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Discussion Starter · #1 ·
Question for those who are building. Bolt contact with M1 guys is if head spaces its good to go. Where those of us putting the M14 type rifle together want bolt contact on both lugs. Also the talk about ideal head space. You head space check with head space gauges making sure you are in SAMI specs. As the rifle is being used head space increases because of wear and if there is dirt&grime lapping. It seems that the bolt is the sacrificial part being that it is lapped to the receiver. It seem keeping the lugs clean&lubed is critical for maximum bolt life and minimizing growth in head space. Some days its seems as if one is picking fly s=== out of pepper and I should have stuck to collecting marbles.
Pfc out
PS if any of you find my lost marbles please PM me
 

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I think your question is about bolt lug contact and headspace setting...

If the chamber has already been reamed for headspace and there is unsatisfactory bolt lug contact, then any lug lapping for more lug contact will increase the headspace.

If the pre-lapping HS is near minimum and only a little lug lapping is needed, then lapping can probably be done and keep the HS 'in spec'.

On a functioning rifle, as long as there is some contact on both lugs (even if the lug contact patches is not the same), I wouldn't do lug lapping.

If one lug does not have any contact, then minimum lapping to achieve some contact would be good as long as HS remains 'in spec'.
Another option is to find someone who has multiple bolts, and see if a replacement bolt works to give better contact and HS.

The proper method when installing a new barrel that has a 'short chamber' and which NEEDS 'finish reaming' to set the HS, is to first check the lug contact and if necessary do the lug lapping before the reaming.

Jay Kosta
Endwell NY USA
 

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Another thing to consider when lapping a bolt to a receiver is the alignment of the bolt. The bolt must fit into the hood of the barrel when it is all said and done. A bolt lapping tool probably is nice. I use a cartridge cut in two with a spring and only lap after the barrel is installed. If the bolt is lapped with nothing to keep it aligned with the barrel it will just be blind luck if the surfaces mate properly after the barrel is installed. It may sound trifling to some folks, but lapping is the ultimate in precision.

Getting it right to start with probably will have a lot to do with how long headspace remains the same. Once you start pounding away, on it shooting it, the errors will be corrected one way or another.
 

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G. T . ,
What most do not consider is he fact that real USGI M14 and M1 receivers were machined to exacting profiles and dimensional tolerances requiring NO lapping because the bolt and receiver lugs were mirror images of each other (helical machined) . Most commercial receivers are flat machined to replicate the helical lead angle but not true form. This is easier for them but requires lapping for the two faces to contact each other evenly. These surfaces are often left to minimum or tight specs so once lapping is done headspace is also at correct depth.This practice is easier for the manufacturers to produce . I've not checked any current receivers so I'm not sure if any of the new offerings are closer than the previous ones.
 

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Discussion Starter · #5 ·
I guess I wasn't very clear in asking the question about bolt contact and head space. In building the M14 Type rifle one is using a commercial receiver. Yes its not a mil spec part,but we check for bolt contact. In helping a guy with an M1 I checked for bolt contact and then checked head space. He looked at me why are you doing that? If it head spaces its good to go,right. I explained it was just taking a little more care in building. Also in buying bolts I check the lug measurements and even in NOS bolts they vary. I just bought a used bolt and I'm very pleased with it. Yet its almost .004 different than a NOS. That didn't come from lapping. What I was getting at is head space changes during the life of the rifle,because the bolt is being worked(lapped if dirt&grime are present on lugs). How much does it change in a life of a barrel I don't know. But I do know in match rifle they cut the chambers and bolt contact is what only matters. Bolt wear really doesn't matter because the head space is determined by cutting of the chamber. Yet with chrome lined barrels bolt lugs is what determine head space. Whether you are lapping to get head space or trying different bolts to get head space. Whether its a mil spec receiver or not. Bolt lugs&bolt lug wear is part of the head space equation. Barrels are changed out because throat erosion,but are bolts changed out because of head space during the life of the gun. The barrel seems to get changed out long before the bolt does.

The question is Bolt&lug wear and head space. During the life of the rifle or barrel is the bolt&bolt lugs ever checked. Checked to see what is the relationship to head space. To much head space the barrel is worn out,the barrel has to much head space,but whats up with the bolt. I'm chasing my trail on this one.

