Home Forums Hunting & Shooting Custom Rifles & Wildcats Here's my 7mm Mashburn, show us yours!

I had my rifle built because of Bob and Big Beretzs, plus, it's an oddball and something different, also recognizing the old Oklahoma Wildcatter that invented it, Art Mashburn!

Probably the biggest proponent of the Mashburn on the forum was Mark "Dober" Dobrenski. He's used it for well over 30 years, and both he and his wife continue to do so. Mark knew Bob Hagel, and of course was inspired through his relationship with Hagel to build one in the 1980's. I'll bet Mark has burned out more Mashburn barrels than anyone alive in the country.

It does seem beretzs has picked up Dober's mantle here...

Beretzs, what twist was Bob's rifle?

He has a 9 twist Krieger on his.

Brad, last Dober said, I think he was on his 7-8th barrel.

I'll gladly carry the colors!

I try to tell folks the same thing he told me. If you want an extra 75 and sometimes 100 FPS, the Mashburn is the one, if you don't wanna mess around and just be happy with 30 dollar dies and a solid hunting rifle, a 7 Rem Mag is your beast.

Is it possible to l9ad the Mashburn without a trim die?

I guess what I'm asking is what is the easiest way to prepare brass?

On my first go around I just stuffed the cases in a FL RCBS die and used a mandrel to open the neck up to the desired dimension

I got the form and trim dies when I got my 2nd Mashburn built.

My buddy just uses the FL dies to make his brass. Form and trim make it a little easier but you could do without them.

Form Die with Virgin 300 Win



Brass after it comes out



Trim Die



Trim die brass



After that I run it through a FL die in order to get the ID to the correct dimension I want.



Or you can just stuff them through a FL sizing die once.. I use the F&T die since I have them, but not needed.

I have the same Form/Trim dies as Scotty, as well as a couple FL sizers (one is out on loan).

I size them ‘close’ with my Trim die but I don’t want them to chamber. I perform the final sizing with the FL die so they are as close size-wise as they can be to the chamber on first firing.

I ran a case through the FL die just for you! No form/trim die at all. It’s not as pretty but it would fire form just fine and then look just like any other Mashburn case.

300 Win Mag Winchester brass




FL die, this one is a Whidden


Finished brass


If you were going to go this route I would recommend a die that sized the entire neck, ie a Redding FL or RCBS FL die and not a Redding Type S bushing die.

Here’s a comparison. I ran this one through the Form/Trim/FL die like normal.

Before


Finished product, just FL die piece on the left. Form/Trim/FL piece on right. Not much difference.

Thanks fellas, great info.

So I should be able to simply run 300 Win brass through a FL die, and then fireform?

Donut issues with this method?

I have RCBS FL dies, Form and Trim dies, Lee seater and neck mandrel dies, and Whidden custom bushing dies. I only have a couple of pieces of unformed brass, but just took the bushing out of my Whidden die and sized/formed the body of the case. Then I ran it into the trim die to form the neck. This seems to have worked very well.

That’s a good looking case!

Should work fine to run them into an FL die and then fire form. The form/trim dies will produce better concentricity but if you fire form it doesn’t matter.

The form and trim does are nice but RCBS 58151 might be discontinued. Maybe you could custom order them from RCBS though. I tried calling but CA is sheltered in place.

Donut issues. Probably. I haven’t been able to avoid them. That 300 Win Mag shoulder becoming the base of the neck is just there. You can ream it out, neck turn it, whatever, but I would be surprised if you didn’t see them eventually.

When I first got the Whidden die I thought my donut issues had went away, but after a few firings I started detecting them again. It’s no big deal to ream the necks with my K&M tool and once finished that brass never needs it done again. Next batch of cases I form up will get reamed right away. They cause all sorts of accuracy and pressure issues so not doing it isn’t smart.

Whidden dies are the way to go now. Doughnuts are a non issue with the K&M tool.

I really want to like the Mashburn, but can't quite get over the hump due to the extra steps with fireforming, reaming, etc.

Thinking if I build another big 7 it will be the Nosler or (less likely) another Dakota with a 3.6 box.

It’s a better balanced cartridge than the Nosler, and brass is cheaper and more brands available. But like many wildcats, it has some baggage to deal with. If you’re not interested in jumping thru a few hoops to enjoy what it offers I’d suggest staying with the the good old 7mm Rem mag. It’s the easiest, cheapest and best alternative. If the Rem mag or MSM doesn’t have enough HP the fix isn’t a 28 Nosler or Dakota, it’s called a 300Wby😎

M700 BDL.
Mark Chanlynn No.4, 1-10
McMillian GP/HTG
Trigger Rifle Basic.
Zeiss 2.5-10x50 VM ..... Dont tell anyone..
TPS rings,rail.
Finished in Duracoat desert digital camo.
Accurate Rifle Works.

I talked quite a bit to Bob about it before I built it.
He was like a little kid everytime I called him about it.
it was a fun project.



dave