Home Forums Reloading Big Game Rifles case dimensions after firing

I've been toying around with a 50 year-old M99 in .300Savage. I didn't check the headspace before firing it like I should have, and had some primers back out on federal factory loads, and winchester cases were well over max length after one firing, so I wonder if I should have. I have gauges on order and will check headdspace before proceeding.<P>But because I wonder about the size of this chamber, and because I am new to handloading, I was wondering how much case expansion I should expect. Unfired federal factory loads are around .465 just ahead of the casehead, but I didn't measure any after the first firing. After full-length resizing and reloading them and firing again, they are .469. Max diameter in the manuals is .471. Is it normal for factory ammo to be so small? Is it normal for this area of the case to expand by .004 in diameter upon firing? Also, is full-length resizing supposed to bring them back down several thousandths under SAAMI? -al

EllieMae -- I am not too sure which dimension you are measuring or with what you are measuring it.<P>The case head and web portion is solid brass and doesn't expand very much and maybe not at all given the 47,000 psi operating pressure of the 300 Savage. If you are measuring the diameter of the case in front of the web, you are measuring the area of the case that is supposed to expand to seal the chamber.<P>I don't know how to explain this exactly, so try and bear with me. The solid web portion of the case extends for some distance up the case from the extraction groove. In front of this you should see an area of the fired case that is definitely larger in diameter. This is normal, and I stongly suspect that this is the diameter you are measuring.<P>If you go out to <A HREF="http://www.ammoloading.com" TARGET=_blank>www.ammoloading.com</A> and click on the Case Condition button and then scroll down to Head Separation, you will see a photograph of an '06 case that shows the normal expansion ring just in front of the solid web.<P>In any event, excess headspace will not result in the case increasing in diameter, but it will result in the case lengthening excessively in its head-to-shoulder dimension (i.e., the headspace dimension). Obviously, if your rifle does have somewhat excessive headspace, it is not enough to cause the head to separate, which is the danger of rifles with excessive headspace.<P>Full length resizing dies will generally not resize the web portion of the case but will resize the expanded portion back to between maximum and minimum cartridge dimensions depending upon the die dimensions and whatever tolerances it might have.<P>If you are taking the case measurements from a loading manual, be aware that these are almost always maximum case dimensions. Factory case dimensions are generally somewhat smaller than the maximum case dimensions.<P>After having written all this, I think you are wise to question the headspace of that rifle. Primers backing out of factory ammunition is an indication that the headspace might be excessive. If it were me, I would take the rifle to a good gunsmith and have it checked over thoroughly.

EllieMae,<P>Those older 99s had a lot of spring in the bolt, they lock at the rear. That might cause the excessive lengthing, but it's more likely the expander ball upon resizing. There isn't much you can do about the former, but Lee's collet dies will go a long way toward solving the latter. Partial sizing can correct headspace problems, if the head doesn't seperate first. Your expansion ring seems within limits. But since you don't want to release all that hot gas inside the action, run one up against a belt sander and see if the brass is migrating from the expansion ring to the neck. That is usually the place it comes from. I once had a .22 High Power, and the difference between the size of the chamber and the size of new brass, was horrendous. The .30-30 bases were larger than the .25-35s but I still had very poor case life. [img]images/icons/frown.gif" border="0[/img]<BR>As for the primers backing out I think the extractor holds the case until it fits the chamber, then the bolt compresses but because the case is stuck to the camber wall the extractor can't hold it up against the bolt face. The primer has to go somewhere. Check out P O Ackley's Handbook. He ran an experiment where he unscrewed the barrel a bit at a time. Fired cartridges at first had flat primers, but as the shoulder got farther from the bolt face they backed out a little more until they blew out. Now that was with a rimmed cartridge but I think the action is similar.

I agree with Slamfire up to a point. It is possible that the expander ball in the resizing die is pulling the case forward as it passes through the neck. An easy fix for this is to clean and lubricate the inside of the case neck.<P>Still, there are no circumstances that I can think of under which the primer should back out of a factory round. That is what makes me supicious that your rifle does have excess headspace. (A low pressure load will also result in a backed out primer, but I seriously doubt that factory ammo will generate pressure that low.)<P>Yeah, the extractor holds the cartridge, but it does not hold it tight against the bolt face. Under ordinary circumstances when the cartridge is fired, the case walls tightly grip the chamber, and the case is forced back against the bolt face.<P>During a brief interval as the pressure builds, the primer will back out a little and then is forced back into its pocket as the pressure forces the cartridge head against the bolt.<P>What I suspect is that the 47,000 psi or less, probably less, of the factory cartridge isn't sufficient to stretch the brass enough to force it tightly against the bolt face. That's why I suspect that your rifle does have somewhat excessive headspace.<P>I strongly recommend that you take the rifle to a gunsmith and have it checked over.

Thanks all, and thanks for the link. I was, in fact, talking about the "expansion ring" - that portion of the case just ahead of the case head. The fired cases taper out (get larger in diameter) from the neck back towards the head, then taper back in very abruptly at the case head. After they've been resized, this "bulge" so to speak becomes very obvious because of the marks left by the resizing die, even though dimensionally they are okay. I had never looked at fired cases that carefully before, and wondered if this was normal, but I answered my own question last night. I dug out some once-fired .30-30 cases and compared it to unfired factory loads. This region of the case expanded about .004 in those as well.<P>As far as headspace is concerned, I suspect that it might be a bit excessive, and will check it. The primers backed out .010 in federal factory loads. After these cases are full-length resized and reloaded, the primers don't back out. This is presumably because they were formed to my chamber at first firing, and the neck is staying put upon resizing. Interestingly, federal cases which had the primers back out during the first firing were all under max length, while winchester cases that didn't have the primers back out, were all at or over max length after the first firing. I suspect the winchester loads were either (1) hotter or (2) smaller or (3) more stretchy somehow (thinner?) and stretched to fill the chamber, while the federals didn't. So in a way, both answers are probably true. Excessive headspace will cause primers to back out, but only if the load is too "cool" to completely stretch the case.<P>Depending on how excessive it is, I wonder how much I can get away with. First of all, word is that nobody around here has the gauges/reamer to work on a .300sav, and it would probably cost me what I paid for the rifle to fix it anyway. Assuming the headspace isn't TOO bad, say, less than .010 too long, several people have suggested I simply keep the resizing to a minimum and live with it, keeping a close eye on my brass and being conservative about what I load. If I can get away with partial resizing and still get them to chamber in this gun, at least for a couple reloads, it seems I should be okay. I know it's always best to have it right, but it also seems that there is a fair bit of leeway that you can use. -al

EllieMae -- The critical dimension as far as headspace is concerned is the head-to-shoulder datum point.<P>You might want to buy the Stoney Point Headspace Gauge. You will need a comparator body (about $15 from Midway) and the appropriate insert (#D for the 300 Savage -- about $7 from Midway). This little tool, in conjuction with your calipers, will allow you to measure quite accurately the "before and after" headspace length of your brass.<P>Partially resizing, or neck sizing if you can get away with it, is always a good idea even if one happens to be shooting a bolt action. It's a trial and error thing, though, to get the FL sizing die adjusted just enough to allow smooth chambering without setting the shoulder back too much. The Stoney Point tool makes this a little easier and a little more precise.

I bought a no-go gauge and it wouldn't chamber. That's a load off. Now I have a new problem with the gun which I posted in Lever Actions. -al