Let's talk M14 headspace

chemo

chemo

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In a previous thread (http://www.canadiangunnutz.com/forum/showthread.php?t=650606), it was mentionned that both Oldsmobiler and I have used the RCBS Precision Mic Cartridge Headspace Tool (which is currently subject for a rebate if you buy from Sinclair Intl) to determine headspace in our respective M14 (or clone for my case)
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The point being, shooting with the gas system off, gives a better idea of the real headspace because the case is not stretched by the cycling.
I have collected data today for 3 different situations:
My reloads which are a PRVI 150gn FMJ over 45.0gn of BL-C2 (classic minimal charge plinking round) in a case that has been fired 3 times prior and with the gas system on and off, and the Norinco 145gn FMJ ammo recently imported by CanadaAmmo (only bought the ammo) with the gas system on.

Gun used:2007 era Norinco m-305. Bubba unitized, later reworked by M14Doctor (repair bolt roller, cut and compensate)


Raw and processed data:
.308 Winchester
GO: 1.630"
NOGO: 1.634"
FIELD REJECT: 1.638"

7.62 x 51mm NATO
GO: 1.635"
FIELD REJECT: 1.6455"




Discussion:
According to my results, gas off does indeed produce different results than gas on, but nothing spectacular. Considering the headspace gauge is good for ±0,5 thou, that leaves 1 thou that is absolutely unrelated to the instrument's uncertainty. Since the usefullness of the tool is to determine how to adjust a full lenght sizer die, I would assume it is safer to use the value obtained with the gas off. I do not know how Hungry determines headspace when he helps m14 nuts out but it is something to consider when you seek help... Which value do you need? Which value do you want?
I had in the past obtained a 1,6415'' headspace (open gas) with the same tool, which is in accordance with today's data. 7.62x51'ish kind of headspace, but I suppose it's good (so far)
Feel free to criticize my method :D
 
I bought the precision mic not two weeks ago. Not only to size brass to a specific chamber, seat bullets at an ideal distance from the lands and prevent overworking my brass but also to verify the 7.62mm Nato ammo I have safely fits in my SA 308 chambers. This was a result of a recent discusion here. In my search I came across this article which I think addresses the issue very well. http://carnival.saysuncle.com/002453.html

I have since bought the mic for .223 and I can see owning one for each calibre I handload for.
 
Thatz great of you to do this chemo for us. As it points out a myth that I have been trying to explain to a few people about. That is most people want the tightest head space possible but in a semi-auto you always want a minium of 2 thou play. Now I know reloaders don't like that but saftey in my mind is better than a 1 thou to tight on the head space. The same goes for excesive head space but ever since the 2009 model's have come on the seen they are far and few between.
As for mic's are great for reloaders but chamber gauges are so much easier and quicker. No shooting required and no multiple readings plus math are required. Just place stripped bolt into the battery postion with the chamber gauge in the chamber. Then with your trusty fealer gauges to exame how much headspace there truley is. I find it more accurate of a reading to. Also me and the Doc were quite suprised at the last Poco clinic that we even found a bone stock Norinco M14 owned by majormarine to have bang on 1.631 witch is the best for 308 but we did warned not to use Nato rounds & it would probaly be good if he was going to only reload for this rifle. Also at a surrey clinic a while back we did come across 2 Springfield that both had the bolt recall issues as post by Springfield witch was also another great thing to be on the look out for when examing your bolt.
As for your headspace chemo you fail to meet the NM guide lines and I would stick to preaty much NATO spec's. Now if you want I do have a spare bolt that you can try for sceintific purpose to post back the resualts here to see if the new bolt gives you different headspace reading's and or improves your rifles accuracy.
Also don't try to compare your rifle to Oldsmobiler cause he has 1 of 3 barrels ever to fall into civi hands & is done to the max! Even Mr. Carlos Hathcock him self would love to own.
 
