338-378Wby

[Casscade]

How does this round run compared to the other 33s (lapua,Ultra,340) What can you get with a 250 and 300 MKs. Can you break 3000 with the 300. Also hows the accuracy with this round. Will do a 28 inch 5.5 bbl if I do the wby. Thanks for any replies.

 

[J E Custom]

338/378

It is the most powerful of the factory 338's

As for the 5.5 barrel it's going to be mean unless you install
a break.

Thats the reason I like the #7 taper (tames it down and no
muzzel break)

As far as 3000 fps from a 28" barrel "maybe" but with a 30"
probably.

J E CUSTOM

 

[Chawlston]

Hello,

I easily get 3000 with the 338/378 using the 300gr Sierra and retumbo.

James

 

[jwp475]

What barrel lenght and how many loads before your brass has loose primer pockets..........How manny grains of Retumbo?

 

[specweldtom]

Casscade; I have a 13 lb, 27 1/4" barrel, rifle that I've started working up. So far, 2760 fps with the 300 smkhp and 110 gr of H-5010. Very mild, 3/4" 5 shot @ 100yds. I believe I can make 2800 fps, maybe not with 5010 though. I expect to get down to 1/2 moa. I don't think I have enough barrel to get 2850, pushing hard.

IMO, a 5.5 is way too light for a barrel over 26" in this caliber, let alone 30".
JECustom is right, it will be unpleasant without a brake, and the brake is unpleasant to hunt with.

Chawlston, ditto jwp's questions. I haven't had any luck with Retumbo. What primer do you use? 3000 fps is a great neighborhood!

jwp, I get 3-5 firings before the pocket gets too loose.

There's been a lot of good discussion pro and con about the Wby calibers and guns recently. The MK V's are my favorite actions, and the only factory action that I will build a .378 based caliber rifle on.

Tom

 

[Casscade]

Have 3 lapuas already and just wanted to do something different. Was hoping I could a 300 at 3000 fps with this round out of a 28 inch pipe.

 

[Chawlston]

I am still working on the original brass that has seven firings on it, 106.90gr on my acculab scale (was 107gr on the RCBS). Federal 215 primers. I am at sea level which is higher humidity (read lower BC) and quicker to hit a pressure limit. You guys higher up in altitude have an advantage on burn rate and bullet flight. Anyway, this is a very good load for my gun which is a Hall Express in a McMillan McHale stock with a 29" cryroed (didn't realize that until now) K&P fluted barrel. I have found that these custom actions will take a tad more powder prior to showing pressure signs.

Chawlston

 

[Chawlston]

One more minor point..... I tune my loads different than most. I first find the point of land engagement and use this for pressure testing. Secondly, I pick a starting load and increase the charge exactly 1gr at the above seating depth. When I encounter a sticky bolt lift, I stop and then back off one grain as this is the starting point for tuning the load. Next I load them up in batches that are incrementally seated .010" deeper with each test batch and then select the best based on chronograph and group size. I have switched exclusively to the Hodgdon extreme powders and usually are tuning the load in the high eighty degree temp range to ensure I am operating at the peak temps I will see during hunts. I only shoot in the first three hours of the morning prior to mirage being present. Hope tis helps.

Chawlston