I've got a 300 Win in a 700 that, like many rifles chambered for belted cartridges, has a chamber so long that the first firing leaves an incipient separation at the base of each case. I don't shoot this particular gun much, except on hunting trips, so that I've been getting by with handloads in fresh brass.

But I've been wondering about the best way to create reloadable brass. I've tried seating the bullet so as to engage the lands - this didn't help. I've read about using a .338 expander to open up the neck and then sizing down to a tough-to-close-the-bolt fit. Would this likely work? If so, what sort of load should I use to fireform? Any other ideas?

BTW, this is a KSS model. I've got three other regular production M-700 300 Mags (kinda like these ballistics) that have tighter chambers. Go figure.

Thanks for your help.

Sam

Yes i`ll suppose it works.

A ordinary training load.

Kimmo

Many factory chambers have a gap of between .015" and .024" between the shoulder of new brass and the chamber but I've never seen a separation of new brass at first firing, even with the larger gaps. If it were my gun I'd have it checked by a competent gunsmith and maybe have it rechambered with a significantly shorter chamber. Yours may have a much larger gap that what is typical.

You could do two things to try to fireform new brass to try to eliminate that initial stretch. First, create the false shoulder as suggested, then size the neck partially for that tight fit. Next, fireform without a bullet. Use a fast pistol powder like Unique. Maybe 30-35g. You'll have to experiment a bit on the appropriate charge for your gun. Try 35g and stuff the case with toilet paper or some other inert filler. If that doesn't quite form the case, add powder until it forms well. Then neck size and proceed to load with normal loads.

I tried all kinds of fireforming and was never successful at eliminating that initial stretch using bullets by any of a number of methods, including the false shoulder and seating bullets in the lands.

Thanks guys.

Bob, I just measured some hulls with a Precision-Mic and I'm getting .026" stretch, just a bit on the large side. I haven't actually had even a partial separation on first firing, but my first attempt at reloading these hulls was met with one partial split, alot of bright rings. Needless to say, I've never had this problem with a non-belted number.

Interestingly, most of the .026" comes from new hulls that are .023" short of the min. ANSI spec. of 2.2791". This means that the chamber is only blowing them to 2.282", well under the 2.2891" ANSI maximum. I had no idea factory ammo and new hulls were so undersized. Don't you just love belted cases. Anyway, sounds like I will go ahead with the fireforming approach.

Thanks,

Sam

I may have misunderstood your initial post. Maybe you're not as bad off as I imagined. Your post referred to case separation at first firing yet you mention only splitting one case.

After that initial big stretch I'm usually able to get anywhere from 10 to 15 reloads on belted brass before the telltale signs of separation start showing. If you have a split in the case on a first reload, that's not too bad depending on where it is. If the "split" in the case is near the base, that IS separation. If in the neck, while not normal, it's not a problem. It would just indicate you might need to anneal.

It's probably not worth it to you but you could form your brass from a longer case, such as a 375. What I've done to eliminate this problem in 338 Win Mag, is to buy 358 Norma Mag brass and size it down to give .001"-.002" shoulder clearance. In the first lot on which I tried this I have 18 reloads without any sign of separation. It's that initial stretch that reduces the life of belted brass. Even lots of brass giving .024" shoulder clearance when new, have been reloaded multiple times without problem, but with that big a stretch, 10 reloads is about max, providing you mostly neck size.

Bob,

Sorry for confusing things. By "incipient separation" I meant a bright ring on the outside, and a thinning that could be felt on the inside of the case. I'll try necking brass up first. .375 seems a long way to go to .308. I suppose if I had some 8MM Mag brass that would work, too. But I've got so much .300 brass - hate to not use it. I rarely get more than 5 reloads in any of my .300s - can't imagine 18!

Thanks again,

Sam

Sam~
That "bright ring" is probably what is referred to by many as the "pressure ring" and has NOTHING to do with separation. When your case starts separating, besides the ridge you feel on the inside, you will see a frosty ring starting at the junction of the web and the body. THAT'S the major sign of incipient head separation. At that point, destroy and dump the brass. What you are seeing, I believe, is normal and is the last spot the case expands either to the chamber or the die. All my 300 brass, and some other belted cases, look like what you describe. The only thing which would concern me would be the ridge and thinning you are noticing, and the frosty ring near the base.

Even with that much initial stretch you should be able to get more than 5 reloads. After fireforming try either neck sizing only, or partial full sizing setting the shoulder back no more than .002". If you full size more than that you are exacerbating the stretch in the body. I get 10 reloads from my 300 even though that thinning you are noticing, is apparent after the fireforming.

There's a big difference between losing cases right after fireforming, which I understood, and getting 5 reloads. That's not too shabby. Many who full size improperly get no more than 3 or 4 reloads. You should be able to do a bit better than 5. Good luck.

SAM,
Easiest way I know of to cure this problem is to replace the expander button with a 8mm expander. I'd suggest that you have the expander adjusted as close to the shell holder as possible without the risk of bottoming out in the case. Donot run the cases up into the die, but just over the expander button. After all the necks have been expanded, replace the 8mm expander with the 30 cal expander. Adjust the sizing die so a sized case will chamber with pressure. I prefer to fire form cases with a 180 grain bullet with a middle of the book load. With a oversized chamber, neck sizing is the way to go. If you have a RCBS precision mic, use it to adjust your full length sizing die to the headspace of your chamber just in case the cases must be full length resized in order to chamber correctly. One fringe benefit to this method is that the case head stamp will be for your rifle. Unlike mine which read .280 Rem but have been converted to .270 and .30-06. I hope that this is of some help. Good luck.

SAM,
I hate getting old, my memory has gone to some place, I forget just where. If you do use the method I suggested, use a tapered expander button. Sinclair has some good ones. I chucked the small end in a drill and used 2000 grit wet/dry emery cloth on the taper. Polished it up like glass. Good luck.

Sam,

Welcome to the forums.

We found we can get over thios problem with rifles we chamber ourselves.

The trick is not to use the GO gage at all, but to cut the chamber slightly short. Just as far as a new case will chamber, but the GO gage will not.

We have built a number of rifles this way, and we never had any problems with chambering any factory ammo in them, and the brass lasts a lot longer than in factory rifles.

Thanks all.

Bob, possibly I'm just more nervous about those inside ridges than I need be. I have been partial sizing to snug bolt closure. I'd still feel better if I could stop that initial stretch by fireforming.

BigBob, I was thinking .338 only because I happen to have .338 dies, but will pick up a tapered 8mm expander if I encounter difficulty with the .338 button.

Saeed, thanks, and I certainly wish the factories would take heed. The tightest 300 (a Sendero) I own would barely close on go, but that chamber is perfect is far as I'm concerned. Case stretch is pretty much non-existent. If I ever have the opportunity to have one of these things rechambered this is one specification to which I'll pay close attention.

Thanks again. This is a great site.

Sam

[ 07-05-2002, 13:38: Message edited by: Samuel_Hoggson ]

Samuel,
Be that as it may and perhaps you can get it done, but the proper fix is to take a turn off the barrel and rechamber with a proper chamber.