I will readily admit to being new to the world of precision reloading and that I've come to realize there are details for which I didn't even know I had to account. This one, however, even being as scrupulous as I can, has me entirely stumped.
I've been loading for my AR-15 and since I can't (or don't know how to) do much to control the bullet's jump into the lands I've been focusing on velocity and neck tension. So I have this lot of remington .223 brass, once fired through my rifle, and I noticed that the neck thickness varied from 0.009" to 0.012" and decided to turn them down to 0.010". (Something about cutting less than that strikes me as simply too thin) When I started loading the first few rounds to do testing I noticed I was getting quite a bit of runout, upwards of 0.010", and since I'm using a wilson inline seater I figured it had to come from somewhere in my brass prep. So I took a few sacrificial lambs and meticulously measured and prepped them.
My routine is to run them through a full length die without the decapping stem, then over an expander mandrel, then turn them down. Measuring fired, sized, and expanded cases I found generally 0.001" in the neck, shoulder, and body in all cases at each stage. I thought it a little strange that the neck showed so little after being run over the mandrel since I figured that would push the thickness variance to the outside. So then I turned them down and found that the runout had jumped from 0.001" to as much as 0.004". Through trial and error I found that cutting too far into the shoulder caused runout, so I try to cut it as little as possible, but I also noticed that I didn't have to be in the shoulder, and just approaching it would increase runout.
At this point I thought I might just have a junk lot of brass, but decided to give one more idea a shot, and prepped some brass just the same save that I didn't turn them. I then loaded some bullets in these and lo and behold these were so straight my gauge could barely measure the runout.
So what's the deal here? Is there something about my prep routine that's causing this runout? Or is it simply inherent in the brass? I could avoid cutting anywhere near the shoulder, but then what to do about donuts and precisely controlling neck tension? Should I just forget about turning altogether? If I had to guess I'd say it has something do with the expanding step, but at this point I'm about to resort to just spending the money on higher quality brass, or even neck reaming. Thanks for putting up with this longish post and any ideas are absolutely appreciated.
I've been loading for my AR-15 and since I can't (or don't know how to) do much to control the bullet's jump into the lands I've been focusing on velocity and neck tension. So I have this lot of remington .223 brass, once fired through my rifle, and I noticed that the neck thickness varied from 0.009" to 0.012" and decided to turn them down to 0.010". (Something about cutting less than that strikes me as simply too thin) When I started loading the first few rounds to do testing I noticed I was getting quite a bit of runout, upwards of 0.010", and since I'm using a wilson inline seater I figured it had to come from somewhere in my brass prep. So I took a few sacrificial lambs and meticulously measured and prepped them.
My routine is to run them through a full length die without the decapping stem, then over an expander mandrel, then turn them down. Measuring fired, sized, and expanded cases I found generally 0.001" in the neck, shoulder, and body in all cases at each stage. I thought it a little strange that the neck showed so little after being run over the mandrel since I figured that would push the thickness variance to the outside. So then I turned them down and found that the runout had jumped from 0.001" to as much as 0.004". Through trial and error I found that cutting too far into the shoulder caused runout, so I try to cut it as little as possible, but I also noticed that I didn't have to be in the shoulder, and just approaching it would increase runout.
At this point I thought I might just have a junk lot of brass, but decided to give one more idea a shot, and prepped some brass just the same save that I didn't turn them. I then loaded some bullets in these and lo and behold these were so straight my gauge could barely measure the runout.
So what's the deal here? Is there something about my prep routine that's causing this runout? Or is it simply inherent in the brass? I could avoid cutting anywhere near the shoulder, but then what to do about donuts and precisely controlling neck tension? Should I just forget about turning altogether? If I had to guess I'd say it has something do with the expanding step, but at this point I'm about to resort to just spending the money on higher quality brass, or even neck reaming. Thanks for putting up with this longish post and any ideas are absolutely appreciated.
