Author Topic: excesive headspace (Read 669 times)

EdSmith · « **on:** June 19, 2004, 09:01:42 PM »

what kind of problems will excesive headspace cause ? thanks ahead of time

John Traveler · « **Reply #1 on:** June 19, 2004, 09:37:00 PM »

Headspace is defined in various ways, but is usually accepted as chamber and cartridge dimensions that are mutually compatible and therefore properly support the cartridge case when it is fired. "Minimum", "Maximum", "GO", and "NO GO" gages are used by manufacturer's and gunsmiths to to measure headspace. The military calls max the "field gage" because it quickly determines serviceability.

Excessive headspace can be caused by either a gun or ammo defect or BOTH.

Excessive headspace is a matter of degree (It is usually, but incorrectly called "headspace") It can do several things depending on how excessive it is:

1. minor excess (a couple or a few thousandths of an inch) is usually not serious or even noticed in normal use. Case tend to stretch more. Many rifles and handguns have this and the owners don't even know it. Measure with gages will show this. It may show as a minor loss of accuracy in very accurate rifles.

2. greater excess (several thousandths of an inch) and cartridge case life is much shorter. The case is not properly supported on firing, and stretches excessively, causing it to fail near the head or body after a few uses. Accuracy is usually affected. Continued firing is not recommended.

3. GREATLY excessive (probably 10 or more thousandths of an inch) makes the weapon unsafe to fire. The case is likely to separate, cause breech gas leakage or complete case failure, endandering shooter and gun. DO NOT USE THE GUN!!!

EdSmith · « **Reply #2 on:** June 20, 2004, 05:38:42 PM »

thanks,john. I know excessive headspace is bad,but I was'nt really sure what it would do. ed

gunnut69 · « **Reply #3 on:** June 21, 2004, 09:49:03 AM »

Headspace is a valid term. It denotes the measurement of a chamber from the datum line(the point where the cartridge is stopped by the chamber) and the face of the bolt. As in most things mechanical there are tollerances(+ or -). the datum line on most rimless rounds is located at midpoint on the shoulder of the cartridge case, on rimmed rounds it's the front of the rim recess and on belted rounds it is the front of the belt relief cut. No excess headspace is 'good'. So headspace is a chamber condition, not a case condition. We may create a headspace problem by altering the case length while the headspace for that rifle remains perfect. There is also the situation common with the belted cases. The headspace(measured from boltface to front of belt recess) is perfect but the shoulder on the case is too far from the shoulder of the chamber. This causes the case to stretch and fill the chamber. If the should of the case is pushed back to where it was in the resizing operation, the case will fail. Sometimes they fail in as few as 3 firings. There are only 3 headspace guages in common use. 'No Go' (bolt should not close on this guage), 'Go' (bolt should close with this guage in chamber), and field. The field guage represents the point at which the cloing of the bolt would indicate that there is an excellant chance the case would rupture if the weapon is fired..

Iowegan · « **Reply #4 on:** June 21, 2004, 10:21:24 AM »

Gunnut, I totally agree with your post. There is one thing that you are probably not aware of. I manufacture bullet seating depth gauges, case length gauges and soon will be making headspace gauges. I am waiting for my patent to come through on the new adjustable headspace gauge. Much like the go no-go or field gauges, it looks like a cartridge. The difference is, mine is adjustable. The gauge is adjusted to minimum length then chambered. If the bolt closes normally, then the gauge is removed and adjusted a few thousandths longer. This process is repeated until the bolt won't close properly, then backed off. When finished, the gauge will be adjusted to the exact headspace dimension of the chamber. The gauge can then be measured and sizer dies adjusted for exact fit. It is premarked for SAAMI specs so it can be used for installing new barrels or reaming chambers. It will be available in most cartridges to include rimmed and belted cases.

Thomas Krupinski · « **Reply #5 on:** June 21, 2004, 11:30:40 AM »

Sounds pretty good to me, I would sure be interested in getting one when they are available.

PA-Joe · « **Reply #6 on:** June 21, 2004, 11:43:24 AM »

Now that you know what it is, how are you going to correct it? One way is to neck size your brass only. Another is to sixe without setting the shoulders back.

Iowegan · « **Reply #7 on:** June 21, 2004, 06:29:11 PM »

If your headspace is slightly excessive (up to .010 or so) the brass case will fireform without head case separation. If you know the chamber dimensions, you can back your sizing die off so it doesn't keep pushing the shoulder back. This will always result in better accuracy and extended case life. I recommend using a Wilson case gauge in conjunction with the adjustable headspace gauge. That way you can drop the preadjusted headspace gauge in the Wilson case gauge, then adjust your sizing die until the brass cases fit the Wilson exactly the same. Doesn't even require a caliper. Actually, a few thousandths of headspace is best. If the cases fit too tight in the chamber, you will have fun trying to seat the bolt.

gunnut69 · « **Reply #8 on:** June 22, 2004, 06:39:48 AM »

