I have a question regarding my small base sizing die for my pre-64, .270 Win. While at the range today, I had a cartridge case almost rupture about 7/16" from the base. The load was 56.0 grs. of Rl-22, a 150 Partition and Fed. GM-210 -M large rifle, match primers. Bullets were seated to 2.762" to the ogive - about 3.29" OAL. Cases were trimmed to 2.53" after sizing. After firing, I noticed the partial head separation and this was the 3rd shot fired.
The sizing die is an RCBS small base die that I've used for years and is set up to partially full length resize. The cases were FL sized initially and partially full length sized after each firing.
I realize the brass has been over worked but I'm wondering if the small base die worked the brass too much or if this case was a bad one. I'd have to guess these cases have been fired 5-6 times since I don't keep track of that. Do you guys think another sizing die - NOT a SB would be a better alternative? I'd like to continue partially FL sizing if possible. Any ideas?
Thanks to one & all for responses.
Bear in Fairbanks

I use small base on .223, 308 and 30-06. I would use them on more calibers, but there aren’t that many choices. I use them on gas guns that have commercial/match chambers. Specifically match AR’s, match M1a’s, and match Garands. This ensures interchangeability of ammunition between my rifles. I called RCBS and asked what the difference was between SB and standard dies, and was told the basic difference was the SB sized the case head. 0.002†more. I also believe that the SB will set the shoulder back more than a standard die. Standard dies seem to be longer and I have had to remove material from the bottom of these dies to get them to size brass to gauge minimum. My small base dies don’t have this problem: in fact without case gauges it is possible to oversize brass with a small base.

This may be the basis of your problems. Let me recommend a new piece of equipment that you did not mention: case gages. I really like the Wilson type case gage. You size your round and drop it in the gage. This gage measures the distance between shoulder and base. It is a "go" and "no Go" gage. And it is a true measurement, as I have dropped my chamber headspace gages in my wilson gages and found perfect agreement between them.

I recommend reading from this web site:

http://www.realguns.com/Commentary/comar46.htm


The set up instructions given with sizing dies assume a lot of things. And seldom following the instructions do you ever get the brass sized to the correct length. In a few instances I have had to grind material off the bottom of a sizing die to get it to set the case shoulder back enough.

Slamfire:
Thanks for the comments. The article is quite enlightening to me & I've printed it out. I do have a Wilson gage for that rifle and after reading your suggestions, I find that there seems to be quite a bit of slop in a new, sized but unfired case. The fired case doesn't go entirely into the gage - not surprising. Gotta follow this up further.
Thanks again for the help. Take care,
Bear in Fairbanks

quote:

Originally posted by Bear in Fairbanks:
Do you guys think another sizing die - NOT a SB would be a better alternative? .
Bear in Fairbanks

To be honest to you, I don't think anybody can tell you until you quantify how much your current die - in its current setting - will set back the shoulder of a fired case. Ideally, you are looking for .001 - .002" of reduced head-shoulder dimension in your PFL sizing operation.

From how you describe your problem, one would have to suspect that the head-shoulder reduction you get is more than what you want. That would be the classic reason for a case head separation.

We have had quite a few discussions in here, regarding whether it is necessary to quantify what a presumed PFL sizing die set-up will do to your head-shoulder dimension. I happen to belong to the crowd of people who believe this is necessary.

I don't know how your Wilson gauges work, or what kind of measurements they will give you. I use a Stoney Point device for this measurement, and although it is not perfect, I still find it a darn site better than nothing.

Finally, just one last question: other than owning this particular die, are there good reasons why you choose to use a small base die for what is (presumably?) a factory chamber?? Regardless of head-shoulder dimensions, you are bound to work the brass more with the SB die, and that is not normally considered beneficial to case life.

- mike

To put it in plane terms your bumping the shoulder back to far causing a head space problem which is spliting your cases at the base, i'll bet if you look at the cases before you have fired them there will be a line there then after firing the split, sometime this doesn't happen after the first sizing and firing might take 2-3 times through.

H-D:
Good point, I'm gonna look closer at that in the future using the bent piece of wire trick.

MHO:
I bought this set of a number of years ago when I was in a rush to get some cartridges loaded. Those were the only .270 Win. dies the
store had at the time. I noticed the "SB" designation on the box but paid no attention to it at the time. I've got another die on order now.
Thanks for all the comments - they're quite constructive. Bear in Fairbanks

Once you get the sizing die set to just set the shoulder back the prescirbed .001 to .002 your problem will be solved, other than brass does have a limited life. I would think that with "partial full length sizing" that the SB die makes no difference, it does if you full length size. Whether the difference in a SB and conventional full lenght sizing die will effect brass life, is arguable. You would have to find out by taking a reasonable number of cases (maybe 20) and process them in two groups, keeping track of each group and see if either lasts longer. Might be a fun experiment, and would get you a lot of target practice.

A commerical loader friend explained the difference between the SB die and a standard die as the SB die is held to smaller tolerances in manufacturing than the standard die, both being within SAAMI spec. Not that the SB die is manufactured "smaller".

Joe A.

I doubt that the use of a small-base die is the cause of that separation. How do the rest of your cases look? Try the "hooked paperclip" test to see if there's any evidence of any of the others developing a separation. (I would say that unless you have the die screwed down all the way against the shellholder, and are only "partially resizing" your brass, you are NOT SETTING THE SHOULDERS BACK. Therefore, you are not creating a condition of artificially-produced excessive headspace. If you were, ALL your brass will now begin to show signs of incipient case-head separation. This condition is easy to see/feel!)

BTW, why do you use a small-base die for ammo that will be used in a bolt-action rifle? Especially if you aren't forcing the cases into the die far enough to size them down that much??

Just curious, but I've never found it necessary to use a small-base die for any reloading, even if the ammo is being used in a semi-auto or a Model 99 Savage!

quote:

Originally posted by El Deguello:
Just curious, but I've never found it necessary to use a small-base die for any reloading, even if the ammo is being used in a semi-auto or a Model 99 Savage!

Me too. I don't even own a set and I shoot more than one gas gun.

The only time I need to use a small based sizing die is when I have bought some once fired mill surplus brass and it turns out to have been run through a machinegun.

muck

Most people will never need a small base sizing die. But then, most people have commerical or military barrels on their rifles. Military chambers are huge.

Commerical chambers seem to be built to advoid lawsuits. I have a 308 Ruger M77 Heavy barrel varmit. I have noticed that the Ruger reamer cuts the large neck expansion to a very large diameter. Well it certainly means that no one is going to have a pinched case neck in this rifle.

If you have enough custom barreled rifles, you will find that ammo sized with standard based dies is not going to work.

I am of the opinion that shoulder set back is a more important parameter to worry about than small base dies.