M1a how close to run headspace for max brass life and 100% reliable cycling

[10mmShooter]

Gentlemen,

I realize my question is not easily to answer since you can not have max brass life and 100% realiable operation simply not possilbe.

Currently my 1x fired brass out of my M1A is running 1.629(50 rounds measured using Hornaday HS guage set). My current sizing die is set at to size at 1.624. So I'm currently running resized .005 thousandths headspace smaller than my 1x fired brass. (using Redding S-type FL die with .335 neck bushing)

I absolutely do not want to have a round not chamber....do not want to experience an out of battery detonation.

So how many reloads of my Lake City brass can I expect using 5 thousandths shoulder setback?? My load is always 40gs of IMR 4895, 168 SMK, CCI#34 and Lake City brass. I have heard recommendations to run headspace as close as 003 thousandths...but that just seems to bit a too close....and I wonder if how many additional reloads that .002 would get me?? I'm hoping for 5 reloads in this config then I can retire the brass after the 5th reloading.

Oh yeah ...currently reloading the .308 on my Redding BB II single stage....have not tried the .308 on the Dillon yet ...I'm afraid the Dillon would give me too much variation in sizing??

http://www.keithrussell.net/guage.jpg

[Jack Stanley]

I'm not sure if my experience loading a Garand will help you or not but here goes .

I wanted maximum case life out of a batch of cases so I adjusted the dies for that particular rifle . I stripped the bolt of the Garand and found that the cases would not chamber before sizing . Good for me I thought , they will fireform of sorts . I backed the sizing dies out , lubed a case and began running the case into the die a little at a time and watching how much sizing the neck was getting . About halfway down the case , I wiped the lube of tried to chamber the case and tried to close the stripped bolt on the case like it was a headspace gage . It didn't close and wasn't close so I lubed another case ran the die down a little more and tried it again . I kept at it untill a case would just let the stripped bolt close , I tightened the lock ring tried another case to make sure and sized all the cases that way .

They were loaded to M-2 specs and ran well , the gun never even hiccuped . I loaded the cases ten times after the initial firing ( total eleven times fired ) before a neck split . I checked each case after that for head separation and couldn't detect any . I pitched the cases thinking that was good enough life . Having a MO gage may have helped me but I think having cases that wouldn't fit to begin with sort of helped in this experiment .


I haven't done the same with my M1A but since I don't have a gage for that either I think I would do much the same . With your gage and all try what you are thinking , just don't go to a match untill you have proven to yourself it works . The out of battery firing may have something to do with primer seating and the safety bridge of the reciever . As long as you aren't having problems with the bolt locking , primers and tolerances of the bridge will be other things to consider right ?

Jack

[NickSS]

I used to shoot an M1A supermatch in competition (I used it and a second one through a total of five rebarrelings). I have this gage that you slip a fired case into and screw it down and it measures the cast length to the shoulder. Typically the case grows between 8 and 11 thousanths between a new round and its fired condition. In most of the rifles I measured. When I ran them into my sizing die (I used redding bench rest dies) it pushed the shoulder back around 5 to 7 thousndths. Doing this I got about three reloads per case before I noticed incippant head separation and had to toss the cases (these were full power loads shooting q86 gr Matchki9ngs and something over 2600 fps). I experimented as I did not want any failures to feed and found that if I resized my shells down to 1 thousandth under fired length I had reliable function and at least double case life. Gas guns are hard on brass and after 6 reloads I tossed them into the scrap bucket as the last thing I wanted was a head separation.

[curator]

Since this is a CASTBOOLIT site, I relay my experience with my M1A reloading with the Lee Collet die and LBT 310-180SP boolits. I have reloaded R-P cases up to 15 times without having to set the shoulder back. I do keep the chamber clean, and check the cases for headspace before reloading them. I am loading 32 grains of IMR4895. I do keep an eye on each case as it is chambered since I do not want a cartridge to fire out of battery either. I use CCI mil-spec large rifle primers exclusively when loading for the M1A and the M1.

I am often lectured about my unsafe practice but understand the risk and pay careful attention to the details. I believe that the low-pressure of these cast boolit rounds barely expands the cases enough to reverse the shoulder set-back resulting from the chambering and firing pin forces . Fired cases drop into the Foster headspace gauge. Possibly my M1A also has very tight chambering tolerances to boot.