Satain said:
Thatz great of you to do this chemo for us. As it points out a myth that I have been trying to explain to a few people about. That is most people want the tightest head space possible but in a semi-auto you always want a minium of 2 thou play. Now I know reloaders don't like that but saftey in my mind is better than a 1 thou to tight on the head space. The same goes for excesive head space but ever since the 2009 model's have come on the seen they are far and few between.
As for mic's are great for reloaders but chamber gauges are so much easier and quicker. No shooting required and no multiple readings plus math are required. Just place stripped bolt into the battery postion with the chamber gauge in the chamber. Then with your trusty fealer gauges to exame how much headspace there truley is. I find it more accurate of a reading to. Also me and the Doc were quite suprised at the last Poco clinic that we even found a bone stock Norinco M14 owned by majormarine to have bang on 1.631 witch is the best for 308 but we did warned not to use Nato rounds & it would probaly be good if he was going to only reload for this rifle. Also at a surrey clinic a while back we did come across 2 Springfield that both had the bolt recall issues as post by Springfield witch was also another great thing to be on the look out for when examing your bolt.
As for your headspace chemo you fail to meet the NM guide lines and I would stick to preaty much NATO spec's. Now if you want I do have a spare bolt that you can try for sceintific purpose to post back the resualts here to see if the new bolt gives you different headspace reading's and or improves your rifles accuracy.
Also don't try to compare your rifle to Oldsmobiler cause he has 1 of 3 barrels ever to fall into civi hands & is done to the max! Even Mr. Carlos Hathcock him self would love to own.
Click to expand...

Yes I know I cannot compare my rinco with the gear of Oldsmobiler ha:
Also, I don't think it would be worth shipping the bolt from BC (which I believe is your location) to QC and back again for the benefit of this thread :p
 
The best shooting M14 type rifle I owned was built be Hungry and was headspaced at 1.628" (2 thou crush).............A tight chamber that required handloads and never saw commercial ammunition.

The rifle was built on a TRW receiver, with all TRW parts , and a Douglas heavy match barrel.

This rifle would hold it's own against any bolt gun......;)

The CrazyHorse DMR clone I built headspaced at 1.630" right on the money.

I built the rifle was based on a Norinco receiver, all USGI parts (TRW), and a very rare Smith Enterprises CrazyHorse Medium weight barrel. :D


I wish I pulled that barrel off when I sold that rig..........:(

The last M14 type I built was a 18.75" shorty that was built all with Norinco parts, and a few Rooster33 parts.

The headspace was 1.638".This was good enough for this rifle as it was K.I.S.S. iron sight only blaster........ ;)
 
Chemo's results are very similar to my observations over the past 20 years of mic'ing .308 rounds from M1A's, .308 M1 Garands, and now the Norc/Poly M14's ...

All good learning and reading!

Barney
 
Hungry said:
Chemo's results are very similar to my observations over the past 20 years of mic'ing .308 rounds from M1A's, .308 M1 Garands, and now the Norc/Poly M14's ...

All good learning and reading!

Barney
Click to expand...

Hungary, Could you please elaborate on the method?

I recently had you mic some 308 rounds and you said that they measured 16, 16 and 16 thou. Now if that's good for 308 at 1.630 and add the 16 thou I'd have a headspace of 1.6460 which would be .0005 over for NATO spec. Does this matter much? As i know we're practically talking Microns here.
 
The mic starts off at zero which is .308 SAAMI (1.630) so like you figured out 16 thou is 1.646 headspace for your barrel with a .308 gauge...HOWEVER you need to realize that HS is measured differently on .308 than 7.62

Some quick info I got from searching the difference...easier to show you with pics

The dotted line represents the point on the shoulder where the cartridge would headspace

rimless2.JPG.w300h266.jpg
 
Ya wanna know your rifle's true headspace without mucking around with a mic.
Get a bolt disassembly tool and clymer headspaces guages. There's no guessing, no mucking with shutting gas system on or off, and every "m14 mechanic" that builds their own rifles should have them.
A precision mic is good for periodically measuring brass and is a benefit to reloaders who are fire forming.
Other than that, it will get you close.
 
