Reloading - FL sizing die setup

[DingoDeerHunter]

Hi all,

A little advice needed if you can assist.

I have 3 different types of good quality brass for reloading, All have been once fired (were high quality factory ammo). As I understand the process, I get a baseline headspace from the fired brass and set the sizing die bump it 1-2 thou. My question is, will I need to do this exercise for each different type of brass or will the same die setting apply for all of them?

Thanks

[tachyon]

The answer is "It depends" because different cases will have different neck shoulder hardness and spring back when sized.

If you measure you will probably find a 1-2 thou difference between the current shoulder position of your different brass (pre-sizing) but if you select the longest base to shoulder case and bump that 2 thou it will probably be ok - simply measure to see.

After 1 firing cases are not quite fully fire formed to the chamber, so a 2 thou bump is more like 4 or more thou ie more than you think and more than you need.

If you are looking for long range accuracy you should not be mixing cases as the internal case volume of ADI < Lapua < Winchester which means different pressures and velocities with the same charge.

[fapope]

For information: This method of case sizing was espoused by Bart Bobbit from testing done back in the 1960's. Here is the link to his original article which is almost essential reading to anyone who reloads. I try to keep my brass within 1thou or less from FL sizing. Bart used the RCBS Precision Mic ($128) (Expensive for what you get) which although slow gives absolutely repeatable measurements every time. Hornady do a kit for use with calipers which I am a bit indifferent to. Wilson have recently introduced their own micrometer kit "Case Gauge Depth Micrometer " ($169) which also need the Brass Case Gauge ($74). The Wilson kit is my favourite and BRT stock them.

As per the above reader. Different case brands and or batches will give varying case volumes and neck tensions and therefore pressures. This will significantly enlarge groups for precision shooting. Ideally I like to start with at least 120 cases from the same batch. About ten can easily be be eliminated for weight and neck thickness variation. This leaves me 100 cases plus ten spares for that particular barrel.

https://yarchive.net/gun/ammo/precision_resizing.html

https://www.brtshooterssupply.com.au/pr ... icrometer/

[Rich4]

I’ve also found annealing to be helpful in getting consistent sizing results, especially if you have mixed brass, definitely segregate at least brand for consistency of internal volume (still not appropriate for serious Fclass) but for a precision bolt action .002” less than actual headspace measurement (not fired brass)would be a good target. I have the Hornady comparator and find it very good, but extremely sensitive to technique.