the 375 Box Monkey Magnum

[yorketransport]

I got two packages in the mail today. One was from PTG, and the other from Midway. The most important was the box from Pacific Tool and Gauge because that had my finish reamer for the 375 Rum Improved (tentatively named the 375 Box Monkey Magnum after my delivery company, Box Monkey Distribution Inc.) All I need now is to get the die reamer, and I can send it all off to have the 30" Brux barrel and reloading dies made.

The other box from Midway had one of the bullets that I'm going to try out of the new gun it's a 350gr Woodleigh solid VLD.


For comparison, here's a .243 105gr A-Max, .308 185gr Berger VLD, .338 250gr MK, .375 350gr MK, and the 350gr Woodleigh VLD. The other bullets look a little stumpy by comparison.

Andrew

[high country]

ever see the 375 mach 1 that state arms was building? he died before it was finished, but it shoved a 375 solid over 5k fps. unreal.
 
looks like a fun project. who is screwing it together?

[carpsniperg2]

Sounds like fun.

[jackelope]

Great pills for prairie dogs.

[whacker1]

Great pills for prairie dogs.

Don't you mean a pill the size of a prairie dog?

[high country]

naw, its just fun to hunt dogs in wyoming from here. 12 clicks high and 2 to the wind.......let'er buck!

[jackelope]

Great pills for prairie dogs.

Don't you mean a pill the size of a prairie dog?

Same difference.

[grundy53]

Awesome!

[JackOfAllTrades]

Wow'sa!  It won't fly any flatter than a 338WbyMag, but it'll sure hit with a lot more energy!

-Steve

[high country]

but think how nice it would be to not have to reach into a rattlesnake den because your brass rolled into it. RUM brass is cheap......walk away and forget it.

[yorketransport]

So here's a list of parts that are going in to this project:

-30" Brux 1-10" twist barrel straight tapered to .9" at the muzzle
-Centershot Rifles 4 port Muscle brake
-Sharp Shooter Supply LVT laminate stock
-Savage RBLP target action tuned by Sharp Shooter Supply
-Leupold Mk4 6.5-20 FFP Mil Dot scope

ever see the 375 mach 1 that state arms was building? he died before it was finished, but it shoved a 375 solid over 5k fps. unreal.
 
looks like a fun project. who is screwing it together?

Devin at SinArms is cutting the chamber and fitting the brake for me. I'm assembling everything myself.

Wow'sa!  It won't fly any flatter than a 338WbyMag, but it'll sure hit with a lot more energy!

-Steve

It may not fly flatter, but with a BC of around .9 I'll bet the wind drift will be less. A lot of this I'll figure out when I actually get into load development. I'm still not sure how fast the 350gr bullets will be going. I'd be pretty happy with 2750fps.

but think how nice it would be to not have to reach into a rattlesnake den because your brass rolled into it. RUM brass is cheap......walk away and forget it.

It's actually based on a 375 RUM case. I gave it the standard AI 40 degree shoulder and minimum taper, then moved the shoulder forward about .13" and lengthend the throat so that the 350gr Sierra would be seated to the base of the neck. Here's the reamer prints for the standard RUM and my version.


I imagine this should split the difference between the 375 RUM and the 378 Weatherby. 

This whole project  came up just so I had something to mount the Mk 4 scope on. Since the big 338s have become too main stream I decided I needed to go bigger. That's when I found the 350gr MK. But since a standard 375 RUM  chamber has such a short throat I would have needed a custom reamer any ways. And if I'm going to pay for a custom reamer, it may as well be really custom.

Andrew

[JackOfAllTrades]

It's actually based on a 375 RUM case. I gave it the standard AI 40 degree shoulder and minimum taper, then moved the shoulder forward about .13" and lengthend the throat so that the 350gr Sierra would be seated to the base of the neck.

'since a standard 375 RUM  chamber has such a short throat I would have needed a custom reamer any ways. And if I'm going to pay for a custom reamer, it may as well be really custom.'

Andrew

I like the longer throat idea.
Taper at the start of the lands or sharp cut?

I think you're going to get more than 2,750fps from that 350gn bullet.

-Steve

[yorketransport]

Taper at the start of the lands or sharp cut?

I think you're going to get more than 2,750fps from that 350gn bullet.

-Steve

It's a taper at the lands. As for the velocity, I'm hoping for more than the 2750, but that's what I'd be happy with. I'm actually thinking it could be up around 2900. I just want to have realistic expectations.

Andrew

[JackOfAllTrades]

One thing about the Sierra's, I can push them but then I lose accuracy. I've found that I can push Speer's and Hornady boat tails to the limits and retain more accuracy. But nothing in my rifles except Nosler BT's come close to the accuracy of the Sierra BT's when I slow them down.  We're all looking forward to your load developement notes.  Someday I'll build something based off of the 358Norma.

-Steve

[yorketransport]

If you like the 358 Norma, I have a reamer print for a 358/375 Ruger you might like.

Andrew