Demilled M14 bolts

ssblair · August 13, 2012, 07:22 PM

Has anybody heard anything about reactivating "demilled" M14 bolts that have had their firing pin holes welded shut? Has anybody tried it? Has anybody heard of any failures among those who have redrilled the firing pin holes? I've got an M14/M1A with a bolt thats got an eroded bolt face (the prior owner apparently let some brass go long enough to let gas back around the primer to cut the bolt face) and what with the prices of bolts these days, I'm wondering if these might be the way to go for maybe 1/10th the cost. (found a source that's offering 4/$50)

Thx.

Dfariswheel · August 13, 2012, 08:05 PM

Don't.

When the bolt face was welded, the bolt locking lugs would have almost certainly have had the heat treating ruined.
Not safe.

Also, you don't just buy a new bolt, stick it in and go shooting.
All rifles need to have the head space checked with head space gages.
This is especially the case where you have a commercial receiver in which you're installing a military bolt.

wyop · August 14, 2012, 12:33 AM

I'll second what Dfariswheel has said. Bolts, and not just M1A/M14 bolts, are heat-treated to increase the yield strength of the bolt lugs and increase hardness to decrease deformation of the lugs under recoil.

But the M14 (later M1A) bolt was one of the most troublesome parts of the M14 design. There were several failures of the bolts in the late 50's, and the heat treatment of the bolt's steel underwent several revisions from 1960 clear up to 1992.

Typical of the heat treatment of the M14 bolt is that the surface case was 0.012 to 0.018 deep, and the surface hardness was in the 54 to 60 Rockwell C range, with the inner core being 33 to 42 Rockwell C. To accomplish this type of hardening treatment would require a furnace with a carburizing atmosphere, then a quench, then tempering to probably no more than the 425F to 450F level.

Translation: Even if you're quite skilled at heat treating steel, you're probably not going to replicate the mil-spec heat treatment of the bolt without some sacrificial bolts so that you can experiment to get the time period for the casing to achieve the correct depth of case.

F. Guffey · August 21, 2012, 11:56 AM

Bolt? I will have to start with “Once upon a time” or “You are not going to believe this” etc., etc..

The bolt was not the only part that was “demilled”, anti-gun types had pistols and rifles demilled, some were cut, others were sheared, cut was good, sheared without support fractured, parts were sold for scrap. 45 ACP became 45 ACPs with long slides/barrels, M14s became M14s, Problem!, a proud owner of a M14 was at a firing range when someone came over and ask him about his rifle, during the conversation it was decided the serial number of the receiver was among receivers that were cut up as in destroyed, the shooter and proud owner was instructed he was going to be given time to strip all the parts from the receiver for future use but the receiver had to be returned to the Government for destruction.

The M14 rifle was built in such a manner as to prevent it from being shot in a full auto. There was nothing suspect about the safety of the rifle.

F. Guffey

ssblair · August 21, 2012, 07:30 PM

So if I understand things correctly, the concern is about the heat treating of the bolt lugs still being proper? And wyop--could you cite your source for the case hardness being 54-60 Rc?

I'm familiar with steel fabrication and heat treat specs, and I hesitate to believe that simply spot welding the face of the bolt would have such a wide heat affected zone as to temper the locking lugs--But it's easy enough to check.

Thanks!

wyop · August 22, 2012, 02:23 AM

It's on the DOD engineering drawings for the parts of the weapon. In this case, look for drawing 7790185. You can find drawing numbers in the back of TM 9-1005-223-34.

You can also find reference to the heat treatment protocol in a book on the M14:

http://www.imageseek.com/m1a/M14%20R...70603%20nb.pdf

August 13, 2012, 07:22 PM	#1
ssblair Member Join Date: April 29, 2010 Location: Indiana Posts: 21	Demilled M14 bolts Has anybody heard anything about reactivating "demilled" M14 bolts that have had their firing pin holes welded shut? Has anybody tried it? Has anybody heard of any failures among those who have redrilled the firing pin holes? I've got an M14/M1A with a bolt thats got an eroded bolt face (the prior owner apparently let some brass go long enough to let gas back around the primer to cut the bolt face) and what with the prices of bolts these days, I'm wondering if these might be the way to go for maybe 1/10th the cost. (found a source that's offering 4/$50) Thx.

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August 13, 2012, 08:05 PM	#2
Dfariswheel Senior Member Join Date: May 4, 2001 Posts: 7,478	Don't. When the bolt face was welded, the bolt locking lugs would have almost certainly have had the heat treating ruined. Not safe. Also, you don't just buy a new bolt, stick it in and go shooting. All rifles need to have the head space checked with head space gages. This is especially the case where you have a commercial receiver in which you're installing a military bolt.

August 14, 2012, 12:33 AM	#3
wyop Senior Member Join Date: July 15, 2012 Location: Wonderful, Windy Wyoming Posts: 133	I'll second what Dfariswheel has said. Bolts, and not just M1A/M14 bolts, are heat-treated to increase the yield strength of the bolt lugs and increase hardness to decrease deformation of the lugs under recoil. But the M14 (later M1A) bolt was one of the most troublesome parts of the M14 design. There were several failures of the bolts in the late 50's, and the heat treatment of the bolt's steel underwent several revisions from 1960 clear up to 1992. Typical of the heat treatment of the M14 bolt is that the surface case was 0.012 to 0.018 deep, and the surface hardness was in the 54 to 60 Rockwell C range, with the inner core being 33 to 42 Rockwell C. To accomplish this type of hardening treatment would require a furnace with a carburizing atmosphere, then a quench, then tempering to probably no more than the 425F to 450F level. Translation: Even if you're quite skilled at heat treating steel, you're probably not going to replicate the mil-spec heat treatment of the bolt without some sacrificial bolts so that you can experiment to get the time period for the casing to achieve the correct depth of case.

August 21, 2012, 11:56 AM	#4
F. Guffey Senior Member Join Date: July 18, 2008 Posts: 7,249	Bolt? I will have to start with “Once upon a time” or “You are not going to believe this” etc., etc.. The bolt was not the only part that was “demilled”, anti-gun types had pistols and rifles demilled, some were cut, others were sheared, cut was good, sheared without support fractured, parts were sold for scrap. 45 ACP became 45 ACPs with long slides/barrels, M14s became M14s, Problem!, a proud owner of a M14 was at a firing range when someone came over and ask him about his rifle, during the conversation it was decided the serial number of the receiver was among receivers that were cut up as in destroyed, the shooter and proud owner was instructed he was going to be given time to strip all the parts from the receiver for future use but the receiver had to be returned to the Government for destruction. The M14 rifle was built in such a manner as to prevent it from being shot in a full auto. There was nothing suspect about the safety of the rifle. F. Guffey

August 21, 2012, 07:30 PM	#5
ssblair Member Join Date: April 29, 2010 Location: Indiana Posts: 21	So if I understand things correctly, the concern is about the heat treating of the bolt lugs still being proper? And wyop--could you cite your source for the case hardness being 54-60 Rc? I'm familiar with steel fabrication and heat treat specs, and I hesitate to believe that simply spot welding the face of the bolt would have such a wide heat affected zone as to temper the locking lugs--But it's easy enough to check. Thanks!

August 22, 2012, 02:23 AM	#6
wyop Senior Member Join Date: July 15, 2012 Location: Wonderful, Windy Wyoming Posts: 133	It's on the DOD engineering drawings for the parts of the weapon. In this case, look for drawing 7790185. You can find drawing numbers in the back of TM 9-1005-223-34. You can also find reference to the heat treatment protocol in a book on the M14: http://www.imageseek.com/m1a/M14%20R...70603%20nb.pdf