7mm Mashburn Super Magnum

[SJB358]

Same here Bob. Between Page and Hagel I used to try and find anything they wrote.

What's funny is I bought a 7mm Rem Mag as a first rifle cause of Hagel and that same rifle will become a Mashburn for the same reason.

 

[Bruce Mc]

Scotty,

I too was heavily influenced by Hagel, Page, and even Jack O'Connor in choosing the 7mm rem mag. Hagel wrote the article for the 7mm rem man in Nosler's 3rd reloading manual. He wrote about taking a brown bear with a 175 Partition. That article kept me with the 7mm for a pending elk hunt instead of getting a 300 that I was very interested in.

 

[SJB358]

Scotty,

I too was heavily influenced by Hagel, Page, and even Jack O'Connor in choosing the 7mm rem mag. Hagel wrote the article for the 7mm rem man in Nosler's 3rd reloading manual. He wrote about taking a brown bear with a 175 Partition. That article kept me with the 7mm for a pending elk hunt instead of getting a 300 that I was very interested in.

I've read the same words Bruce. Love that guy and all the same stuff makes me more of a 7mm guy than a big 30. Still love the big 30's but it seems those heavy 7's can/will do the same work.

We shall see when the rifle is done in a few weeks.

 

[gerry]

I would hunt anything here and almost anything in the world with a 175 gr Partition out of a 7 mm mag of some sort, those bullets will dig deep and have less recoil than a 300 Mag shooting a 200 gr at the same speeds. No animal would ever be able to tell the difference. One of the all time classic bullets, anyone run one through some jugs yet?

 

[nvbroncrider]

I would hunt anything here and almost anything in the world with a 175 gr Partition out of a 7 mm mag of some sort, those bullets will dig deep and have less recoil than a 300 Mag shooting a 200 gr at the same speeds. No animal would ever be able to tell the difference. One of the all time classic bullets, anyone run one through some jugs yet?

Yes I did they are impressive Gerry!!! Although my velocity was pedestrian. I was hoping for 3000 but only got 2860 if I recall correctly and 7 jugs.

 

[longrangehunter]

Yeah, but what a terrible thing to do to an 8X68S case! That hurts! Still, not everyone has a 7mm Mashburn Super Magnum. :wink:

Oh come on now Mike, that's taking the euro out of it and putting the cartridge case to good use.... as it should have been, in 7mm!
That gun was wickedly accurate, and back in the day, very fast in anyones opinion. But the brass is $$$ and I didn't like being bent over the barrel to get it! Plus the work FF the brass, I prefer to load and shoot without the extra work involved.

 

[DrMike]

Kevin,

I'm having some fun working with some of these lesser known European cartridges. Here in NA we often reinvent the wheel, unaware of what has gone on elsewhere. I don't gain a thing from working with a 6.5X68 RWS, an 8X68S, a 358 Norma Magnum or a 9.3X64 Brenneke; but it is fun to have something others aren't working with hereabout. For that reason, the 7mm Mashburn would interest me (as does the 280 Ross). So many cartridges; so little time. :grin: I don't mind fire forming brass, but I confess that I do like properly head-stamped brass. And that, in many instances, is going to set me back.

 

[IdahoCTD]

There numbers must be way off on the Boo Boo case. They list the case capacity at 86.1grs of water in a standard 6.5x68 with a 14* 40' shoulder angle and .019" more case taper not to mention that is in a 6.5mm not a 7mm. I measured my 6.5-300wm and 7-300wm cases and here is what I got:

6.5-300wm RWS cases 86.1grs of water (same as a 6.5x68). I get 3230fps with 140's
6.5-300wm Winchester case 90.8grs of water. I get 3300fps with 140's
6.5-300wm Winchester case to the base of the neck 87.4grs of water
7-300wm RWS case 87.8grs of water.

That tells me a 7-300wm in Winchester brass should be roughly 92.5grs full and 89.1grs to the base of the neck. Now look at the case dimensions of a 300wm or 7-300wm compared to the Boo Boo drawing or Mashburn drawing. The Mashburn is smaller than a 7-300wm and would have a bit less usable capacity. The Boo Boo on the other hand is larger in every dimension and would have more capacity. You can't tell me a 6.5x68 with a 86.1gr capacity blown out won't far exceed the capacity of even Winchester brass as a 6.5-300wm. We've blown out 30-8mm Mag cases to 30-358STA (.011" larger at the shoulder and a 10 degree sharper shoulder) and obtained 3.5grs more case capacity. Going from a 6.5x68 to a 6.5 Boo Boo you'd be about 15 1/2 degrees sharper on the shoulder and .019" less taper. That should be at least 6-7grs more powder. When I do my version I'll go to a 35 degree shoulder angle and .504 or larger at the shoulder.

Another example is my 30-338 Norma Mag versus a standard 300 Norma mag. Mine has .008" less taper than a 300 Norma (the same shoulder dimension as the 338 Norma hence the 30-338 Norma Imp. designation) and a 35 degree shoulder versus a 20 degree for the 300 Norma. Mine has 110.3 grains of water capacity in a fireformed case and a unfired 300 Norma is 103.1grs. Even if you give it 105grs for a fired case mine gained 5grs for very little modification. On average it runs 75fps faster or so. I did it so I didn't have to trim brass all the time and the loaded case length would fit through a standard magazine of 3.68". My cases loaded with 230 Bergers are 3.608". It's basically a shorter and fatter 300RUM with better brass.

 

[longrangehunter]

There numbers must be way off on the Boo Boo case. They list the case capacity at 86.1grs of water in a standard 6.5x68 with a 14* 40' shoulder angle and .019" more case taper not to mention that is in a 6.5mm not a 7mm.

