20 Practical Dies & Headspacing Question

[hogpatrol]

So tell me this given i'm kinda new to this advanced reloading... how do I measure that? Measure the OD of the brass after sizing? ID after sizing? Take the OD before sizing subtract out the .204 bullet size? whats the best formula for determining the best bushing to order?

Brass thickness x 2 + .204 - desired neck tension, e.g. .001, .002 etc.
Say your brass neck is .013 and you want .002 neck tension.
(.013 x 2) + .204 - .002 = .228 bushing.

 

[jpx2rk]

I use a .226 bushing for all of the different headstamps I use, (LC, Win, GFL, Frontier), no significant different in group size. Powder charge may be .1 grains +/- depending on the headstamp.

 

[TheCZKid]

I have an AR 20 Practical, and with the bolt slamming forward it needs a bit more neck tension to keep the bullet from sliding forward into the lands when it cycles.
With LC brass and .013 neck thickness, I use a .225 bushing. If I skim turn the necks, I use a .224 bushing. Using a .226 bushing in my AR, the bullet was sliding forward and jamming into the lands... took me a while to realize that was happening, so all my seating depth tests meant nothing until I increased neck tension! Now I have the bullet actually stay where I intend it to.
I also found some bullets are actually slightly different diameters. Hornady V-max in 32 is .2040" OD, and 40 V-max is .2035" OD, so that was kinda odd to find out.