7mm Mashburn Super Magnum

[SJB358]

Nathan it was a straight up rechamber job. The plan is to see if I like the cartridge and how it performs. If I like it, then a Bartlein, Krieger, Brux or similar will get ordered. I wanted to try it out a little before going all out.

The FF loads are supposedly running between 3100-3200 and most guys report excellent accuracy. Figure it'll give me a chance to shoot some and get a feel for the rifle again.

Mike, I'm thinking the Gatorade would really keep the electrolytes up for max performance! :grin:

 

[pre6422hornet]

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:

I heard through the grapevine Dr. Mike when you mix the gatorade with the 4350 your rifle will be upgraded to .270 win power :grin:

 

[SJB358]

If this rifle performs like a well tuned 270, I'd imagine I would have spent my money wisely. Honestly, the goal of 3150-3200 with a 160 is just about like the classic 130 from a 270 with a touch more bullet weight. Seems like a good place to be.

 

[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:

I heard through the grapevine Dr. Mike when you mix the gatorade with the 4350 your rifle will be upgraded to .270 win power :grin:

So, there is hope that it can reach .280 Rem velocities?

 

[pre6422hornet]

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:

I heard through the grapevine Dr. Mike when you mix the gatorade with the 4350 your rifle will be upgraded to .270 win power :grin:

So, there is hope that it can reach .280 Rem velocities?

Yes there is hope.. :grin:

 

[pre6422hornet]

If this rifle performs like a well tuned 270, I'd imagine I would have spent my money wisely. Honestly, the goal of 3150-3200 with a 160 is just about like the classic 130 from a 270 with a touch more bullet weight. Seems like a good place to be.

Seriously Scotty that is some major speed with the 160. Talk about a long range hitter.

 

[gerry]

Looks nice Scotty hope you have a blast at the range :lol:

Hornady is pretty decent stuff, I had no issues with the 375 Ruger brass. Those look like they necked down well.

 

[JD338]

Those speeds are nipping on the heels of the 7mm RUM with a 160 gr AB at 3300 fps.
Good show Scotty.

JD338

 

[DrMike]

I've used a fair amount of Hornady brass over the years; I've had no particular issues with it. I would guess you will find it more than acceptable for forming your cases.

 

[IdahoCTD]

Nathan it was a straight up rechamber job. The plan is to see if I like the cartridge and how it performs. If I like it, then a Bartlein, Krieger, Brux or similar will get ordered. I wanted to try it out a little before going all out.

Sounds like a good plan. I don't usually do rechambers because the smith work is free for me :mrgreen: . It will be interesting to see your numbers.

 

[SJB358]

Well, here are some results from the fireform loads.. Overall, I could just about hunt happily with the fireform loads the way they sit now. A little seating on the 140 AB and it would be good to go!

Here is the 139 grain Hornady, Hornady Case, 3.520" COAL and CCI250 primer.



Speeds ran pretty much around 3200 from what I could tell.



The 140 AB's were a COAL of 3.575". Everything else was the same..



They ran about 25FPS faster than the Hornady's..



What I was surprised about the was the POI difference. Both groups were shot using the center bull. The 139 SPBT was zeroed about 2" high, while the AB's went high and to the right. Not a big deal, but it was drastic for two bullets that differ about 1 grain!



At 3200 with a 140, this thing is just loafing along, even with IMR4350 which is a big on the fast side, but everything worked well. Cases chambered tightly with a good crush fit, but they extracted with no resistance at all..

The rifle shoots well and it's pretty gentle. I just put an old M8 4X on it for now. Not sure what I will put on it for hunting, maybe nothing different.. Who knows..



Either way, for a 120 bucks for the rechamber, I am calling it a success so far. Doesn't seem to be overly fussy. Once I get a few more empty cases, I'll load them up with some 160 AB's and see what happens..

 

[JD338]

Nice work Scotty. The 7mm Mashburn is looking good

JD338

 

[gerry]

Bob Hagel would have approved of the 4X Leupold. That is a big difference in where those two bullets hit for sure, maybe the vastly different construction of the bullets is why. You are already at the max speed for a 264 WM and 140's with that load.

 

[SJB358]

That's why I put it on there Gerry. Good scope and very serviceable. Still clear and tracks well for an older scope. Might be tougher than my other Leupolds.

It seems like it should come together quick. Ran a few through the FL sizer and adjusted for a .002" shoulder bump and they chamber slick. Dieing to load up some 160's or 175's and see what it does.

 

[DrMike]

Very gratifying, Scotty. That is looking good. It will come together very quickly.

 

[SJB358]

Got some 160 ABs and PTs loaded. Hoping to get them out tomorrow. I found a pound of H1000. Supposed to be real good with 160's.

 

[DrMike]

I would imagine that H1000 is ideal for the Mashburn. It is excellent in the 7mm RM with 160s.

 

[SJB358]

I've never used it for much. Can had a good layer of dust on it. Other 7mm MSM shooters said to try it. Scared it'll work as it's about non existent around here right now.

I'll guess I'll cross that bridge if I get there.

 

[IdahoCTD]

In my 7-300wm I shoot 73 grains of H-1000 in RWS brass with a 162. In Winchester brass most guys shoot 76-77grs.

 

[SJB358]

So I gave the old 7mm a good run this morning. Ran through some 160 AB's and 160 PT's.

AB's were loaded to 3.560" COAL.

Loaded from 74 to 77 grains of H1000

This is the target, from L to R with the AB's on top and PT's on the bottom row.



76 grains looks the best for me with the 160 AB's.



Speeds were very good across the board. 77 had some case head scuffing, along with the ejector mark on one of the cases.

So the 76 grain charge will get run again.



Everything across the board looked like the classic 2 in and 1 out, so I am going to shorten them up a little and retest at 75.5 and 76. Both of them should be right around 3200 and if the accuracy pulls in, I'll be set.

The PT's probably need to be seated out towards the rifling some. They were at 3.527" and seemed to hit the wall a little sooner than the AB's did today. Didn't shoot the 77 grain charge weight as I was pretty sure what kinda speeds I would be seeing..



Either way, it was a successful day with the rifle. Seemed to track as it was supposed to and wasn't real tough to guess what was going to happen.. I liked that..