Neck sizing for accuracy???

[kelbro]

Good points made here about the chambers and boltfaces. In a trued chamber/boltface system, the once-fired brass is going to be in a much more concentric state than if fired in a standard mass production chamber. I've seen quite a few egg-shaped chambers and dished boltfaces. Hard to get consistency there.

 

[MCMXI]

Bart has made the comment in the past that even custom chambers are "egg-shaped", which although technically correct as the units of measurement become infinitesimally small, in the real and practical world, tolerances of less than +/- 0.0005" are becoming commonplace in quality machining processes. Tolerances of +/- 0.0001" are commonplace in lapping/honing/polishing processes. In other words, some VERY dimensionally accurate and true chambers are possible such that any angle of rotation of the case in the chamber amounts to the case being in the same position relative to all surfaces in the chamber.

 

[Bart B.]

1858 states:

I've shot the same W-W Super .300 Win Mag cases four times in my "match" rifle now, neck-sized only. The bolt is as easy to open/close as it was for the first firing.

Headspace on belted cases is measured from bolt face to the front of the chamber's belt relief; .220" on all H&H cases. And belted cases don't quite work the same as rimless bottleneck ones I've referred to above. Their shoulder doesn't get slammed into the chamber shoulder by firing pin impact. What you've observed is normal; I've seen it happen before I went to double-body full length sizing for belted cases.

 

[USSR]

I posted a target that I shot last week with 20 rounds shot in 20 minutes at 600 yards in less than ideal conditions by a less than qualified shooter. The deviation of those 20 shots in the vertical direction was 4-1/2" (0.75 MOA) and 18 of them were within 3-1/2" (0.56 MOA). I BET that someone like you or Don could cut that in half using my rifle and my reloads. Those loads consisted of neck-sized Lapua brass and Nosler bullets.

1858,

That's d@mn fine shooting, and personally, I wouldn't take your bet. As you know, we have similar setups (Krieger MTU barrels and Redding Competition Die Sets). While I started out necksizing only, I quickly switched to using the body die AND the necksizing die, essentially FL resizing in two distinct operations. I also only resize about 3/4 of the neck. Very satisfied with the results to date.

Don

 

[Bart B.]

1858, that's excellent grouping. A high standard by any means. However, should you try full length sizing and do it right ending up with 20 to 30 percent better accuracy, I'll not give you a rasberry but instead applause.

 

[something vague]

Bart,

you're def. presistant on the f/l sizing issue compared to neck sizing, so much so that I am going to have to do some testing with it on my own. I will compare to my neck sizing techniques which have really proved to be very effecient and accurate thus far. But I am by no means against trying new things and love trying to tweak things around until my results start to turn the other way, then revert back to where all was well. I am far from an experienced reloader, just someone who has been enjoying the hobby for the last 3 years or so.

Now without having to go back through both these threads, how would you recomend F/L sizing the RIGHT WAY? For the most part I'm shooting .223 out of a bolt. And at the moment I have a RCBS Comp. F/L die.

 

[Bart B.]

Something vague, take your RCBS FL Comp die and get its neck lapped out to 2 to 3 thousandths smaller than a loaded round's neck diameter. It's already about 4 to 5 thousandths, but measuring it with a hole micrometer will tell exactly what it is; you'll need this tool to measure it anyway. How much depends on the actual bullet diameter, neck wall thickness and how springy the brass is. I'd start with only 3 thousandths smaller and if the necks are too tight, lap it out a bit more. Chuck the die base out in a lathe's headstock to do this.

Decap fired brass in another die; a standard seating die works well with the decapping rod in it and backed off 1/4th inch.

Set the FL die in the press such that fired case shoulders are set back no more than 2 thousandths.

After cleaning/tumbling cases, be sure they're lubed uniformly enough so case headspace stays within a 1 thousandths spread. Too much lube and they'll end up too short; too long with insufficient lube.

 

[Bart B.]

1858 says about my references to Sierra:

You always talk about Sierra and what they do, but frankly, I could care less what Sierra does or did 20 years ago. They make very good bullets ... that's it. They're not in the reloading business per se so I look to Redding for guidance.

Sierra loads more bullets in more sizes and weights and shoots them through very accurate test barrels than anyone I can think of. They have been masters in reloading very accurate ammo for many years.

Who has done more reloading for as many calibers and bullet types and weights measuring the results to the nth degree?