Rail Alignment and Receiver

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Rwt987265
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Rail Alignment and Receiver

Post by Rwt987265 » Thu May 30, 2019 5:57 pm

Hi,

I recently purchased one of the M3 kits with a receiver that was cut in three pieces. I drilled and removed the rails that came with the receiver because portions of them were torch cut. I am attempting to test fitment of a set of used rails and was wondering if anyone could provide a link to bolts that can be used to align the rails and test how smoothly the bolt moves on the rails. Bolts that I have previously tried interfere with the bolt movement. I'm also curious as to how one would expand the receiver due to shrinkage that may occur during the torch cutting process.

Summary
-Please provide a link to bolts (or specific dimensions) or device to test bolt fitment before riveting
- I have been told that during the torch cutting process, the receiver may shrink a bit. How have people remedied this problem?

Thanks

Countryboy77
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Re: Rail Alignment and Receiver

Post by Countryboy77 » Thu May 30, 2019 7:53 pm

Used small 6/32 screw head on the inside,nut outside.Make sure the bolt clears the bolt heads. Now to making up metal from torch cuts.Use a set of salvaged rails with holes present to line up receiver sections so you can see how much material is missing,bolt in recouperator as well.If it's a semi get your denial in and make a cut so FA grip stick doesn't fit. 3ways to make up for missing metal. A doner receiver section for fill in, sheetmetal welded into the spaces , 1/4 copper stock as a backing and filling with weld. Don't try to weld the receiver at the same time.Add metal to each section till they overlap tightly then weld together.This approach will greatly reduce shrinkage.The more metal you try to fill the more it will shrink/warp.Small short passed ,jumping around to give time to cool in between each one.Good luck, love to see guys bringing these back to life ,and if you get it going you have earned your bragging rights.If your mg3 kit is crushed and cut ,there's your doner sheet metal,go get a real receiver to start.Those smashed cut kits are useless unless your a blacksmith with too much time on your hands.

86Merk
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Re: Rail Alignment and Receiver

Post by 86Merk » Mon Jul 06, 2020 8:15 am

I took a slightly different approach. Somewhere in my wanderings I came across the spec that the rail rivets were/should be on 80mm centers. I made up a set of what were essentially 1/4 inch aluminum fake rails and tapped 8-32 on accurately measured (DRO on the mill) centers. Using this, with a few parallels and as many clamps as I could fit (if you have room for another clamp you haven't used enough) I welded it up. After All was said and done I found a spec with a tolerance for the length from the rear of the receiver to the rear of the camming window somewhere on this site. Overall tolerance said it could be .2mm short, mine came up .4mm short so at a guess its out ~.005". I've seen post where people were on the order of .040" out and made it work.

At least on the de-mil I used that seemed to be a viable approach. The new rails I purchased were undrilled do no issue with lining up for rivets when I finally get to that step.

as always YMMV

ges

86Merk
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Re: Rail Alignment and Receiver

Post by 86Merk » Mon Jul 06, 2020 8:22 am

I think I answered a completely different question, sorry not enough coffee yet.

If you make/buy a riveting jig made from a 7/16 coupler nut you should be able to spread the receiver with that. There will be spring back so take it slow and test often.

When you rivet, given that the buck (coupler nut assembly) is properly adjusted it shouldn't shrink any

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