neck clearance question

[Bulseyetom]

I just got a wildcat with a .309 neck. I have ordered a bushing die from JLC and while I was waiting for it I thought I would fireform some brass. I necked some cases down from 30 caliber to 28 caliber to form a false shoulder with a 7x57 Mauser sizing die adjusted to give me a crush fit. I then turned most of the cases necks so that when I seated a bullet I was measuring .306 over the pressure ring. I gave it the old creme of wheat treatment and got 20 cases slicker than anything with rounded shoulders but otherwise filled out nicely. I did 10 cases without neck turning to see if it would be easier to turn them after the creme of wheat firing. The jury is still out on which way worked best but I think that neck turning first seemed easier to get a good stopping point. Anyway, I loaded up a series of charges that were in the 48,000-52,000 range according to QuickLoad and shot them yesterday. I lucked out and found a super load right off the bat with a nice 3 round cluster of .431 center to center give or take. I really wanted to take the rifle hunting next week but my 7x57 sizer won't work very good after the case has been blown out as the diameter at the shoulder is now larger than the Mauser case. Thinking I would just size the first 1/4" of the neck so that I would not set the shoulder back, I screwed the die in and smoked the neck to see how much I was sizing. Sometime about then I picked up a bullet and put in the fired case and low and behold, it was a tight fit already. Now from my limited benchrest shooting I know that if you don't have enough neck clearance the case actually does not need to be resized but that was certainly not my intent. I received several fired cases with this rifle and I sent 3 to JLC for the die build and kept 1 for my reference. A bullet falls into this fired case as normal. I broke out the ball micrometer and my neck thickness plus the bullet measures that I should have .003 clearance, just as I measure from my loaded rounds. I checked the other fired case and it has .0035 clearance as best I can measure. Is it because the brass is new that it did not fill out to the chamber at the pressures I think I am at, or am I way lower in pressure? This has me puzzled. I loaded up 20 rounds for my hunt and the bullets are all seating with what feels like the same pressure and as it is a single shot I need not worry about recoil jarring the bullet loose in the magazine. The case is a 30-40 Krag necked to 7mm and blown out resulting in a case capacity of 64.1 grains, a case length of 2.280 after fireforming and trimming, and an oal of 3.24 with a 160 grain Accubond. 47.6 grains of Re-17 is the load I selected as it shot a perfectly round group with absolutely no vertical. What is the obvious answer to why my cases don't need resized even though I measured again and have .306 to .3065 diameter over the pressure ring for a .309 neck? Thanks. Tom

 

[Keith Glasscock]

I have a 308 that I run .003" neck clearance. After firing, I have a neck that will pass the bullet, but just barely. This is with a neck thickness of .012" and freshly annealed brass.

If the brass work hardens much, I can seat a bullet pretty solid in those same cases after firing. My guess is that you have hardened the necks a bit in necking down. Between that and the light pressures of your loads, I suspect that the spring back is enough to make the necks not stay expanded.

Here is what I think, it is worth every penny you spent for it:

If the cases do not need resized after firing, and the accuracy is good enough for your needs, just shoot them, skip the resizing and shoot them again. If the accuracy remains what you need, problem solved.

 

[Bulseyetom]

I loaded up enough with the load that shot so good to go hunting next week and after the hunt I will shoot them and see if they still remain tight. I should have my bushing die in a few weeks so I can set the shoulder back .001 if need be as I start working up to see if I can find the next higher node. Thanks for your thoughts. Tom