Rebuilt 7 Mashburn Super

SJB358

Ballistician
Dec 24, 2006
32,127
2,492
I have had a 7 Mash since about 2015 now. It’s been a great cartridge for me. The first was a rechambered old 70, then I had one built. As most of us who have had rifles built, the first time, it was a little heavy. I also didn’t spec the throating on my custom and it had a mile of throat. Made getting near the lands with any bullet nonexistent. So, I set it back to Kevin Weaver, had him knock the shank off, turn it down to about .6 on the muzzle and put it into a Hunters EDGE McMillan. I also traded the Blackburn bottom metal for Winchester Featherweight metal.



Got it down to about 7lbs bare. My goal is to have it scoped and such around 8lbs with a NF 2.5x10 or a 3x9 SS. Well, I didn’t have any 30mm rings so I grabbed a Meopta 4-14 I had at the house and fitted it up, till the rings come in.



Just a tic over 8 1/4 scoped. I was pretty happy with how it felt.

So I decided to zero it with some old ammo I had with 175 PTs and RL33. I shortened them some so they weren’t jamming and was pretty happy for the first group out of the gun.



Once I had it zeroed close enough I decided to try some VV N570 and 175 ABLRs. I seated them so they were about 70 off the lands and did a quick load work up.



With 77 grains looking pretty decent I loaded up three and let em fly.



I was quite happy with that. Butttttt I’ve been tricked so many times by ABLRs I decided to put three more on top to see if they held up.



Now I was very happy. It’s a fairly light rifle with a decent amount of recoil but man, I am ready to get this one out long.





I’m pretty happy with how it turned out. Seems like it’ll be ready to hunt in no time.
 
Sweet rifle Scotty. You have it set up as a long range hammer that shoots flat as road kill.

JD338
 
sure looks like a winner .




edit to add ;

I never weighed mine all in . I hung it on my lyman trigger gauge. with the scope , 8 pound 13 oz . 25" bbl , .630 muzzle dia , edge stock . I'll guess my extra weight is in the scope rail
 
8 and 3/4’s ain’t too bad either. This rifle was up over 9 with a 3x9 SS on top and to me, my brain says that’s too heavy for a 7 mag.

Jim, what was the load you’re using?
 
SJB358":2t9wkiat said:
Jim, what was the load you’re using?





Scotty , I'm using 175ABLR , 76.5 gr H1000 , Fed 215m , Hornady brass , .070 jump . my COAL is 3.500" off the tip , 2.840" with my ogive tool . it's usually about a half moa load , at 3145 FPS .
 
Scotty , I've been using Hornady brass . it's what I could get easy at the time . I'm going to say I'm about at the pressure limit of this brass , 4 or 5 cycles and it's loosening the primer pockets .

I got some ADG brass I've been slowly working with . die forming , and dealing with donuts . reloading supplies are so scarce I hate to use components fireforming it .

I also bought some quality cartridge brass . it has the correct headstamp for crossing into Canada . I need to run some of this brass , to see where it's at . depending on the covid , I might have a moose hunt that I'd like to use this rifle on .
 
what length barrel do you have ?

in your notebook , you have bullet lengths listed , is this to touch the lands ?
 
Lovely rifle, Scotty. Accuracy does appear to be there, and nearing 3100 fps for a 175 grain pill is getting near stepping out there. The difference between your load and that reported by Jim is academic. Not an elk in the world can tell the difference. Excellent.

Jim, hope you're able to make that moose hunt here in the Great White North.
 
Scotty, that looks like a great set-up. I bet you will get a lot of enjoyment out it. Already shooting pretty good. (y) Dan
 
I like it. As to the Quality Cartridge brass; I bought some three years ago to have headstamped brass for the 338 Jarrett. Ive only used a little of it and it appears every bit as accurate as the fire formed Remington or Nosler 8mmR/M brass I normally use.


Sent from my iPad using Tapatalk
 
jimbires":1bugfspm said:
what length barrel do you have ?

in your notebook , you have bullet lengths listed , is this to touch the lands ?

Yeah, that was was to the lands with a couple of the bullets I might wanna try. I had it throated for a 175 ELD seated at 3.580 to touch.

It’s a 25” barrel.

Mike, you’re absolutely right, once you’re up above the 3k mark, extra is nice but it doesn’t change too much as far as trajectory.

So far I’m pretty happy with it. I might load up a few more 25 further back just to see what happens. I have a few more cases I wanna shoot up so I can anneal and tumble.
 
Scotty , your throated about .100 deeper than mine , I think your at a good place . I've often felt I'm a little short with these long bullets . another bullet you might want to grab a box of is , Sierra # 1940 , 175 gr , SBT these shoot great for me .my load is 71.6 gr H1000 , .012 jump , FED 215 , 3000fps . this load is easy on brass .

I questioned your notebook info , because I need to get something like this put together . kind of like an owners manual for that particular rifle .


Dr Mike , I hope the covid goes away , so I can do this hunt .

salmonchaser , thanks for the quality brass info . it's appreciated
 
I shortened up my load another 25 thousand for a total of .100.



I tried to shoot 3 more on top, but sometimes I should leave well enough alone :lol:



I also ran some BBCs through the gun at a 1/2 grain less in order to match the ABLR speed.



I ran a ABLR in to that group.




Okay! Now I think I’m done messing with it :mrgreen:
 
Good looking, useful hunting rifle and dang Scotty - you've worked up great loads for it.

Love the 175's in a 7mm Rem Mag, has to be just that much better with the Mashburn.

Guy
 
Good looking, useful hunting rifle and dang Scotty - you've worked up great loads for it.

Love the 175's in a 7mm Rem Mag, has to be just that much better with the Mashburn.

Guy
 
Thanks fellas. I’m a sucker for the cartridge.

If I had to start over I might just build a 28 Nosler, but it wasn’t around when I got my first Mashburn and I’m pretty heavily invested in dies now :mrgreen:

So get this, these are the same 50 pieces of RWS 300 Win Mag cases I formed in 2016 when I had the second gun built. I have lost 1 case to a neck split in all that time. I quit keeping track of firings after 12x.

I anneal most every firing, but God, it’s hard to believe they’ve taken that amount of abuse and are still in like new condition. I can’t make the primer pockets loosen and I’m not really using baby loads either.

Definitely taught me to spend my money on great brass.
 
Oh, yeah, great brass makes all the difference in the world. I've certainly had good luck with several European brass manufacturers (Norma, Lapua, and RWS).
 
SJB358":3el8v1vr said:
So get this, these are the same 50 pieces of RWS 300 Win Mag cases I formed in 2016 when I had the second gun built. I have lost 1 case to a neck split in all that time. I quit keeping track of firings after 12x.

I anneal most every firing, but God, it’s hard to believe they’ve taken that amount of abuse and are still in like new condition. I can’t make the primer pockets loosen and I’m not really using baby loads either.

Definitely taught me to spend my money on great brass.

Nice rifle and great shooting too! RWS is great brass, years ago I bought quite a few boxes of their ammo on clearance at Sportsman's Guide just for the brass (for around $17 a box) for my 270 and 280 and kicking myself for not getting more! Ironically the 130 H Mantle in the 270 shoots great in my M70, so I guess I have to use it up first hunting!

In addition to the others, I've had great luck with PMC brass too.
 
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