M14Doctor said:
Ya wanna know your rifle's true headspace without mucking around with a mic.
Get a bolt disassembly tool and clymer headspaces guages. There's no guessing, no mucking with shutting gas system on or off, and every "m14 mechanic" that builds their own rifles should have them.
A precision mic is good for periodically measuring brass and is a benefit to reloaders who are fire forming.
Other than that, it will get you close.
Click to expand...

I'm starting to like that advice. I'm from the Precision Mic side of things and I prefer the Clymer method. Either way, Bart212, your rifle is safe to shoot!

Cheers,
Barney
 
Hungry said:
I'm starting to like that advice. I'm from the Precision Mic side of things and I prefer the Clymer method. Either way, Bart212, your rifle is safe to shoot!

Cheers,
Barney
Click to expand...

Mine too, remember? 1.634 as assembled (USGI bolt/barrel) with factory .308....shoots great!
 
M14Doctor said:
Ya wanna know your rifle's true headspace without mucking around with a mic.
Get a bolt disassembly tool and clymer headspaces guages. There's no guessing, no mucking with shutting gas system on or off, and every "m14 mechanic" that builds their own rifles should have them.
A precision mic is good for periodically measuring brass and is a benefit to reloaders who are fire forming.
Other than that, it will get you close.
Click to expand...

Too many assumptions using the feeler gauge method:

How can you confirm that the right bolt lug doesn't contact the receiver before contacting the rear of the HS gauge? Most guys don't know the "feel" when using feeler gauges either. If you wanted a ballpark idea of where you're at then sure its quick and dirty but the fired case method is by far one of the most accurate.

Regarding the headspace gauges, the Forster set I have only goes up to 1.638 and I find most of the Norks I tweaked swallowed that one no problem

Then again I like knowing the exact size of my chamber so when I'm adjusting the dies for reloading I know what to do it to. I like using precision measuring tools and I'm kinda picky :D
 
A full set of head space guages cost quite a bit and it's true using feeler gauges properly is learned. I spent years working in a machine shop and on my own machinery. I have feeler guages as well as dial calipers, dial indicator and micrometers. I am comfortable using feeler guages. Properly cared for these tools last a lifetime. If you play with other machinery they are indispensible.

The precision mic:
Allows us to determine headspace with fired cases.
Enables us to set our sizer die to bump the shouder just enough to provide adequate clearance and avoid overworking our brass.
Gives us overal length to the lands where we can fine tune our hand loads for accuracy(within magazine dimensions of course).
Allows us to confirm the dimension to the seated bullets ogive which is more important than case head to bullet tip in relation to the lands.
Makes it possible to confirm loaded rounds provide enough clearance to shoot in our rifle.

The head space guages:
Give us precise head space dimensions before we shoot. (that's kind of important and if I was assembling I would insist on using them)

The precision mic set me back about $70. Each head space guage is about $40. In the case of M1A's you have a head space dimension from the factory. The standard I bought new had a dimension of 1.632" which is right on the money to fire 308 and 7.62mm. Maybe the Springfield guys know what they are doing after all.

It is possible to add shim stock behind the case head to change the dimension of the guages and get exact lengths without a full set. I've done this with my No4 Mk1. In any event neither will prove there is adequate clearance between the front of the right bolt lug and rear of the receiver in battery. The guages effectively push the bolt away from the receiver so they will make the clearance if it exists. The fact that the bolt closes without undue force is confirmation that there is some. Perhaps machinists blueing can be utilized there. It should leave some tell tale marks on the lug face if it is tight.

I bought the mic to prove the 7.62 mm Nato rounds I have are dimensionally the same (or at least safe to fire) as commercial 308 win rounds. I have yet to confirm this. I'll have to dig them up and give it a try.
 
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