375-338 Lapua Improved

[Bubba Boomstick]

Does anyone have information or has tried to neck up the 338 Lapua to 375, reduce taper, and improve the shoulder to 35 degrees?

What are the best powders for this cartridge?

What is an optimal twist rate for the 350+ grain Cutting Edge bullets? Looks like they recommend 1:7 twist.

How heavy should I build the rig?

 

[Evlshnngns]

I think Tubb worked with a 375-338Impoved. Im not sure where you can read more about it.

I wish there was a standardized 338 improved setup on the shelf(like 280ai or dasher). 33xc and 37xc are close.

 

[Bubba Boomstick]

I think Tubb worked with a 375-338Impoved. Im not sure where you can read more about it.

I wish there was a standardized 338 improved setup on the shelf(like 280ai or dasher). 33xc and 37xc are close.

I agree with you. With a 375 bullet it looks like a giant 280AI. And with the larger diameter bullet, I'd expect to see better efficiency kind of like the 338-06.

My only concern with the 37XC is long term availability of components. Bunch of companies make 338 Lapua brass and with its military adoption it will be around for the rest of my life. I don't know if Peterson will be making brass for the 37XC in 10 years.

According to an article David Tubb wrote, the 375 Cheytac is overbore with poor throat erosion and barrel life.

 

[swed6.5]

Wheeler Accuracy has just gotten a reamer recently for a build we had been discussing, hoping to get the new bergers soon, the rifle weight will be over twenty lbs

 

[ISS]

Just a thought, if you will.
Ohio Farmer here has a couple thousand 300gr .375 bullets for sale at a reasonable price.

 

[SKWERLZ]

Does anyone have information or has tried to neck up the 338 Lapua to 375, reduce taper, and improve the shoulder to 35 degrees?

What are the best powders for this cartridge?

What is an optimal twist rate for the 350+ grain Cutting Edge bullets? Looks like they recommend 1:7 twist.

How heavy should I build the rig?

For hunting or ELR?

 

[Bubba Boomstick]

For hunting or ELR?

I was thinking for ELR.

How would a hunting rig work for this, anyways?

 

[SKWERLZ]

My buddy had a custom 338/378 for a bit, it beat the snot out of him
I refused to shoot it.
338 Norma isn’t bad at lighter weight hunting rifles.

I 100% would run the 338 lapua improved case for 375, the lapua case responds well to improved case geometry.

I neck up 33XC brass to 37XC easily, .358 mandrel then .375.

My 338 is 25+ pounds.
I wouldn’t go much lighter for a 375.

 

[B23]

I don't think the 338 Lapua even the improved version really has enough case capacity to sling the heavier 375 cal bullets to have any benefit over the 338. Most that step up to a 375 particularly one that requires the effort of a wildcat they go to much larger cases. The least I'd consider would be the big 378 Wby or the XC case.

 

[SKWERLZ]

I don't think the 338 Lapua even the improved version really has enough case capacity to sling the heavier 375 cal bullets to have any benefit over the 338. Most that step up to a 375 particularly one that requires the effort of a wildcat they go to much larger cases. The least I'd consider would be the big 378 Wby or the XC case.

The biggest benefit would be impact spotting and in ELR depending on conditions that’s a big deal.
It certainly not gonna shoot as flat as my 338.

 

[Bubba Boomstick]

My buddy had a custom 338/378 for a bit, it beat the snot out of him
I refused to shoot it.
338 Norma isn’t bad at lighter weight hunting rifles.

I 100% would run the 338 lapua improved case for 375, the lapua case responds well to improved case geometry.

I neck up 33XC brass to 37XC easily, .358 mandrel then .375.

My 338 is 25+ pounds.
I wouldn’t go much lighter for a 375.

I agree. I think the 338-378 Weatherby is a bit whack. I can always find those rifles used haha. Must be for a reason.

My 338 Norma in my 15 pound gun isn't bad, I agree.

 

[B23]

The factory Weatherby 338-378 is kind of a turd. I bought a new Wby Accumark in 338-378 a number of years ago and the only way I could ever get it to shoot well was if I ran it with slightly over medium loads. I tried a variety of different bullets from Nosler and Barnes 225-250's and Sierra 300gr MK's. A variety of different powders H1000, 7828, 7828ssc, Retumbo, H870, US869 and nothing really stood out better then another. Even Sierra 300 MKs which generally shoot really well at about any speed didn't like to be pushed but throttled back to a mid-ish load and they shot pretty well. With my custom 338 Lapua Imp the Sierra and Berger 300's, even with fireforming loads, shoot crazy good with a variety of different powders or load combos.

IMO a custom built 338-378 with a good quality barrel at least 28in in length chambered by a good smith is a completely different animal compared to one off the shelf made by Weatherby.

If anyone is looking a full custom 338 Lapua Improved 40° I have a brand new one complete with Redding dies for sale.

 

[Bubba Boomstick]

I don't think the 338 Lapua even the improved version really has enough case capacity to sling the heavier 375 cal bullets to have any benefit over the 338. Most that step up to a 375 particularly one that requires the effort of a wildcat they go to much larger cases. The least I'd consider would be the big 378 Wby or the XC case.

True. I don't think it'll be superior to a high BC 300 grain bullet in an improved 338 Lapua going 3100 FPS.

But it would be more akin to what the 280 AI is to the 28 Nosler. Cheaper to build and cheaper to shoot. And trading inferior ballistics with superior shootability.

I have a ton of 338 stuff already. So to scale it up would save me a lot of money. I can buy 338 Lapua brass and either make it an improved 338, improved 375, or just shoot it the way it is.

 

[SKWERLZ]

I agree. I think the 338-378 Weatherby is a bit whack. I can always find those rifles used haha. Must be for a reason.

My 338 Norma in my 15 pound gun isn't bad, I agree.

My buddy’s 338 Norma is even a smidge lighter but I really enjoy shooting it.
Enough recoil to test your fundamentals but not punishing in the least.

 

[Bubba Boomstick]

My buddy’s 338 Norma is even a smidge lighter but I really enjoy shooting it.
Enough recoil to test your fundamentals but not punishing in the least.

Great. So 12 to 15 pounds is the sweet spot for a 338.

And 25 pounds plus is for 375. Makes sense!

 

[SKWERLZ]

Great. So 12 to 15 pounds is the sweet spot for a 338.

And 25 pounds plus is for 375. Makes sense!

For a ELR 338 and up I’d go 25 or heavier

I think most light gun class rules limit you to 25.
My ELR 7mm Is 26 pounds and is amazing to shoot.