1750 ca French Lock Screws help

[cornstalk]

The lock screws on one of my 1750 ca flintlock pistols are striped. The pitch appears to be 32, but the diameter is just a little smaller than no. 8 but larger than a No. 6.

Unfortunately the shoulder in the lock isn't big enough to allow me to enlarge the holes to accept an 8-32 lock screw.

Ideas on how/who can help with this?

Thanks

 

[TNBandit]

Possibly use a metric screw that falls between a #6 and a #8 ? If my math is correct that would be 4mm.

 

[cornstalk]

Possibly use a metric screw that falls between a #6 and a #8 ? If my math is correct that would be 4mm.

I initially dismissed metric as it didn't become a standard in France until something like 1796, but I guess that doesn't mean it didn't exist before then. I'll give that a try. Thanks.

 

[user 34300]

If it is original it could be some non modern standard thread. If you can not go to a larger screw then you can to bush the hole. Tap the hole to a larger convent size. Making a threaded bushing and securing it high temp silver solder would be my first choice. If you put a shoulder in the bushing you might be able to secure it with Loctite 638 or soft solder. If you did it right this way It would be hard to see.

This how Jim Kibler does it.


Welding it closed and re drilling and tapping might work. IT might make a mess too. The filler may not finish the same as the rest of the lock.

 

[Phil Coffins]

I’d do a custom made screw rather then alter an old gun. The saying about the minor part is apt here.

 

[user 34300]

True. IF the OP can determine the major diameter and thread pitch of the hole that is best. The internal thread might be cast with lead alloy or Cerosafe. You could also thread a tapered hardwood stick into the hole and make an impression. The next step would be to make a custom screw in a lathe. This path requires a more skill.

Bottom line is that a skilled Gunsmith that understands antiques needs to look at it.

S & S Firearms Home Call these guys?

 

[rich pierce]

I have several original screw plates for making threaded screws. I think that is the way to go. Back then threads were swaged, not cut. If you send me accurate measurements I will see if I can help you. Overall length, length of threaded portion, diameter of threaded portion, diameter of non-threaded portion, head diameter, height, and shape.

 

[cornstalk]

I have several original screw plates for making threaded screws. I think that is the way to go. Back then threads were swaged, not cut. If you send me accurate measurements I will see if I can help you. Overall length, length of threaded portion, diameter of threaded portion, diameter of non-threaded portion, head diameter, height, and shape.

Huge thanks regardless of the outcome.

Looks like the original screw rolled up a bit but I hope the measurements make sense. The screw at the top I bought from TOW:
Lock bolt, 8-32 thread, 3/8" diameter cylindrical head, 2" length

The thread matches up just about perfectly but the diameter is .162

I got the head to the correct diameter by chucking the new screw in a drill and using a file.

 

[rich pierce]

Just so I’m sure, the issue with the one you bought is that the diameter of the 8-32 is .162 and the original is .145. Right? And on the original the threads are worn down.

If so then I could swage an 8-32 down in my screw plate.

 

[cornstalk]

Just so I’m sure, the issue with the one you bought is that the diameter of the 8-32 is .162 and the original is .145. Right? And on the original the threads are worn down.

If so then I could swage an 8-32 down in my screw plate.

That is correct. Down from .162 to .145. I need two lock screws. Do I need to send you some of the screws I bought from TOW? I got a bag of em.

I've been trying to wrap my head around swaged screws and then I remembered as a youth seeing screws with seams down the threads. Is that what they were?

 

[rich pierce]

I’ll see what I’ve got in the box. When swaging screws, the shaft starts out with a diameter about halfway between the diameters of the grooves and tops of the threads. Then the die squeezes rather than cuts, and moves metal outward toward the tops of the threads and inward to the base of the threads. Bicycle wheel spokes are threaded this way even today.

 

[cornstalk]

Ahhh, that explains why the original screws are ever so smaller in diameter behind the threads than the threads themselves.

 

[rich pierce]

Got 2 done. Sending a PM