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sight rail

F

Frank McCarthy

.410
The other day at the range, a screw fell out of the sight rail. No biggy, screwed it back in as best I could at the time. Yesterday, while cleaning the gun, I checked all the screws. All 4 were loose. Got an allen wrench and proceeded to tighten everything up. The back 2 went fine, but when I went to tighten the front 2, they both stripped out. Now these are the threads that are in the receiver, so I'm thinking that I'm pretty much screwed. Just when I got the thing to run consistently well. Anybody else have this problem or suggestions on how to fix it without having to send it back to Mossberg...again?
 
Sorry to hear about your problem.

I would fix the problem with a few Helicoils. You should be able to find them in a good hardware store or auto parts store.

Once you install them it will be stronger than the original threads.

helicoil.jpg

forgot to give you the screw size,,,,,,,

receiver mounting screws Pre 1997 was 6-48 and after is 8-40.
 
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You can buy what they call a kit just for that one size. It usually comes with several heli coils a drill bit and a tap. About $15.

Keep us posted on the repair.
 
It looks like the hardest part of this will be finding the kit. I've tried 2 hardware stores and an auto parts store with no luck. Looks like a trip to Lowes tomorrow. Maybe Home Depot if I have to.
 
Mcmaster carr online is your friend....they have everything and the website is easy to follow and narrow down your choices. You will have to bend over a bit on shipping though!
 
old mossy said:
Sorry to hear about your problem.

I would fix the problem with a few Helicoils. You should be able to find them in a good hardware store or auto parts store.

Once you install them it will be stronger than the original threads.

View attachment 13298

forgot to give you the screw size,,,,,,,

receiver mounting screws Pre 1997 was 6-48 and after is 8-40.
Click to expand...
I've been able, with much difficulty, to locate helicoils in 8-32, but nothing in 8-40. Please advize. I've also learned that this is not an uncommon problem with the SPX.
 
I was looking around myself and also found 8-40 is not very common. You could also just drill and tap it out to the next larger size and just use the larger screw. Not needing a heli coil.
 
old mossy said:
I was looking around myself and also found 8-40 is not very common. You could also just drill and tap it out to the next larger size and just use the larger screw. Not needing a heli coil.
Click to expand...
I would use the 8-32 if I could find the appropriate screw to match, but that seems pretty unique as well. From what I could find, the only place the 8-40 is used is in scope/rail mounts.
 
Whitey said:
We use 8-32 in the aviation industry, very common. What type of screw head does it take?
Click to expand...
If you have a rail mounted on your shotgun, take a look at it. It's an allen screw, tapered at the base of the head, the rest of the head is very square. I'll try to post a pic tomorrow.
 
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Frank McCarthy said:
If you have a rail mounted on your shotgun, take a look at it. It's an allen screw, tapered at the base of the head, the rest of the head is very square. I'll try to post a pic tomorrow.
Click to expand...

Okay so it has a tapered base but are the straight parts really contributing to anything?If not then McMaster Carr lists 8-32 Allen "flatheads" with your choice or an 82 or 100 degree bevel on the bottom. Would that work?
 
DDEL said:
O


Okay so it has a tapered base but are the straight parts really contributing to anything?If not then McMaster Carr lists 8-32 Allen "flatheads" with your choice or an 82 or 100 degree bevel on the bottom. Would that work?
Click to expand...
I'm not sure. I think the taper centers the rail to the receiver and the straight area is solidly holding the rail in place. I'm no expert on this so maybe we can get others to weigh in on this.
 
8-40 is not a common size so forget finding one in your local hardware store. Next common size up is 10-32, which could take a 5/32" drill bit which is a tiny bit undersize. 10-24 drill size is a little smaller but I'd wonder if you still have the meat in the receiver for it. If you do go up in size, don't forget to enlarge the holes in the sight rail, if necessary.

Or try a Heli-Coil--Debay has a lot of surplus kits for far less than McM will charge you. Whatever you do, be careful the new screw or Heli-Coil does not protrude into the receiver! :eek: Good Luck!
 
Bobster said:
8-40 is not a common size so forget finding one in your local hardware store. Next common size up is 10-32, which could take a 5/32" drill bit which is a tiny bit undersize. 10-24 drill size is a little smaller but I'd wonder if you still have the meat in the receiver for it. If you do go up in size, don't forget to enlarge the holes in the sight rail, if necessary.

Or try a Heli-Coil--Debay has a lot of surplus kits for far less than McM will charge you. Whatever you do, be careful the new screw or Heli-Coil does not protrude into the receiver! :eek: Good Luck!
Click to expand...
I think Amazon has them too. I'd thought about the insert going into the receiver. A little grinding on the top with a dremel tool should fix it. I suspect some Locktite would benefit the situation as well. The metal in the receiver seemed a bit soft as the holes stripped out way too easy. Thanks for the info.
 
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