Thread: 7mm RM rechambering

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 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.

Thanks mate

the 8x68s case is a really strong non belted case you could neck down

Originally Posted by 57jl

the 8x68s case is a really strong non belted case you could neck down

The BOO BOO series of cartridges!!!

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.

if you're keen on a non belted 7mm mag, do some home work on the 7mm BlaserMag.

It will fit your mag better & will give you ~ 100fps over a 7mmRM burning less powder .
Not quite up there with 7-375 or N28's in terms of speed (~100 - 150 fps) but an extremely efficient and accurate cartridge. I have all three - RM, BM & N28 - so can provide a real world side x side comp.
Ask @Kiwi Greg about 7mm BM vs other options.

Originally Posted by chainsaw

if you're keen on a non belted 7mm mag, do some home work on the 7mm BlaserMag.
Attachment 128186
It will fit your mag better & will give you ~ 100fps over a 7mmRM burning less powder .
Not quite up there with 7-375 or N28's in terms of speed (~100 - 150 fps) but an extremely efficient and accurate cartridge. I have all three - RM, BM & N28 - so can provide a real world side x side comp.
Ask @Kiwi Greg about 7mm BM vs other options.

Given what I want to do the 7BM is looking more and more likely, thanks for the side by side comparison

Reading what you are trying to achieve, I’d suggest doing things properly the first time, probably saving yourself money in the long run and re-barrelling your T3 to 7 Blaser Magnum.

This gets rid of the belt and a 26” 1:8
7 Blaser will push the 180 ELD-M at well over 3050fps, these ballistics are VERY hard to beat in any other sensible cartridge combination.

IF you have the skill, it will also kill big bodied red deer at over 1000m and is very capable of hitting steel to well over a mile consistently.

I initially went the 28 Nosler route, had some fun and burnt through that barrel in 800 rounds, re-barrelled in 7BM and am very happy with the results.
It’s an excellent long range cartridge.

Hindsight is a wonderful thing. I bought the T3 early last year, knowing the 7RM and loving it. And then went and snapped my Achilles’ tendon... twice. And while recuperating after a couple surgeries (and still working on it), going nuts stuck at home I managed to talk the wifey into setting myself up with reloading equipment. To keep the mind ticking over. But that also opened the wild cat door.

So if I could, I’d do things a little different for sure. But, I’ve got what I’ve got, and I’m using that.

Originally Posted by Matt2308

Reading what you are trying to achieve, I’d suggest doing things properly the first time, probably saving yourself money in the long run and re-barrelling your T3 to 7 Blaser Magnum.

This gets rid of the belt and a 26” 1:8
7 Blaser will push the 180 ELD-M at well over 3050fps, these ballistics are VERY hard to beat in any other sensible cartridge combination.

IF you have the skill, it will also kill big bodied red deer at over 1000m and is very capable of hitting steel to well over a mile consistently.

I initially went the 28 Nosler route, had some fun and burnt through that barrel in 800 rounds, re-barrelled in 7BM and am very happy with the results.
It’s an excellent long range cartridge.

If you are happy to single feed, a real easy solution could be to just increase the throat length on your rifle while keeping it as a 7mm mag. Seat the projectiles way out, which will free up case capacity for more powder resulting in a bit of an increase in performance without expensive brass & without burning disproportionately more powder.
Once that barrel is toast and you have some practice under your belt then put together something that is a bit more niche. (specialty cartridge, faster twist /longer barrel)

I recently got a long throated 7mm mag put together. It got up to 309x fps without pressure signs shooting the 180ELDMs. It would have gone higher but that's where my ladder test that i'd loaded up stopped so have no data past that. It does have a 30inch long barrel though.
Just something to consider.

My long throated 7RM has a COAL of 91mm, which leaves around 2mm of space in the standard T3 magazine. 7BM would give you more still.

Originally Posted by Spitfire

My long throated 7RM has a COAL of 91mm, which leaves around 2mm of space in the standard T3 magazine. 7BM would give you more still.

Cancel that - absolute rubbish. Getting my rifles confused. It’s either impending senility or I have too many rifles.

Originally Posted by Spitfire

Cancel that - absolute rubbish. Getting my rifles confused. It’s either impending senility or I have too many rifles.

No worries mate, I figured you had made a mistake.

here a comparison including N28.

I'm getting ~3060 fps with 7BM with 180 VLDs & RL26 with groups around 0.3moa if i do my part well.