours.  I ran a few shots thru it (in a vice at an outdoor range pulling the trigger with string for safety) and can say with reasonable confidence that it’s pretty solid.

I will be using the gun very carefully for the next few weeks putting a lot of rounds thru it and checking / re-confirming a very tight and strong fit of the tube in the body of the gun.

Thank you all again for the wisdom - I will continue to proceed with caution, but I’m thrilled to have my M4 back together as our Italian overlords intended.

[RxArms]

49 minutes ago, Knoob07 said:

All, i wanted to just follow up on my results here for posterity on the off chance that google brings some other lost soul to this thread in the future.

I was able to buy an M21x1 tap and with it I was able to “restore” sufficient thread for a good solid fit.  I did slather it up with loctite and i let it cure for 24 hours.  I ran a few shots thru it (in a vice at an outdoor range pulling the trigger with string for safety) and can say with reasonable confidence that it’s pretty solid.

I will be using the gun very carefully for the next few weeks putting a lot of rounds thru it and checking / re-confirming a very tight and strong fit of the tube in the body of the gun.

Thank you all again for the wisdom - I will continue to proceed with caution, but I’m thrilled to have my M4 back together as our Italian overlords intended.

I think the worst that can happen is a round will fire, bolt goes back, recoil tube dislodges, your buttstock comes off with a bit of force.  I don’t think there is any real danger other than that, the bolt can’t exit the rear of the receiver it will just impact the back of the receiver and will be contained.

if this were to occur I think you’d have warning signs, such as a slightly loose recoil tube before it happens.

I’m glad you got it sorted out!  Sounds like it will work just fine as you felt the torque of the nut was sufficient.

[StrangerDanger]

Glad you got it salvaged. Did the tap go in pretty easy and find the existing threads?

 

You can use Alumablack to hide most of the scratches on the receiver. You might just have to scuff them up a little bit to remove the oxide layer that forms on bare aluminum. 

[Knoob07]

Thanks again all.

The tap did go in quite easily once I got over the initial resistance - there were a couple of tighter spots but it was all easily done by hand.  I expect anytime it was a little tighter it was cleaning the existing threads up.  It definitely cleaned out well and completely aligned to the original threads.  

I was also able to run the receiver tube thru a matched thread cleanup which i think was also important to ensure i didn’t repeat my mistakes.

Thanks for the recommendation on alumablack - i didn’t even know that was a thing and I’ve got a bottle on the way.

[SOCOMguy]

The last ditch solution would have been to bore out the thread and install a threaded bushing, it appears that there is sufficient "meat" to accept a thin bushing.

Joe B