I do not do this when shooting J-word bullets with full loads, but those cases show more expansion and do need to have the shoulder set back a couple of thousandths to pass the headspace gauge test.

[Doc Highwall]

For bolt guns I set the shoulder back .002" and for a semiauto I set the shoulder back .004". These dimensions are from rounds that were fired in your gun. I take 10 cases that were fired in my gun to get an average and keep the information incase you have to switch presses and need to reset the dies.

[Larry Gibson]

10mmShooter

I suggest you let the chamber of your M1A tell you how much to set the shoulder back. Back the die out one turn and size 3 fired cases (wipe the lube off them). Place a case into the chamber and with the bolt about 1/2 way back let go of it and let it close over the rim and try to chamber the case. The bolt probably won't close. Screw the die in 1/8th tur, size the 3 cases and try chambering a case again. Keep screwing the die in 1/8th turn at a time until all 3 cases chamber with the bolt completely closing , the slide moving all theway forward and the cases extracting easily. When you have achieved that the cases are then sized to your rifles chamber, not to some arbitrary figure.

My load is always 40gs of IMR 4895, 168 SMK, CCI#34 and Lake City brass.

With that load and those dies sizing them to the chamber as suggested you may get 4 or 5 firings at best before incipient head seperation sets in. If you want to get 16 to 20+ firings per case then use a regular (the SB dies is not needed) RCBS .308W X-Die. Read the directions and set it up correctly. You will get very good case life (16 -20+ firings) and you will not need to trim. I've conducted an extensive test o them with my Rack grade M1A which gave the worst case life of the 3 M1As I have. I have subsequently used the X-Dies with very good case life in all my gas guns and those which I FL size the cases for ammo use in different riles. I can post the results of the test I did or PM it to you if you want.

Larry Gibson

[milboltnut]

Try a dillon case gage. Drop the sized case in and see if the head falls between the steps.

http://www.dillonprecision.com/content/p/9/pid/25547/catid/3

[mike in co]

Try a dillon case gage. Drop the sized case in and see if the head falls between the steps.

http://www.dillonprecision.com/content/p/9/pid/25547/catid/3

not....................

[mike in co]

again ...larry comes thru....

[milboltnut]

not....................

ooooo mighty one... ooo bullet master.... LOL

I guess you out post me, huh?

[mike in co]

ooooo mighty one... ooo bullet master.... LOL

I guess you out post me, huh?

you have missed the intent of his post....
THE OBJECT IS TO MIN SIZE FOR FULL FUNCTION IN HIS RIFLE.

anyone can size to fit a gage..but that will kill brass life in a semi auto rifle.

he wants brass the works in HIS RIFLE without sizing dowm to min spec...



go read....

mike in co

[45 2.1]

you have missed the intent of his post....
THE OBJECT IS TO MIN SIZE FOR FULL FUNCTION IN HIS RIFLE.

anyone can size to fit a gage..but that will kill brass life in a semi auto rifle.

he wants brass the works in HIS RIFLE without sizing dowm to min spec...

go read....

mike in co

Lots of opinions here. 5 firings is POOR............... Even 10 is POOR.
Standard dies and partial sizing works partially. Dies cut for the chamber in question work fine....... or carefull methodology. Fire one case with each headspace length you choose until case failure, then you'll know which one is the longest serving. Of course, thicker military brass helps also.

[Doc Highwall]

Years ago when I was on a state rifle team shooting a National Match M-14 I was using a RCBS die and I had to lap the top about of the shell holder about .002" to stop the gun from jamming when the bolt was closing. If I recall I use to get about 17 reloads out of the cases before I replaced them. I was always getting M-118 ammo for free and even got some M-72.

[jmh54738]

Yea Doc, Just to demonstrate the tolerances that exist, I run a .01 shim between the shellholder and my CH 308 die for my M1A. I bump hard against the shim when sizing. Just backing up the die doesn't work because of the "spring" of the press linkage and a variable amount of force applied to individual cases. Without the shim, cases will seperate on second firing. IIRC all shellholders are .125 from the top to the case surface.

