how does a bolt effect trigger reset? - M14 Forum

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how does a bolt effect trigger reset?

This is a discussion on how does a bolt effect trigger reset? within the The M14 forums, part of the M14 M1A Forum category; I understand the basics. heres the deal, I ran across a Polytech receiver that has had the bolt conversion by warbirds, The guy I bought ...


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Old October 5th, 2012, 07:22 PM   #1
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how does a bolt effect trigger reset?

I understand the basics.

heres the deal,

I ran across a Polytech receiver that has had the bolt conversion by warbirds,
The guy I bought it from sent nearly all the parts except a barrel, he sent a TRW bolt that has had the rear of the lugs just barely ground on but ground none the less, he told me that up front as a safety issue, Warbirds confirmed bad bolt,

The lug contact and headspace is good so I thought it could fill the spot till I get another while I did the build, H&R 18.5" barrel, (I did nothing to fit the bolt to the receiver untill I get the new one)

Rifle is done except for a new bolt, did all the function checks and everything checks out but the trigger reset, I tried three different groups, 5 different stocks and still no reset, changed the bolt and shazamm works perfectly,

long story short, the bad bolt looks perfectly good save for the rear of the lugs that have been worked over, I'm having a hard time understanding why, I know we're talking thousandths here but the rest of the bolt looks just too good to cause a reset issue,

(Total waste of a good TRW bolt but got the receiver, poly op rod and the rest GI parts for $540.00)

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Old October 5th, 2012, 08:23 PM   #2
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Check the BACK TOP LIP of your bolt for too much wear and too small over all diameter at that point.

Too small here, too much clearance between top of bolt and bottom of receiver, and the bolt rises up under spring tension enough when passing over the hammer, that it does NOT push the hammer down far enough to catch the sear.

PS: BTDT a few times my self.
This is a tough thing to diagnose unless you have run in to it before, but if you do enough GI parts to Chinese receiver swaps like I have, you figure it out on your own eventually.
[;)
LAZ 1

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Old October 5th, 2012, 08:36 PM   #3
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Well, the hammer gets pushed down by the bolt, so if it is not recocking, either:

1. The bolt is too thin over the hammer.
2. The bolt lugs are too thin on the top surface (so they ride high in the raceways)
3. The hammer is too thin on the top (not likely, since it worked with another bolt)
4. The trigger group is too low.
5. The receiver is too high.
6. The raceways are too wide, or too high, allowing the bolt to ride high.

I think 4 and 5 are the same thing, being the TG is too far from the receiver, AKA the stock is too fat.

Given that it is a TRW bolt in a polytech receiver, I'd be leaning towards #6, or some similar question of tolerence stackup that makes the clearance not work.

If you do decide it is a scrap bolt, let me know, I might be interested. I'm thinking of drilling one out and installing a rod of some sort for the hammer to launch out the barrel. That way, I can see how high the rod launches as a measure of hammer energy. However I'd want to do it with a donor bolt, not something that has value.

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Old October 5th, 2012, 09:15 PM   #4
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The bolt, receiver and trigger group have an intricate relationship that affects much of the M14’s accuracy and functioning. Basically, as the bolt travels fully to the rear of the receiver, it rides over the top of the hammer, rotating the rear of the hammer far enough down to engage the sear in the trigger group.

The trigger guard on the trigger group engages the cut-outs in the legs of the receiver; this ‘locks’ the trigger group and stock to the receiver. However, the stock has two contact points with the trigger group: the front trigger pads and the rear trigger pads. These two contact points allow the trigger group to rotate within the receiver. If the front of the trigger group is too high, there may not be sufficient clearance for the hammer to clear the inside top of the receiver as the bolt travels over the top. If the front of the trigger group is too low, the bolt may pass over the top of the hammer and not push the hammer far enough down for the hammer to engage the sear.

