Home Forums Hunting & Shooting Custom Rifles & Wildcats Rechamber to Mashburn or 7-300WM

I couldn't tell you to be honest. Haven't tried it.

I'll give it a whirl the next time I load some more up.

Okay, so I knew from last time out I wanted to shorten my rounds up about .010" since I was getting the 2 in and 1 out. I also split my load with 75, 75.5 and 76 and here is what I ended up with..



Averaged out to 3210 today over the chrono. So, I am happy. I am sure I could monkey with it, but honestly I am very happy with it. I met my goals with it. 3200 with a 160.

I know there is more speed to be had, if I dropped down to a Retumbo or RL33, but I am good with the consistency I am getting with H1000.

Also, I have a sweet shooting deer load with the 140 AB and IMR4350 at 3200. I figure the 280 Ackley guys are on to something there. The nice thing is it is really easy shooting load in the MSM.



I figure I can monkey with it as time permits, now that I have the main load out of the way.

So, all in all, not counting the fireforming loads, it took 12 rounds to find my powder charge, then 9 rounds today to find the seating depth.. Pretty happy with it.

Cartridge was very mild mannered across the board. Case forming is nothing more than I do with new brass anyhow, so turning 300 Win Mag cases into Mashburn cases was too easy.



Speed came pretty easily without feeling like I was standing on it. The cases all have three firings on them and they seem tight. Even the couple I ran up to 77 grains that were hot stayed tight, so the Hornady brass is holding up well.

My box is 3.630" and I just tried a 162 AMax and saw rifling marks on the bullet when I chambered it at 3.630", so I'd say YUP..

Well, I took the Mashburn out yesterday, just wanted to run a few rounds through it to see how well the 160 AB, 75.5 grains of H1000, CCI 250 and reformed HDY cases are holding up...

Pretty happy with it..





Feel like I am ready to stretch it out a little...

Nice Scotty. That works.

Of course we knew it would. Not too hard huh?

That's your factory barrel re chambered, right?

Is there much difference between the Mashburn and the 284 Jarret round.

The 7mm RM is just fine.

Instead a more effective upgrade would be to trade in that entry level 700 for a better designed rifle.

If only your mother followed the same advice.....

Bertzs,

Looks to me like you have found some great loads for your rifle! Congratulations on a terrific upgrade and the results you are getting. I hope as much for mine when I am feeling up to toying with it again.

I am going to see how fast I can run some Moly'ed 140's of various manufactureres and hopefully report back here.

The last two years I ran Moly'ed Barnes 120gr TTSX's at 3600fps and they were terrific. Just going to toy with some bullets with a bit more BC. My rifle will be a deer rifle only, so no need to play with heavies here. And, I would have no fear of punching an Elk with a TTSX 120 or 140 if I needed to.

Thanks for the report, data and pictures here. I am so drinking in all of the 7mm MSM talk. Makes me miss Dober just a little bit less, him having been the resident (and very succesfull) 7Mashy pusher here for a long time.

154 Hornady at 3290 fps. 7mm Bee Euromark

Beretz rifle is a M70 PF punched to Mashburn,so what this post about Rem 700 bolt handles falling off has to do with expansion penetration tests of a Bitterroot I have no idea. But in usual CF fashions wandering minds seem incapable of sticking with the topic of the thread.

Kind of like little kids with ADD.


As to these tired old conversations about which of the Weatherby and the Mashburn are "faster" it may be worthwhile to think about the history of the two cartridges.

Why, if the Weatherby came first in the mid 1940's,did guys like Art Mashburn develop something else? Why did people like Page and Hagel not latch on to the Weatherby and use the Mashburn instead? Why did Mashburn also develop other wildcats in 30 caliber,much like the 300 Weatherby at the same time? Not hard to figure out...


The Weatherby came first,was proprietary and featured a 12 twist designed for light bullets,and had very long freebore. So if it existed why did guys like Art Mashburn develop their own wildcats similar to the Weatherby,not only in 7mm but 30 caliber and other calibers as well?

It was because they did not want to pay for expensive proprietary brass,did not want to form radiused shoulders(which serves no useful purpose at all and is mere hype), and did not want free bore which, with bullets of the day caused accuracy to suffer. Art Mashburn mentioned this in his load data.

.Plus, then as now, savvy riflemen knew that the LR magic in 7mm rested with the heavy 7mm bullets and the 12 twist of the Weatherby rifles would not stabilize 160,175,or 180 gr bullets. The riflemen of the day were not really all that happy with this arrangement with the 7mm Weatherby, the reason the cartridge was never very popular until the 7mm Rem Mag became available. It took Weatherby a few years to wake up and give their barrels a faster twist and shorten the free bore.

