Casing weight tolerances?

prairiedoghunter · August 28, 2011, 02:27 PM

Just started my first batch of .204 ammo, fired some test rounds yesterday with the best group at 1/4moa, second best at about 1/3moa with charges being 25.6gn RL-15 and 27.3gn RL-15 respectivley. All brass used for the test rounds was the same weight. Now heres the question, how much tolerance in weight from shell to shell should be allowed for reloading say 100 or 200 rounds (have 100 to do right now)? I weighed 20 casings, with an average of 102.28gn and a standard deviation of .90. I allowed a tolerance of +- 1gn within the average to sort my brass. These loads are not competition loads and should shoot about 1/2 moa. Is this close enough, or should I sort casings within .5 or .1 gn?

**Unclenick** · August 28, 2011, 03:14 PM

Cartridge brass density is 8.53 gm/cc, according to Matweb. That means 0.853 grains, in identically trimmed and primer pocket uniformed cases, will represent 0.1 grains difference in powder space. Since pressure goes up exponentially with increase in powder charge, this is about like a 0.05 grain charge difference. Not usually a significant error. If you charge cases ±0.1 grains, then figure cases ±1.7 grains are roughly equivalent to that.

243winxb · August 28, 2011, 08:13 PM

Sort new brass by .1gr after fl sizing, trimming, uniforming the flash hole.

August 28, 2011, 02:27 PM	#1
prairiedoghunter Member Join Date: February 14, 2011 Posts: 19	Casing weight tolerances? Just started my first batch of .204 ammo, fired some test rounds yesterday with the best group at 1/4moa, second best at about 1/3moa with charges being 25.6gn RL-15 and 27.3gn RL-15 respectivley. All brass used for the test rounds was the same weight. Now heres the question, how much tolerance in weight from shell to shell should be allowed for reloading say 100 or 200 rounds (have 100 to do right now)? I weighed 20 casings, with an average of 102.28gn and a standard deviation of .90. I allowed a tolerance of +- 1gn within the average to sort my brass. These loads are not competition loads and should shoot about 1/2 moa. Is this close enough, or should I sort casings within .5 or .1 gn?

August 28, 2011, 03:14 PM	#2
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,060	Cartridge brass density is 8.53 gm/cc, according to Matweb. That means 0.853 grains, in identically trimmed and primer pocket uniformed cases, will represent 0.1 grains difference in powder space. Since pressure goes up exponentially with increase in powder charge, this is about like a 0.05 grain charge difference. Not usually a significant error. If you charge cases ±0.1 grains, then figure cases ±1.7 grains are roughly equivalent to that. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

August 28, 2011, 08:13 PM	#3
243winxb Senior Member Join Date: July 26, 2011 Location: USA Posts: 1,730	Sort new brass by .1gr after fl sizing, trimming, uniforming the flash hole.