Pfc out
 

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If I understand your question you are asking about measuring the bolt lugs and the receiver lugs rather than using headspace gauges. The answer is these surfaces are quite difficult to measure. You mention measuring bolt lugs. I would like see how you measure bolt lugs. I find it impossible to measure bolt lugs, because of the complexity of the surfaces involved. If you pick a certain spot and try to use this spot on each bolt you get a good approximation, but that is all. Trying to measure the receiver without some fairly expensive stuff is not very practical. IMHO
 

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I doubt that actual 'wearing' of the chamber would occur to cause much chamber HS change.
If the chamber HS does increase significantly, then it is probably due to the receiver lugs or the bolt lugs.

Have you come across a situation where there was a large change in chamber HS using a USGI or US commercial bolt?

Jay Kosta
Endwell NY USA
 

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G.T.
Like MM said its very hard to get an accurate measurement of the locking lugs because the surfaces are part of a continuous helix. You can rough check right and left lugs to see if someone has lapped them but because of the helical angle and twist a caliper will rock and can only be considered comparison .

Bill Ricca I believe had the actual ordnance style gage that consisted of a fixture with a precision dowel place at each lug centerline and lead location ,and a dial indicator was used as part of the fixture to check bolt face locking lug distance. This is far more accurate.

If a bolt and receiver was made to USGI specifications and in civilian conditions ,I dont believe the average person could shoot enough rounds to wear them out.
or even come close to changing headspace from wear.

If you have a USGI M1 receiver and a USGI M1 bolt other than checking headspace and inspecting condition prior to a build, you will never have to lapp the lugs for contact.

In another thread sometime back I checked a bunch of USGI bolts in a nice demill front receiver for depth of bolt face and actual headspace in several USGI barrels and .001'' - .002'' with .001'' being average was all the varience I obtained .And they were all well used componants.
 

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Discussion Starter · #9 ·
Memphis,checking the bolt measurements. I use a digital caliber(Mitutoyo) to get just a reading to compare with a NOS TRW I have. I measure from the flat of where the bolt contact the receiver to front of the lug(both the right&left lug). The reason I do this is just curiosity to see if there is any wear and its not to determine if bolt is within spec. From what I have been taught&understand HS can only be determine by using HS gauges. HS is from the bolt face to mid point on the shoulder. I listen to guys who are working on M1's say they need multiple bolts to make HS,because receiver stretching or is it because of bolt lug wear. I believe checking bolt contact should be one of steps in determining if this bolt should be used in this receiver. After that HS needs to be checked then what steps needs to be taken to make HS(always with HS gauges:go,no-go&field).
Jay,HS and chamber. I just curious how much the HS changes in the life of a barrel. Match barrels are changed out after aprox 5,000 and chrome lined SWAG(scientific wild ass guess) 10-20,000 rds. Having not put that many rds down a barrel I don't know. Just know the bolt in a rifle being fired has rear bolt thrust and operation in being fired is the same being lapped. There seems that there would be wear(receiver&bolt different type metals or hardness) Maybe Memphis can shed some light on this.
Its just lapping lugs its always interesting to see where the bolt contacts the receiver in the process. Its also amazing you can buy a new bolt rifle and have only ONE LUG touching. Just a post to get some feed back on to gain more understanding of how's&why's of working on these M14 types.
Pfc out
 

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PFC Thomas, the first time I met Tony Geek several of us had been discussing this very subject. He was going to show me how to measure a bolt. GI1
Iron worker is the one that enlightened me as to what is actually happening with the interaction of the bolt and receiver. He posted a thread on it.
http://m14forum.com/m14/139925-locking-lug-helix.html
The bolt actually is screwing into the receiver exactly as a bolt does a nut. The surfaces we see are just such a small cross section that they appear almost flat. As the bolt rotates it moves forward and exactly opposite in reverse. This allows for a really tight lockup, but quickly loosens up as it reverses. Pretty clever, I think.

Edit: The idea of which part wears the most is another hard one to decide or prove. The hardness of commercial receivers and bolts vary. The thickness of the Carburizing or surface hardening also varies some. I don't have the time or money to do adequate research, but it seems somewhat obvious.
 

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Discussion Starter · #11 ·
Memphis,thanks for sharing Iron Worker post on bolt lugs&how they are cut. I didn't realize they were cut in such away as the bolt closes by rotating in. My comment about the bolt and its locking&unlocking as the rifle is being fired has caused some confusion for me. With the bolt lugs not being like a bolt rifle should the lugs be lapped to the minimum. Allowing for either wear or break in. Also noticed in building that the right lug has contact first or a greater amount on the commercial receiver I have built on. What is the proper amount of contact on the lugs?

THANKS,Memphis&Iron Worker
 
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