Cases shrink after firing?

[grego88]

I've been reloading mostly .308, and 30.06 for a about two years now. Just recently, I got an AR-30 in .338 LM, and have since started reloading that. My first batch of re-loads for this gun I used 88.0 grs of H1000 and 250 gr SMK's. I'm using Norma brass. I measured the cases before and after I fired them, and found that after firing, some of them actually shrank a few thousandths. Most however measured the same, or slightly longer than before.

Maybe I just never caught it before, but I never noticed .308's or 30.06's shrink, only grow. Can someone explain what would cause a case to shrink?

 

[wilecoyote]

Re: Cases shrink after firing?

they can shrink about their lenght,but growing in widht,depending from the conformation of the chamber,from the kind and thickness of the brass,and from the angle, more or less acute,of the shoulder_

 

[Temp9]

Re: Cases shrink after firing?

Measure after sizing. A lot of cases will get shorter after firing, but they lengthen after sizing.

 

[Bison]

Re: Cases shrink after firing?

My .45 Colt brass, fired from a lever action rifle, and my .308 brass, from a bolt action rifle, both have shorter cases after firing. The 45 is .005" shorter and the 308 is .003" shorter.

Should I be concerned? If not, shoudl I be concerned if the cases are lengthened after sizing? That is, should I try to keep them at the length they became after fire forming?

 

[BuzzBoss915]

Re: Cases shrink after firing?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Temp9</div><div class="ubbcode-body">Measure after sizing. A lot of cases will get shorter after firing, but they lengthen after sizing. </div></div>

This is most likely the answer.

Example; fireforming an Ackley, the cases always get shorter in overall length. The difference is in subsequent reloading, they don't gain in length, and never need trimming. This is due to the 40 degree shoulder, but in most standard cartridges, the time to measure the length is after resizing. BB

 

[MALLARD]

Re: Cases shrink after firing?

think of it like a space shuttle launch. When the rocket lifts off there is allot of exhaust/backblast coming out the bottom of the rocket. The blast is pushing down,propelling the rocket up. Same is true with your gun, the blast pushes the brass rearward, causing it to shrink.

brass does not stretch upon firing

 

[NCHillbilly]

Re: Cases shrink after firing?

Don't worry too much about the length until after you have resized the cases.After sizing,you'll want to keep the length below the listed max case length.If you're a real stickler,you can trim all your cases to match the shortest case(as long as it meets min. specs)so that you have consistent neck tension among all of your cases.That's kinda splittin hairs unless you shoot competitively.Just keep 'em above min. and below max and you'll be fine.

 

[former naval person]

Re: Cases shrink after firing?

Mallard...they can. Over full length size your case, create excess head space...they stretch just ahead of the web. Few times like that and you get case separation.

 

[NCHillbilly]

Re: Cases shrink after firing?

I should have been a little more specific with my last post.Get yourself a wilson headspace gauge,or Hornady and sinclair both have a nifty tool that you can use to measure your once fired case.These last two tools measure from the datum on the shoulder.Once you have that measurement,you can adjust your resizing die to just set the shoulder back about .002".This will keep you from overworking your brass,and prevent you from creating excess headspace.Measure length after all this is done and trim if need be.Also,keep track of how many firings you have on your cases.You don't wnt stuff fired three or four time mixed in with the new stuff.

 

[grego88]

Re: Cases shrink after firing?

Thank you for all the helpful posts everyone. I learned something new today.

I measured all of the cases before I loaded them (they were all brand new) to make sure I did 't have any that were too long/short right out of the package. They were all 4-5 thouanths of each other. The second time I measured them was after I ran them through the sizing die (after being fired), and a few were still a few thousandths shorter than before.


<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: NCHillbilly</div><div class="ubbcode-body">I should have been a little more specific with my last post.Get yourself a wilson headspace gauge,or Hornady and sinclair both have a nifty tool that you can use to measure your once fired case.These last two tools measure from the datum on the shoulder.Once you have that measurement,you can adjust your resizing die to just set the shoulder back about .002".This will keep you from overworking your brass,and prevent you from creating excess headspace.Measure length after all this is done and trim if need be.Also,keep track of how many firings you have on your cases.You don't wnt stuff fired three or four time mixed in with the new stuff. </div></div>

I actually just read about this tool on one of the reloading stickys in this forum. I already put it at the top of my "to get list"

As far as separating my brass according to how many times its been fired, I learned that lesson the hard way. When I first started with .308, I didn't do this. Like an idiot I mixed it all up with range brass. I started getting split cases in my M1A, and I tried the trick that involves sticking the end of a paper clip into the cases and feeling for a low, or thin spot. I found a bunch that would have split if fired again. After a while, I just gave up and threw it all out, and started over with brand new ones.

 

[NCHillbilly]

Re: Cases shrink after firing?

Hope I was at least a little help.Handloading can be a very enjoyable and rewarding hobby,but the more you learn,the more questions you'll have.An invaluable source of info is the tech service depts. at the major component manufacturers.They are usually more than happy to help.It's also in their best interest to keep you safe.Happy loading!

 

[Clark]

Re: Cases shrink after firing?

The hotter the load, the more the case shrinks on firing, and the more it grows on FL resizing.

The further the sized die is adjusted lower in the press, the more the brass grows during FL sizing.

Neck size if you hate trimming.
Adjust those FL sizer dies to push back the shoulder .001" if you moderately hate trimming.