We’re talking somewhere in the neighborhood of 0.040” inches between a hammer being too high to allow the bolt to pass over on its way to the rear and a hammer that is too low for the bolt to force the hammer down enough to engage the sear.

Your problem seems to be the latter; the hammer is not too high as the bolt can move fully to the rear, but the hammer does not engage the sear. That indicates that the trigger group is, perhaps, not rotated properly in the receiver. If the rear of trigger group is too low, then the sear is too low and will not catch the hammer hooks as the bolt passes over the hammer.

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Old October 6th, 2012, 04:28 AM   #5
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OK I'm getting it

One thing I failed to mention is that the bolt resets the trigger normally except when pulling the op rod back with the trigger pulled, then the hammer follows the bolt home,

I will check the rear of the bolt for abnormal wear, after work today

tried it with several stocks so fit is not a issue

all remaining lug surfaces seem to be untouched,

for the record I will not be using this bolt for anything but a paperweight

Thanks guys

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Old October 6th, 2012, 06:55 AM   #6
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The sear on the trigger is slightly higher than the sear on the disconnector, so it is entirely possible that the hammer is going down far enough to engage the trigger sear if your finger is off the trigger, but is not going down far enough to engage the disconnector, if your finger is holding the trigger back.

If you have a minimal value for the bolt in mind, PM me, as said, I want to drill a hole in it, so don't want to use a nice bolt.

Thanks from Lazerus2000
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Old October 6th, 2012, 08:44 AM   #7
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Reads to me like the trigger group needs to seat in a hair higher in the stock. Often comes about by someone undertaking to do trigger job on M14 or M1 without the whole rifle.

Bolt lugs have to be lapped in when you put a USGI bolt in the Chinese rifle. If there were a way around it with barrel selection or timing everybody would be doing it.

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Old October 6th, 2012, 09:39 AM   #8
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Yep! What art7 said

Quote:
Originally Posted by art7 View Post
The sear on the trigger is slightly higher than the sear on the disconnector, so it is entirely possible that the hammer is going down far enough to engage the trigger sear if your finger is off the trigger, but is not going down far enough to engage the disconnector, if your finger is holding the trigger .
Now that you clarified that this is occurring ONLY with the trigger held back, I would bet $$$ that the back of that TRW bolt is about .005 _ .010" smaller than the bolt that works properly. Take your digital caliper and check,
TTFN
LAZ 1
:-)

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Old October 6th, 2012, 02:12 PM   #9
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Bingo....
Back top lip of the bolt is .701 as compared to a good bolt of .715 + - .001

Absolutely hard to see the file work unless you're looking for it.
Such a good looking bolt otherwise.
Oh we'll at least he wasted a bolt instead of the receiver.

Thanks again for the learning experience

Thanks from Lazerus2000 and budster
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Old October 6th, 2012, 02:55 PM   #10
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WELLLlll,
better to learn here from advice from those who BTDT.
At least you found out you had a problem BEFORE you shot the rifle with that bolt.
Count your blessings [ and your fingers and eye balls] that you got off with only some damage to your wallet.

Like I said, this is a very difficult problem to diagnose unless you have BTDT, and know what to look for. Even after all my years of M14 Gun Smiting, I got stung the same way a few years ago. I was at a gun show in Puyallup Washington, where a guy had a dozen or so M14 bolts and op rods on his table. ALL OF THEM RE-PARKERISED TO LOOK BRAND NEW.

I was stupid enough to go to the show without my digital caliper, and so I took a chance on an "AS NEW" TRW bolt, at what I though was a very good price.

TOO BAD,
SO SAD,
money flushed down the toilet.
[;(

PS: When fitting a GI bolt to a Chinese receiver, you may get lucky and find one that gives you a "drop in" fit, where only a few minutes of lapping will set the lugs up with near perfect bearing. This is why pro M14 smiters have a box of bolts around, they want to start lapping with a bolt that gives as close to possible proper lug bearing and head space right from the start.

