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  #1  
Old 11-06-2019, 03:06 PM
JRL423 JRL423 is offline
 
Join Date: Apr 2014
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Default Longest Bolts

Is there a list of USGI M14 bolts from longest to shortest similar to the one on the Garand sites? I am wanting to tighten up my headspace on a rifle and thought an easy way to do it would be to fit a longer bolt. That leads me to another question. Can you reliably mic a loose bolt to see if its longer than another one? Seems it would need to be mic'd from the rear of the locking lug to the face accurately.
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  #2  
Old 11-06-2019, 03:49 PM
nf1e nf1e is offline
 
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Bula produced bolts from -.006 to +.006 in .002 increments.
Of USGI, seems TRW as replacement bolts were slightly longer.
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  #3  
Old 11-06-2019, 07:13 PM
IRON WORKER IRON WORKER is online now
 
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USGI bolts have only a .002'' total tolerance from face to right lug datum .
.617'' - .002'' If its not been lapped on they will be within the specs .

Remember the lugs were precision ground on a thread grinder post heat treat so they are accurate.

They say the last TRW bolts were held to longest specs ,most I have had were on the max length .617''
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Old 11-06-2019, 10:05 PM
4gun-drill 4gun-drill is offline
 
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The specs from the right lug to bolt face were the same for both the M1 and the M14. However, M14 bolts tend to much more consistent and in my experience most were held close to max dimension. Why there is so much variation in Garand bolts, I don’t know. But, based on the price of M14 bolts and the low likelihood of it making a measurable difference is also low, I would not recommend blindly buying new bolts.
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  #5  
Old 11-08-2019, 10:05 AM
M14 M14 is offline
 
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Quote:
Originally Posted by JRL423 View Post
Is there a list of USGI M14 bolts from longest to shortest similar to the one on the Garand sites? I am wanting to tighten up my headspace on a rifle and thought an easy way to do it would be to fit a longer bolt. That leads me to another question. Can you reliably mic a loose bolt to see if its longer than another one? Seems it would need to be mic'd from the rear of the locking lug to the face accurately.
What make rifle receiver? and what is the current headspace?

Measuring a bolt is tricky with a mic or calipers, but it can be done if you are good at math. The problem arises from the fact that the back of the locking lugs are cut or ground on an angle, which can skew your measurements, but it can be done to get close enough for government work.

A height gauge is best if you have access to one. But you still have to subtract the bolt's cartridge shroud length to get the bolt face measurement if you stand it on it's nose. Set on a precision plate on it's rear, you simply measure to the face and record that, then measure to rear of locking lugs, about the center of them, and subtract to get the specs.

There is more involved in headspace than just the bolt and there is actually a total on the M14, if everything is in within spec, of .008" difference from one rifle to another.

The barrel ring having a tolerance of .004", the bolts having a tolerance of .002", and the receiver lug abutment faces having a tolerance of .002". This factoring in, and assuming, that you are using a g.i. chrome lined barrel with a finished chamber, and not getting in to the tolerance or variance allowed on the barrel specs either.

With all that said, and using rudimentary tools for this, like calipers, you can free measure from the back of the bolt to the bolt face with it turned right, then use the tail feature of the calipers to measure from the back of the bolt to the rear of the locking lugs, and do the math. Like I wrote, close enough for government work.

If you headspace is 1.638" or below, and you are not concerned about working your brass too hard and reloading, then just shoot it, it's fine. Headspace has nothing to do with accuracy if all the ammo specs are the same that you shoot through it.

If you do reload, then you label ammo anyway, just size those rounds to fit your chamber (.003" to .005" smaller than actual chamber headspace) and keep them separate for accuracy or functionality concerns in other rifles.
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  #6  
Old 11-12-2019, 05:37 PM
Sailormilan2 Sailormilan2 is offline
 
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From what little research I've managed, at least one source says that Win bolts tend to be the shortest (lengthening headspace), while TRW are often the longest(shortening headspace). TRW got a contract to make replacement bolts, so bolts were made to account for estimated receiver wear.
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