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I was just wondering, did the manufactures, TRW, H&R, Winchester, lap the bolts to receivers during assembly, or is this something that is only done with non military made receivers.
 

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The reason they didn't do it is it was not needed due to the precision machining that went into the receiver and bolt locking lugs. The bolts were precision ground on a thread grinder after heat treat and are pretty much perfect.

The receivers were radially shape cut probably with a cam operated special purpose machine.Usually any deviation will be in the receiver as it can move slightly during heat treat.

Usually USGI receivers were machined middle to upper specs resulting in enough clearance in the bolt centering areas to allow for minor movement in lugs resulting in a nice fit without need for and lapping.

It can be done today just as easily as it was done back then but most manufactures do not cut true helix formed locking lugs .I have several threads in the gunsmith section showing how to properly machine them and the results are equal to USGI fit.
 

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i have done all of ONE single lap for contact, and it is a CHORE! took me 3 nights with a single grade of lapping compound before I asked the forum if it was sufficient or not? they agreed that it was indeed sufficient for my purposes and i proceeded with the build. NEXT time, i'm getting some heavier grit!

Not really relevant to your question, I know...but just figured I would blabber about nothing in your general direction.
 

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While some do a reasonably good job, the quality controls and gaging used in the manufacturer of military parts is much more demanding that that used commercially.

Commercial receivers almost always require bolt lapping. It's interesting that this is not the case with the AR15 even though the parts are less costly. It has to do with simplicity of design. The M14 receiver is a very complicated (and expensive) part to manufacture. Keep in mind that the true receiver in an AR15 is the barrel extension. To keep costs down, commercial M14 receivers are not made to the exacting tolerances used in military production.
 

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One should always keep in mind that when lapping the bolt you are also lapping the receiver.
I would guess that then proper lug geometry (on both bolt and receiver) would mean longer receiver life, if you're going to lap the bolt to make it mate most correctly, as that would mean less lapping.

Personally, between spreading rounds around between rifles, and historically lacking free time/opportunity to do a significant amount of shooting, I'm not really on track to shoot out a barrel, let alone wear out a receiver with multiple lapping jobs, but it's always nice to do the best thing possible, if you can.

Out of curiosity, how many barrels, with and without lapping, is a receiver good for?
 

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About 200,000 to 250,000 rounds. That’s a lot of barrels.

Tony.
Each barrel needs another bolt to get headspacing. That's a lot of bolts to lap in.

Are bolts just a scosh softer than receivers? So you lap away the cheap part?

And just how much gets lapped away? How bad is the Service Grade fit?

And another thought- While un-demil-ing a couple bolts, I noticed that the bolt faces were slightly crooked. I assume the body of the bolt had warped in heat treat. Mightn't it have warped to one side, making the lugs uneven? Or even, the receiver warped, it pushes the bolt to one side necessitating lapping for best, most consistant fit?
 

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I've never seen it written that a bolt and barrel must be married to each other. Admittedly, I've never read the government tech manuals. Why would anyone change a bolt if it doesn't need to be? There are procedures for gauging a bolt and I would only change one if it were obvious that it needed to be changed.

I personally would only lap a second bolt into a receiver and only if the first bolt were damaged for some reason like blown primers cutting the bolt face or the bolt roller tower breaking.

My comment about receivers lasting 200k rounds was taken out of context. I never said to lap a bolt with every barrel change. A receiver and bolt should outlast many barrels and the bolt should at least out last a few barrels. In this day and age with ammo prices, I don't see anyone burning though a barrel a year unless they're shooting highpower every weekend.

Even shooting 1,000 rounds a year, a barrel should last 5k to 10k, so 5 to 10 years. A bolt should last a few barrels.

I change barrels because I'm chasing the next new shiny thing, not because it's burned out.

The government never lapped bolts, so it wasn't an issue. They threw in a new one and just went with it.

I will say that all the commercial SAI rifles I've handled had about 10% contact on each side and they are never lapped, except the custom shop rifles. If the need arose, one could simply throw in a bolt, contact be damned, but at least have some on both sides and make sure one is not free floated, and run with it if you need to. There are a few hundred thousand commercial rifles out there like that and they rarely have catastrophic bolt failures.

