Need Help: Weird Headspacing Problem?

[Bob Bishop]

Guys,

I am really scratching my head on this one and hope that you all could help me out a bit. The question is: do I have excessive headspace?

The story...

I have just finished assembling my first FAL from a number of separate parts. The barrel is an Imbel from our recent group buy and is in VG or better condition with a darn nice bore. The receiver is a DSA Type I which I also got through the group buy. The bolt/bolt carrier are matched Austrian Stg58 and the internals are a combination of Austrian and DSA. Everything fit together with absolutely no problem and was a lot of fun to do.

I did the headspacing using MSC gage pins and torqued the barrel in with Casey Elliot's barrel wrench. I also used Forster headspace gages with a 1.630" GO and 1.634" NO GO. These were checked out on a RCBS .308 precision mic with the GO gage lining up on ".000" and the NO GO mic'ed out on the gage at ".004". In other words, the Forster gages, when compared to the RCBS case gage, were dimensionally in order.

I very carefully headspaced my FAL last month and determined that a .252" locking shoulder was needed to give me 1.632" overall headspace. This was because I shoot a combination of Radway Green milsurp ammo and USA commerical rounds. Headspacing was performed with a clean chamber and the extractor removed from the bolt so no false measurements would occur. ARS machined me a beautiful .252" locking shoulder and it went in with no problem. I also re-checked the headspace after the shoulder was installed and it was perfect....it closed on the GO gage and would not even come close to locking up on the NO GO gage.

So far - so good!

The entire rifle was sent out to be parkerized and it came back absolutely gorgeous. This thing was truly becoming a work of high art.

My first trip to the range was this past Saturday and I took out 200 rounds of Radway Green ammo made in September, 1988. The wooden box was fresh and I broke the rounds out of the plastic bags/paper boxes for the first time. The ammo looked bright with nothing visually wrong.

The first round was chambered by hand (no mag) with the gas wide open to "7". I fired the shot and the bolt recoiled back maybe an inch with the case still in the chamber. I tried to cycle it out by hand and it would not go. I then placed the butt on my foot and moderately tapped the charging handle 2-3 times until the case came out. I examined it and found out THE NECK WAS SPLIT! This really bothered me as I have rarely had this happen to me before.

I placed another cartridge in and fired it, too. The same thing....the bolt would recoil a little bit and the case would stick in the chamber. I would have to hand cycle it out by tugging on the charging handle a few times. At least the extractor and spring were in first class condition!

I closed the gas down over the next 15-20 shots until it read "3.5" (mag was in) and at no time did it ever lock back on the BHO.

After getting a bit worried/disgusted, I took out my RCBS .308 precision mike to check the headspace on all these fired cases and was absolutely shocked to see they averaged an INCREASE of .013" over their unfired size. To double check, I hand selected 15 more cartridges which were all measured (prior to firing) on the RCBS gage to read ".000" and then shot them. They, too, all experienced the same average increase in size: .013"

Plus, a few of them had split necks.

I never got the gas adjusted to cycle the action as every shot seemed to hang up in the chamber and they all had to be cycled out by hand/charging handle. None of them ejected at all.

I felt that extremely excessive headspace was occuring as evidenced by split case necks and every round getting somewhat stuck in the chamber. Consequently, I quit for the day and took everything back to the shop...rather disappointed and disgusted to say the least!

After getting back I thoroughly cleaned everything and discovered a very large amount of black carbon buildup in the throat of the barrel. It had obviously not been there before the firing. Also, the chamber looked fine with nothing visually wrong.

Just to see what was going on, and figuring out that somehow I had screwed up the calculation for my locking shoulder, I once again used the Forster headspace gages to see what the headspace was.

It was PERFECT!!! The GO gage allowed the bolt to close and the NO GO would not close at all.

Guys - something seems real wrong here. How in the Lord's name can I seem to have such excessive headspace increase when firing the RG88 cartridges and yet everything gages perfectly well when using the Forster gages in a static test?

The questions:

1. Is an average growth of .013" in fired cases normal?

2. Are 4 split necks out of 40 shots normal for excellent condition milsurp ammo?

3. How can the rifle headspace perfectly with the Forster gages and then seem to be so darn bad with real ammo? Could the Forster gages - or the ammo - be not to spec?

Finally, the only thing I could see was that the first .25" of the chrome lined chamber was fairly rough from the sand blasting it received when the whole rifle was parkerized. Could this rough chamber in some way have "gripped" the case so tight during the firing process that as the bolt unlocking and came out of battery the case hung in the chamber for a few extra milliseconds and was "stretched" about .013" at this point with the neck rupturing?

