The Perfect 7mm?

[762 ULTRAMAGA]

Last year I built a short barreled 7-300 wsm improved on a Tikka action, it's an awesome round but all that extra space in the Mountain Tactical magazine got my gears turning.

I'm a huge fan of the fat wsm and nosler case designs with 35 degree shoulders, I got to looking at the 33 Nosler case dimensions and realized it's pretty short at 2.46", for reference the 7 prc is 2.280".
This got me thinking "what if I necked it down to 7mm and possibly pushed the shoulder back to fit a Tikka mag"?

I scored a few Peterson 33 Nos cases from another shooter and went to work sizing it down.
I used an old 300 wsm FL die to neck to 30 cal, then ran it through my 7 wsm die for the final step down.
It was super simple and resulted in a perfectly sized neck, the internal capacity measured 92 grains after necking down, landing right between the 28 Nos (101.5 grains) and 7 PRC (83 grains)

Next I decided to experiment with pushing the shoulder back to seat a 180 ELDM just above the donut area at the neck shoulder junction.
I turned the wsm die down in sever steps and ended up with a case that has 88.5 grains H20 capacity, and an OAL of 3.375" with a properly seated 180 ELDM.
This fits my Tikka mag with .025 clearance.

Now here's the dilemma..
The easy button is to simply neck the 33 Nos down, get a custom reamer, and use Redding 33 Nos bushing dies off the shelf. The 180 ELDM OAL with just a neck down is 3.49" so it'd require a Tikka DBM conversion if I wanted to run it in that action.

Option 2 would be to push that shoulder back requiring custom dies, no big deal (and only $250), and while I'm at it blow the body taper out and give it a 40 degree shoulder.
This would take more effort for sure but would result in the fastest 7mm to fit properly in a Tikka action, and have a case capacity around 89 grains.

Yes I like to tinker, and no I don't need another project, but this one really interests me.
So what do you guys think, option 1 or 2?

Right to left:
33 Nos, necked down only, shoulder pushed back for 3.375 OAL, and 7 wsm


Loaded in Tikka mag behind 7 wsm

 

[Mag_7s]

Defently out of my wheelhouse, but I vote for option # 2. Create your own wildcat! What would the reason be to go with a 40 degree shoulder over the 35?

 

[wind gypsy]

Sounds like a giant unnecessary PITA but I agree that route #2 sounds like a bitchin cartridge. Route #1 is probably what I'd do if forced to choose(with 700 pattern LA though) because it sounds easier.

I don't know enough about brass but was under the impression that hardness and thickness is prone to vary as you go down the case. I'd wonder on if that would cause issues with route #2? Wouldn't you end up with thick ass necks or need to neck turn and then get donuts with firing case stretch that you'd want to turn off again?

Just necking down 200 pieces of 7 SAUM to 6.5 and turning the necks was enough for me to avoid dicking around with this stuff again anytime soon.

 

[Mag_7s]

Sounds like a giant unnecessary PITA but I agree that route #2 sounds like a bitchin cartridge. Route #1 is probably what I'd do if forced to choose(with 700 pattern LA though) because it sounds easier.

I don't know enough about brass but was under the impression that hardness and thickness is prone to vary as you go down the case. I'd wonder on if that would cause issues with route #2? Wouldn't you end up with thick ass necks or need to neck turn and then get donuts with firing case stretch that you'd want to turn off again?

Just necking down 200 pieces of 7 SAUM to 6.5 and turning the necks was enough for me to avoid dicking around with this stuff again anytime soon.

Good point, would annealing alone solve the potential hardness issue ?

 

[B23]

If you like to tinker and want to spend the time, money, and effort I'd say go with whichever one excites you the most but for me, for only a tiny gain over the 7PRC, it wouldn't be worth it but that's me and we all have a different idea on what we consider "worth it".

You could probably push the shoulder forward a little then square it off with a 40 degree on the 7PRC and gain the same or even more with a little less work but you'd still be in it custom dies and reamer and for how much gain, maybe, 100fps.....

 

[762 ULTRAMAGA]

Sounds like a giant unnecessary PITA but I agree that route #2 sounds like a bitchin cartridge. Route #1 is probably what I'd do if forced to choose(with 700 pattern LA though) because it sounds easier.

I don't know enough about brass but was under the impression that hardness and thickness is prone to vary as you go down the case. I'd wonder on if that would cause issues with route #2? Wouldn't you end up with thick ass necks or need to neck turn and then get donuts with firing case stretch that you'd want to turn off again?

Just necking down 200 pieces of 7 SAUM to 6.5 and turning the necks was enough for me to avoid dicking around with this stuff again anytime soon.

Yeah it'd definitely be a bit of work going option 2, and probably kinda silly just to get it in a standard billet Tikka mag. It wouldn't necessarily require neck turning if the reamer was specd right but I'd probably skim turn for consistency.
The donut would be a non issue cuz I'm seating the bearing surface just above that junction where it forms.

If you like to tinker and want to spend the time, money, and effort I'd say go with whichever one excites you the most but for me, for only a tiny gain over the 7PRC, it wouldn't be worth it but that's me and we all have a different idea on what we consider "worth it".

You could probably push the shoulder forward a little then square it off with a 40 degree on the 7PRC and gain the same or even more with a little less work but you'd still be in it custom dies and reamer and for how much gain, maybe, 100fps.....

Yeah I really dislike everything about the PRC case design, it's long and skinnier for comparable capacity, and from past experience fire forming a 30 SM (300 prc improved) a 40 degree shoulder would get less than a 1 grain capacity increase.
In short there's no way a prc will directly compare.
For a real advantage though option 1 would make more sense

 

[762 ULTRAMAGA]

Defently out of my wheelhouse, but I vote for option # 2. Create your own wildcat! What would the reason be to go with a 40 degree shoulder over the 35?

It's a small capacity gain and retards brass growth, only worth doing if custom dies are in the mix with a more radical case redesign

 

[B23]

Yeah I really dislike everything about the PRC case design, it's long and skinnier for comparable capacity, and from past experience fire forming a 30 SM (300 prc improved) a 40 degree shoulder would get less than a 1 grain capacity increase.

I was suggesting pushing the shoulder forward, not just changing the shoulder angle. Pushing the shoulder forward increases the body length which would increase case capacity. It'll leave you with a shorter neck, how much will depend on how far forward you go, but lengthening the body will definitely increase CC more than 1 gr. Rocky Gibbs creations were kind of an extreme version and left his cartridges with a pretty short neck, don't think I'd want to go that far forward, but he certainly increased their case capacity beyond what the Ack Imp versions of the same parent case were.

 

[762 ULTRAMAGA]

I was suggesting pushing the shoulder forward, not just changing the shoulder angle. Pushing the shoulder forward increases the body length which would increase case capacity. It'll leave you with a shorter neck, how much will depend on how far forward you go, but lengthening the body will definitely increase CC more than 1 gr. Rocky Gibbs creations were kind of an extreme version and left his cartridges with a pretty short neck, don't think I'd want to go that far forward, but he certainly increased their case capacity beyond what the Ack Imp versions of the same parent case were.

Oh I'm tracking now,
It'd basically be like the 7 wsm with a super short neck.
It still wouldn't get more than a couple grains though, the 30 and 270 Gidds were based off a case that started with a super long neck and had more room to blow the shoulder out.