Crimp effect on Velocity
 

Yesterday, while loading 15 boxes of 12 gauge AA's on my PW 800 Plus (boy, do I like that press!) I got thinking about the effect on velocity of a shell which has been reloaded 6-8 times compared to a once-fired hull. Has anyone ever seen a discussion of that? Thanks.

Yes, Tom Roster had an article about it in the Sporting Clays magazine a while back. I cannot remember the actual numbers but the general gist of it was that velocity decreases with each reload. And again, if I remember correctly, I believe the velocity loss increases at an increasing rate with each subsequent reload.

I have a PW LS1000. My past experience with AA hulls is the base wad compresses each time it is fired. Hence the inside measurement changes and the hulls don't crimp properly. Got rid of all my AA's and only reload Remington Nitro hulls.

As I remember shells reloaded a lot of times didn't mean squat - but that could have been a different article. In another article crimp depth effected pressure. Factory depth is around .055 to .060. They said .080 would increase pressure about 1000psi - going less would decrease pressure about the same. In my Accurate powder reloading guide they claim the crimp depth has the greatest effect on pressure seeing how only the shell effects pressure, not the barrel, like a rifle. I've never worried about how many times a shell has been reloaded so long as the crimp depth is still good. One would always have an excuse if he missed - poor crimps. As a side note, man do I love the way my Mec9000H makes a good looking shell. The once fired ones look like factory ammo.

Tom, I believe the base wad is plastic, same as a Remington. I too just reload Remingtons so I'm not sure; but from what I've read on a reloading forum the Win hulls are different lengths and that could be your problem.

I'm in agreement with Tom regarding the AA hulls, and I too prefer Remingtons. But getting back to the original question, after 5-6 reloads, using IMR 7625 in a 12 gauge hull I would occasionally get incomplete combustion and what seemed like lower velocity. NOT EXACTLY A BLOOPER, but a very weak load.

Paul,
The info I received through 3rd, 4th, or 5th hand, was when Winchester went to the two piece hull, the grade of plastic changed. Some are of the opinion that the plastic base wad in the AA two piece hull is softer than the original AA hulls. Thus the base wad compresses more with each firing. All I know is that I have tried to keep track of how many times I reload my Nitros and lost count. So I just look at them and when they look a little iffy, I toss them.
Tom

There is no doubt that the old style AA and the new HS AA are different in volume. I had a mixed batch and it caused me fits for a while. I had to adjust my press to accommodate the HS. Once I separated out the two different vintage hulls the problem went away.

A side note though is that my current batch of HS hulls are on their 4th loading. This summer I had 3 instances (red hull) out of 3000 where the case tube separated from the brass head. I'll be watching closely when I reload this winter. I never had that happen with the old style hulls.

Here's an article on the subject. Might be the one others were thinking of.

http://www.armbrust.acf2.org/caselife.htm

Not the article I was referring to. Yours is much more detailed and pretty much sums up the answer to the original post. Thanks for sharing.