Any thoughts or guidance you all can provide will be greatly appreciated. At a minimum, I will polish the chamber (especially the first .25") to clean up any remaining roughness left from the sand blasting and then try it again this coming weekend.

Thanks so much for bearing with this long plea for help!

Your Friend,
Bob

[Derby FALs]

Did you get this ammo from DSA? Try some different ammo.

Put some green or gray scotchbrite on a cleaning rod and chuck it in a drill. Hone the chamber a little like you would a cylinder in an engine. Keep it moving in and out and don't stay on one spot. Don't overdo it.

My $.02. I would not take anymore guns to someone that sandblasts the chamber or the inside of a new receiver.

[Upside Down @ 100 MPH]

I don't think the split necks are due to a headspace problem. I am curious about the diameter of the neck portion of your chamber though, it may be big. I wouldn't polish it any more, that will only make it larger in diameter and may worsen the neck splitting problem.

If the gun is headspaced where you say it is I don't think it's possible to have .013" headspace with RG. My guns are at 1.632"-1.633" and with RG that gives me .002"-.003" headspace. Are you comparing unfired rounds? A phenomenom I've seen with my guns is that a fired case will measure longer than the chamber dimensions leading me to believe that something is moving (like receiver flexing) and allowing the headspace to increase during firing. This happens to me on the grenade setting too.

HTH

[Valknut]

could be, as some has suggested, an out of spec chamber. Headspace dimension at the one critical shoulder datum point could be fine - while the rest of the chamber could be oversized, egg-shaped, overthroated. Perhaps casting the chamber would yield some answers.

[Bob Bishop]

UD100,

I, too, was thinking about this and am going to have to figure some way to measure the case neck area of the chamber. It is possible that it is too large...but a visual exam shows the chrome lining appears fine in that area. If it was too large I imagine that I would see a color differentiation...or the factory built it wrong to begin with?

The polishing I plan to do is only for the base of the cartridge area where the blasting roughness occurs. The rest of the chamber is fine and does not appear to need it.

Also, when I hand selected the RG88 cartridges for testing, they were all at .000" on the RCBS precision mic. I then fired them and measured what their "after" measurement would be. It averaged out to be .013". Thus, the before was .000" and the after was .013". I interpreted this to mean that my cases stretched .013" in their fired state...and this just seemed excessive to me. Perhaps .002-.004", but not .013".

Finally, let's say that I left a good coating of BreakFree CLP in the chamber and forgot to clean it out before firing....could this have caused the first round to split the neck and subsequently foul the case neck area of the chamber? What would this have done to all 39 rounds which followed? I am not saying that I forgot - I just cannot positively remember that I actually scrubbed it out before firing and am searching for all possible causes of my problem.

Thanks for you help!

Bob

[W.E.G.]

Split <u>necks</u> are not a definite indication of headspace dimension problems.

HEAD SEPARATIONS are the usual symptom of excess chamber <u>headspace</u>.

In the absence of case head separations, the cause of split necks is usually brittle brass, or sometimes an excessive diameter in the <u>neck area</u> of the chamber. The best way to learn the diameter of the neck area of the chamber is to check it with an inside-diameter micrometer tool. Alternatively you make a casting of the chamber, then measure the appropriate area of the casting.

As for the failure-to-cycle, this could possibly be attributed to the split necks. Since the neck must expand (but not too much) to seal the case to the chamber, it is possible that the neck never fully seals, preventing sufficient gas pressure from being available to cycle the action.

As for the stretched "headspace" on your fired brass, I have to tell you that I have seen match-grade M14's stretch brass that much during normal cycling. (When I refer to "headspace" of the brass, I'm talking about the dimension from the base of the cartridge to the datum line on the shoulder of the cartridge.) The amount of brass-stretching will differ between brands and lots. Brittleness/ductility and the thickness of the brass are important factors which always affect the amount of stretching in bottleneck cartridges. However, the norm seems to be "headspace" stretching of fired cases of .003" to .007" Gas guns are brutal in how they treat fired brass. Some are more brutal than others, even among like-kind gas guns. I theorize that the reason your brass is at the long end of the spectrum of stretched brass is because the brass is not letting go of the chamber as soon as it could be. The longer the brass holds onto the chamber after the bullet passes the gas port, the more the brass stretches in "headspace" dimension.

I'd try different ammo (preferably newly-manufactured) first. If the problems persist, I'd measure the neck of that chamber.

