7mm-300WSM wildcat

[nheninge]

I am starting my first wildcat project. I am having a fully chambered 7mm-300wsm being built and I want to neck down 300 wsm cases to 7mm (this is not just prepping 300 wsm brass to eventually fit a 7mm wsm).

My usual new brass prep (not specifically in this order but...):
Norma brass preferred, winchester as a last resort
sinclair expander mandrel
flash hole debur
sorting by neck variance (keep cases with < 0.0015)
weight sort (remove top and bottom 5%)
neck turn to uniform neck thickness
resize
primer pocket uniform
trim to uniform length
outside debur
polish w/ 0000 steel wool

I need input specifically regarding:

Should I neck turn the 300 WSM, followed by necking down to 7mm

OR

Neck down the 300wsm and then neck turn the 7mm after case forming?

I will be using redding S type FL sizing dies w/ bushings.
What increments should be used to minimize work hardening?
Neck ream to minimize doughnut? When?

Since this cartridge is not uncommon, any help/experience is appreciated.

 

[Pdvdh]

I don't have your cartridge but I've necked down quite a few cartridge cases over the years.

The first question is easy. Neck it down to 7mm before outside neck turning. There's no way to know that the case neck would size down uniformly if you outside neck turned the 300 first and then necked it down.

You should be able to neck down from 300 to 7mm in one step without causing any problem. I would anneal the case neck after sizing it down, personally, just in case the neck hardened some during the size down process. Whether you anneal before or after outside neck turning the 7mm neck, I don't believe it would make much difference.

I wouldn't inside neck ream at all. If at the time you ouside neck turn you cut back into the shoulder just a tad (that's what I do with my K&M Services outside neck tuning tool), you shouldn't ever form any dougnuts. The K&M Services cutter is angled at 35 or 40 degrees where the cutter contacts the shoulder to allow a slight thinning of the shoulder brass. Upon firing the case in the chamber that cut is blown to the outside of the case - leaving a slight recess on the inside of the case neck where the doughnut might otherwise eventually form.

Hope this makes sense and helps. That's the way I would do it. Someone else that has this specific wildcat may have keener insights on this specific cartridge case, but I believe this advice to be sound for your wildcat too.

 

[RockZ]

Here's some good info:
Vince B's 7mm WSM Record-Breaker (7 Win Short Mag)

7mm Cartridge Guide

 

[B23]

I'm sure i'm missing something quite obvious but I still have to ask. Why don't you just use 7mm WSM brass? I know the cases aren't identical but is there enough to be gained for the time involved?

 

[loaders_loft]

I'll bet he likes norma brass better, plus the long neck of the 300wsm case may be an advantage. The slightly smaller volume may also be an advantage? 300 wsm brass probably has a better future than 7wsm brass anyhow.

Plus, the time involved is what most of us enjoy about reloading...

It seems like a good idea, to me. I may even go this route next time...

 

[nheninge]

Yep, norma brass is so superior to win brass. Not that win is bad, but it takes twice as much. I routinely order 100 brass to make 50 good cartridges. Might as well just order the Norma. I don't push my cartridges too hard so case volume is not a problem. Just over 3000 fps seems to be the best accuracy which has been easy to achieve. Easier on throats too maybe over the long haul. My thoughts for light turning before necking down are that maybe sizing down would be a little more even. I am not even against neck turning lightly before, and then again after, but maybe it is not necessary? I am surprised to see that I can neck down in one step!. I'll give it a go! Thanks in advance. Any more input is still appreciated.

 

[Pdvdh]

You're stepping down the neck about 0.024" (.308-.284), so one-step resizing of the neck should be no problem whatsoever. Good luck and this sounds like an interesting cartridge - which is what drew my attention to your post in the first place.

