Author Topic: Example of lot-to-lot variation (Read 708 times)

Questor · « **on:** June 14, 2004, 04:08:10 AM »

A couple of years ago I made up some 221 fireball cartridges using CCI primers, Speer TNT bullets, and IMR 4198 powder.

I just made up some new cartridges using the same brass, the same lot of primers, and bullets from the same box. But I am using powder from a different lot of powder. Die adjustments are exactly the same (because they had not been changed since the last loading session.) OAL is therefore the same.

The new cartridges shoot about 150fps faster than the old ones. (I am chronographing both loads during the same range session.)

This is a concrete example of how all other things being equal, the change of one component can make quite a difference.

ricciardelli · « **Reply #1 on:** June 14, 2004, 05:04:05 AM »

Powder lots can vary up to +/- 5%

Sometimes more the the difference between two different powders.

Questor · « **Reply #2 on:** June 14, 2004, 05:29:30 AM »

Ricciardelli:

I found it illuminating to see a real example because I've heard people complain, for example, that they weren't getting the velocity they expected from a particular proprietary or wildcat cartridge. In my case, I have not been able to get my 6.5JDJ to shoot much faster than 2300fps, but others claim over 2400fps and the manufacturer claims 2400fps. It's a small thing, but sometimes a particular velocity level is a psychological thing even though there's no real world performance difference.

Graybeard · « **Reply #3 on:** June 14, 2004, 06:26:54 AM »

Lot to lot variation is NOT the only factor that might be at work here. Some times older ammo can increase in pressure due to some odd factor like a bit of corrosion starting between case and bullet.

I loaded a large quantity of 7-08 ammo many years back. It was a super accurate load in my R7 SS often shooting under 1/2" and always under an inch at 100 yards. So I loaded up all the bullets I had using the same lot of bullets, power, cases and primers.

A couple years later I pulled some out to resight the rifle as I'd swapped scopes and wanted to resight it before hunting season. First case out kinda stuck the bolt big time. What the heck I say. Over the chrono the velocity was way up, like 200 fps or so. I shot a couple more with same results.

Pulled all bullets and noted an increase in adhesion of the bullet to case that shouldn't have been there. It appeared there was a bit of corrosion setting up between the two metals. Dunno why as they'd been stored inside the house all the time but it happened. Made otherwise safe loads at time developed unsafe. Strange things can and do happen.

GB

Questor · « **Reply #4 on:** June 14, 2004, 07:01:40 AM »

GB: In my case,the old loads are slower. I also kept the cartridges and brass in a cool dry place (easy to find such a place here in the frozen toondra.)

GrampaMike · « **Reply #5 on:** June 14, 2004, 08:02:31 AM »

GB... This brings up a good question. Exactly what is the best way to store ammo and components? (cool and dry)... How cool? and how dry? Old refrig? I don't know but I would like too. Thanks. Mike

Questor · « **Reply #6 on:** June 14, 2004, 08:50:53 AM »

Actually, GB may have been barking up the right tree after all. Those cases were new that last time I loaded them. Now they're once-fired. That could change the bullet tension.

Duffy · « **Reply #7 on:** June 14, 2004, 07:41:04 PM »

I had that happen with some H110 in my 44. My pet load of 24.5g gave an even 1400 fps. When I used a new jug with a different lot# you couldn't get enough powder in the case to reach 1400 fps. About 1320 was tops and accuracy suffered too.

Blackhawk44 · « **Reply #8 on:** June 16, 2004, 01:55:43 PM »

While I have never found signs of corrosion in old handloads, I have run into the variable neck tension. It seems that the old ash mixed with resizing lube and/or just its reaction with the two metals causes the bullets to try to bond to the case to one degree or another. This bond is quite variable. Many old high power shooters would seat their bullets long for storage then the week of a match final seat them to correct length, breaking the bond. Since I don't tumble, after sizing and priming, my long term loads get a quick shot of the stainless bore brush (not oversize) in a drill to gently clean them back to metal before bullet seating. Since adopting this ploy, I no longer get handloads that "go sour". As a side note, this phenomenon does not seem to occur with factory loads (fresh metal to metal?) or with cast bullet handloads. Now you know everything I know. BOL BH