Home Forums Hunting & Shooting Hunting Rifles Another 7mm Mashburn Super question

So let's talk logistics on the 7mm Mashburn Super...
Sounds like it will fit my Win M70 magazine just fine, JGS and PTG both have reamer specs on file.
Now what about dies and brass forming again?

Use .300 Win Mag brass, and then what? Run it through a neck bushing die? Then fireform?

Sorry for the dumb questions, never had to deal with this aspect of reloading before.

Then what do you use for a bullet seating die?

Why? What would the 7mm Mashburn Super Magnum do that an available 7mm magnum cartridge wouldn't? When looking at the ballistic tables all of the short 7mm magnums and the Remington and Weatherby 7mm magnums duplicate or better it. Other than the slightly longer neck, a dubious benefit, is it worth the hassle? Mashburn formed it out of .300 H&H brass (except the Long version which used full length brass). It would require similar tooling to my .375 Epstein Magnum formed on the .375 H&H, form and trim die, ream die, full length die. Necks should be annealed due to moving so much brass and forming the neck from the parent brass shoulder. I'm sure that forming the cases out of .300 Winchester brass would require similar tooling if the new neck will be moved into the old shoulder.

Now a days I could just buy a .375 Ruger and open a box of ammo or brass.

Is it worth the effort?

If you wish pm me your phone # and I'll talk you thru it.

Dober

It's a snap...run a 300 Win Mag case through the form die, then the trim die...next FL die and charge your FF load if you want to do it that way.

I hear some others simply run 300 win mag brass through a Mashburn F die, and let it go at that...I'm going to try that as well.

BTW the FF load is as fast at milder pressures than what 280AI's strain at the gills to get.Perfectly useable for hunting at that stage.The load Dober gave me does 3190 with the 139 Hornady. That works...

OR, you can charge the case with 13 gr Bullseye,dry tumbling media,large pistol primer,and have nice new, perfectly formed Mashburn cases.

Why do it? well you don't have to...but it is not true the 7RM is as fast...it is not, unless you really lean on it....the case holds more powder than either the 7mm Weatherby or the 7RM, not as much as an STW.

It gives 3200-3250 with a 160;3050-3075 with a 175 easily from a 24" barrel.The smaller 7's are not as fast IME, not at pressure I'll live with day to day.

I have not encountered any ofthe problems Wrangler John mentions above.

I am not wildcat guru...this thing is stupid simple, maybe superfluous today,but it takes a back seat to no 7 mag on the market today.

Thanks guys. Looks like RCBS makes the form die. What are you using for a seating die? Are you using one specifically made for the Mashburn Super? Could you get away with backing off some sort of commercial 7mm seating die?

exbio we have two sets....my pal has an RCBS set which includes form, trim,FL and seating. Thisis just like Dober's sent which (bless his little heart he loaned me to get started.

I have this set on order from RCBS also.I have not tried this but suspect this set up might have been required when cases were formed from 300H&H cases.

Just the other day, I got my FL and seat die from Redding which I have not used yet.

I hear through the grapevine that a prominent gunmaker who has recently built a Mashburn for a client, has just been running 300 Win Mag cases into the FL Mashburn die,and then fireforming.Again I intend to try this and see how it works.

This die set cost me $175 bucks.

OU76,who posted on here,did the fastest Mashburn conversion I know of....he got the RCBS dies. He had is rifle up and running in no time.

You should follow up with a call to Dober as he will fill you in on any little details. This is not a tough wildcat to form.

If I can do it,anyone can.

Just got off the phone with Dober.... and basically I blame you all you guys for getting me into this.

I found a reamer in stock with PTG and that's on the way right now.
Talked to Redding earlier, and they had a full length die set, but it was claimed by another customer. Said they'd call me back if it wasn't actually sold.

Now that, I'm getting myself commited, I still need some sort of dies. I believe, and correct me if I'm wrong here (and it sounds like a call to the 'smith is in order), I can just use that reamer in a $25 die blank to at least build a full length sizer die, and get away with a backed off seater for the time being.

From an earlier post, it sounded like people managed to survive shooting 7mm Rem Mag brass in a Mashburn chamber, but I'm not sold on that idea yet.

I'm pretty sure a die reamer will need to be a little smaller in each dimension than the chamber reamer.

Correct.

NO don't do that!Not as far as I know anyway.... Others may know different.....

I know about that die set at Redding...Chuck and Rick (both from Canada), Matt and I started the whole thing at Redding...they used cases from my rifle and Matt's to build those dies....Matt's rifle and mine were cut with Dober's reamer.

As to making the die,I'm sure it can be done...Redding has the blueprint now though...might be easier to go that route.
I guess you could se a 7RM or STW seat die to get by for now but really do not know....never tried it.

Blame Dober;he started it ....think you will like it...everyone else has so far.

Alright, so here's where I'm at....
Like you guys pointed out, smithy wasn't about to use the chamber reamer to cut a sizer die.

BUT....... there's a guy on gunbroker that is offering a 7mm Mashburn loading service that might be able to get me up and running while I wait for dies. Still gonna need some brass though

Uhh, so if anyone else wants to get in on this, RCBS has already scheduled a production of 1 set of case forming dies at the end of this month. They said it wouldn't be anything to add another one or two to the production.

The Rick from Canada here. Just to let you know, I can verify that the customer who has his name on that set of Redding FL dies is taking them. Cuz that customer is me.

Payment should be there by now.

I always knew you were a smart fella there Rick..

Dober

Exbio thanks...I think my dies are in that run they are gonna do, but I will verify the order was placed tomorrow.


You do good work

Blame Dober!

Perhaps. But obviously I take advice from unsavory characters!

Should that be blame or thanks...

Just trying to show the world a betta way.

Dober

It would be thanks.

Looking forward to seeing a 160 TSX clocking 3250 out of a 24" barrel.

Reettuummbbooooooo