That tells me a 7-300wm in Winchester brass should be roughly 92.5grs full and 89.1grs to the base of the neck. Now look at the case dimensions of a 300wm or 7-300wm compared to the Boo Boo drawing or Mashburn drawing. The Mashburn is smaller than a 7-300wm and would have a bit less usable capacity. The Boo Boo on the other hand is larger in every dimension and would have more capacity. You can't tell me a 6.5x68 with a 86.1gr capacity blown out won't far exceed the capacity of even Winchester brass as a 6.5-300wm.

Going from a 6.5x68 to a 6.5 Boo Boo you'd be about 15 1/2 degrees sharper on the shoulder and .019" less taper. That should be at least 6-7grs more powder. When I do my version I'll go to a 35 degree shoulder angle and .504 or larger at the shoulder.

Are you going to use the 8x68S/6.5x68 to make a 6.5 or 7mm Boo Boo or something like it?

 

[IdahoCTD]

It will be blown out more than a Boo Boo but yes that is the case I'm going to use. Per the print above the Boo Boo is .499 at the shoulder and a 30 degree shoulder angle. Mine will be .505 and 35 degrees.

 

[SJB358]

Is the 7mm/300 Win blown out?

Not sure, thought it was a straight 300 Win case necked down. The Mashburn does blow the taper out of the 300 Win, while not much, it does straighten it out.

I get about 92 grains on fireformed Norma cases out of my buddies rifle. Mine should be close as its being cut with the same reamer.

No idea on whose fastest though. Didn't build it cause it was the fastest, more so that it gives a useful jump over a 7mm Rem Mag with a longer box with a little extra jump in powder space. More so in that it seems to maximize the seating of 140-175 class bullets while allowing the bullets to be seated at or near the lands with them all cause of the long neck.

 

[IdahoCTD]

Scotty,


No the 7-300wm is just a necked down 300wm.

The Mashburn is .006" wider at the shoulder and a 5 degree sharper shoulder angle. If the neck shoulder junction was in the same place as the 7-300wm it would gain 1-2 grains of capacity but the shoulder is moved back to lengthen the neck. That reduces the capacity below that of a 7-300wm. It's not much and both are close enough not to fret over the difference. 1-2 grains is worth about 20-30fps at most.

 

[SJB358]

Scotty,


No the 7-300wm is just a necked down 300wm.

The Mashburn is .006" wider at the shoulder and a 5 degree sharper shoulder angle. If the neck shoulder junction was in the same place as the 7-300wm it would gain 1-2 grains of capacity but the shoulder is moved back to lengthen the neck. That reduces the capacity below that of a 7-300wm. It's not much and both are close enough not to fret over the difference. 1-2 grains is worth about 20-30fps at most.

Got ya. Makes sense to me. I was originally thinking a 7-300, but I kinda dug the longer neck. Plus, cases are ultra easy to form. Either way, it should be fun.

Since I have your ear, what do you think about RL33 for the Mashburn with 160's and 175's Nathan? The data looks right, just wondering if you have monkeyed with it in the 7-300 at all. I'd imagine the data is just about the same for both.. I'd bet the only difference in the kinda case used.

 

[IdahoCTD]

I use it a lot in my 30-338 Norma Imp and I have used it in my 6.5-300wm. My 6.5-300wm is just a touch more accurate with Retumbo even though it's 60-70fps faster with R-33 and since barrel life is limited already I don't play anymore then I have to. I put nearly 200 rounds through the gun playing with loads before I settled on the one I shoot now. The reality is that is at least 1/4 of the barrel life so I jump on what worked and now I have about 350 rounds through that barrel. I do have a spare barrel in the safe though. It's pretty crazy accurate at long range too so I don't mess with it. I don't shoot my 7-300wm's nearly as much as my 6.5's and 30's so I haven't really played much with them. The second one I built shot what the first one likes and shot a 1/4" 3 shot group the first group out of the gun. A few days after that it went 11 for 12 shooting rock chucks and pigeons. It's hard to mess with that but I will try R-33 in it some day soon as I think there is a bunch of velocity to be gained over my RWS brass H-1000 loads. I'll most likely have to use Winchester brass to get enough case capacity though.

 

[SJB358]

Well, I was able to get a few boxes of Hornady 300 Win Mag brass. No one that I know of that's running a Mashburn has used Hornady, but my experience with the 375 Ruger / 35 Newton has been very positive so I decided to take a chance..

I also grabbed a pound of IMR4350 in order to fireform some cases and let me see how the rifle will shoot. A few guys have said 65 grains of IMR4350 with a 139/140 grain bullet work real well.



I also received the call my rifle was completed, so that was another positive. Picked up the rifle in the afternoon. Spoke with the gunsmith for awhile and we made sure some resized cases fit in the rifle and it functioned..Everything was good.



I ran through one box of 50.. Really nice, a little media on the neck and it flowed right through the FL die.. Pretty slick.



Then I loaded up some rounds with the 139 grain Hornady SPBT and 140 AB's. The Hornadys went to about 3.530 and the Noslers were at 3.565"..


So, all that is left is a little range time..

 

[DrMike]

Looking good, Scotty. Your range time will be of interest to me.

 

[IdahoCTD]

Did you just rebarrel your 7RM Scotty or did you do a new barrel? I guess I missed that part.

 

[JD338]

Scotty,

Those FF loads look great.
Hope you can get out to the range soon.

JD338

 

[DrMike]

I do have one question for you, Scotty. When you mix the Gatorade and IMR 4350, how much of a boost in velocity do you observe? :shock: I've never tried this particular technique, but if it works... :mrgreen:

 

[pre6422hornet]

Looking great Scotty!


Can't wait to see the targets your get from her.