338 Cal, What Chamber to use?


Well-Known Member
Nov 11, 2003
La Grange, TX
Hello to all:

I feel fortunate to find this board. I was referred off of one of our competitive shooting highpower boards.

A tiny bit of background. I've shot competitively for about 12 years in the service rifle class. I have a High Master ranking. I have hunted since I was old enough to hold a gun. I used to think 200 yards was a long way. Now with all my background 300-400 seems like a chip shot.

Heres my dilema. I have a couple of 300 wtby rifles. I want a bit larger bullet and after having shot a 338 win mag a bit and seeing how it performs with the superb 225 X bullet I want to build in that caliber. The one gun I have that needs a barrel anyway is a Wtby Fibermark in 300 wtby.

I"d prefer a non belted round. A 340 wtby would be easy but has the same belt. I"d prefer about the best MV I can get so I have room to manuever. I was hoping for ballistics along the line of the 338/378 round.

I will be shooting barnes X bullets and I load my own ammo(going through some 4000-8000 rounds of reloads a year depending on how many matches I can make)

Finally I managed to borrow a 338 this year while I was bowhunting in Alaska. We could not get close enough to any decent bulls for my recurve. But the 338 was fun and allowed me to make 2 hits at 802 yards to collect my 'bou. So I feel that the 338 diameter works really well.

The rifle will be for large and dangerous US game. I am working on a 7mm for a 1000 yard prone gun so I'll have a smaller mag for smaller game.

Awaiting your advice. PS wildcats don't bother me either. I want something that works and will fit my action.

Thanks in advance, and Happy Thanksgiving!

Jeff Rost

I think you'd be happy using the 338 Lapua, or an improved version of it. You would be edging the 338/378 WBY pretty easily, especially with the lighter 225's. Lapua 338 brass is nice stuff, and it's built like a little brick **it house too.

I'm building one this winter for the same reason. My brother has a Rem 700 in 338/378 WBY and its a nice round too. Much better brass with the 338 Lapua though.

A good friend of mine is going to be building a 338 Lapua IMP with my reamer at the same time.

I'm really impressed with the 30/338 Lapua IMP I had done this fall.

Do a serch for "338 Yogi", it's an improved design of Dave Tooley's, and a few of the guys here use it too.

Brass costs more than the Ultra Mag does ($130 a hundred at Sinclair, or Brunos Shooter Supply) but it will last three times as long as the soft Remington hulls and is top quality stuff.

I can't wait to get started on mine.
I have been shooting a 338 yogi for about 1 year now I shoot the 300g SMK bullets. I have taken deer out to 1225 yards with this combo. I am putting a new barrel on it this winter and building a long range hand gun in this cartridge. I am getting 3050 fps with a 34" barrel 10T with the 300g bullets. The brass is excellent and I have 17 firings on 48 of them. I have been thinking about using the 408 CT brass and necking it down to 338 for a long range hunting rig also.
Crow Mag
Will a 338 Yogi( or Lapua or Lapua Imp) work in my Wtby action for the 300 wtby? I dont' have any dimensional data for the round as of now.
If you aren't wanting to modify your bolt I would go with the 338/300 Rem UltraMag. Just neck up the standard 300 RUM case or down the 375 RUM and you have alittle more capacity than the standard 338 RUM which uses a slightly shorter case. I think the Weatherby has a generous mag box so length shouldn't be a problem, you'd just have to work on it alittle to get it to feed properly. This is just my opinion and others may and will vary, good luck with your project.
You would have to have the bolt opened up the 338 Lapua is the same size bolt as 338-378 WBY
Crow Mag
Does anyone know if my 300 bolt face can safely be opened to that size? Anyone have suggestions as to someone that would rebarrel to a 338 Yogi or similar round for me? I'll provide the barrel and action? I'm in Central TX but don't reallly care where a good smith is. My AR smith is located in Illinois as an example.


I'm not sure if it's the same one they chamber the 338/378 Wby in or if it is doable. Chris at G.A. Precision is who I'd ask about it. Maybe he'll see the thread here and let you know if he can do it for you.

