Fire-forming .300WM brass...?

[memilanuk]

So... took the new .300WM to the range today. Shooting Winchester cases... even with a mild load (72gn H1000 behind S220MK, 0.020" jump, 215M primers), the primers were *flat*. I mean really *flat*, and accuracy was pretty erratic. No ejector wipe, bolt click, or any other indication of excessive pressure. Testing stopped there.

When I got home and measured things, I found that the case shoulder (headspace) had moved forward ~11-13 thou, and the cases were now 7-9 thou longer OAL (case head to mouth). Maybe its just me... but that seems a bit excessive...?

I sized the cases, bumping the shoulder back 0.001" from fired, loaded everything back up with the same load, and went back to the range. Accuracy was much better, and the primers looked fine (i.e. not flattened at all).

I've had some experience in the past with Winchester. 308 Win brass being grossly undersized in a variety of dimensions, but not *this* much. I've also read a post or two here that mentioned having to fire-form Winchester 300WM brass before being able to do anything useful with it. I'd kind of dismissed the latter, thinking that couldn't possibly be right...

So... now that I've seen first-hand that this 'stuff' is not going to be useable without some fire-forming... I'm curious how others are going about it. COW, seating cheap bullets jammed long into the lands, false shoulder, what?

Monte

 

[ChadTRG42]

Re: Fire-forming .300WM brass...?

I've never measured the head space expansion on new brass to fired brass. There's not much you can do about it, honestly. After firing, I neck size my 300Wm brass, and chamber check them. If it needs a FL sizing, I bump it back .001-.002" on the shoulder, and I'm good for a few more neck sizes.

 

[Bigwheels]

Re: Fire-forming .300WM brass...?

I have only had that happen when I didn't neck turn my new brass. My chamber is tight, & if I don't neck turn I can fire a rnd, & pull the brass out, & can't get a bullet in the neck without a press. So obviously it wasn't able to expand, & let the bullet go when fired. Now I take a few thousandths off, & I'm gtg.

 

[Rob01]

Re: Fire-forming .300WM brass...?

My new Win cases in my GAP that I shoot grow around .020" when measured at the datum line on the shoulder. A more pronounced shoulder angle as well. No growth in OAL though.

Not too worried about it. Got an accurate load with the new stuff and when I reload the once fired I will just adjust a little on the powder charge if need be.

 

[mdmp5]

Re: Fire-forming .300WM brass...?

300 win mag factory brass and factory ammo has the shoulder set back really far, with the intent of headspacing solely off the belt. The brass will bump forward considerably on the first firing. I think the case capacity increased a bit in your case, which would explain the disappearance of the flat primers on the 2nd firing. Try stepping down the charge on the 1st firing

 

[former naval person]

Re: Fire-forming .300WM brass...?

It is as palmik says. You have got "stretch marks" inside your fired cases now. That, of course, shortens the life. You are correct in sizing for the .001 bump of the fired case shoulders. If you are using Lapua or other costly brass, you can neck expand the new cases up to .338 or so, then full length size to your bumped length. That will keep the case head back against the bolt face during the first firing and avoid the stretching that occurs just above the base.

 

[memilanuk]

Re: Fire-forming .300WM brass...?

I checked inside the fired cases with a feeler/pick (paper clip straightened out with a hook bent on the end)... no indication of any ring or thin spot yet.

I had forgotten about the belt limiting how far forward the case can go forward... so most of the 'stretch' is probably coming from the far end of the case/body, not necessarily right @ the web.

With the forward movement of the shoulder + the change in shoulder angle (sharpening, more so) you're probably right about the change in volume.

My concern about doing load development w/ the virgin cases is two-fold: one, with the primer completely *flat* even with starting load I'm down at least one pressure indicator right off the bat, and two, working with higher powder charges (as I work thru the ladder) with under-capacity cases seems to be like trying to cram 10 lbs of crap in a 5 lb bag...

I'd thought about sizing up and forming a false shoulder as mentioned (done the same thing in my 6 Dasher)... but thats more parts (tapered expander, at a minimum) to order, etc. On the other hand I was considering running some reduced loads (Hodgdon lists some reduced loads w/ H4895 and light bullets) to blow the case out to something more resembling the final chamber dimensions...

As an aside... what would be a better option for future brass purchases in this caliber? From what I've heard, Lapua stopped making .300WM brass a while back. What's the next best choice?

Thanks,

Monte

 

[mdmp5]

Re: Fire-forming .300WM brass...?

I love my 300 win mag. I hate the fact that Lapua stopped making brass for it. I only have 100 pieces, and you can really tell the difference between the Lapua and other mfrs like Hornady and Winchester. However, most guys who shoot 300 swear by Winchester brass. I have no reason to doubt them, so I would have no problem going with win brass. I do have some Nosler brass too, which is also pretty good.

 

[winxp_man]

Re: Fire-forming .300WM brass...?

I had the same thing happen to me with new win brass. I didn't charge your writing did you say your brass is new ? For me on the second firing it was all good.





Aron-

 

[bcuzisedso]

Re: Fire-forming .300WM brass...?

Does this scenario hold true for all new brass in other calibers? Basically, should all new brass be fire-formed before productive load development can start?

 

[winxp_man]

Re: Fire-forming .300WM brass...?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bcuzisedso</div><div class="ubbcode-body">Does this scenario hold true for all new brass in other calibers? Basically, should all new brass be fire-formed before productive load development can start?
</div></div>


With my .223 Rem, 6.8 SPC, .308 Win, 300 Win Mag this was the case. I had to fire form all cases before you get consistent loads.



Aron-

 

[memilanuk]

Re: Fire-forming .300WM brass...?

Winchester .308 Win, yes. As mentioned, also grossly undersized to the point where a max load in a fired case may be unwise in a virgin case. Haven't had that problem with Winchester .223 Rem; then again I was firing that in a gas gun for XTC use, not a scoped precision rifle.

Lapua... never had that sort of issue in .223 Rem, 6BR, 6.5x47L, 6.5-284 or .308 Win - except when fireforming 6 Dasher brass. Actually, when I described what I was seeing with the shoulder moving so much on the Winchester .300WM brass to someone else, their first remark was '.300 Win Mag Improved?'

 

[buffybuster]

Re: Fire-forming .300WM brass...?

With belted magnums, since the headspace is determined by the belt, the shoulder can vary either in chamber or case by quite a bit. Once the cases are fireformed, they can be headspaced to the shoulder, which is the conventional method. At that point the belt become completely superfluous.

 

[gray1974]

Re: Fire-forming .300WM brass...?

I have some new IMI brass in 308 Win and need to fire form it. I was going to load a 110 grain soft point at about 1200 fps, using trailboss powder. Is this enough to get the case to chamber dimensions?

 

[Supersubes]

Re: Fire-forming .300WM brass...?

If I knew the brass was short I would seat the bullet out further to keep the head against the bolt face. You could also run it into a FL die partially to bump the shoulder forward(by the body getting squeezed). That wouldn't help if you were way short.

I don't load hot enough where the jam configuration will cause an issue. I would not however load up a fire form load using anything other than my intended bullet and powder. I don't have time for that.

edited: Some of the best consistency I have ever experienced come on the first firing of new brass. No reason to waste that.