If you have your receiver with you and have several STRIPPED bolts to pick from, and IF you have a .308 GO gage, a simple feeler gage measurement of the clearances between the back of the right lug and the front of the the receiver lug cut out, will get you into the ball park for head space measurement. You will can mark the lugs with red permanent marker pen, and cycle the bolt through a few times to judge lug bearing.

REMEMBER HOWEVER THAT MANY CHINESE RECEIVER / GI BOLT drop ins will have head space that may be less than .308 GO. THIS IS WAY MORE DANGEROUS THAN A FEW THOU LONG ON HEAD SPACE!! And a lot more work to fit up properly as well.

So a slightly worn GI bolt might actually be a better fit in your Chinese M14 receiver than a brand new in the wrap TRW replacement bolt [ which usually will be a few thou longer ].

Another trick, if picking out a spare bolt and when you don't have your receiver handy for test fitting, is to measure the bolt lug widths on both sides of the bolt with your calipers. If you know what these measurements are on a known good bolt that head spaces properly in your 14, picking out a spare bolt that will come very close for the same fit is easier.

Does any one here know the width of their bolt lugs?

Does any one here know the head space of their M14?

Does any one know how much of the right bolt lug is engaging the right receiver lug cut out when the firing pin tail becomes free to slip forward through the slot in the receiver bridge?

Does any one really care?

as always,
advice you get for free on the internet MAY BE WORTH MUCH LESS THAN YOU PAID FOR IT,
there is no warranty nor liability implied with this advice,
opinions are like you know whats, and some opinions are stinkier than others.

I am no longer a professional gun smith, nor do I play one on TV,

any one who works on their own M14 had better have at least some clue as to,
WHAT IS SAFE AND WHAT ISN'T.


YardDog1 made the right call in asking here before he shot his M14.
Having the hammer follow CAN contribute to an out of battery KABOOM, which CAN indeed be a very bad thing.
Otherwise,
if he went to the range with that bolt,
he might have been changing his name to "Lefty" or "One Eye".
YPMMV
[;)
LAZ 1


Last edited by Lazerus2000; October 6th, 2012 at 03:07 PM.
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Old October 6th, 2012, 04:14 PM   #11
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Check the height of the bolt lugs and the width of the receiver rails.
Here are couple of pictures of an M1 Garand with the bolt forward and back.
You can see the gap in-between the trigger sear and hammer hook when the bolt is all the way back.
Hope this helps.




Thanks from budster

Last edited by HD Bee; October 7th, 2012 at 08:30 AM.
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Old October 6th, 2012, 07:26 PM   #12
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Got it, I was having a hard time realizing that the back top of the bolt could have been bad,

Not realy out anything on the bolt as I was warned beforehand, he actually threw that in afterwards for the bolt parts,
Receiver has already had the GI bolt conversion



Quote:
Originally Posted by Lazerus2000 View Post
WELLLlll,
better to learn here from advice from those who BTDT.
At least you found out you had a problem BEFORE you shot the rifle with that bolt.
Count your blessings [ and your fingers and eye balls] that you got off with only some damage to your wallet.

Like I said, this is a very difficult problem to diagnose unless you have BTDT, and know what to look for. Even after all my years of M14 Gun Smiting, I got stung the same way a few years ago. I was at a gun show in Puyallup Washington, where a guy had a dozen or so M14 bolts and op rods on his table. ALL OF THEM RE-PARKERISED TO LOOK BRAND NEW.

Yeah A good repark job hides alot of flaws, kinda like make up

I was stupid enough to go to the show without my digital caliper, and so I took a chance on an "AS NEW" TRW bolt, at what I though was a very good price.

TOO BAD,
SO SAD,
money flushed down the toilet.
[;(

PS: When fitting a GI bolt to a Chinese receiver, you may get lucky and find one that gives you a "drop in" fit, where only a few minutes of lapping will set the lugs up with near perfect bearing. This is why pro M14 smiters have a box of bolts around, they want to start lapping with a bolt that gives as close to possible proper lug bearing and head space right from the start.