Small world, but no, Craig hasn't done any work for me, but he does do a lot of AR's and M14's. He showed me his Police model 700 308 a couple weeks ago, he's been healing up from knee surgery here the last few months, still competing tho! He has my gunsmith, Dave Caboth, do some things for him when it pays to. He needed to have Dave mill something for him, I forget what, Craig doesn't have a mill, and I told him he'd probably let him do it himself if he asked him. Dave caught a broken drill bit in the eye last month, so he's havin a rough go of it right now. There talkin like he'll need a lens transplant, but they won't know for sure for a year I guess. That's wait's gotta suck.
I would have to see your action and take a couple of measurements to double check but I'm pretty sure it's do-able. Especially with the RUM's.
Jeff, I like the 338 Lapua myself. I finally got my M-18 action from Prairie Gun Works. They really do great work. My gunsmith should have the rifle finished before New Years.

I just want to comment on your bullet selection. I used the barnes on my last hunt with my 7STW. They do drop the animals in their tracks, but the groups were far from good. I passed up a 330 yard shot (like you said - a chipshot!) on a beautiful antelope because the groups are so inconsistent. One day they group 1" @ 100yards, then 4" fliers. I now use 156 Cauterucios with my 7STW and they shoot about 1/2". Good enough for my needs with that rifle.

With the 338 Lapua I'm debating between the 225 nosler accubond and the 300 SMK. I only shoot out to 500 Yards so the AB's will do it for me. But that Lapua is such an accurate round I may opt for the 300SMK so I can get those 1/4" groups. I know with that kind of accuracy I'll be extending my 500 yard limit soon enough and I'm a 1 Load/1 Gun type guy.

So, my point to you is....
If you do go with an accurate caliber like the 338 Lapua, why lose it with the barnes X?

I'll add this, if Bob cauterucio made a 338 VLD, decision time would be over for me!
Jeff, If my gun consistently shot the barnes-X with good results I would use it too. Just remember, a lot of guns do not shoot them well. If you get your lapua to shoot them well then you have a homerun. I will definitely attest to the killing power of these bullets. The guides on my Mulie & Antelope hunt were amazed how the animals dropped in their tracks. I hear they will be making the new triple shocks in 338 soon.

I have been searching for results for the 225 accubond but so far no one has posted any results on paper or game.

The 225's also intergrate real nice with the NP-R2 reticle on the nightforce scope.

Good luck with whatever you end up using.

Send me an email with contact info

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Appreciate the thoughts. I happen to have very good luck with flat base X bullets. And they expand down to very slow speeds. And they shed the petals and penetrate like crazy as needed.

I have read lots of thoughts on bullets and be assured that I'm taking that into account. I target shoot a lot and am still scared of all the MK bullets used. I see so many of them in the impact areas that have zero expansion at all. I'd rather not go that route at the moment.

Plus, as noted, the performance of the X at 802 yards for 2 shots on my caribou was superb. Neither stayed in the animal and the second broke the spine. Lots of internal damage. Which leads me to think if I'd have goofed and hit the shoulder I'd have still had the energy to kill.

But, like I said, I'm always open for new thoughts and certainly folks luck with all the other bullets is good news.

In the end maybe a 338 heavy bullet is good enough without expansion.

Thanks for your time.

I have built many of the big 338's. Yes you can easily open the 300 wby bolt face in a mk v. You also must get the 378 magazine box, etc. I have built several 338-378's and various improved Lapua's off the action. Like someone else said, the best without modifying the action would be using the ultramag case which has no belt. If you opened the bolt face then one of the Rigby or Lapua improved versions would be the best choice if you don't want a belt. The 338-378 wby or the rigby would be the fastest with the 338-300 ultra and the lapua being a bit slower with virtually identical velocities.

I disagree with an earlier post. I have never seen a lapua that could shoot faster than one based off either the 378 or rigby case. Those two are the supreme velocity rounds. I own about four off the lapua case and like them very much. They have some great attributes but are not the fastest. I think I have six 338-378's, four lapuas and seven off the ultramag case all in 338 caliber. All of these are within a couple hundred fps of each other so no big difference either way. Then I have several of these same cases necked to 358. And then a few more still in 30, 8mm and 375.

I learned long ago in my hunting career that there is a reason they use big calibers in Africa. They work best on big game! That is why I have plenty of them.
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