Acceptable tolerances for COAL with this setup.

[YerrowSniper]

Ok, this is my first dabble in precision loading.

Here is the process and setup:

1. I am using all new 308 Hornady match brass, all from the same lot, run them under a Lee Colette die with an RCBS RockChucker so that all mouths are uniform.
I use a tiny amount of Unique lube every3 or so cases

2. After that, I use the Hornady Brass Prep Center for the chamfer and deburr. Prime them all with the Lee bench primer.

3. I charge the cases with the RCBS ChargeMaster.

4. I seat some 308 Hornady 168 BTHP and 308 Hornady 178 ELD Match with a target COAL of 2.830"
The die that I use is the Forster Ultra Micro, I set it so that it touches the shell holder and lock it up with the Hornady LNL bushing and ring.

When I measure the COAL I get +/- 5 Thou, is this acceptable?
What additional step can I take to get it down to +/- 1 Thou?

Now, I am not measuring it with a comparator or anything like that just put the round in a quality caliper and I try to center everything as best I can.
I am sure if, in the grand scheme of things it really matters but at this stage, it is more of a hobby for me, I am trying to get it as consistent as possible.

What do you guys think?

 

[want2learn]

i would imagine that a .005 inch difference in cartridge overall length in either direction is not too bad at all

from a purely academic perspective i wonder where most of the variability comes from....length of the projectiles, seating die depth consistency?

i'm not sure exactly to what degree of accuracy i can trust my calipers but i went ahead and measured 7 rounds of brand new in box factory loaded Lapua .222 Remington ammunition. This round has proven both very consistent as well as accurate in my rifle. The COAL demonstrated a spread of of .006 inch length

 

[TheOfficeT-Rex]

That's acceptable. Look at the meplat (tips) of the BTHP. Notice how they're all slightly different? There's your variation. ETA or the hornady LNL Bushing. I'm not sure how stable those are.

Check it at the ogive with a comparitor and you'll probably find it much closer. (I like SACs, despite the cost)