If you have your receiver with you and have several STRIPPED bolts to pick from, and IF you have a .308 GO gage, a simple feeler gage measurement of the clearances between the back of the right lug and the front of the the receiver lug cut out, will get you into the ball park for head space measurement. You will can mark the lugs with red permanent marker pen, and cycle the bolt through a few times to judge lug bearing.

REMEMBER HOWEVER THAT MANY CHINESE RECEIVER / GI BOLT drop ins will have head space that may be less than .308 GO. THIS IS WAY MORE DANGEROUS THAN A FEW THOU LONG ON HEAD SPACE!! And a lot more work to fit up properly as well.

So a slightly worn GI bolt might actually be a better fit in your Chinese M14 receiver than a brand new in the wrap TRW replacement bolt [ which usually will be a few thou longer ]. and a few bucks cheaper

Another trick, if picking out a spare bolt and when you don't have your receiver handy for test fitting, is to measure the bolt lug widths on both sides of the bolt with your calipers. If you know what these measurements are on a known good bolt that head spaces properly in your 14, picking out a spare bolt that will come very close for the same fit is easier.

Does any one here know the width of their bolt lugs?

Does any one here know the head space of their M14?

Does any one know how much of the right bolt lug is engaging the right receiver lug cut out when the firing pin tail becomes free to slip forward through the slot in the receiver bridge?

Does any one really care?

as always,
advice you get for free on the internet MAY BE WORTH MUCH LESS THAN YOU PAID FOR IT,
there is no warranty nor liability implied with this advice,
opinions are like you know whats, and some opinions are stinkier than others.

I am no longer a professional gun smith, nor do I play one on TV,

any one who works on their own M14 had better have at least some clue as to,
WHAT IS SAFE AND WHAT ISN'T.


YardDog1 made the right call in asking here before he shot his M14.
Having the hammer follow CAN contribute to an out of battery KABOOM, which CAN indeed be a very bad thing.
Otherwise,
if he went to the range with that bolt,
he might have been changing his name to "Lefty" or "One Eye".
YPMMV
[;)
LAZ 1
And thats why this place is so great, a wealth ok knowlwdge and you guys are always more than willing to help

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Old October 8th, 2012, 12:46 PM   #13
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I would reject any bolt that has been ground or lapped in. There is only a thousandth to two thousandth of case on these bolts, and grinding that off, or lapping that off, is in my opinion.

"Gunsmiths" or "Armorers" applying bench rest rifle build techniques to service rifles are doing their customers a dis service.


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Old October 8th, 2012, 01:39 PM   #14
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I am not sure if "Lapping in bolt lugs" came earlier in the Bench Rest or NM community. Early NM Armorers lapped in bolt lugs on NM 03's back in the 30's. Bench Rest does go back the days of using Pope barrels and Ballard, Hi Wall and other "Schuetzen" rifles, but that was not in bolt action rifles until later.

With serviceable GI bolts and serviceable GI receivers, there was never a need to lap the bolt lugs in on either a NM M1 Garand or NM M14. There was enough "lug contact" designed in by the blue print specs AND both the M1 Garand and M14 bolts have a lot more "slop" or "tolerance" to move about that do bolt action rifle bolts. So for both those reasons, Lapping bolt lugs on either rifle was never found necessary or even mildly important/or useful, as long as we were using GI receivers.

I submit the reasons we got into lapping commercial semi auto M14 receivers were:

(!.) To get chrome lined GI barrels to fit because there were no carbide chamber reamers until fairly recently. So that's how we got the chambers to safe minimum headspace AS LONG AS it did not take so much lapping that the surface hardness of the parts was jeopardized. If so, then meloniting is used to reharden the surfaces.

