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Posted: 1/23/2006 12:38:15 PM EDT
Fellow build it yourselfers:
I am working on machining up an AR lower from a casting and realized (too late) that I had drilled the trigger pin hole to .204" diameter instead of .156!  The fire control group well in not machined out yet, so I have this over size hole all the way through the solid casting. The mag well is cut and the exterior is all profiled, so the darn thing is pretty far along. Has anyone any ideas as to how to salvage this lower? I'm thinking TIG welding over the holes to a depth of .15 or so then milling the top of the hole flat and then redrilling..... Over size trigger pin? Trigger pin bushings?  Regards, efxguy |
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Posted: 1/23/2006 12:48:45 PM EDT
[#1]
Colt "mil-spec" fire control parts
 Nick |
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Posted: 1/23/2006 1:09:44 PM EDT
[#2]
I thought .156 was "milspec". Are you refering to Colt's large, oversize pins?
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Posted: 1/23/2006 1:13:26 PM EDT
[#3]
Thats what I understand him to be saying is that you can use the Colt oversized pins and FCG in that lower.
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Posted: 1/23/2006 1:36:50 PM EDT
[#4]
Drill it out to 1/4 and use that alumalloy stuff, they say it will fix anything except a wifes infidelity.
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Posted: 1/23/2006 1:46:00 PM EDT
[#5]
Colt's oversize pins are not "milspec". Maybe he was being sarcastic and I missed it.
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Posted: 1/23/2006 1:57:15 PM EDT
[#6]
I said nothing about Colt...
I did mention something about oversize pins. ASFAIK, Colt uses larger "upper to lower" retaining pins for some models, but I don't know. The CORRECT hole diameter IS .156". And this diameter is, AFAIK, "mil spec". It is called out on the lower reciever print. I drilled thoe ONE hole, for the trigger pin, to .204". That is the only issue I brought up... Regards, efxguy |
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Posted: 1/23/2006 1:59:35 PM EDT
[#7]
What is allumaloy? Some kind of epoxy? efxguy |
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Posted: 1/23/2006 2:44:23 PM EDT
[#8]
Mil-spec firecontrol pins are .154"
Colt's large firecontrol pins are .170" That rules out using either in a .204" hole. If it were a forged lower, I'd recomend welding it up and redrilling. I know nothing about welding aluminum, so I don't know if being cast makes a difference. You might just have to make your own custom pin and drill out the trigger and disconnector. |
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Posted: 1/23/2006 2:52:26 PM EDT
[#9]
how about a bushing to fit your oversize holes to reduce it to standard with an "outboard" flange lips. your pins would need to be longer than standard, but you incorporate your own anti-walk set up with screws or a small link between them... if you don't tell anyone you screwed the pooch they might think you're the coolest...
just a suggestion. s.tank 
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Posted: 1/23/2006 4:50:23 PM EDT
[#10]
It is a forged lower, the cast ones are pretty flimsy. I think I'll put it in the oven for awhile at 400 degrees or so, then try to tig weld the holes closed. This will be the, I think, strongest repair. Otherwise, I may turn two steel bushings with a tiny flat flange and insert them from the inside and set them with a bit of lock-tite bearing anchoring compound. Unless I first bore out the holes to .250, those bushings would be very thin.... efxguy |
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Posted: 1/24/2006 4:37:13 PM EDT
[#11]
Quoted:
Drill it out to 1/4 and use that alumalloy stuff, they say it will fix anything except a wifes infidelity.[/quote] YOU TOO? HUH ! 
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Posted: 1/24/2006 5:30:34 PM EDT
[#12]
I guess you could try plugging that hole too.....might have some reprocussions though.
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Posted: 1/24/2006 5:53:23 PM EDT
[#13]
i know nothing of welding, but i do remember wayyyy back when...(i'n old) when they usta take m16 lowers that had been demilled from the military(sheared completely thru the trigger guard area)and spread the crushed reciever back open, and welded them back together.so i suspect your too big hole ain't as much a problem as you might think...weld it up, drill it again...don't ya just hate it when you do stuff like wait? wait till you get my age, you'll be doing fubars most everyday!