 

[MBrown]

I have a rifle chambered in this round. This was my first wildcat round also. I searched for info when I had it built without much success. I am no pro but this is what I do and it works well for me. I use Norma brass and a Redding competition bushing neck sizing die set. A rep. from Redding told me not to move the brass more than .007" at a time, so worried about scrapping brass this is what I did. I used a .330" bushing, then .324", .318", and .315" to final neck size. This was much easier than I thought it would be. I didn't aneal at all. It took me about an hour to do my first 50 pcs. and have fired it 4x. I have not had any donut problems. I shoot 180 bergers and it is a tack driver! I have no regrets about having my rifle chambered in this round. Hope this helps.

 

[Pdvdh]

You're stepping down the neck about 0.024" (.308-.284), so one-step resizing of the neck should be no problem whatsoever. Good luck and this sounds like an interesting cartridge - which is what drew my attention to your post in the first place.

nheninge,

MBrown's post caused me to realize that you were planning to neck down using a Redding S-type FL sizing die with neck bushings. I had to go back and read your initial post to confirm this. I've never sized necks down a full caliber using the Redding FL neck bushing style resizing die, so you better follow MBrown's advice if that's what you're planning to do.

I was thinking you'ld be using a standard 7mm WSM FL sizing die to neck down the 300 WSM brass by setting the die depth so that it only sized the neck down - without setting the shoulder back. It would be possible to proceed as I envisioned, but it appears you would need to grind 0.200" off the bottom of the 7mm WSM die so that the 300 WSM case neck could be sized all the way down to the shoulder. Using this approach you could neck down up to ~ 0.030" in a single step. I know grinding 0.200" off the base of a 7mm WSM FL sizing die sounds crude, but I've done this before and the die is completely functional for its purpose. It just looks rough on the bottom end. If you have a lathe, then the 0.200" can be turned off in a lathe and the die will both work and look nice too. Purchasing 4 Redding neck bushings simply to size down your case neck in four small steps will cost more than purchasing a standard plain-Jane 7mm WSM FL resizing die, and will require four separate steps. Just tossing this option out there for your consideration. I wouldn't even use the expander ball if you went this way. Set the die in the press to resize the entire case neck, then use the outside neck turning expander mandrel to expand the case neck to the proper ID for outside neck turning.

Sorrry for not providing information applicable to your specified neck-down process the first time around. I don't know how far you can neck down in one step with a neck bushing style die. You better follow MBrown's method if you go that route.

 

[nheninge]

Thats the kind of detail I need!. Thanks guys. I was surprised to think it could be done in one step, but it is so easy to order intermediate bushings. I too want 180 Bergers with a 1:9 barrel twist. At least this is what I think I need after reading Bryan Litz's test data (nice work, and a hell of a reference).

With the norma brass, what was your final bushing size with the norma brass? I am guessing about a 0.309-.310? Here is my quite possibly faulty equation:
0.284 + 0.028 - 0.002 - 0.001 (bullet diameter/neck thickness X2/neck tension desired/brass springback, respectively).

Have you noticed any springback with the Norma brass? (0.001?)
What was your final neck thickness after turning (if turned)?

I'll be taking the brass down as soon as I get the bushings!
I plan on annealing after every firing

I want a long range tack driving SOB that can outshoot my abilities. Hope this is it.

 

[nheninge]

Expander balls might just be the root of all that's evil. However, the Forster press with its floating die seems to negate most of the case runout problems seen in fixed dies. Still don't plan on using expanders.

 

[MBrown]

The final bushing I use is .315". Norma loaded with a 180 berger measures .316".

My brass doesn't show any spring back but I measured it with a digital caliper so it is under .0005" at the most.

The wall thickness measures .0165" and I have not turned the necks.

P.S. I use a 300wsm Redding competition bushing die set.

 

[nheninge]

I do plan on taking the necks down to 0.014 or so, although the necks on Norma brass are pretty even anyway.

Since I have your attention, what primer/powder combo has given you the best results?

I too will use redding comp dies for sizing and a wilson style bullet seater cut with the same reamer.

 

[MBrown]

The loads that are popular with the 7wsm work with this cartridge also. I like federal GMM 215 primers and Hodgdon H4831SC @ 62.5 grn in my rifle.