This post is intended for RECREATIONAL purposes only
I helped a friend sort some mixed-headstamp 6.5mm Creedmoor brass that he had purchased.
Hornady, S&B and Winchester were the high-runners for headstamps.
Aguila and Norma were low-runners and there were the usual onsie-twosies.
I asked if I could weigh a few of each headstamp and my friend was agreeable.
Hornady was the lightest at 157 grains per case (with the primer still in). Then Norma at 160 grains, Winchester at 165.2 grains, S&B at 166.8 grains with Aguila the outlier at 175 grains per case.
Using a Volume Mass Density of 0.066 CC per grain of powder (which is fairly dense powder), that implies a volume difference the equivalent of -.3 grains for Norma, -0.9 grains for Winchester, -1.1 grains for S&B and -2.1 grains for Aguila.
This applies ONLY to the samples I pulled from the collection my friend had purchased. Weights of cases can vary as manufactures twiddle with processes. Don't just weigh one or two cases. Weigh a bunch of them.
USMC Weapons Battalion used to buy entire lots of brass, bullets, powder and measure/weigh EACH bit to get 'exact' rounds within 1/10th of a gram. I don't know if they still do that, but it made the snipers amazingly consistent.
ReplyDeleteI used to work in a factory that used multi-stream processing. The economic rational was that when you have five parallel streams (for instance) the percentage of time wasted transferring the old-job out and the new-job in shrinks to a very small percentage of the total cycle-time. Fewer robots and stations are required, in total, at the expense of more conveyor.
DeleteThe problem was that each of those five processes produced dimensionally unique sub-components which were shuffled again in downstream processes.
One of our dimensional engineers, in the dying days of our plant, set a record in the corporation by producing the most dimensionally consistent vehicle, up to that point in history.
His name was John Godbehere. I asked him how he did it. He said "That model is our low runner at about 15% of volume. I just told the controls electricians to force it down the legs in our process with the least variation.
So all of the bodies were built on the "best" stations and undiluted and multi-modal by pollution from other, parallel stations.
Tbe weight of a piece of brass is probably not as important as the internal volume.
ReplyDeleteThe weight of the brass is a good indicator of uniformity withing head stamps. Case volume, using water and a scale would be the criteria that will bring you the most consistency between head stamps. Uniform primer pockets and flash holes and cut to your OAL and full size your brass before weighing, empty or full. I was very impressed with the new brass I bought from Starline
ReplyDeleteThat way lies madness, Joe. Beautiful sirens sing of tiny groups and surgical accuracy and consistency. But the second you start shooting off your hind feet or the positions, the wind blows up, and the demons that control your pulse and breathing come out…all that stuff goes out the window. I don’t even sort my practice brass anymore. In real world shooting, the big three are bullet, barrel and shooter…if you have those three things going for you…then you are off to the races.
ReplyDeleteI think my friend's goal is to have the finished rounds fire to the same point-of-aim regardless of headstamp and to not have any excessive-pressure rounds.
DeleteDoes he have a chronograph Joe?
DeleteAs a matter-of-fact I have a chronograph.
DeleteHis rifle loves the Hornady 129 Interlock (not boattail). He is a hunter rather than a shooter.
He bought Ramshot Big Game powder.
There is not much easy-to-get data for that combination.
Based on 130 grain Sierra bullets, 2750 fps looks very do-able.
John Barnesse (a gun writer) says that he thinks the Ramshot powders are more consistent when they are run at or near max-loads vis-a-vis pressure.
"Tbe weight of a piece of brass is probably not as important as the internal volume."
ReplyDeleteThe two are related; IF the brass is all fired in the same chamber (creates brass with identical external dimensions due to "pressure forging") AND the brass is sized and then trimmed to length the external dimensions of the brass will be identical.
Sorting the fire formed, primer flash hole uniformed, sized and trimmed brass by weight is simultaneously sorting by internal volume, and it's internal volume which determines uniformity of pressure during firing. Find someone who shoots seriously in benchrest competiton and follow him around for a while. BR is the epicenter of Anal Retentiveness and OCD in the shooting world. It's not uncommon to see a BR shooter buy 1,000 pieces of brass, do an initial sort by weight, uniform the primer flash holes on the best (most consistent by weight) 25-50 then fire form those (light loads of Unique and kapok, no bullet), clean, size and trim the brass to get external dimensions identical, then segregate them by weight +/- 1 grain (FYI, 437.5 grains per avoirdupois ounce, 7,000 to the pound) to get brass that's as uniform as possible in internal volume, then use those 10 pieces of "perfect" brass for an entire competition season, reloading 6 at a time at the shooting bench during a match using hand tools (BR allows 1 fouling round, then the goal is put 5 rounds through the same hole at 100, 200 and 300 yards).
I've seen 10 rounds chronograph at the exact same velocity. Not +/- 1 or 2 FPS, the exact same FPS. Same external dimensions, same weight, same charge weight (EXACTLY the same charge weight), means same pressures which means the chamber pressures are the same, which means barrel "whip" is the same, etc.
If you can't consistently keep group size at 100 yards under .200" you will not finish in the top 20% at a large BR match, and your goal better be < .170"
Yup. Wanna see those guys guys go catatonic, and curl up on the floor and suck their thumbs? Show them the accuracy statements on their scales, vernier calipers, chronographs, etc.
DeleteYou are not going to over pressure on brass, generally speaking. You could do it, I suppose, if you were running right on the maximum edge of the cartridge pressure limits but you’d be showing pressure signs before you ever got there….