(Even the guys like Les Bowman, Wayne Leeks and Mike Walker of Remington had enough brains in 1962 to give the 7 Rem mag a twist of 9.5 so they could use 150-175 gr bullets, But those guys were experienced hunters and shooters.....not insurance salesmen).

So, the Mashburn was an engineered solution to an engineering problem; designed to seat heavy bullets closer to the lands and still have enough capacity to give a 175 gr bullet over 3000 fps. It is no trick to push them at 3100 fps. with modern powders. 160 gr bullets will easily hit 3250 from a 24" barrel and ,like me,Beretz exceeded that number during load development but backed off and settled on 3200 fps with the same load I use with H1000.To grab another 50 fps is like breaking sticks.

There are today a slew of 7mm magnums out there that give these same general performance levels; the Weatherby, the STW,the Dakota,the LRM,and the new 28Nosler among them.The Mashburn sits about squarely in the middle of these in terms of capacity and a formed case holds 90 gr of water ( the new 28 Nosler holds 93 according to figures I have seen).This is not an accident; it was by design. More capacity in a 7mm bore does not get appreciably more velocity and in many cases will require a longer barrel and heavier powder charges to do so.

The Weatherby seems to hold a couple of grains less; It gets its speeds with free bore and pressures likely in the 65,000 psi range.Even today some smiths cut chambers for Weatherby rounds with standard throats to seat bullets closer to the lands (everyone seems obsessed with this today) and (almost) everyone knows that you can't run Weatherby data for hand loads,and Weatherby factory ammo in a short throated rifle without freebore. You will probably run into pressure issues either way.

So if Weatherby rifles,and freebore,and long jumps into the lands with factory rifles are your thing that's fine.....get a Weatherby factory rifle and be happy. But none of that is a feature I will deliberately build into a custom rifle.

I think in some circles on here, this long jump and not being able to reach the lands is known as a "goat puck",and I agree. YMMV.

For all those scared to death of forming a wildcat,my good acquaintance on here 79S was good enough to show me a source of factory Mashburn brass so I don't even have to sweat the forming process,(which was never really a big deal anyway). I bought 140 rounds of the stuff so I am all set for now(It cost about the same as 7mm Weatherby but not close to $4/round)....I can still make all I want from 300 Win Mag instead of paying $3-4$ bucks each for the boutique chamberings. All this wheel spinning and madison Ave hype, and Art Mashburn gave LR riflemen what they needed in a belted 7mm 60 years ago....hilarious.



Scotty, that BBC shows typical performance and what I've seen from the bullet on animals up to elk sized. I'd happily shoot that combo on anything here,including an Alaskan brown bear.It will make short work of your elk this season.I hope to take the Mashburn with that bullet moose hunting this fall.

Excellent summary, wrap up to now 12 pages of disscussion, and history. Long live the 7mm Mashburn Super! A perfect 7.

Your on another planet..

Bob nailed the Mashburn. I didn't do it cause it is appreciably "better" than a 7mm Weatherby or even as fast as the STW but the cartridge fits very well in a 3.6" magazine box on my Model 70. It was an older 7mm Rem Mag that was my very first big game rifle. Having the reamer run up into the chamber cleaned up any/most of the throat erosion that was there from years of shooting.

Making the MSM cases is very easy. I have been shooting Dober's fireforming load (IMR4350) with 139 Hornady's and 140 BT/AB's. They all shoot very well and run right at 3200 with around MOA accuracy.

The whole works cost me 125.00 for the rechamber job as I borrowed a reamer. So I figured I wouldn't be out of much money if it turned out to be a dud. It's not..

Right now I am working with 175 PT's and H1000.. Everything is looking pretty good at first glance. Just like the 160 AB's did.. A little tweaking should have me sitting squarely in the 3050-3075 range for the 175's. All I was hoping for was 3050, so it met that goal and my reformed Hornady cases are holding up very well. No trimming yet either, nice byproduct..







I did try a little Retumbo I had left as well.. Looks decent as well.





So, all in all, I couldn't be happier. Rifle weighs right at 8lb's 8oz's with 3 rounds in the rifle..

[img]http://i723.photobucket.com/al...-998F-B61D0A9BAB29_zpspyq7fvfm.jpg[/img]

Just to add some more to this.

This is where I ended up with the 175 PT. Pretty happy with it.