No, not a misprint....
2001 or thereabouts brought us the 7mm Whizzum, aka 7mm Winchester Short Magnum(WSM)....a sorta stout,vertically challenged affair and really a copy of a design that originated back in the 50's in the Gradle Express line
But also back around the 1950's a guy from Oklahoma named Art Mashburn(actually known by OU76 who posts on here)gave us,after much experimenting,the cartridge known as the 7mm Mashburn Super Magnum,aka 7mm MSM.The Gradle Express series went nowhere at the time, but the Mashburn was popularized by such notables as Bob Hagel and Warren Page back in the 50's and 60's;and by our own Mark Dobrenski today.
(Worth noting here the 7mm Weatherby was around in proprietary form, but Roy gave his barrels a 12 twist which did not stabilize the 160 gr bullets that LR elk hunters wanted to use.)
Unlike the WSM, the MSM is a long, leggy affair that can fit handily into a 30/06 length action,but adapts nicely to a H&H-length action as well, which means any run of the mill Remington 700 or Winchester M70 can be adapted to it.
After fully half a lifetime (30 years) of using the 7RM, I wanted something a little different in the way of a portable,relatively lightweight all-round BG rifle,with the ability to "easily"(a key component)push a 175 gr 7mm bullet in excess of 3000 fps,a 160 gr from 3150-3200 fps, from a 24" barrel,with moderate powder charges,and would not kick me into next week.Something "optimum" but not too much,as with the 7STW and the Ultra Mag,both of which seem more at home with thick, heavy 26" tubes and/or gobs of powder.The 7 RM with various throatings came close in a 24" barrel but I sometimes thought I was pushing the envelope;I always thought the 7RM could use more capacity and a longer neck.
After watching Dober's results on here with the Mashburn,and talking to him a good bit,I sent a #2 9 twist Krieger to Gene Simillion,along with a M70 Classic action from a 270.A friend from back here did the same thing.Dober was kind enough to lend us his reamer and I am still using Dobers dies until mine show up from RCBS(we had an ordering snafu with another die maker which delayed having dies delivered on time)....
I told Gene I wanted a 375H&H-length box,and he got me an Echols box which easily swallows cartridges loaded to about 3.575 OAL,with room to spare;throating was set up for a 160 Partition with base of bullet even with base of neck;the 175 seats a bit deeper into the case.
The stock is an Echols Legend Edge;very nice!
So what did I end up with here? Well, as Gene said the cartridge is not about ultimate speed;it's about building a portable package for mountain and open country hunting with an optimum velocity level, with long 7mm heavyweights, reasonable powder consumption,and flat trajectory,and without the weight and recoil of a 300 magnum.Near as I can tell, he described it spot-on....
Load development is still in progress but what I am seeing so far is:
Dobers fireform load of 65 IMR 4350 139 Hornady at 3160 to 3190,(which to me is a 280AI in a similarly configured rifle. The Mashburn will of course push a 139-140 gr bullet much faster with full loads).
After fireforming, you have the blown out Mashburn.And 72.5-73 gr H1000 gives the 175 Nosler Partition 3040 to 3075.This bullet has an SD of .310 and a BC of .519.According to the Nosler tables, when started at these velocities,it has about the same trajectory as a 180 gr 30 caliber Partition started at 3200 fps...(the 30 caliber taking a bunch more powder and recoil to get there). My shooting so far is showing this to be true.
Or if you like plastic tips, this cartridge easily starts a 160 AB at 3150-3175 with about 75 gr H1000.I see no logical reason to go with any bullet weighing less from this case,although you can certainly do it.
As to recoil? I have sat behind a bunch of blown out 300's over the years.In comparison, with its' heaviest loads, this rifle is a cakewalk.
Pretty hard to justify the wildcat in light of all the other 7mm's that provide similar performance;but this one "gets there" in an efficient fashion,being just enough without being too much, yet not lacking the capacity, so that one does not have to stand on it to get the desired velocities,as with smaller 7 mags.And the MSM does this in a 24" barrel to boot.
I have had a 7mm Dakota, which is similar,but did not like being tied to one source of brass, and a case not easily formed from anything else.The MSM can be easily formed from 300 Win Mag cases,available anywhere.And if I get tired of the wildcat,a 7 RM is only a rebarrel job away.
Looks to me like Mashburn,Page,Hagel,and Dober knew (know)what they were talking about,even back 60 years ago!A very cool cartridge!
Wish I had built one sooner!
