What Diameter and How Deep?

rep1954 · February 9, 2013, 03:07 PM

I'm going to be doing a pin and weld job on a 11 1/2" barrel and a 5 1/2" flash hider for the first time and need to know what diameter I should use for the pin and how deep must it enter the barrel? Is a high speed or cobalt pin okay for this or should I use something else? Should a crush ring be used?

slappy · February 9, 2013, 03:22 PM

I was under the impression that silver solder alone was considered a permanent attachment. No pin needed. I would check with local laws but that is what a friend in NY said was required where he lived.

tobnpr · February 9, 2013, 07:52 PM

Yes, silver solder is acceptable

Quote:

The ATF procedure for measuring barrel length is to measure from the closed bolt (or breech-face) to
the furthermost end of the barrel or permanently attached muzzle device. Permanent methods of
attachment include full-fusion gas or electric steel-seam welding, high-temperature (1100°F) silver
soldering, or blind pinning with the pin head welded over. Barrels are measured by inserting a dowel rod
into the barrel until the rod stops against the bolt or breech-face. The rod is then marked at the
furthermost end of the barrel or permanently attached muzzle device, withdrawn from the barrel, and
measured.

Never done it, but I'm sure someone has fluxed the barrel threads, drilled a hole or two in the side of the hider and "wicked" silver solder into the assembly with a torch.

BTW, a crush washer serves no purpose when it's going to be permanently attached. If the hider needs to be timed, you're obviously going to time it before you weld or solder.

madcratebuilder · February 12, 2013, 11:20 AM

The heat needed (1200*) for silver solder can discolor the finish on the barrel and FH.

I use old 1/16 drill bits as a pin. I drill about .090 into the barrel, the top of the pin is about 1/16 below the surface. TIG it then dress with a file, touch up with a B/C Super Black paint pen. It's invisible. I do use a crush washer for clocking and torquing before I drill and pin.

tobnpr · February 12, 2013, 06:18 PM

Does seem that pinning would be the way to go- minimal heat to the barrel and a lot less hassle...

rep1954 · February 12, 2013, 08:26 PM

madcratebuilder, Thanks for the info it's a big help.

rep1954 · February 16, 2013, 08:15 PM

Well I got my flash hider mounted to the barrel today with the pin and weld method, Everything worked out great. This is all I have so far on this build, my stripped lower is due in 2 to 3 weeks and just waiting for the rest of the things to become available.

AR15barrels · February 17, 2013, 03:24 AM

Quote:

Originally Posted by rep1954

I'm going to be doing a pin and weld job on a 11 1/2" barrel and a 5 1/2" flash hider for the first time and need to know what diameter I should use for the pin and how deep must it enter the barrel? Is a high speed or cobalt pin okay for this or should I use something else? Should a crush ring be used?

I do pin and weld jobs almost every day.
I use 3/32" dowel pins in 3/16" and 1/4" long depending on the diameter of the muzzle device and the bore size.
I like to see 0.050" to 0.060" of the pin below the top of 28 pitch threads.
Depending on the muzzle brake diameter, sometimes I have to shorten a pin a little bit to get to this dimension without drilling so close to the bore.
Hi speed steel bits are fine unless you have a hardened muzzle device.
Then you might need carbide.
There are some really hard muzzle devices out there!

February 9, 2013, 03:07 PM	#1
rep1954 Senior Member Join Date: July 5, 2009 Location: Mid Western Michigan Posts: 683	What Diameter and How Deep? I'm going to be doing a pin and weld job on a 11 1/2" barrel and a 5 1/2" flash hider for the first time and need to know what diameter I should use for the pin and how deep must it enter the barrel? Is a high speed or cobalt pin okay for this or should I use something else? Should a crush ring be used?

February 9, 2013, 03:22 PM	#2
slappy Senior Member Join Date: November 6, 2011 Posts: 928	I was under the impression that silver solder alone was considered a permanent attachment. No pin needed. I would check with local laws but that is what a friend in NY said was required where he lived.

February 12, 2013, 11:20 AM	#4
madcratebuilder Senior Member Join Date: November 2, 2007 Location: Northern Orygun Posts: 4,864	The heat needed (1200*) for silver solder can discolor the finish on the barrel and FH. I use old 1/16 drill bits as a pin. I drill about .090 into the barrel, the top of the pin is about 1/16 below the surface. TIG it then dress with a file, touch up with a B/C Super Black paint pen. It's invisible. I do use a crush washer for clocking and torquing before I drill and pin.

February 12, 2013, 06:18 PM	#5
tobnpr Senior Member Join Date: August 1, 2010 Location: Tampa Bay Posts: 2,206	Does seem that pinning would be the way to go- minimal heat to the barrel and a lot less hassle...

February 12, 2013, 08:26 PM	#6
rep1954 Senior Member Join Date: July 5, 2009 Location: Mid Western Michigan Posts: 683	madcratebuilder, Thanks for the info it's a big help.

February 16, 2013, 08:15 PM	#7
rep1954 Senior Member Join Date: July 5, 2009 Location: Mid Western Michigan Posts: 683	Well I got my flash hider mounted to the barrel today with the pin and weld method, Everything worked out great. This is all I have so far on this build, my stripped lower is due in 2 to 3 weeks and just waiting for the rest of the things to become available.