7-300 Norma Mag Improved. IT’S ALIVE!!

[Huntnful]

Gathered some more pressure data today, but this time with the brass formed in this chamber.

And it looks like the other dummy brass I was using to get initial charge weights was giving a little bit of forgiveness on the pressures signs. By about a grain or so.

So here's my legit numbers that I can feel pretty confident in sharing as of now. These are top end charges, but below pressure signs.

180 ELDM
N570 - 90-91gr. 3300-3330fps
Retumbo - 87-88gr. 3240-3265fps
H1000 - 84- 85gr. 3190-3225fps

190 LRHT
N570- 87-88gr. 3200-3230fps
Retumbo 84-85gr. 3140-3170fps
H1000- 82-83gr. 3100-3130fps

 

[Phil Rizzo]

Gathered some more pressure data today, but this time with the brass formed in this chamber.

And it looks like the other dummy brass I was using to get initial charge weights was giving a little bit of forgiveness on the pressures signs. By about a grain or so.

So here's my legit numbers that I can feel pretty confident in sharing as of now. These are top end charges, but below pressure signs.

180 ELDM
N570 - 90-91gr. 3300-3030fps
Retumbo - 87-88gr. 3240-3265fps
H1000 - 84- 85gr. 3190-3225fps

190 LRHT
N570- 87-88gr. 3200-3230fps
Retumbo 84-85gr. 3140-3170fps
H1000- 82-83gr. 3100-3130fps

Impressive!
Do you have a fired case h2o capacity?

 

[Huntnful]

Impressive!
Do you have a fired case h2o capacity?

Just measured it at 108gr.

 

[slikmrc]

Couple of questions. How many groove barrel and what brake are you using? Thanks, that rifle is a beast.

 

[RH300UM]

Those 7-300 (338) NMI are a beast. I've been working with them since 2009 or so. Many barrels torched and many reamer designs (6).
I average 600 rounds now on a barrel (proof research 8 twist) before the throat is beyond use. Barrel number 3 for this build is coming. My sons rifle (the original build for my ideas) is on its 3rd barrel.
My load is N570, Berger 195 eol, Lapua brass, Fed 215gm full length sized in a Whidden die.
It will push the 195's 3300 fps but I'm around the 3250 fps mark because at the 33 mark it has a large amount of torque at the rifle lifting the bipod onto 1 leg.
Yes horsepower comes at a cost but I think it's worth it. Yes I push it.
Having a cartridge like this and going easy on it isn't in my playbook. I'll always have it in my stable of rifles

 

[Huntnful]

Couple of questions. How many groove barrel and what brake are you using? Thanks, that rifle is a beast.

This barrel is a 4 groove Brux and a SRS 4 port .760" stainless brake.

Those 7-300 (338) NMI are a beast. I've been working with them since 2009 or so. Many barrels torched and many reamer designs (6).
I average 600 rounds now on a barrel (proof research 8 twist) before the throat is beyond use. Barrel number 3 for this build is coming. My sons rifle (the original build for my ideas) is on its 3rd barrel.
My load is N570, Berger 195 eol, Lapua brass, Fed 215gm full length sized in a Whidden die.
It will push the 195's 3300 fps but I'm around the 3250 fps mark because at the 33 mark it has a large amount of torque at the rifle lifting the bipod onto 1 leg.
Yes horsepower comes at a cost but I think it's worth it. Yes I push it.
Having a cartridge like this and going easy on it isn't in my playbook. I'll always have it in my stable of rifles View attachment 548788

Awesome! Appreciate the info! So your getting 600 rounds of barrel life using N570 from start to finish?

 

[RH300UM]

Awesome! Appreciate the info! So your getting 600 rounds of barrel life using N570 from start to finish?

Yes
That's my "average" for the last 2 proof barrels
I define barrel use life as when accuracy degrades to over 3/4 moa @100 yards. Your mileage may vary.

 

[skipglo]

Only thing I can say is .....Don't Cerakote that beautiful barrel!!!!!

 

[Huntnful]

Happy with the cartridge and speeds. So time to go back to @Barehandlineman11 for the new hunting barrel. Going to finish it at 25". Definitely dangerous having such a good gunsmith only an hour away. I want 10 new builds now hahaha.

Benchmark #5 8.5 twist. About 14oz lighter than the current barrel. Going to fire form with H1000 in this barrel and hopefully just go straight to the 84gr. of H1000 area and 180 ELDMs. Possibly 87ish gr. N565 is a potential also.

 

[RH300UM]

I'm at 86.7 of N570 with the 195's for my rig

 

[Huntnful]

I'm at 86.7 of N570 with the 195's for my rig

That sounds right on the money. Because I still had just a little pressure at 88gr. N570 and 190 Berger's

 

[Huntnful]

The ugly truth of mega overbore hahaha. 123 rounds in. Some decently fast paced shooting I guess. But all my 5 shot groups were shot over 5 minutes. And I always waited at least 5 minutes between groups with the barrel cooler going and 40 degrees outside.



We'll see what being a little more cautious and with H1000 does in the next barrel haha.

 

[Barehandlineman11]

She gone

 

[E4aker]

Wow…That looks like a 300 nmi with 800rds on it!