Iowegan! One gauge replacing three, a great idea! I have seen adjustable guages before but they were cumbersome at best. Most smiths don't use field guages. The go guage-no go guage, will get you a very functional rifle... Your adjustable guage would give a lot of flexibility to the gunsmith... Actually you can't fix the problem by altering the cases. The measurement is of the chamber not the case. You can adapt and survive by modifying the case but what you are doing is dangerous. If there is a headspace problem it is there for some reason. With mauser rifles there is a likelyhood of setback. Also called imprinting it occurs when the locking lugs create dents in their recesses in the receiver. Usually caaused by over pressure loads, there is no real fix other than replacement. Modifying the cases to adapt will just keep hammering at the 'dent' in the locking abutment, caausing further damage.. It is possible to 'wear' the locking mechanism into creating a headspace problem but it is a very unlikely most bolt actions and is uncommon in most other action types.. The process you described is very appropriate in rimmed and belted cases where the nature of the headspace measurement doesn't take into consideration the measurement from the shoulder to the bolt face. I've some 300 WinMag cases that have been reloaded by setting the sizer to just touch but not move the shoulder for more than 7 loadings. I started using them in the mid 70's and they are still going strong. If you believe you have a rifle with a real heaadspace problem I strongly reccomend you take it to a smith and find out why?!!

Iowegan · « **Reply #9 on:** June 22, 2004, 08:18:35 AM »

Gunnut69, I wish all gunsmiths were as knowledgable as you. Many don't have a clue what excessive headspace is or how dangerous it can be. I've been a gunsmith since 1971 and did a lot of rebarreling, rechambering, and repairs on rifles. Getting the headspace right can be quite a trick, especially when barrels have sights installed. I kept the Clymer company in business buying chamber reamers and go no-go gauges.

Even though altering the brass does not "fix" the headspace problem, it does allow the owner to safely use the rifle without costly barrel work. I've used .015 as the max allowable headspace that can be dealt with by altering the cases. Any more than that would require barrel work.

Here's the technique I developed many years ago. It works well although quite a hassle. Buy new cases. Stand the brass up in a cake pan and put them in an oven preheated to 500 deg for 5 minutes. Immediately dump the hot brass in a bucket of cold water. This will anneal the entire case making the brass soft. Dry the cases then load with 6 grains of Unique (308 sized case) and cheap bullets. Go to the range and fire all the cases. This light but fast burning load will fire form the soft cases without fear of case separation. Back at the reloading bench, neck size or full length resize without setting the shoulder back then load your "normal" powder charge and bullets. Future loads require using the same brass with the same sizing technique. This "work around" improves accuracy considerably and makes the cases last just as long as standard cases in a rifle without a headspace problem and is safe. I would not recommend this procedure for guns with problems like the Mauser you mentioned.

It's amazing what the rifle manufacturers allow to escape from the factory. I've tested several hundred rifles in the past year while "tweaking" the function of my new headspace gauge. The two worst rifles were both Remingtons. One brand new 700 BDL in 30-'06 had .024" headspace. I talked my dealer friend into taking it to the range for test firing. I predicted case head separation and sure enough, the first round fired had separation with factory ammo. Another 700 ADL in 223 Rem measured .004 short. We couldn't even get a factory round to chamber without strong force on the bolt. Most of the rifles tested at .003 - .005. My proto type headspace gauges are in 223 Rem, 7mm-08, 308 Win, and 30-'06 so I couldn't test all calibers. I did find a dozen or so in various brands that were pushing .010. 30-'06 had the most variation and 7mm-08 had the least.

gunnut69 · « **Reply #10 on:** June 22, 2004, 08:39:13 PM »

I must agree about the level of quality controll. I think the decline started when the factories quit test firing the rifles before they left the factory.. A dear friend runs a local gunshop and he had a new M700 BDL come back a couple years ago. When they cut the chamber a saving left a ring around the chamber. The bolt handle had to be hammered open the remove a fired case which then showed a bright ring located a bit above the expansion ring.. A friend bought a new 223 in a BDL standard weight barrel for coyote hunting. Found the rifle had a sear return spring in the ejector(much too short, no pressure of the ejector plunger) and the barrel had no crown. It still showed the lathe cut off tool marks!! As for as the reloading fix I should have been clearer. It will work but in the casehardened actions at least it may continue to deteriorate.. I once had a shop try and sell me a beutiful Mauser Sporter with a ribbed barrel in an ultralight format. Probably set up as a chamios riflle but it had a quirk..about 1 in 3 cases would seperate when fired(new factory ammo). I told the 'gunsmith' running the shop he should be horse whipped for selling (or trying to) a dangerous piece like that and left never to return... I fire form cases in a similar manor. A light charge of shotgun powder, then top the case with corn meal. I sometimes seal the mouth with a bit of wax to hold everything in place... These loads also do a creditable job of cleaning/polishing the bore. I suppose one could use cream of wheat or some such but I've usually got corn meal in the cupboard. Good luck with the heaadspace gauges, we'll have to talk about them in more depth at a later date.. Be certain to let us know when they become available and their cost. Do they come with a device to define the datum line for easy measurement?? Perhaps a size designed to measure the shoulder to boltface measurement on the belted mags. Would make setting the sizer a much easier task...