Shrinking brass

I've reloaded both rifle and pistol cases over the years but have not come across this particular situation before.

I've worked up loads in 45 colt for my new rifle. I bought unprimed Starline brass, measured and trimmed all to length. I have a Dillon 550 press with Dillon four die set. I've settled on 19.5 gr 2400 using Oregon Trails 250 gr hardcast bullet with a Remington primer (2 1/2 as I recall) for a muzzle velocity at just over 1500 fps with a 20 fps spread in a five shot string. Accuracy is good as expected from the tight spread.

After sizing, priming the brass, the brass measures .011 over the trimmed dimension showing that the resizing is drawing the brass out a bit. The balance of the dies are set accordingly so the loads are consistent. I figure with these changes in length, I'll just load all the brass the first time before I start any reloads so that I'll only have one more die adjustment.

Now to the part I'm not understanding:

In looking the brass over that has been once fired, the length changed again from the reloading operation......it got shorter. The brass lengths very but generally are .004 shorter that the original trim so total shrinkage of +- .015 from the loaded rounds. I'm having a hard time understanding why the cases get shorter from being fired?!

I like to keep my brass length consistent for decent accuracy etc and will have a few more weeks before having to decide what my new trim length will be after I've once fired all my cases.

I'm assuming that the lengthening due to the resizing draw out should be substantially complete. The shortening due to firing is not as consistent as the lengthening due to the resizing and if it happens every time, it will less than ideal. I'm hoping to have several reloadings of each case as pressure signs don't indicate I'm pushing the brass.

Thanks for any insight you can give me.

Jim

From what you're suggesting, since I haven't seen this on other cases I've worked on (357 mag, 44 mag), am I to believe my chamber is over size?

I'm not noticing anything unusual near the head but may have to keep an eye on it to catch future case separation at the head..........

Jim

In this case, I trimmed before sizing to get a standard size. In checking case length after sizing, the increase in case length is very consistent. I understand I could resize first, then trim. Either way, as long as I come out with consistent case length, I'm a happy camper (shooter ).

So cartridges are going into the rifle at consistent length but are coming out shorter and with some variation in their final length. From the comment regarding the 45 colt chamber being typically oversize, I take it that this will occur every time the cartridges are fired?

I guess I'm not used to having to trim every time cases are reloaded. Learn something new every day (maybe I should have bought the 44 mag version of this rifle instead of the 45 colt....)

Thanks,

Jim

Bob,

I'm hoping that's true regarding the trimming.


I'll work up a batch sizing first then trimming. Although with the couple of dozen cases I measured after trimming, then sizing were remarkably consistent in the final length (all with in .001 length), there will be virtually zero difference in length by trimming second.

I'm more concerned of the un-even shrinking which then puts the cases at various lengths (.004-5 range of lengths measured so far). I'm curious as to why the case length changes are so consistent with sizing (good brass I assume) but so inconsistent when fired (especially considering the low fps spread). However, perhaps that much variation will not affect accuracy too much, with the amount of crimp I use, to be a real factor and it all becomes a moot point.

Thanks for your comments.

Jim

rcmodel,

You folks type faster than I do.

As I don't use any more crimp than necessary to hold under recoil, I'll probably be fine.

And of course, I'm not shooting long range so these variations are probably not worth the bandwidth we're using to discuss them......

(and we're not even mentioning the fact that I probably can't shoot that well anyway! )

However, I do appreciate the discussion if for nothing else than to help with my education and curiosity!

Thanks again,

Jim

rcmodel,

Good point to keep in mind when I load for my pistols but I'm loading for a rifle (see first post).

gamestalker,

In this particular instance, trimming first worked out but I agree, in general, sizing first then trimming is the way to go.

I was looking at my notes, after getting home from work, and the once fired brass has a case length variation of the .004-5 as mentioned earlier with a few outliers.

I think I'll take 25 cases with the variations and load them (without any trimming). I'll take the chrony to the range one more time and see what kind of variance in fps I'm getting as well as group size.

I'll take a second group of once fired, resize, trim to same length and check them. Then I can get a good feel for how critical the case length is in this cartridge.

Jim