7 Mashburn Rework

I was done getting new rifles...and then I caught the Mashburn bug from Bob, Scotty, and Matt. Matt had this rifle he was willing to part with, and after a brief negotiation and semi approval from the spouse...

Then I took it hunting last fall in Wyoming.



We did well, and I brought home a good bull off public land. Much thanks to Bill, Scotty, and Matt.

But something wasn't quite right. I had to really stand on the pressure, still got ejection marks, etc., and only get about 3050 fps with 160 ABs. The low velocity itself didn't bother me, but the low velocity combined with high pressure signs did. I wondered if the barrel bore was weird, or the chamber, or something. And it just plain didn't like slow powders, often giving me 4 inch groups. The load I took hunting was an H4831 load that shot well, but barely got 3000 fps. And even the shot that took the bull I pulled the brass piece out of the chamber and it had an ejector mark.

So this winter I sent her off to Pac Nor for a new barrel, still chambered in 7 MSM. I also got a custom Lee Collet Die made, etc. When I got her back from Pac Nor I sent her to Kampfeld. He replaced the Rem extractor with a mini-16, gave her a new coat of paint (the stock had some chips out of the finish), replaced the recoil pad that had hardened over time, and touched up the bedding. I also replaced the 6x36 scope with a VX-6. I haven't used a variable scope for several years.



Kampfeld did some really great work! Thanks to Karl for his high standards.

And I'm sure the Pac Nor barrel will shoot great, I'm taking her to the range Monday to start to get to know her. Since she's a wildcat it will take longer than normal, as I have to fire form brass, etc. Scotty and Matt have a wealth of knowledge about loads which is really helpful.

Auuuugh!!!!!!!


Between Scotty's pictures and all this 175's at 3050 business I'm going to want one too! :lol:

Very good looking setup, Joel. I have to believe you are going to find it most exciting. Congratulations.

Good looking rifle!

That does look good Joel. I have a M70 in 7RM that just might get rechambered yet.

Beautiful rifle, Joel. With a Pac Nor barrel that should shoot very well for you. Congratulations!

First range trip today.



The weather in ND is not optimum just yet...and the winds matched that white stuff.



It looks like she will shoot once I get her all figured out. This pic is fire forming brass loads. There are 10 shots on here, 5 in the upper middle shot at 25 yards. Then moved the target to 100, shot 3, adjusted the scope 2 clicks left, shot 2 more. These are all IMR4350 with 139 Hornady bullets. I think it's 65 grains IMR4350? I'd have to look at my notes.



Then I cleaned her to get the Dyna Bore Coat process all done, and moved on to 160 grain Sierra Matchking bullets with Retumbo. I hooked up the Magnetospeed for some pressure information...
73 grains 2977 and 2941 fps
74 grains 3004 and 2986 fps
75 grains 3084 and 3086 fps
76 grains 3119 and 3134 fps

I started seeing ejection marks about 74 grains. But oddly, two of the cases with 76 grains don't have ejection marks. There was also quite a bit of resistance chambering the rounds. I think I probably had the Matchkings seated into the lands, making the pressure spike. I didn't have a good way to measure the distance to the lands without fire formed brass; I'll be doing that today.

Then I put 3 rounds of 76 grains Retumbo with 160 SMK downrange...still work to do. I will try and make it back to the range tomorrow, and I anticipate loading 160 PTs first.

Looks like it will shoot.

Nice looking rifle and set-up! Congratulations.

Nice looking rifle that's for sure! Better luck this time, you should see paydirt with what you have in your hands now!

Very nice! That rifle looks great to me. I think you'll be in business pretty danged quick. I like my VX6. The glass is really danged good.

Pretty mine is going on my 338.

That is a nice looking rifle and the 7mm Super Mashburn sounds like it's what the 7RM should have been.
Can one just run a reamer in a 7RM chamber and set the barrel back 1 turn to clean up the chamber to convert a 7RM?

truck driver":1d1hx3ee said:

Can one just run a reamer in a 7RM chamber and set the barrel back 1 turn to clean up the chamber to convert a 7RM?

Click to expand...

Yep, that is exactly how I made up the first one. The beautiful part is it'll clean up a worn throat on a 7mm Rem Mag a little as well pretty nicely. Mine shot better after the rechamber than it did before. Thinking the good gunsmith setting things straight made it better.

It's about as easy as it comes. Kinda like a 7mm Rem Mag Ackley if that helps :mrgreen:



That's an unfireformed case, but you get the picture.

Thanks Scotty looks like something I might want to do once I get the 338 figured out.