[Doc Highwall]

What happened is I think that the rifle chamber head-space was on the min dimension and the die and shell holder was on the max dimension where I either had to take some off the die or off the cheaper shell holder.

[c3d4b2]

Below is an article on M1A Slam Fires. One of the causes listed is minimum chamber, minimum head space, and inadequate sizing.

http://www.scribd.com/doc/2649554/The-Mysterious-Slamfire-

Here is also an article on reloading for the M1A

http://www.zediker.com/downloads/14_loading.pdf

[jmh54738]

A reprint of an NRA article exploring all of these concerns came with my rifle many years ago. That is the reason that I was sizing my cases until the die contacted the shellholder. On my first DCM rapid fire string 8 out of 10 of the ejected shells could be snapped apart with my fingers. I made up a gauge which locates on the cartridge shoulder. The gauge is used with a dial indicator test stand and calibrated with factory loaded commercial and military cartridges. I am saying that there are manufacturing tolerances. If a rifle is headspaced on the long side and the dies are made on the short side, and the shellholder is made on the low side, these tolerances will stack up. In my case, with my dies and my shellholder, my cartridges will have .010 greater headspace than a commercial round, hence the .010 shim. I had to gauge every shell that I had loaded, some of which I had to pull down and throw the cases away. While I agree that dangers exist if minimum headspace is combined with other factors such as overly sensitive or high primers, the danger exists for grossly excessive headspace also.

[milboltnut]

The M2 ball surplus ammo I have falls in the dillion case gage the same as my full length sized cases. My Lee dies are where the case needs to be when I run a case completely into the die.

[jmh54738]

Looks like you got a combination that works for you. How is your case life? My C-H dies are about 30 years old and lacking in quality control. I just live with them. When I was investigating my headspace problem, I completely disassembled the bolt of my M-1A Match rifle so that I could rotate the bolt closed by hand. I used a headspace gauge and shims between the sized case and the bolt to determine the situation. I would not want to fit my cases to the chamber by slamming the bolt of an assembled rifle onto the cartridge case and also having the extractor jump over the rim. I will measure a sized case and slam it into the chamber a couple of times with the bolt and report on any headspace changes. You could do this also and use your Dillon gauge.

[milboltnut]

It looks like my case life will decrease from not sizing they way these guys descibed.

The primers are seated below the head, and I stripped the bolt to see the lug drop in full battery, and it did. I understand that all military chambers are oversized for battle conditions, and cases will stretch. But we are warned not to full length size only neck size to increase case life on bolt guns. I have a friend who only full length sizes and has 10 loadings and counting. Hot loads aren't my thing, so I doubt stretching will be a major problem. What the average life of a case with the M-1 with mild loads if sized to chamaber?

I will go back and size accoringly. I use LC brass.

[jmh54738]

Here are the results..............I inserted a sized empty LC 308 case in my M1-A. This case was gauged and the dial indicator set to zero. I let the bolt slam forward from the 1/2 open position. The indicator read -.001. Repeat with the same case, indicator -.002. Repeat with same case with bolt in full open, indicator -.005. Repeat same case with bolt fully opened, indicator -.006. Not suprisingly, slamming the bolt on a cartridge will increase the headspace of that round. When you had your bolt stripped and the bolt closed on a case, how much shim would be required to give a little drag to turning the bolt shut? That is your headspace for that combination . I just looked at the cartridge specs, the total tolerance on the shoulder dimension is .007. Of course, those cartridges have to fit every rifle every time.

[frank505]

I am only on my third barrel for my Super Match. My process is, starting with fired cases picked from match, tumble clean, lube with SharpShootr spray lube. Size all in Redding full length die with carbide expander button, bumping shoulder .004. Run all through Gracey (love). Now ready to go through Dillon 550, starting with RCBS X die set at case length of 2.10, Gracey trims and chamfers to 2.00.
I have found the case lube is very important, not enough and the expander pulls the neck out and all this work is for nothing. Once all are loaded a short tumble cleans the cartridges and into ammo cans they go. Another tip for tumbling cases, I use corn cob media and mineral spirits, no abrasives.