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Extraction of broken bolt on rifle barrel


Nov 3, 2019
I’ve got rifle barrel which had couple of M4x8mm screws which were loctited on. One of them unfortunately snapped flush to the barrel but screw head is not flat. This is spare barrel so I haven’t spent time on removing the broken bolt out of it. Now however I’ve came up to an idea how I could take it off. I do not want to apply heat to it to mess with the possible heat treatment. Includes welding a nut on the bolt is out of question. I’ve been thinking to bring it somewhere for EDM the stud out. That would be most likely the safest but expensive. My attempt would be to use flat end 3.3mm carbide stub drill and after measuring the exact location of the hole, drill the screw out with very slow feed by CNC mill to prevent drill bit wander and any excess force to the remaining screw. Then there should be only the screw lands or thread remaining (or whatever you call it). Then soak the hole in Acetone for some time and removing the lands by dentist pick.

What’s your thoughts, would this method be successful? Thank you in advance.
I've had success picking out just the threads after machining up to the minor thread diameter. It might be pretty difficult with a hole that small though.
I have been known to take 1/8 carbide endmill shanks and grind them into a left handed spade bit to use for screw extraction. That left handed bit in a 1/8 endmill holder combined with the soldering iron to break down the locktite and maybe a 1/16 pilot hole seems like a sure path to success.
Use the existing ooen hole to locate the center of the broken screw. Ide the LH spade bit after the solder iron trick. The screw will likely just screw out. Don't use a positive feed, only hand feed.
+1 on left hand drill/cutter with mild heat, just to hot to touch. Don’t forget to fast peck to give the screw room to back out.
What possible heat treat goes into a rifle barrel that would be lost or damaged by heating loctite to the softening point. Or resistance welding a spot on a broken screw?

I know of none, so I ask.
Loctite should soften at or below 500deg F depending on grade. Not high enough to cause any damage to the barrels heat treatment.

If you use a soldering iron the actual barrel will see significantly less than 500deg. So some mild heat should be fine if it helps.

Thank you everybody for the excellent suggestions. That soldering iron would have been excellent and as a thermostat controlled surely no problem on overheating. All of the holes had good chamfers so I was able to accurately measure hole center. So I went with the original idea of flat end carbide stub drill and let CNC mill do the drilling. Only problem that I faced was to get the thread end from the groove. Once I managed to get that, threads pulled like yarn from ball of yarn and the threads remain intact.
I had a cllection of old Dental burrs (the ones used to hollow out your teeth for fillings), that were pretty handy for cutting a slot in to a busted off screw, so it could be backed out. The 60,000 rpm pencil grinder was a godsend!
I've taken out quite a few broken screws. Heat will soften loctite, so heat above too hot to touch. center drill as near center as possible then use small LH drill about 1.5mm or #52, keep increasing drill size about 1 or 2 gauges (51,52), slow spindle speed and so on while keeping the barrel hot. As most know increasing drill size small amount, drill wants to grab. When it does because previous holes weaken the screw the left hand rotation will back out the screw. I would Not use CNC because when the screw starts to back out I want to lift the spindle as it rotates
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