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Discussion Starter · #1 ·
SARCO has USGI bolts with a spot weld near the firing pin hole. There are two varieties one with a spot weld at the aft end of the bolt and another with a weld at the forward end. They are only 29 or 39. I was toying with the idea of buying one of each variety to see if they could be re-machined into service. ANY thoughts?

The URL for the CARCO bolt is
sarcoinc.com/usgispottym14bolts-type2

Just found someone selling a re-machined bolt as described above on gunbroker

gunbroker.com/Auction/ViewItem.aspx?Item=202101927
 

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"Death From Above"
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Run away! These came off of drill rifles that were decomissioned. The rest of the parts are sitting at cmp. Did you ever wonder why the cmp kits don't come with bolts? They are expensive paper weights.
 

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The general consensus...

on this site has been NO. I'd do a search for the threads. When the heat treat has been changed by welding, it's your face that's in the target when failure occurs. Spend a little extra and get a proper bolt. 82nd ABN is "dead" on.
Bruce
 

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Everyone talks about these bolts as if they are going to blow up. But the only way these would blow up is if the locking lugs are some how compromised.

I believe these bolts have the firing pin hole spot welded. If you were to mill that down and redrill the firing pin hole how would that exactly blow up?

Are you guys telling me that the unheat treated bolt face would fail before the primer and the soft brass of the case? If so you guys need to get a reality check. Also generally speaking the weld material is supposed to be harder than the steel.

Don't mean to be rude but, COME ON!!! Someone please explain to me how the brass would somehow hold but not steel.

SARCO has USGI bolts with a spot weld near the firing pin hole. There are two varieties one with a spot weld at the aft end of the bolt and another with a weld at the forward end. They are only 29 or 39. I was toying with the idea of buying one of each variety to see if they could be re-machined into service. ANY thoughts?
In my opinion if you want to go cheap than get the bolt and remachine them. I wouldn't mind trying one just to prove everybody wrong. I explained in my previous post why I don't think it would be a problem as long as the locking lugs aren't compromised.

You could always send it to SEI and get it heat treated again after machining.
 

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The type of steel that the bolts are made of is not suitable for welding. What happens is the crystaline structure changes and the area all around the weld becomes extremly brittle and subject to break. I don't have any experience welding these things or trying to machine them after welding, but I have done this type of crap in Punch press dies. When prodution is down in a factory prodution managers scream untill something is done. Welded die parts always failed in short order and wasted plenty of man hours and some material. Think about how close to your face the bolt is. It's not worth taking a chance.

Edit: Do you think these things would be out there if they could be re heat treated. I'm gonna go out on a limb and say that springfield would not consider trying to heat treating them or touching them in any way. Toolsteels can be annealed after hardning then more machining and then re hardned but that is not the same thing.This is tricky stuff.
 

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Discussion Starter · #6 ·
Great discussion..

Great discussion gents. I think this warrants an experiment. Is there a way to test a re-machined and heat treated "spotty bolt" without risking your face or more importantly your beloved M14.
An interesting point is that the guy on Gunbroker trying to sell one of these does not mention the source of the bolt nor any danger involved. See below:

"Up for auction is a HRT (Harrington & Richardson) M14 bolt. When I received it there was a light weld over the firing pin hole. I had this weld machined off and had the bolt face tested for hardness. It tested to be well within the hardness numbers listed on the set of government blueprints I have for the M14. I also had it reparkerized. It is a very dark grey/blackish color as you can see in the pictures. Because the face of the bolt has been machined on, THIS BOLT SHOULD ONLY BE USED IN CONJUNCTION WITH A NEW BARREL SO THAT PROPER HEADSPACE CAN BE OBTAINED. Because of this, the bolt is sold as is with no returns and no warranty expressed or implied. "


Here is a picture of the spotty bolt before machining:
 

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+1 Memphis. You get done welding that die block up you might as well start making a new one. Because by the time your through with it, they're gonna need it too.

The only way you can actually test the hardness of the bolt per the government drawings is to cut it in half. There are two different specs. Core hardness and surface hardness. The bolt gets heat treated after it's machined. Which involves heating it up to a certain temp. for a certain period of time. [Different temps and times for different steels and sizes] After that it's either quenched or allowed to air cool. This leaves you with a very hard but brittle piece. So you have to draw it back (or anneal) to the hardness you want and that takes the brittleness out of it. This leaves you with a hard bolt that can withstand 50,000 psi trying to shove it in your face. The next step is case hardening. Which is an entirely different heat treat process that forms a very hard and brittle outer skin that allows the surface of the bolt to resist wear, but yet still leaves the rest of the bolt hard and tough.

The only thing that could have been checked was the surface hardness. Which is actually the less important (safety wise) of the two. And even then as Memphis stated the weld and the area around it are going to end up extremely hard anyway. There's no way to know what the heat from the welding has done to the core hardness without actually cutting the bolt in half to check it. That's why the bolts have heat lot numbers on them. It's impossible to check every bolt made by cutting it up. So out of each lot of steel used for bolts (or whatever part), a certain number are pulled out of the line and checked. So long as all the bolts out of that lot go through the exact same heat treat process, it's fairly safe to assume that if the test bolts from each lot check within spec., all the rest should be good to go. But all the bolts are proof fired just to be sure. Then if something goes wrong with a certain bolt, you know what the heat lot number is and can pull that lot only without worrying about every bolt ever made. Example: Springfield Armory's recalled bolts. Only apply to a certain lot number.

