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September 14, 2015


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Seems to me, tempering the bolt would save you a lot of grief. You could do it yourself with a small home made forge (better option) or even with a torch in a pinch. Torch, tho, will yield less uniform results. Or, find a machine shop with a tempering oven. Then, when you've completed drilling, re-harden the bolt. Anyhow, that's how I'd approach it. Good luck.

john jay


agreed on all points.

i have a friend who is a knife maker, and something of an expert w/ laminated steels.

the last time i visited his shop, he'd made an oven out of a mail box, and a big tank of propane.

the mail box wasn't big enough to line w/ fire brick, so he just used some sort of foam stuff, sprayed it on, and away he went.

it was still in use, the last i knew. it was more than sufficient to heat a fair chunk of steel really really red hot.

btw, thinking of how to make a bolt holder out of something a little lighter than steel. my friend the engineer reminded me that a hunk the size i speculated upon was about 168 lbs, or so.


oh, well, i'll figure something out.

john jay

p.s. grandpa jay was a blacksmith/welder, grandpa beckius was a blacksmith/welder, and my dad was a blacksmith/welder/mechanic. i became a lawyer. too bad, so sad, that i didn't learn something more or less useful.

(so i do know about tempering & hardening, and that sort of stuff, along w/ the various hardening states of steel. but, i cannot weld a lick. *sigh*)


This is a great idea john. You got me thinking. I might try a fabricated lower/upper assembly in 4130 Chromemoly myself. (One in Titanium alloy would only be a bit more complex. Ti would be considerably less weight than Aluminum Alloy. Though nobody has bolts in Ti the size required for the barrel nut. Ti is difficult to drill, and some milling operations it is a bear to machine. Have to cut that thread on my lathe. I have the experience in both metals, so its a toss up between the two.)

A piece of tubing, 4130 chromemoly would be the top choice, but any seamless steel tubing will do for the receiver section. Take your bolt, cut off the appropriate length of threaded end of it, heat that thread section to 1100 degF, (dark red in a darkened room), sink it in a pail of wood ashes, let it cool to ambient. Better yet, if the bolt isn't shouldered, i.e. threads right up to the hex cap or socket head if it is an allen socket screw, leave the head on. Still cut the required length of thread, anneal as above, now you have a carbon steel bolt, likely 1045 carbon steel or similar, if it aint chinese junk, which you can drill easier. The cap is good, because you are going to need to jump from the thread OD to the tube OD, (or ID, for a press fit), you can chuck the bolt by the threads, drill, or bore the ID, and turn down the cap, and shorten the offset down to the minimum thickness. This way it is easier to line up your thread piece to your bolt carrier section. Because these two parts can be welded, or brazed together. If you have the bolt/carrier assembly, barrel with extension, and the barrel nut, you have a dandy perfect jig to line everything together for tack welding. Or, you can turn the OD of the cap of your bolt to the ID of the tubing, and use small cap screws drilled and tapped thru the tube OD, into the OD of your bolt head, while it is inserted into the tube stock, and your dandy jig lines it all up. No weld method option there.
Be a stout assembly for sure.

4130 is a good choice. It is precision drawn, comes annealed, good mill finish, has around 100,000psi tensile, and astronomical yield strength. Easy to weld or braze in all commercially common metal joining processes. Machines, drills, taps and turns like a dream using regular high speed steel tooling.
No need to stress relieve it after welding either for this use.
Great stuff.

Decent selection of 4130 tube:
http://www.aircraftspruce.com has a

Cap screws here:

I could fabricate an upper in my basic shop in say about 8 hours on the first one. If I ganged up on each process, saving set up time by producing lots, maybe some simple filtering and jigs, cut the time to under an hour per piece.

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