The Gunsmithing section in EE is closed to "I need" type threads, so I didn't know where to post...

I decided to replace the stock on my SBR with a UCIW. Unscrewing the old stock and the detent retaining spring got caught in the QD socket on the end plate and kinked.  I figured, no big deal, I'll cut off the end of the spring, tap the hole, never have to worry about it again.  I even paused and asked myself if that was a good idea with my NFA/SBR lower, but decided it was fine, Ive done it a number of times before.

It was totally not fine.  I was tapping the hole and the tap bound up, I stopped and gently tried to back it out... it decided to snap instead.  I guess it was a low quality tap, I'd had it for years and don't remember where I even got it.  That doesn't matter, it's my fault anyway.

So now my SBR lower has ~1/4" of a tap threaded into the detent hole and *flush.* I'm sure this will not be a cheap fix, but that's what I get.   Who can I trust to fix it properly?

I don't know how it could even be fixed, I have some ideas but I'm not sure what would work.

Thanks for any help or recommendations!

Taps have flutes. You can usually work a thin probe (dental pick or the like) into one or more of the flute grooves and use that leverage to worry the tap fragment back out. It's what I've almost always done when a tap has broken off on me.

Failing that, taps tend to be brittle - may be possible to shatter the remnant with a fine probe and a hammer, and remove the pieces.

If neither of those work, maybe a strong magnet will attract the tap metal but will of course ignore the aluminum of the lower, and allow you to work it out that way.

Thank you for the ideas, I have some dental picks and just tried that but it didn't even budge.  I gave it a few good taps trying to shatter it, but no luck there.  I'm scared to hit it any harder than I did.

My father in law has a drill press, I was thinking if I brace the lower perfectly I could drill it out, but I'm not sure how well I could clamp something that oddly shaped.

Use a left hand drill bit to drill into it. Rotation of the drill will be backwards and should back it out as the bit locks up in it. Never done it on a firearm but have done it with flywheel and head bolts

Aluminum is resistant to sulfuric acid.  If you can't get the broken tap out by mechanical means, you might soak your completely disassembled lower receiver in sulfuric acid and see if you can get the tap to dissolve enough to free it.

Taps are hard metal. I have had zero luck at drilling one out. Best to take it to a competent machinist or gunsmith.

If you are close to the Weatherford/Granbury area, I could burn it out with an EDM drill.

I noticed you're in Texas.

Hit up Atwell Tactical if you're around the DFW area. Just did a cut/pin/weld for me, seemed very competent and knowledgeable, he may be able to take care of it for you.

They make a tool for that. Tap extractors, $80 for a whole set, Amazon. They work very well.

https://www.amazon.com/dp/B0006NGGCM?tag=vglnk-c102-20

Same thing happened to my SBR I just trimmed the spring and detent pin and inserted it "backwards " thru the detent pin hole and left the broken tap as the retaining screw

I am going to go with this.

Or take it to a machine shop that has a FFL working for them, it is a small area with a small tap, I would not want to take the chance of cracking the receiver.

If one of these fit... this would be worth a shot

Those tap extractors are way to big for the he broke 
The tap thatg broke is probably a  4-40 tap or 0.11"  its tiny

I have seen this method used on 6-32's but nothing smaller. Try some diff size neddles/pins & see if u can pass one thru a flute, use the largest one you can pass thru as a gauge. Get some piano wire same diameter. Thread it thru a flute and then back thru the opposite flute. Twist ends counter-clockwise and then use pliers to twist tighter and remove. This will put even pressure as it removes. Don't forget to use lube.

This is what I ended up doing, I owe you a beer!  Just measured & trimmed the spring, filed down the detent so it would fit from the front, and good to go.  I'm ashamed I bubba'd it in the first place, but at least I didn't destroy the lower.

Thank you very much to everyone who posted with advice and ideas!!

This is the best way.



If you try to drill out the tap you should use a carbide endmill or drill. Proper speeds/feeds and oil are needed.

Most drills are high speed steel, taps are the same. You will have a hard time cutting HSS with HSS.

Day late and a dollar short on this one-

This is a classic example of "A Hardware Fix For a Software Problem"

Unless you are constantly swapping end plates, buffer tubes etc loosing detent springs is a non existent problem.

If it aint fixed don't broke it.

These actually work really well. You can buy them individually and get replacement fingers for them.

Powder Alum + Water will dissolve the tap