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.

Hodgdon max load is 59 gr H4350 with 140 gr 2,927 fps 50,000 CUP, but I find the threshold of extractor groove growth to be at 72 gr.
I find 70 gr 3.34" Nosler Ballistic tip moly has plenty of safety margin for all my rifles over all my hunting temperature ranges to ensure long brass life over many years. It varies between rifles, but typically 3400 fps over the chrono.

I am a fairly careful handloader and the 7mm Mag makes me nervous. My last 7mag an early SS barrel Remington that was really clean wouldn't hit 2800 before ejector marks and cratered primers with 175 NPTs and a few feet per second better with 160s. That was with Retumbo.

Bob you ever play with a 7-300? Seems a lot easier to neck the 300 Winny straight down instead of forming cases for the Mashburn.

7mm RM on the left, 7mm Hart on the Right. No significant difference in performance.

7mm RM on the left, 7mm Hart on the Right. No significant difference in performance.

Bob, are your above 7mag classics using the longer box?

you ever play with a 7-300? Seems a lot easier to neck the 300 Winny straight down instead of forming cases for the Mashburn.

STW...BTDT. No interest.

All I did was answer his question......

I went with the 7x300 for the reasons I stated.

We all know about your passion/obsession with the Mashburn.

I know it's fun to tweak a cartridge or load and pushing it to find a better whatever.
I shoot a simple Tikka SL in 7 RM. My load is a simple 175 Gameking at 2,950, maybe that is moderate to some thinking.
But, when I hit steel at 1,200 yds with a good smack, I know I have enough to do anything I want with it.

Here 's a picture sent by Rick Camuglia. Rick runs a Mashburn with 195's to 1500+ yards.

On the left is a 7 Rem mag, in the middle a 7mm Mashburn Super, and on the right a 300 Win Mag. We can easily see the 7 Mashburn and 300 Win Mag are longer. Th mash burn has the longer neck.Hader to see but it also has less taper. It does not look that much bigger but a charge of 75 gr of H1000 does not even come to the base of the neck! Water capacity is 90 gr.


How'd that happen? Smarter guys than us worked htis out in the 1950's,and optimized the cartridge to give OVER 3000 fps....with a 22" barrel....with a 175 gr bullet. The most modern 7mm magnums don't really beat those performance levels by all that much.

To wildcat the 7RM where you gonna go? Blow it out? it'a already pretty straight. Blow the shoulder forward? That makes the neck shorter than it is which is already a drawback.Compromises bullet seating.

Simply put the 7RM does not have enough case to work with if you want the next step up in velocity.

BobinNH
I have a 7mm mag. Why do I need all that other stuff?

Why do I build anything other than 7mmRM rifles?
I don't have to make sense.
It is a hobby.

I have never gotten over 2900 with a 150 without very high pressures. I am going to try R26 and 7977...perhaps they will deliver more.

Whelen Away: Here you go. I think this is a drawing of my Mashburn reamer so you can play with numbers. My eyes are too fuzzy in the middle of the nite to start playing with numbers.

I have measured once fired Masburn WW cases many times. They hold 90 gr of water to mouth of case. Ditto for all my pals who now have Mashburns.

Other than a shorter neck there is precious little difference between the Mashburn and the 7mm/300 Win. They are both very good cartridges.

Bob and I have been fooling around with the 7 RM since the early 80's.
I had an Echols Legend and several others. I tried longer throats.
All had very good custom barrels. The best you are going to get, on average, is 3200-140, 3125-150, 3050-160, and 2950-175. If you get much more it is because of higher than normal pressures.

I have had so many custom 270's that I can't count them. The longest were 25". I have never gotten over 2900 with a 150 without very high pressures. I am going to try R26 and 7977...perhaps they will deliver more.

Is the 7 more? Well yes the numbers are bigger, no question. Does it translate into a decisive in the field difference? I can't see any difference until you get to the 175's and then the big 7's are more like the big 30's. Me, I can't tell the difference in recoil between a 175 or a 180 at 3000+. Both have more recoil than I want to deal with so I use a 270.

The 7 RM is what it is...very good but neither magical nor mystical. Actually, I don't think anything is.

I just bought an early 80s Rem 700 Classic in 7mm Rem. Got it home and think it is unfired. I may have to get an action wrench and some take off barrels and do some experimenting.

Is it bad that I'm thinking of building another Mashburn?

I have over 50 rifles, and none of them run. What am I doing wrong?

I have over 50 rifles, and none of them run. What am I doing wrong?

Timing? Spark plug gap? Fuel?

Found it!

I agreed to purchase a 7mm Weatherby today and was looking at Nosler data. They are showing in many cases 8-9 grains in additional powder charges for the Weatherby over the Remington and significantly more velocity with the Weatherby, but are listing case capacity as identical.

Interesting that powder charges are that much higher with the Weatherby round. I have never loaded for a Weatherby, but the one I played with did 3200 with 160s and both Weatherby and Federal factory ammo.

Never, never, never shoot the donor.
I'd still throat it long and give it the powder it begs for.