Like Memphis said heat treating is some tricky stuff. You could spend years studying heat treating and never become an expert at all of it. If it has anything to do with barrels, bolt or recievers being welded, be safe and do what Jenny said, "Run Forest run".
 

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Everyone talks about these bolts as if they are going to blow up. But the only way these would blow up is if the locking lugs are some how compromised.

I believe these bolts have the firing pin hole spot welded. If you were to mill that down and redrill the firing pin hole how would that exactly blow up?

Are you guys telling me that the unheat treated bolt face would fail before the primer and the soft brass of the case? If so you guys need to get a reality check. Also generally speaking the weld material is supposed to be harder than the steel.

Don't mean to be rude but, COME ON!!! Someone please explain to me how the brass would somehow hold but not steel.
Hard means brittle. If the bolt face fractures here comes a reality check straight for your face. Its the support of the steel that keeps the brass from failure. IMHO its not worth a $150.
 

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I'd feel better about a weld in the rear end than a weld in the front end but who know I'd bet a bolt could be re-heat treated and be safe.. is it worth the risk.. that is up to the buyer or user... B2B
 

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I've seen pics of these bolts and all they have is a tac weld on the firing pin hole. These are not cut up or repaired in anyway by welding.

When they weld the hole shut all they are doing is adding material. They are not filling in cuts or damaged areas with weld. There is going to be some penetration with the weld material but when they get milled back down to correct specs the original material is still there. So I wouldn't think it would be to brittle if all the weld material is off of the face of the bolt.


Sure I would prefer a un modified bolt and I wouldn't pay more than $100 for one of these bolts either. You can still get used bolts for under $200 last I checked. I just don't think one is going to blow up in your face.

I frequent a gun building site and those guys are rewelding mg42 recievers back together. People also use reweld oprods. I know a guy that lathed the threads off of a FAL and press fit it in a 80% reciever and pinned the barrel. I heard of someone using wooden dowel rods for rivets in AK front trunnions. When we bugger up a AK47 ejector rail we weld it up and grind to "specs". I think sometimes people in the m14 world get a little "Purist" on things.
 

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I've seen pics of these bolts and all they have is a tac weld on the firing pin hole. These are not cut up or repaired in anyway by welding.

When they weld the hole shut all they are doing is adding material. They are not filling in cuts or damaged areas with weld. There is going to be some penetration with the weld material but when they get milled back down to correct specs the original material is still there. So I wouldn't think it would be to brittle if all the weld material is off of the face of the bolt.


Sure I would prefer a un modified bolt and I wouldn't pay more than $100 for one of these bolts either. You can still get used bolts for under $200 last I checked. I just don't think one is going to blow up in your face.

I frequent a gun building site and those guys are rewelding mg42 recievers back together. People also use reweld oprods. I know a guy that lathed the threads off of a FAL and press fit it in a 80% reciever and pinned the barrel. I heard of someone using wooden dowel rods for rivets in AK front trunnions. When we bugger up a AK47 ejector rail we weld it up and grind to "specs". I think sometimes people in the m14 world get a little "Purist" on things.
None of those things you mentioned see the pressures that the bolt sees. I mean, to each their own, I just don't get trying to save 100 bucks by going this route. And don't fire the thing around me.
 

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I've seen pics of these bolts and all they have is a tac weld on the firing pin hole. These are not cut up or repaired in anyway by welding.

When they weld the hole shut all they are doing is adding material. They are not filling in cuts or damaged areas with weld. There is going to be some penetration with the weld material but when they get milled back down to correct specs the original material is still there. So I wouldn't think it would be to brittle if all the weld material is off of the face of the bolt.


Sure I would prefer a un modified bolt and I wouldn't pay more than $100 for one of these bolts either. You can still get used bolts for under $200 last I checked. I just don't think one is going to blow up in your face.

I frequent a gun building site and those guys are rewelding mg42 recievers back together. People also use reweld oprods. I know a guy that lathed the threads off of a FAL and press fit it in a 80% reciever and pinned the barrel. I heard of someone using wooden dowel rods for rivets in AK front trunnions. When we bugger up a AK47 ejector rail we weld it up and grind to "specs". I think sometimes people in the m14 world get a little "Purist" on things.
It's the heat from the welding that's the real problem. It changes the properties of the metal. Just to give you an idea of how much or how little heat can effect steel. We harden A-2 (tool steel) at 1750 degrees, but draw it at just 500 degrees. And your talking about all this heat from welding about a half inch from the two points that if one or both fail, your going to get a face full of bolt.
 

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The area behind the face of the bolt is one of the thinner spots on the bolt when you figure the hole for the firing pin body is just short of the firing pin hole and face of the bolt. That area is thin and weak enough as it is in a properly heat treated bolt and there is 55,000 PSI of force going on inside the brass cartridge case just ahead of it.