(2.) Commercial semi auto M14 receivers are not made to spec and you don't get as much lug contact as GI receivers gave. Some receivers are not bad and then it goes down to some receivers have NO lug contact on one of the lugs and that is NOT GOOD. If all the pressure is taken by only one lug, then that is going to wear out that one bolt lug much sooner and you won't get cartridges to seat consistantly.

Some to many folks may not realize that in many bolt action rifles, one lug often does not have what we have come to think of as "Enough lug contact" on both lugs. We can't SEE the lug contact on the receiver because it is so far up the chamber and the only way to see it is to remove the barrel. Most people who use bolt action rifles for hunting have never been concerned about how much lug contact they had and many would not know "WHAT the Heck" we make all the fuss about. Those of us who were trained by military Amorerers or older custom gunsmiths who worked so much on 03 and Mauser actions, were taught to CLOSELY examine the amount of wear on receiver lugs when we pulled a barrel and before installing another barrel. Sometimes, before the days of meloniting/salt nitride treating came along, we had to REJECT the receiver because one or both bolt lugs was worn too much.

I do agree that the Pendulum has swung perhaps TOO MUCH about bolt lug contact on Garands and M14's in popular thinking for better accuracy. Still, there needs to be some contact on both lugs.

Thanks from Lazerus2000, budster and YardDogOne
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Old October 8th, 2012, 04:00 PM   #15
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Quote:
I do agree that the Pendulum has swung perhaps TOO MUCH about bolt lug contact on Garands and M14's in popular thinking for better accuracy. Still, there needs to be some contact on both lugs.
Absolutely agree that both lugs need some contact. While I have no data from the manufacturing TDP or from target testing as to what is, or was, an acceptable amount of contact, I decided that 75% lug engagement was good enough for me, either bolt rifle or M1a/Garand.

Early in my shooting career I thought the “savants” actually knew something, so I had the action and lugs trued on a stainless M70. Once the case was removed from the lugs I started having galling . Material removal also changed the relationship between the front of the bolt and back of the bolt with the resultant that my three position safety was out of alignment. I soon decided that lug lapping and lug truing was not something I wanted unless things were severely out of tolerance, and then, it would be best to toss the bolt, or the receiver!

Grinding material away to fit out of tolerance parts is a poor practice.

My first M1a had something like 75% one lug, 80% the other, and now, on its third barrel, it sure looks like I have 99% contact on both lugs!. The proper way to lap a bolt to the receiver is through firing.

I am of the opinion that receiver face truing is probably a good thing, barrel shoulder truing a good thing. You do want the barrel and receiver to be in line and the centerline of the barrel to be in the same axis as receiver centerline.

I will challenge the assumption, inherent in this lug lapping philosophy, whether it improves accuracy for the M1a. It probably does in a turnbolt action, but the quality target actions, are extremely stiff and so precisiely made they don’t need lapping. The Bernard, a very good target action, is single shot, there is no magazine cut out, it may not have an ejector, you pull the empty out of the port with your finger, and these features are common across the class of custom target actions.

A service rifle is very different thing. An M1a has asymmetric bolt loading, a receiver optimized for weight reduction, not stiffness, and based on the number of holes in the thing, a very complicated load path, resulting in complex vibration modes.

Accuracy was not the primary design criteria for the M14. In the 50’s reports I have reviewed, the thing shot about four MOA with the ammunition of its era, which was equal to or slightly better than the FAL, AR10, of the era.

I would like to see data on whether lug lapping improves accuracy in the M1a. Something like the tests Aberdeen ran where hundreds of rounds were fired with shooters, bench rest, and machine rest. I am certain this does not exist, and the only “data” is assurances from “gunsmiths” and the owners, whose objectivity will be questionable. Back in the day when the M1a was the dominant rifle on the firing line, I never heard of lug lapping and the guys I know who won, won with bolts that were not lapped to the receiver.

My opinion is that lapping only adds wear to the bolt and receiver seats and may mess up dimensional characteristics.


Last edited by slamfire1; October 8th, 2012 at 04:11 PM.
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