Headspaace quandry

[Xring1shot]

I recently had a ruger #1 re-barrelled from a 300 Weatherby to a 300 WSM. The barrel is a Shilen supere match grade, 26" length.

My dillema is that when I measure the headspace of a fired case, the length mics out to 1.740". The factory new brass that I use (Remington and Winchester) measurement to the datum line is 1.738". The result is that the cases strretch appreciably when fired the first time. Will neck sizing help prolong case life or is some barrel work in order, ie; have it shortened minutely?

Please advise. ??? ???

 

[infantrytrophy]

Did I read your numbers right? The shoulder is expanded forward by only .002"? (Actually, this might be .003", with springback of .001").

This is miniscule. When I make similar measurements of my new cases and fired brass in several AR's and a .223 bolt gun, the case shoulders are blown forward by anywhere from .004" to .008" (difference between new brass and fired brass).

This is fine. As long as you size the fired cases so the the shoulder is bumped back by .002 or less, you should be fine. The brass manufacturers and rifle manufacturers always want to maintain clearance between the shoulder of the case and shoulder of the chamber. If not, the bolt would either close hard or not close at all. You have to allow for variance in the brass cases and dirt/carbon in the chamber.

For a bolt gun or a falling block like the Ruger #1, you need less clearance than for a semi-automatic (like an AR). Even so, I wouldn't think that .002" is excessive at all. In fact, it might be on the small side.

I'm no expert, but I have measured a lot of new and fired cases. Your situation is about the smallest difference that I have seen (or heard of), other than custom benchrest rifles.

Randy

 

[Steve Blair]

Infantrytrophy is correct. Your headspace is set correctly to minimum or near-minimum. This is about the same as the match rifle that Borden barreled for me.

 

[mkihne]

Many cartridges are fire formed(ie 6br to 6brx) and move the "headspace" forward 0.01 and even more with some wildcats. You are essentially "fire forming" your initial cases. With bolt guns, you should strive for about 1 to 1.5 thou setback of your shoulder measuring from base or belt, whatever your cartridge. This should prolong life of your cases substantially.

 

[Kenny474]

Since you have a falling block that lacks the extraction power of a bolt gun, you may want to full length size so as to avoid stuck cases or difficult extraction.

 

[mkihne]

Since you have a falling block that lacks the extraction power of a bolt gun, you may want to full length size so as to avoid stuck cases or difficult extraction.

Good point Kenny, I failed to note the rifle. Full lenght sizing is likely the way to go. We do that even with our bench rest rifles. Just be sure to pay attention to the bump of the headspace and keep it less than 1.5-2 thou. Some sizing or sticking issues could persist as I am assuming a SAMMI spec chamber and not tight chamber. If sticky cases persist, you may have a minimum spec chamber and might benefit from a custom die. Your gunsmith that chambered the barrel should know, however.

 

[Xring1shot]

I much appreciate the posts in response to my first post. I posted some bogus information. The following numbers are the correct ones.

The new brass that I measured to the datum line are as follows:
Winchester - 1.731"
Remington - 1.726"

The average of the seven fired cases from the Ruger #1 is as follows:

Winchester - 1.7405"
This give a stretch of about 0.009" for the first firing. Will this amount of stretch precipitate head separation? Will I be able to have decent brass life for reloading more that one time? I need some advice. :-\ :-\

 

[watercam]

Cheese and rice. Set your sizing dies to push your shoulder back .002-.003" and be happy.

 

[fdshuster]

Adjust your sizing die so you get the same headspace as fired, or .002"/.003" shorter. The Hornady chamber over-all-length gauge will give you the proper, accurate headspace dimension. I have a Shilen barreled Ruger #1 and it's fine using the above headspace criteria. Brass life is every bit as good as with my custom built bolt guns. New, unfired factory brass is always minimal dimensioned so it's guaranteed to fit in all chambers.