Threads stripped out of receiver on M4

[ApexinM3]

Group,

I am currently running a Mesa Tactical 8-shot shell holder on top of my M4 and have a Eotech 553 on top of that. Recently while at the range, the holder came off, shells & Eotech still secured. Upon inspection, I noted the threads in the receiver are stripped, and several screws are missing. So my questions are these:

 

1) Can I retap the the holes, and if so what is the thread pitch & fastener type; and

2) What can I do to prevent this from happening again?

 

Thanks for your help all!

[heckler&kochp2000]

yes get a thread counting tool at a industrial hardware store , and lock tight .

[OhioM4]

1) I couldn't find the screw size anywhere on line. As mentioned previously, take one of the screws into a good hardware store and see if they have a thread pitch gauge.

 

I'm not as optimistic as H&K2000. When the threads strip, it pulls the screw out of the hole and essentially cuts the hole to the same size as the major thread diameter. If you try to re-tap the threads the same size, there is little or no metal left to cut. You could drill and tap it to the next larger thread size, not an ideal fix but it would be cheap and easy. One correct way to fix it would be a process called heli-coil. They tap and thread the hole to a larger size and then screw in a sleeve with an internal thread that is the same size as the original. The receiver may be too thin for that operation and it would probably need to be performed by a gun smith. They could also heliarc new aluminum into the hole and re-drill and thread to original spec but the heat would likely mess with the finish.

 

If you want to try the simple "re-thread to the same size" fix, make sure you use one of the permanent Locktite products like the red one all along the rail. The glue effect of the Locktite will be the primary means of fixation.

 

2) Red Locktite is essentially a glue. It can go between any mating metal parts that can be tightened together with little or no gap (it depends on the absence of oxygen to cure). You could use some on the rail where it contacts the receiver. You may want to use Blue Locktite on the small screws as the Red may cause them to strip out again when you disassemble it in the future. You can disassemble the parts again but you will need to heat them up with a heatgun to get it to release.

Edited October 8, 2009 by OhioM4

[StrangerDanger]

Very sorry to hear. What size shell carrier were you using?

 

Brownells sells the screws and lock washers I believe. They are not cheap. If the threads are stripped, those screws are useless. You'll need to see a gunsmith and have the receiver threaded for a larger screw. I would get rid of the Mesa carrier honestly.