Thread: 7mm RM rechambering

Originally Posted by rupert

Check your mag length for the cartridges you are interested in for a rebarrel. Also, will the cartridges load and feed from your mag? And have you got a spare minimum of $800 for the rebarrel job (not counting the brass, dies, bullets, powder, etc)?

When I get into it I’ll fit the atlasworxs bottom metal using aics mags which will allow 3.6” COAL. That should allow a decent length projectile seating (although I don’t have any info as yet) and the actual case lengths are very similar to the RM, so should be ok there. And I found a thread of kiwi Greg that indicates the 7-375R would be suitable. And as for the cost, I assume a rechamber would be cheaper than a rebarrel, and I could utilise some projectiles and at least reuse the seating die.

Thanks for that info, working up a suitable 180gr load is where I’ll start, and just hand feed when shooting at distance. At the end of the day if I’m not capable of making those shots, then it would be a waste of money to step up to a larger cartridge

Originally Posted by r87mm

Talk to Kiwi Greg. As above 180 eld or berger 180. 7mag 2900-3000ish give or take. Your barrel twist is boarder line and will show at distance more than close. Just because it's stable at 1000 doesn't mean it will be at a mile. 30 or 338 cal would be better. Comparing figures of energy etc isn't comparing apples with apples. 7mm doing over a 100fps faster and 45gn lighter bullet doesn't mark a steel plate that I use. A 30cal cal going slower with the heavier bullet both of the same construction puts holes in it. On paper nothing between them. In real world there certainly is. Like comparing a v8-v6 4cyl with the same hp and similar toque . Put a hill in front of them and see who runs out of puff first

I’ve been halfway through a .338 edge build for the past 6 years or so. I’ve used a Winchester P14 action, but to complete that build, I need to spend a bit on a decent barrel and stock... and grow some nuts to see if the action will take it. So for now I’m just looking at 7mm cal which I really like.

Muzza's quick suntan make you a bit wary on the p14?

My opinion from doing the research, 7 Saum 1-8” 24-26” and 180gr eldm or similar with ADG or similar brass to give 3k a nudge...

Hi Grimus,

This is a great idea and I hope you pursue the project and post pictures of your progress. Do have a chat with Kiwi Greg as he has a 7mm 300NM reamer that could make your life easier.

The previous statement that a .30 cal would do better in wind doesn't mathematically stack up when you compare a 300NM running a 230gr Berger Hybrid @ 2934 fps VS a 7mm 300NM running a 195gr Berger EOL @ 3150 fps. In a full value 12mph wind from 3 o'clock with a density altitude of 0ft (sea level) you will have the following holds (excluding aerodynamic jump, spin drift, etc):

300NM @ 2934fps
1000m: 7.60mils up / 1.85mils R
1500m: 15.50 mils up / 3.24mils R
2000m: 28.03 mils up / 4.96mils R

7mm 300NM @ 3150fps
1000m: 6.42mils up / 1.66 R
1500m: 13.08 mils up / 2.91mils R
2000m: 23.68 mils up / 4.56 mils R

MV's are close to actual. You can possibly ramp MV in both up but intent here was to compare apples with apples as much as possible. I'm not sure what barrel length you are running but have a chat to your gunsmith on what will work best for your 7mm wildcat.

Lastly, make sure you have good glass with the required elevation capacity and rail.

Cheers,

JT

Some good advice above.

T3s are great donors for custom or semi-custom builds, but not ideal for magnum cartridges. The action is not really strong enough, the magazine is too short, the barrels too thin and the recoil too stout. The max OAL you will be able to extract an unfired round is 3.5” in a T3.

As others say, the ELD-M 180 in your 7 RM would be the go, but you will need to forget mag feeding. Powders like RE26 and 33 will fix you up. If you want to go .30 cal you will need to be in the 230+ grain projectile range to match the 180s and recoil will be stiffer.

Do you have a reason for wanting a non-belted magnum? I keep reading about blokes who want this but they rarely seem to know why other than reading that belts are superfluous. A belt is not an issue at all and the case only headspaces off it on the first firing anyway.

It’s your choice and you should have what you want, but the T3 isn’t the best choice for your project.

BTW - I have a T3 based .300 Win Mag and it’s good, but not ideal.

.......... and talk to Kiwi Greg. He has a huge variety of 7mm ways to deplete your bank account.

Originally Posted by stevodog

Muzza's quick suntan make you a bit wary on the p14?

Haven’t found that thread, but even the thought makes my nuts shrivel a little bit...

"Cleanly take animals out to 1000m"



I'd urge against that unless you're really sure in your own and you your rifle's abilities. The chances of maiming/wounding an aminal goes up and up, as your ability to guarantee perfect shot placement goes down and down. 1000m is getting really sketchy and better balistics can only reduce the margin of error by so much. There's just so many variables, some of which you cannot account for.

