Home Forums Hunting & Shooting Custom Rifles & Wildcats Wildcatting the 7mm Rem Mag

Why not a 7mm Mashburn? It will do everything your asking and then some.

Get the Weatherby or the Mashburn. The homework has already been done. No sense reinventing the wheel as MANY have BTDT way before you even start.

The 7 Rem Mag has three drawbacks IMO:

a) Deep bullet seating (unnecessary in a 3.6" action like a rem 700 or M70)

b) neck is short

c) limited capacity.

You can't do anything to significantly improve the thing without too much hassle. The Mashburn is a FAR superior design in a belted H&H case.

If you want to max it out,then seat a 160 gr bullet to the base of the case neck,and put it in a 3.6" box.Throat accordingly. This is kind of like the free bore in the Weatherby.

After maybe 5-6 rifles built this way going clear back to the early 80's, I decided i don't want to roll that way anymore. I take the 7 Rem mag for what it is and built a Mashburn.....FAR superior and willing to please. Friend doing the same thing, have said the same things.


Headstamp brass? Get the Weatherby and problem solved.

But a pal who used to post here has killed all varieties of NA BG trophies 3 times over .. He is Dallas SCI member. He is working on Round #4 with a 7mm Mashburn Super and has traveled to Mexico and Canada several times with his hand loads the last 5-6 hers and never a problem.Killed a record book desert ram in Mexico recently on his second hunt.

He can afford anything he wants and today uses the Mashburn exclusively. With 175 gr TBBC's, he say it kills like his 300 Weatherby.

No one seems to mind that 7mm Mashburn brass is head stamped 300 win mag.

I have had 3-4 7mm Remington Mags and really love the original concept and original ballistics (3260 with a 150 and 175 at 3020) but have a hard time loving the actual cartridge.

Today, the cartridge struggles to get anywhere near original ballistics. Mine have all been finicky, though some have been accurate with certain loads. What I haven't achieved with the big 7 is accuracy, velocity and lack of pressure with a given load. In fact, I have struggled to get much more than hot .280 or .280 AI velocity without pressure signs.

I have read in multiple places that the combination of a shorter neck and just the right shoulder angle lead to quick throat erosion, which causes some of the problems with the cartridges. My assumption is that this is what makes the cartridge in my words "finicky."

I can't seem to find an AI version of the cartridge on any reamer list so am thinking of designing a wildcat, unless something similar exists. My goals are as follows:

1. Stable, accurate cartridge that is not subject to odd pressure excursions.
2. Targeted ballistics of 3000 with a 175, 3100 with a 160 and 3200 with a 150 with below 64,000 PSI MAP (not having a ballistic lab, this may be hard to determine).
3. Ability to use 7mm Remington Mag ammo with no adverse consequences to gun or brass (other than fire forming).

I am thinking starting with a 7mm Rem case and:

1. increasing shoulder angle to 35-40 degrees
2. possible decreasing body taper, but maybe not
3. increasing leade to closer to tight Weatherby type freebore, Maybe .250" freebore of just over bullet diameter.

The 7mm Weatherby acheives all my goals other than number three so maybe that would be cheaper. Not sure what custom reamers and dies cost.

For those, who have created or messed with wildcats, what are your thoughts on the above?

Bob, How did your long-throated 7mm Rem Mags compare to the 7mm Weatherby in the velocity department?

Nosler shows case capacities to be identical between the two rounds with 160s.

I can't seem to find an AI version of the cartridge on any reamer list so am thinking of designing a wildcat, unless something similar exists. My goals are as follows:

It's called the 7mm Hart.

It's called the 7mm Hart.

I'm with BobinNH on the 7 Rem Mag. It may have some drawbacks but it's not a total loser. I've had a few of them. My current one has no problem getting 140's to 3300 with Rel22 or H4831sc and it's Rel25/160 Accubond load would probably average near 3000, I've never done the math. This is a factory 700 24" barrel.
The only drawback it really suffers from is lack of kool

I think the drawback for me is the 7mm Rem has been a disappointing cartridge for me. I always walk away from it thinking why don't I just use a .270? I am currently shooting 150 NPTs out of my 24" .270 and with RL26 getting 3000 fps and good accuracy without pushing hard. I have had difficulty getting a 7mm Rem to do much better but others have more experience with it and get it to do more.

Will it work on game? Absolutely. I'm just not enamored.