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BobinNH Offline OP
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No, not a misprint.... smile

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. grin

(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! smile

Wish I had built one sooner! wink


Last edited by BobinNH; 09/30/10.



The 280 Remington is overbore.

The 7 Rem Mag is over bore.
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Because people are going to ask.................
[Linked Image]

[Linked Image]



This makes the "ugly stocked" M70 in 7mm Mag that you have redundant. Send it over Robert. laugh











[Linked Image from i.imgur.com]

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BobinNH Offline OP
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Scott, TFF! Laffin here!

Thanks for that!I know how they wail to the high heavens on here with no pics. grin

To me, it makes lots of things redundant..... wink

Last edited by BobinNH; 09/30/10.



The 280 Remington is overbore.

The 7 Rem Mag is over bore.
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Thanks for sharing your project, ole Dober knows the Mashburn all too well. And you'll be giving the critters the Mashburn dirt nap soon too!

MtnHtr




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always thought the Mashburn would be the best 7 mag in creation , but it seems to me that if pushing 175s over 3000 and 160s to 3200 . then recoil has to be alot like a 300Winny ?

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SD: It really isn't...it is just "lighter" somehow..hard for me to explain,and don't get me wrong, it recoils.... but I notice a level of muscle tension needed with the big 30's,and a level of fatigue that sets in with the 300's, not present with this and the 7RM.

Might be nitpicking I know(much of this project is grin,

....but even Gene said it was a pleasure to shoot compared to the 300's.So at least I know it ain't just me smile

At 60, I am a lOT more recoil sensitive than I used to be frown




The 280 Remington is overbore.

The 7 Rem Mag is over bore.
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Bob, do you see any advantage over the weatherby chambering? (one I've thought about) I always "felt" the remington mag was "not quite there", but close!

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Bob,

Good luck with the rifle. Sounds very well thought out and just what you are looking for. I understand the recoil issue but at those velocities, there must be some kick, how is it in comparison to the 7 STW's you have shot?

Don't feel bad, at 41 my recoil tolerences are not what they used to be frown

By the way, I love the name, Mizzum

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pat I have never worked with a 7 Weatherby,and know the manuals show it similar to the Mashburn;but i also know it has about the same capcity as the Remington case,so I really can't explain how the weatherby gets where it does,except due to the freebore,a 26" tube,and Weatherby-type pressures.

I have had a few "long throat" 7 RM's and they nudge right into 7 Weatherby load data territory.But again, I always felt I was leaning a bit hard.The thing that struck me about the Mashburn was how "easily" it reached these velocities.And velocitiy variations are very low,maybe 10 fps in a 5 shot string,at least with H1000.I think Art Mashburn did his homework.




The 280 Remington is overbore.

The 7 Rem Mag is over bore.
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Bob,

I like my long throated custom 7mm Weatherby,but find the 7mm STW to be a lttle much recoil wise.

Likewise.I can do the 300 win mag,but the 300 Weatherby is uncomfortable.

All of this had me thinking about a 7mm/300 Win.

My gunsmith has dies and reamers for this one.

What's the difference between the Mashburn and the 7mm/300 win?

Is it just a 7mm/300 win Improved?

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Chip; Thanks!The STW's I have fired were the M70 Classics,longer, heavier rifles,so it is hard to compare;this stock design of D'Arcy's is very good at mitigating rcoil in a magnum chambering.i fired the rifle off hand yesterday and it is very pleasant,not inclined to jump back hard or climb during recoil.It is more manageable than the 300's, to me anyway.

BTW I gotta give credit where it's due....my buddy Matt took the other Krieger #2 and built the same rifle,metal by Gene,and stock work by Charlie;veddy nice also and Charlie did a great job on the stock.

Yesterday at the range Matt said...."I'm gonna shoot the "Mizzum"........I said "The what?"...he said. "You know,the Mashburn Super Magnum, the MSM!" I laughed! grin




The 280 Remington is overbore.

The 7 Rem Mag is over bore.
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BobinNH Offline OP
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Britt; It is a necked down 300 WM case;first pass with the form die forms the new shoulder and longer neck;second pass with the trim die brings the neck down to 7mm(no trimming required,then through the FL die to tighten up the neck.(Dober had to walk me through all this).

FFing the case blows it out to a straighter contour;the 300 Win Mag has more taper and a shorter neck.

The longer neck is part of the beauty of the Mashburn design, plus the straighter case,which gives a skosh more capacity. The longer neck helps if you build with a longer throat,as I did, because I can seat even 140 gr bullets close to the lands.No bullet I have used is seated into the case,except the 175, and that very little.

The 160 AB is seated to about 3.575 OAL;and the 175 Partition to about 3.515,due to the ogive mostly.

At the end of the day, I doubt there would be much practical difference between the Mashburn and the 300 WM necked down.




The 280 Remington is overbore.

The 7 Rem Mag is over bore.
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Originally Posted by BobinNH
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.


Do you not have one anymore?


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Interesting build; thanks for sharing.

I went to a Mashburn's gun store in OKC as a kid. I wonder if it was the same guy.


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Sounds like a good round Bob.Wanna race for pink slips?grin

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Originally Posted by BobinNH
Britt; It is a necked down 300 WM case;first pass with the form die forms the new shoulder and longer neck;second pass with the trim die brings the neck down to 7mm(no trimming required,then through the FL die to tighten up the neck.(Dober had to walk me through all this).

FFing the case blows it out to a straighter contour;the 300 Win Mag has more taper and a shorter neck.

The longer neck is part of the beauty of the Mashburn design, plus the straighter case,which gives a skosh more capacity. The longer neck helps if you build with a longer throat,as I did, because I can seat even 140 gr bullets close to the lands.No bullet I have used is seated into the case,except the 175, and that very little.

The 160 AB is seated to about 3.575 OAL;and the 175 Partition to about 3.515,due to the ogive mostly.

At the end of the day, I doubt there would be much practical difference between the Mashburn and the 300 WM necked down.


Sounds suspiciously like a .284 Jarret designed by the greatest gunmaker in the whole wide world smirk

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Gene S. ?
M70?
Echols?
Mashburn?
Dober?

WTH were you thinking? Sounds like a, er, well, ah, hmmm, you know, ah, well, eerrr, a pretty sweet rig. cry

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No doubt.

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Mike: I won't bet....you might win grin

Karnis: I did the best I could..... frown smile

oldelkhunter:Seems Jarrett is about 50 years late...gotta admire his taste though...... grin




The 280 Remington is overbore.

The 7 Rem Mag is over bore.
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MtnHntr:There is no doubt Dober knows the Mashburn....he helped make this a pretty easy deal,and was spot on in loads vels, etc.he and Gene got me started really well...been an easy wildcat to deal with.




The 280 Remington is overbore.

The 7 Rem Mag is over bore.
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