Originally Posted by DBL

Hi Grimus,

This is a great idea and I hope you pursue the project and post pictures of your progress. Do have a chat with Kiwi Greg as he has a 7mm 300NM reamer that could make your life easier.

The previous statement that a .30 cal would do better in wind doesn't mathematically stack up when you compare a 300NM running a 230gr Berger Hybrid @ 2934 fps VS a 7mm 300NM running a 195gr Berger EOL @ 3150 fps. In a full value 12mph wind from 3 o'clock with a density altitude of 0ft (sea level) you will have the following holds (excluding aerodynamic jump, spin drift, etc):

300NM @ 2934fps
1000m: 7.60mils up / 1.85mils R
1500m: 15.50 mils up / 3.24mils R
2000m: 28.03 mils up / 4.96mils R

7mm 300NM @ 3150fps
1000m: 6.42mils up / 1.66 R
1500m: 13.08 mils up / 2.91mils R
2000m: 23.68 mils up / 4.56 mils R

MV's are close to actual. You can possibly ramp MV in both up but intent here was to compare apples with apples as much as possible. I'm not sure what barrel length you are running but have a chat to your gunsmith on what will work best for your 7mm wildcat.

Lastly, make sure you have good glass with the required elevation capacity and rail.

Cheers,

JT

Impressive data, thank you very much for that, and will definitely look into 7-300 NM too. I hadn’t planned on opening the bolt face, but that is definitely an easy option, especially seeing the info you’ve just given

Originally Posted by Spitfire

Some good advice above.

T3s are great donors for custom or semi-custom builds, but not ideal for magnum cartridges. The action is not really strong enough, the magazine is too short, the barrels too thin and the recoil too stout. The max OAL you will be able to extract an unfired round is 3.5” in a T3.

As others say, the ELD-M 180 in your 7 RM would be the go, but you will need to forget mag feeding. Powders like RE26 and 33 will fix you up. If you want to go .30 cal you will need to be in the 230+ grain projectile range to match the 180s and recoil will be stiffer.

Do you have a reason for wanting a non-belted magnum? I keep reading about blokes who want this but they rarely seem to know why other than reading that belts are superfluous. A belt is not an issue at all and the case only headspaces off it on the first firing anyway.

It’s your choice and you should have what you want, but the T3 isn’t the best choice for your project.

BTW - I have a T3 based .300 Win Mag and it’s good, but not ideal.

Now I could say that the belted magnums don’t like being FL sized and end up with case separation due to work hardening... but I’d be full of s****. Honestly, i don’t like the belt purely because of looks... shallow I know!

And I know the T3 isn’t ideal, but it’s what I have, and what I’ll use.

Originally Posted by PommyMcPomFace

"Cleanly take animals out to 1000m"



I'd urge against that unless you're really sure in your own and you your rifle's abilities. The chances of maiming/wounding an aminal goes up and up, as your ability to guarantee perfect shot placement goes down and down. 1000m is getting really sketchy and better balistics can only reduce the margin of error by so much. There's just so many variables, some of which you cannot account for.

Absolutely agree with you. But having the theoretical energy (1000 ft/lbs) to take an animal cleanly and taking that shot are two very different things.

Originally Posted by Grimus

Impressive data, thank you very much for that, and will definitely look into 7-300 NM too. I hadn’t planned on opening the bolt face, but that is definitely an easy option, especially seeing the info you’ve just given

I dont believe 300NM class cartridges will fit in Tikka action. The cartridge is closer in size to .338lapua. It certainly wont fit in a Tikka magazine.

7mm with the right projectile will generally have better ballistics than the .300s. The only mainstream .308dia projectiles im aware of that has a higher BC than the 7mm 180 ELDM are the Hornandy 230 and 250gr A-tip projectiles, which only just edge out the basic (and cheap) 180ELDM. Hornady have not yet published the BCs for the new 7mm A-tips, but I have no doubt they will easily top the best BC 30cal projectiles commonly available.

The other thing to keep in mind is the twist rate of the standard barrel. It may not be sufficient for the heavy 7mm's.
The added velocity will offset some of the lack of twist rate, but will it be enough? Im not sure...would be borderline id think. (if we are talking 180ELDM)

Originally Posted by Grimus

Now I could say that the belted magnums don’t like being FL sized and end up with case separation due to work hardening... but I’d be full of s****. Honestly, i don’t like the belt purely because of looks... shallow I know!

And I know the T3 isn’t ideal, but it’s what I have, and what I’ll use.

That’s a good enough reason - it’s your rifle after all.

Good luck whatever you decide on.