Next build 375 something

Frank7mm

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Mar 26, 2008
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Well I've decieded my next build will be a 375 of some sort. I plan on using a Rem action as a single shot so cartrigde length isn't important. What chambering would you choose? I was thinking of a 375 RUM imp. The cost of brass, being overbore, and messing with brass doesn't matter. This build will take me a year or so complete. Any ideas?
 

Tikkamike

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Being a 375 fanatic myself I love that you are gonna build a 375. I have a 375 rum and absolutly love it, I dont see much of a way to improve it. you may gain a little but it would be insignificant. Right now brass is hard to find and our only choice at the moment is remington brass. However that doesnt stop me from pounding away with mine. improved or not you wont be disappointed. One thing you may look up is see if anyone who has improved it has had extraction problems. I have not had any but there is very little taper as is so I wonder if it would become an issue with the improved version?? Although with your action you have an M-16 style extractor I assume? so it may be a non issue. keep us updated!
 

J E Custom

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The 375 RUM is a great cartrige and brass is still available (I would recomend buying 200 or
300 + cases if you start one just in case).

In factory 375s it is only bested by the 378 Weatherby, and for the Remington 700 action
the Rum is the best and most logical choice.

The 375 RUM is powerful enough to use for any game in the world.

There realy is no reason to change it (Ackley improve) so I would stay with the standard
case dimension.

If you can find any 700 action set up for any RUM the build will be straight forward with no
changes nessary.

Good luck and have fun.

J E CUSTOM
 

Frank7mm

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Truthfully I don't expect alot of improvment, but I love my other improved cartridges and the long brass life. Possibly a 338 excalibur necked up to 375. I have plenty of other guns for typical hunting so it's more of a venture in to extreme long range.
 

Tikkamike

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Dec 26, 2009
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Big Horn Basin, Wyoming
Truthfully I don't expect alot of improvment, but I love my other improved cartridges and the long brass life. Possibly a 338 excalibur necked up to 375. I have plenty of other guns for typical hunting so it's more of a venture in to extreme long range.


I am on my second 375 ultra, honestly its like no other gun I have. They are inherently very accurate and can launch an really big bullet at an incredible speed. and the way they kill is amazing. I think the 375 ultra idea is an awesome one. Also Look at the 416 buff that JE custom does. he uses the 375 ultra as the parent cartridge. That would be a pretty amazing rifle i believe also.
 

Frank7mm

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Are you using the 350 SMK? What kind of velocity's are you getting out of the RUM?
 

J E Custom

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10,726
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Truthfully I don't expect alot of improvment, but I love my other improved cartridges and the long brass life. Possibly a 338 excalibur necked up to 375. I have plenty of other guns for typical hunting so it's more of a venture in to extreme long range.


In my opinion the Excalibur is about the ultimate 338. But it needs a larger action than the 700
Rem.

At one time I looked at necking it up to 416 because of case capacity and with the requirement
of a MK 5 or a custom action plus the cost and availability of brass and loading equipment it
more than tripled the cost.

The 416 buff will push a 400 grain bullet almost 2700 ft/sec without being overloaded and case life
of the 416/375 is very good.

Without a Muzzle brake it is just about all the recoil I can deal with and after 40 or 50 rounds
at the range the fun has gone out of it.

I also designed a 338 super based on the 375 RUM brass because it is available and works
in a magnum bolt faced 700 REM. It has been improved and the capacity increased to 115
to 119 grains of powder (Depending on what powder).

Testing is still on going but it appears that case capacity may be unusable, so the standard case
may be the way to go for the .375 bullets.

Rather than improve on the 375 RUM I would elect to go with a 378 Weatherby and a mark 5
action.

Just an opinion, But it is fun to play with different ideas.

Keep us posted on your project.

J E CUSTOM
 

Frank7mm

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Mar 26, 2008
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401
Location
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Rather than improve on the 375 RUM I would elect to go with a 378 Weatherby and a mark 5
action.

You wouldn't use a PTG bolt and go with the Excalibur case? I have been playing around with the WSM cases in long actions and find if you can seat the big long bullets so the boattail is just above the doughnut the gain is sugnificant. To get the most out of the big boomers I throat them so I can seat heavy bullets long. My 338 WSM gets the 300 gr Bergers 2600fps, witch I feel is pretty darn good. Has anyone throated their 375 RUM for a very very long AOL?
 

J E Custom

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Jul 29, 2004
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10,726
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You wouldn't use a PTG bolt and go with the Excalibur case? I have been playing around with the WSM cases in long actions and find if you can seat the big long bullets so the boattail is just above the doughnut the gain is sugnificant. To get the most out of the big boomers I throat them so I can seat heavy bullets long. My 338 WSM gets the 300 gr Bergers 2600fps, witch I feel is pretty darn good. Has anyone throated their 375 RUM for a very very long AOL?


When you open a Remington bolt face up more than .540 it doesen't leave much. and the extractor
needs to be thinned making it weak.

I personally don't like to open up a remington beyond .545 for any reason and the PT&G bolts are
good but they are the same size.

I know they do it, but when you increase the bolt face Diameter you increase the bolt loading, and
exceed the original design loading. This can cause recoil lug set back with heavy loads.

Also if you load longer than the magazine length you must load it like a single shot.

I build all of the big cases on Weather mark 5 actions if a factory action is used because of bolt dia.
and mag length.

J E CUSTOM
 

Lefty7mmstw

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May 13, 2012
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4,800
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Dakota del norte
I shoot a 270gr. Barnes TSX at 3130fps
My pet load in my 375 [email protected] is the 300 tsx with I4320 under it at 2550 fps. Gotta love how the 375's hit with these pills. And it's scary accurate for a lightweight rifle(8# with a scope on it). If it's an inch or more I know I messed up, as it WIL hold sub moa all day. Hell, it was sub moa one day with the scope shook loose.
 

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