Gunsmithing 7mm RM test fire. Questions...

[steelcomp]

Test fired my new 7mm RM at the gunsmith today. After digesting what he told me, I'm a little unclear as to how to interpret the results. I'll go back and ask him to help me understand, but I thought I'd also ask here.
He said that the 7mm RM head spaces off the belt, and that he has the head space set right under .001", but then also said the test case expanded .005" in length, most likely at the shoulder. He reamed a small section of my barrel to use as a gauge for measuring case length, and he says just to be sure that when i re size my brass, to get it back down to the original length.
Does this sound acceptable on a precision build? Isn;t this like fire forming the brass, and why would I want to resize to the original configuration again?
I know very little about reloading, so go easy on me.

TIA.

 

[300sniper]

Re: 7mm RM test fire. Questions...

the first firing of a belted mag in a factory chamber will most likely headspace off of the belt. after that, most people set their sizing die so it sets the shoulder back about .002" (or less) so it headspaces off of the shoulder from there on out. if you set the shoulder all the way back to what new factory brass was, you will have very short case life because the case wall will get thin in front of the head from stretching. this will lead to case head separation.

also, you may have better responses in the reloading forum here.

 

[glock24]

Re: 7mm RM test fire. Questions...

Scott,

After three firings with my 7mm RM brass (Norma), I have yet to resize my case shoulders or bodies. I am only sizing the neck. Per 300sniper's point, I don't want to push the shoulder of my cases back to the original position, especially with a belted magnum. It will shorten case life, and hurt accuracy.

I will at some point have to push my shoulders back a few thousands with a Redding body die. I'll know when that day comes because I'll start feeling resistance when I close my bolt on a loaded round. I only plan to push back my shoulders when I feel that resistance, not after each reloading.

Now for the bad news . . . the belt on any belted magnum also keeps any standard reloading die from properly resizing the portion of the case body immediately ahead of the belt. Basically the belt doesn't allow the case to fit deep enough into the die. This is a problem because this area of the case will expand eventually, and not allow proper chambering of reloaded rounds. I've actually had my cases expand in this area after only two firings. At first I thought I needed to bump the shoulder, but it turned out the area just ahead of the belt was too big and needed resizing.

Be ready to buy one of these;

http://www.larrywillis.com/

It is a required extra step for us belted magnum reloaders, but it takes care of the problem I've described. Because my cases expanded ahead of the belt after only two firings, I've decided to resize that area with the above collet die after each firing. This process ensures my case shoulder remains in its fire-formed position with each reload.

I also agree moving this topic to the reloading section will provide you with a lot more answers.

So how'd it feel to fire your first shot?

 

[steelcomp]

Re: 7mm RM test fire. Questions...

Thanks guys. . So my hunch was right, not to want to keep working the brass back and forth at the neck. That pretty much answers my question. I'll take it to reloading if I have any more, or if a mod reads this and wants to move it, OK by me.
Hey Jason. I remember discussing the collet die with you earlier. Probably need to get that on the way.
I sent you an email. It wasn't me that fired it...it was at the gunsmith in a test chamber. I still have LONG way to go before I get my cherry.

Thanks again.