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Posted: 1/24/2006 6:12:09 PM EDT
[#14]
Brother, I'm in my 40's, and daily fubars are the norm... efxguy I'm going to try the welding when I get the chance. Thanks. |
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Posted: 1/26/2006 6:40:40 AM EDT
[#15]
Hi Guys, i'm new to this forum and i would like to say Hello from the UK! i have been reading you threads and post for some time, approx 18 months and find them very interesting! i've only just got around to joining and posting my first posthavethis was my first attempt at building one, and i done the exact same thing and forgot to change the drill bit and then drilled the hole too bigherethe best thing about the kit you only need a household Blowlamp to use it! and no expensive alloy welding equipment, or searching around to find someone with a TIG welder. the kit takes a little practice on some scrap alloy to master the technique but the end resaults were very good, i then filed down the excess braze and then re-drilled the hole to the correct sizehesei also have a AR 80% lower drill jig with most drills and all the long detent drills + The bluebook guide by Ben Hughes for sale at the momnent. Hope this helps, sorry for blagging sales on my first post...i thought it may help somebody |
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Posted: 1/26/2006 11:54:19 AM EDT
[#16]
If you are good at welding aluminum that would be the best fix. Since I suck at welding thin or small aluminum parts (I am great at making aluminum slag blobs
) I would make it .250 and turn a couple of bushings with a flange on it and install it fron the inside. The machine the trigger down the thickness of the bushings and use you favorite bonding agent to hold the bushings. The narrowed trigger along with the chemical bond would hold the bushings from moving and not require longer trigger pins Only problem I cound see and even welding might be when it comes to the finish if you plan on anodizing it since the bushing or weld might not come out the same as the rest of the receiver. Of course one of those fancy paints could cover the upper and lover to match if it was a concern.
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Posted: 1/26/2006 12:58:37 PM EDT
[#17]
Just thinking out loud
 so maybe it might work.(I am not a machinist)You say it is still a solid block, not opened up for the FCG. What if you oversized the hole you already drilled and tap it with a pipe thread, put in a solid pipe plug with an external square or hex to tighten, that can be ground or milled flat. Then start fresh and square. |
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Posted: 1/26/2006 1:07:55 PM EDT
[#18]
The problem with any kind of threaded insert is once the fire control group cavity is cut the walls are pretty thin (I'm too lazy to pull one out of the safe to measure right now) and you would have to use a very fine thread to get more then one ot two threads to remain in the receiver. Pipe threads are fairly course so no threads would remain after milling out the cavity. It is possible to make a insert with a really fine thread but more trouble than it's worth really. If the walls were thicker there would me more acceptable fixes to use. With that all said, any ideas tossed into the pot are helpful and gives a person more options towards fixing a mistake. |
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Posted: 1/26/2006 1:40:25 PM EDT
[#19]
Id go with welding the holes back up. The other option would be to make small bushings that have about a .0005 pressed fit. Heat up the lower and then drop the bushings in. You could pre-drill the bushings with a small dill and then redrill/ream to the right size once they are installed.
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Posted: 1/26/2006 1:55:11 PM EDT
[#20]
Press fit two hardened bushings. Your firing pin holes will never wear out.
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Posted: 1/26/2006 3:29:44 PM EDT
[#21]
Pre-heat the part, and TIG the holes shut. Just rosette the holes on each end, and refinish the exterior.... only drawback is if you anodize, you will have 2 shades, as filler will not likely be same formula as the parent.
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Posted: 1/26/2006 4:07:41 PM EDT
[#22]
If you have a lathe, make an aluminum pin with a very slight taper. Tap it into the hole, file (or mill) it flush, then redrill.
OR, you could fin some alminum screws. Drill and tap the holes, put in screw, mill flush. Either weld it or peen it in with a punch. Red loctite might work too. John |
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Posted: 1/26/2006 5:15:47 PM EDT
[#23]
Agreed. Preheat and TIG |
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Posted: 1/26/2006 5:41:07 PM EDT
[#24]
THis will be my course of action. As soon as I get home from Texas. I'll post my results. Thanks a million, efxguy |
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