300 AAC Case Neck Tension

[DougGuy]

What would be an acceptable neck tension? I am loading j-words just trying to duplicate factory 220gr subs. After sizing once fired brass, the ID of the case is .305" and the 220gr HPBT bullet is .308" would this work without buckling the case or would you suggest a bit less difference between the two?

[Gtek]

300 AAC, Lions and Tigers and Bears, Oh My! Factory brass, Fat necked military brass, loaded OD neck/chamber dimensions, fired case neck ID? HPBT condom in a 0.305" neck ID, snug but I would pop them. You been on here long enough to know the .001"-.002" thing?

[M-Tecs]

For jacketed .003" is not an issue and on the lower size for the interference fit. Double that amount is not unusual.

[DougGuy]

300 AAC, You been on here long enough to know the .001"-.002" thing?

All my fitment experience has dealt with revolver cylinder throats, boolit diameters, throats and freebore in autoloaders, but I have not been loading for a bottleneck cartridge in quite a few years, so please enlighten me on the .001"-.002" thing.

Since I got some smooth turrets and got the press working very smoothly, I have been tweaking the dies, assembling them to the turrets by caliber, etc. Cleaning and de-burring the new ones, adjusting them using spent cases, machining and modding them as needed.

Lee doesn't make a powder through die for 300 AAC so I went back a few years and read some posts to see what others were using, it looked like the 30 Carbine M1 powder die was the closest fit so I got one in the mail today from ebay.

The die body is .355" and I bored it to .375" to fit the 300 AAC case and the nose on the expander plug was short, and too much flare angle so that got machined to reach a little farther down the neck, and put barely enough flare on the case to feel it with your fingers.

It bumped the case mouth ID from .3045" left by the decapping/resizing die to .306" so I am at .002" neck tension against the .308" bullet so I should be good to go.

The Lee 300 AAC die set comes with a collet crimp, and I modded it by shortening the nose of the collet to narrow the crimp band to .045" wide from the factory .125" and shortened the bottom of the collet so it puts the crimp band even with the case mouth. Same exact mod I do for the 44m and 45 Colt collet crimp dies.

[popper]

My Lee die is at 305, works fine for jacketed in AR BOs.

[barrabruce]

My Lyman necks down to 0.305"
What a pain for lead.
I made a Lyman type M die with step to flare the case neck slightly as well.
Could make one with a hole in it though.
I haven’t shot full length gas checks for years but couple of thou neck tension and just touching the lands or a bit off up to 20 thou is the norm. Chasing the lands can up the pressure so work up your loads if you are going to do that.
Also you need clearance for bullet release.
Jacketed has no tolerance for that like cast.