Folks, I learned a long time ago to listen to machinists, welders and metallurgists. I would not trust such a bolt unless the bolt was properly rehardened and a metallurgist/mechanical enginer ensured the procedure was correct.
 

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The bolt that I had purchased and almost got taken for a ride with had a weld in both the front and the back of the bolt. They made sure that firing pin was never going to go back in. The depth of the weld on the back of the bolt was at least a 1/4 inch deep and there was a distict line between the weld material and the actuall bolt. Why on earth would you want to screw around with such a bolt or even advocate using one? It should be illegal for sarco or anyone else to sell the dam things. They are nothing but a liability you don't need to be a metalurgist or machinist or have a dam phd to see that. Have at it if you will just let me know if you are the one next to me at the range so I can move.
 

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This is about the third time this has come up in as many weeks. Obviously this is going to be a problem. Whoever sold those parts kits should have cut those bolts up or something. They should never have been sold to the public. Sarco's ad should have a warning about not trying to use these in an actual firing gun. People's greed and stupidity are why there are so many stupid laws around. Some one is probably already buying up a bunch of them for repair and resale. I see nothing good coming from this.

Are bolts made of 8620 that has been carburized? I am trying to research and figure out exactly what is going on with this. What I see so far is that 8620 is weldable if done properly.
 

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bolts

It is weldable MM...But, the problem comes in when you try to re-heat -treat it.....I talked to a gentleman that is very knowledgable about the processes involved....He said that after an object is re-heat-treated.....it is never the same as it was initially....no matter what you do to it...period.

Therefore, we can assume that any of these bolts will be substandard when done by even the best of us.....and trust me, this guy is the best of us.........I can't tell you who he is, but he knows more about metal than anyone I ever knew.

Our initial conversation , oddly enough, was about reweld receivers that TRW made.....
 

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I'm no expert here but I have machined alot of bearings out of 8620 material. This is the same material that the bolts and receivers are made out of. This material is typically very soft when it is first machined very similar to mild steel. In this condition it is very weldable however we have no need to weld on it so we don't.

We always machine it small and leave some material in critical areas before sending it off to heat treat. During the heat treat process it is heated up in a carbon rich enviroment the surface of the material absorbs the carbon and becomes very Hard 58-60 rockwell while the inside only get to about 30 something.

THINK OF IT LIKE A M&M.

Hard on the outside softer on the inside. The part also gets bigger. After heat treating we have to remachine the final contours of the bearing we have to use a ceramic insert instead of carbide because it is so hard .We only take off a very small amount (.007) off the surface so the part remains hard. Usually the hardness of a receiver only goes .012-.018
deep.

Now think of it as a M&M again, hard on the outside soft on the inside. When you weld on it it burns the hard candy shell off that section and lays plain chocolate on it. When you remachine it, it may have the same contour or shape as before but all the hardness in the area is gone and replaced with soft chocolate.

In addition the heat can cause very tiny cracks to accure in the hard surface that can be dangerous.

I'm not saying that it couldn't be done by somebody who knows what they are doing but I wouldn't try as a hobby gunsmith.

The process for welding heat treated 8620 is anneal the whole thing (Soften it) when you do this it will become slightly smaller, then weld it,and the reheat-treat the whole thing. During this process no telling what will happen to the tolerances of the part or guarantees that it won't crack.

Who knows how these bolts were originally welded.

Anyway do some research about welding 8620 steel on the internet and you will learn a bit.
 

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Case in Point

The process for welding heat treated 8620 is anneal the whole thing (Soften it) when you do this it will become slightly smaller, then weld it,and the reheat-treat the whole thing. During this process no telling what will happen to the tolerances of the part or guarantees that it won't crack.Who knows how these bolts were originally welded.
Exactly my point, the part will never be as it was, or as intended, therefore very dangerous to open speculation,... thanks, great post !!!
 

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As a welder and amatur metalurgist and part time machinist, this topic lacks common sense in most areas. I have made parts, cast parts, machined cast parts, and parted cast machinesMCORPS1. Yes there are issues. and there are things that should not be done. There are things that could be done. I will not condone either. "I the willing have seen and done so much with so little for so long for those unable to accept "no" that now I feel qualified to do anything with nothing for infinity" I have taken less and done much more,,,,,,,, but the learning curve was a b""tch.------- Would i do it now??? I thrive on it. --------------Is it sensible? HMMMMMMMM------------ Is it feasible? How many hours do you have to work to make $150??(for a new bolt)----- Is it cost effective??? Call the local mach shop and ask them to rent the measuring tools/ machining tools(6-12 hours to recondition one of these with heat treat and dimension verification)-----------Is it practical? If by practical you mean reaching deep inside yourself and finding out if you are capable of doing the most basic and most critical
of metalwork all while risking the most on it then YES.

But this is just from an dumb old metal junky that likes to make all old into new. Commit all the way or none at all. Used bolt:$50,,Shipping:$12,, Machining/Heat treat: $1200 Knowing that another taxpayer part is not going to China to be made into the same part and shipped back to US: PRICELESS if you can do itGI2
 
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