Some owners like a better fitment of parts than others. Some like GI chrome lined barrels and others like short chambered CM or SS barrels and that's okay.

Some people want their Remington 700 action trued and timed by a pro. Some believe it's malarkey. To each his own.

Tony.
 

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......

Some owners like a better fitment of parts than others. Some like GI chrome lined barrels and others like short chambered CM or SS barrels and that's okay.


Tony.
My guess is that you are the short chambered kind. Am I right that chrome barrels need their headspace set, done by swapping bolts?

10,000 rds per barrel, (I'd heard 15K) would mean 20 barrels in a 200k receiver life. That would be a LOT of perfect headspace matches to never need another bolt lapped.

Sorry to pluck a heart string, but can we discuss any of the other points I brought up in my previous post?
 

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My point is that I think people can overthink things.

Yes, I prefer short chambered and cut headspace to desired length.

If I could estimate the average it takes for full contact after lapping, maybe 0.003” total, so 0.0015” from each surface. And that’s to knock off the high spots. Once you have full contact, there’s fresh surface area that will have not had hardly any material removed.

And my responses are written on short breaks at work. I can’t always answer thoroughly.

Tony.
 

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Each barrel needs another bolt to get headspacing. That's a lot of bolts to lap in.

Are bolts just a scosh softer than receivers? So you lap away the cheap part?

And just how much gets lapped away? How bad is the Service Grade fit?

And another thought- While un-demil-ing a couple bolts, I noticed that the bolt faces were slightly crooked. I assume the body of the bolt had warped in heat treat. Mightn't it have warped to one side, making the lugs uneven? Or even, the receiver warped, it pushes the bolt to one side necessitating lapping for best, most consistant fit?
USGI bolt were precision ground between centers on a thread grinder post heat treatment to final qualification spec .So unlikely you will finds a warped one .More than likely the demill welds did this or uneven wear.

There was only a .002'' total tolerance on bolt face to right lug during final grind so they are consistent specially with all the gaging that took place.

Receivers had a little more devience as there were machined before heat treat and due to the right lug cut out some warpage can occur there . The bolt passages in the USGI M14 receiver are usually always max spec which allows the bolt to float and finds good marriage between the surfaces.

You ocasionaly see one that hits a little harder on one lug but most are in the 90% or better range.
 

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I might add too that not only were the lugs ground after heat treat between centers the lug shoulders that center the bolt in the barrel bore minor i.d. were ground at the same time as they dressed the stone at a 90 degree angle with .020 radius corner .I've got a picture in the SA ordnance thread.
 

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I might add too that not only were the lugs ground after heat treat between centers the lug shoulders that center the bolt in the barrel bore minor i.d. were ground at the same time as they dressed the stone at a 90 degree angle with .020 radius corner .I've got a picture in the SA ordnance thread.
Radius sure, everything need to be radiused. But I think the cartridge is what centers the bolt in the bore- the end of the right lug is sticking outt in space and has a roller on the end.

But then my FED ORD is AKA POS.
 

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Hi,
Seeing how the OP'S question has been pretty well answered...

I'll throw this in.

A couple of years ago, Jeff was selling BULA XM-21 receivers, and new logo bolts for a good price, and I bought a set, so to speak.

The receiver, looked like a work of art, and when I inserted the bolt, it went into battery like shutting a bank vault.

You could not only feel it, but hear it also.

Just sayin, when I build the rifle, I don't think lapping will be needed!
 

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Extensive M1 Carbine and Rifle collections with current focus on standardized Army rifled arms
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Don't forget the rear of the bolt

Lapping is focused on getting both lugs engaged with a round in the chamber.

But remember that the rear end of the bolt can shift a tiny bit left to right.... and IF the bolt lugs aren't quite exactly in the same slanted plane, the bolt can shift to gain contact to both lugs. I've always used GI bolts and never had lug trouble with extensive shooting. The government instructions for building match M1s and M14s say nothing about lapping bolt lugs. It wasn't taught at the NM school at Rock Island.

Seems a more theoretical issue than actual. Absent proof, I don't spend time or accelerate wear with lapping.

Has anybody got data?
 
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