[Templator]

I can only guess,.. but I doubt that an oversize chamber would cause the necks to split unless it was grossly oversize. Brass is pretty mallable stuff,.. it'll stretch quite a bit before seperating. Sounds to me as if the neck of the case may possibly be extending past the neck area of the chamber and extending into the throat. If this happens, the neck of the cartridge would be pinched against the walls of the throat upon firing, not allowing it to properly expand and release the bullet. I'd pull a few of the bullets and measure the OAL of the cases. It might be a case of some slightly long case necks being fired in a rifle with a slightly short chamber in the neck area. This situation wouldn't be revealed by headspacing since the datum for a headspace guage is the shoulder of the chamber. The case stretching that you're experiencing could be the result of the extractor tugging on the rim of the cartrige while the neck of the case is pinched into the throat.

[ November 19, 2001: Message edited by: Templator ]

[ November 19, 2001: Message edited by: Templator ]

[ November 19, 2001: Message edited by: Templator ]

[Bob Bishop]

All,

Darn good assistance/thoughts on all your parts. I had forgotten that excessive headspace usually leads to case head separation and not split necks.

Which puts me somewhat at ease on headspacing since there was absolutely no evidence the RG88 ammo had distended cases (no swelling, bright shiny stress line at the base, etc.). Which starts to somewhat narrow the problem down to weirdness in the neck area of the chamber.

I will buy some US-made name brand ammo later today and give it a try this weekend to see what happens. Also, I will order some Cerrosafe from Brownells to cast my FAL chamber.

Finally, I will pull some bullets out of the RG88 brass tonight and measure the case length and compare it to a standard.

Starting to sound as if my chamber is cut too short in the neck area, or, the neck is somehow too large to allow proper sealing of the neck when firing, or, the ammo is suspect.

We shall see!

Thanks so much.

Bob

[Rifle_Guy]

Chamber casting metal is avilable from Brownells and doesn't cost much. All you need in addition is a good micrometer. I think that I wuould want a cast if this keeps up with comercial ammo.

[Grinder]

Bob, just a heads up on the RCBS gage. I use mine alot and have found that ANY extractor or ejector damage on the base will give you false readings. Most of my FALs will pull the rim .005-.010 on the extractor side of the brass when set at a normal 4-5 gas setting. I usually check my brass after using the "G" setting and manually extracting
the case. I have found most neck splits to be bad brass. Good luck

[Bob Bishop]

Grinder and all,

Thanks so very much for all the advice....I am going out this weekend to shoot both US-made commercial .308 ammo and the RG milsurp cartridges.

I totally cleaned up the chamber of the FAL last night and it is absolutely spotless. Also, I slightly polished out the rough area in the mouth to the chamber which was definitely rough from the sandblasting it received when being parked last month. It is now smooth and the hard chrome lining has an even color throughout. Nothing is worn through to the base steel.

Close visual inspection revealed nothing amiss except for some slight tool chattering marks where the chamber reamer cut the shoulder of the chamber. These marks were the same depth and location as those of a Belgian 50.00 I have...so those do not worry me. Also, the neck/throat all looked fine with nothing visibly out of round.

Just to be sure, I dikem blued a fresh/unshot RG cartridge in which I had pulled the bullet and powder. This was then carefully inserted into the cleaned chamber and then the bolt was pushed forward to check for any rubbing or interference. Headspace was perfect as it took a slight thumb pressure to get the bolt to drop into battery. I then reciprocated the bolt a few times by hand to ensure the blued cartridge would contact any high spots in the chamber.

The case was then carefully extracted and then examined to see where the blue had been worn off. The mouth and neck of the case were untouched while there was a fine even wear line around the circumference of the case at the place where the shoulder begins. So, this should mean that the mouth and neck are not being pinched by a too-short chamber.

The headspace was checked one last time with the Forster GO/NO GO gages and once again it came our right on the dime. The GO closed with no problem and the NO GO would not even come close to locking up.

Thinking this through, I think Grinder's comment about using the RCBS case gage is dead on. I had not even considered the fact that the extractor would slightly deform the case during the violent extraction process (particularly if the case was hanging up slightly on the rough chamber) and probably give a false "excessive" headspace reading. My next shots will be made with the gas plug in the "G" position so that extractor does not deform the case at all. This ought to give a true reading.

My current thoughts are that I probably had a heavy coating of BreakFree CLP in the bore and chamber which I had forgotten to clean out, a rough chamber mouth which could slightly hang on to the ejecting case, and a misinterpretation of the RCBS case gage. Plus, with all this going on, the first shot with the split case just might have happened anyway.

Throw all this together with a FAL being shot for the first time by someone (me) who had just built one for the first time and you have a recipe for worry.

I will let you all know next week what happens.

Bob

[scattergun]

Try different ammo. I had a .303 British that split almost every case neck on 2 boxes of Norma ammo, but when I changed to some Remington, the problem disappeared.