Help with fire forming a wildcat

Hello fellas. I have a 7mm wildcat on a 300 WSM case. I need help with COW fireforming, I neck down 300 WSM to .314 neck diameter in two steps. It’s a tight crush fit in my chamber. I have no issue using Winchester, Hornady or Norma 300 WSM brass. After fireforming I use a bent paper clip to check for case head separation and no issue. As soon as I use Bertram 300 WSM I get severe case head seperation. The pictures show my necked down 300 WSM brass on the left the neck 3 cases are Bertram. The next cases are Winchester, Hornady and last Norma.
All these were done today using exact same die set up and loads. I have used Winchester and Norma brass the last couple years and no issue. Now I want to fireforming some more brass since the corona thing and I’m having issues.
What do you guys think is going on? Any help would be appreciated!!

 

My guess is that it still isn’t enough crush to do the COW fireforming technique. You may have to use a bulletin jammed into the lands or hydro forming. The other method is to neck UP to 8mm then Down to 7mm to get a better definition.?

 

When I set up the headspace on my 6mm ackley I noticed that some 6mm rem brass would crush fit and other wouldn't as much or at all. This was done at the time with cheap new Winchester brass. I actually ended up setting my headspace tighter so that I needed quite a bit of force to close the bolt. I made sure to line the lugs well. Perhaps a false shoulder would help?

 

Go away from COW and use heavy bullets with stout loads and the issue will probably go away

 

it is a very tight crush fit. I do have to use pretty good force to close bolt. I haven't had any issue before. I did use a 325 WSM sizer die to neck up the brass and then took it back down to .314 in three steps. I only have the problem with the Bertram brass. I fireformed today using a 4 brands of brass.
saw carver, I have used heavy bullets jammed into the rifling before....Just wanted to do these in the garage today.

 

I've had far better consistency forming from a false shoulder with bullets, than with the COW method.

Size a portion of neck down until your bolt will only close with medium heavy pressure. Back off about 2-3 grs of powder from your regular loads using the bullet you'll be forming with. I back off my load 3 grains and get 90+ percent forming on annealed brass.

 

Since your not using bullets with COW there is nothing to hold the case head against the bolt face. I FF with the cheapest bullets I can find and jam about 10 thou to push the case agaist the bolt face.

 

I used the COW method on my last wildcat, a 280 AI. I wasn't happy with the results at all. So, I burned some bullets and barrel and got way much better results. I am not worried about using bullets because it is a hunting rifle and will still outlive me.

 

Seems that the necks are longer on the Bertram; that brass flowed from somewhere. Is that really present or an illusion?

 

Have you tried annealing the problem brass before forming? If it's not flowing well in the neck/shoulder area, it might be too hard and is drawing the body of the brass up.

Or, just dont use that brass...

 

I had heard of norma 300 wsm being soft in the past. Is it possible it's bad brass? Willing to sacrifice a virgin piece? Cut it open and measure web thickness and maybe compare it to a piece of winchester?

 

I suspect the virgin case diameter at that expansion ring is a thou or two smaller than the "good" cases. Measure the distance above the base to that expansion ring, lock your caliper there. Mark virgin cases at that spot with a sharpie, them measure their diameters there, comparing Bertram to some others from your assortment. I know, I'm crazy, but humor me and report back.
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I just got thru putting a false
shoulder on 200 cases of RWS 270 brass to form for a 6.5 Sherman. I necked up to .284" and then partially sized the neck enough to close bolt under med. heavy pressure.

I've used this method for 10 years or so, to not have to deal with COW. Been a big improvement.

It's pretty simple, if you use a generic neck sizer or a bushing die. Just be sure your parent case length is not longer than your forming chamber OAL.

 

Folks, as far as I can see the OP is forming a false shoulder which (in theory) should work fine. Since the Bertram brass is the only brand that's misbehaving, this seems to be a brass issue and not a problem with technique. Also appears that the Norma brass might be a little undersized since it looks - from the photo - to have a slight bulge above the web.

 

Guys, I am creating a false shoulder. I neck the 300 WSM brass up in a 325 WSM die then neck back down to 284. The only issue is with the Bertram brass. Yes the necks are longer on the Bertram brass don't know why. As I said I fireformed 4 brands yesterday and know issues with the other. the primers are flat on the Bertram. So yes the primers are backing out upon firing. Im just baffled why only Bertram is doing this.

 

I had a similar issue with 308WIN brass (well-used before f’forming) I started out with when I built a 284INCH LR rifle in ‘16. COW to f’form before first bullet loading.

Last year, with new factory brass the set I started got necks sized up first with a 0.350 mandrel. This leaves a stouter false shoulder once I bring neck ID down to 0.282” then fire once with 168’s, not the 180’s used in ‘16. That’s as far as I got.

This season - whenever it starts - will tell me whether it’s been resolved... or needs more attention.

 

Form the false shoulder AFTER you trim the brass i.e. "The only issue is with the Bertram brass. Yes the necks are longer on the Bertram brass don't know why."

I have been making the false shoulders for years and using a moderate load for hunting and shooting. Load similar (same box) of one in photo dropped a nice whitetail at 200 yards last year.

 

You ignored my suggestion to measure and compare virgin cases. If Bertram is a bit undersize in the body there, that's exactly what it should look like after firing.
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brian356, I didn't ignore your suggestion to measure and compare. Ive been at work since 6am and just got home hour ago. the necks are longer on the bertram brass ONLY after fire forming. Before fire forming the brass are 2.090" after forming the Bertram brass comes out to 2.095 to 2.100". I think you might be right about the brass being undersize. Ill check tomorrow and get back. Thats the only thing that makes sense right now

 

this won't be much help, but most of the people I know who have tried Bertram were unhappy with the results. Their QC seems very inconsistent. The other brands you listed worked great. Just save the Bertram until you see Zombies in your yard...