looking for 338-378 load data

[338-378 lineman]

338-378 wby mark 5 30 in barrel 1-10 twist hoping to get 250 gr smk or new burgers to fly thanks for any info I am new to this cal.

 

[winmag]

338-378 wby mark 5 30 in barrel 1-10 twist hoping to get 250 gr smk or new burgers to fly thanks for any info I am new to this cal.

Sorry I dont have any data on the Berger or the Smk. I can give you ''book'' loads for 250gr to give you a ball park idea with Hornady's if you want. let me know.

I know it kinda looks like your post is being ignored, but its not. Its just that not too many folks load for the big 338-378wby.
Sorry I couldnt be more help.

 

[Kevin Cram]

I shot the 338-378 Weatherby for years. It was a custom rifle with a 40" barrel and I used 300g SMK's. My load was 106g of Retumbo with a Fed 215 primer. This was a winter time load and was on the verge of pressure. With the 250g I would start around 95g of Retumbo and work your way up. Be careful and watch for pressure signs.gun)

 

[RDM416]

I have a couple of rifles chambered in 338 Kahn, which is an improved 338-378. The fireformed Kahn case has a little more capacity, but my load data should still work if you start at the low end and work up.

I just tried some of the Berger 300s using Retumbo.

102 grains 2895 fps
103 grains 2927
104 grains 2947
105 grains 2959
106 grains 2986
107 grains 3023
108 grains 3044
109 grains 3056

At 109 the bolt was stiff, so it was definatly OP. I have only done one round of testing and fired one round of each load. I really think 106, maybe 107 will be the max load in this rifle. This rifle is built on a Wby action with a 27" Lilja barrel.

I think with the stock 338-378 case you should be fine to start out at 102 grains of Retumbo and work up from there. I was using Federal 215M primers.



The load I have shot for several years is RL 25 with 250 grain Match Kings.

I get 3350 fps with 108 grains of RL 25 and Fed 215M primers. (30" Lilja barrel)

I would suggest you start out at around 102 or 103 and work up from there. This rifle has a 30" barrel and a Nesika action, so I don't think you will be able to get the same speeds because of the longer barrel and the fact the Nesika is a much stronger action than the WBY. Start at the low end. Your rifle may take the 108 grain load but I would certainly want to start much lower than that.

 

[338-378 lineman]

thanks that gives me a good place to start

 

[bozo699]

338-378 lineman,
Welcome to the forum.I have used a 338-378 accumark 30"tube for years and love it.I have found any of the slower burning powers works great in this rifle,and 250gr. bullets as well. There or mine anyway just isn't picky. my pet load for the 250 smk is 102 RL-22 @ around 3000fps. Although with the exception of win. failsafes it will shoot any 250gr bullet w/102gr rl-22 same poi . I plan on building a new one with no weatherby free bore. Use your chronograph watch for pressure signs,have fun and good luck.
Wayne

 

[signature542]

104gn of retumbo but be warned it spikes quickly.. I'd start a few grains lower .That is with the 300gn SMK..... speed around 2830 with the Accumark tube 26 inches

 

[Long Time Long Ranger]

28" Hart barrel with wby freebore. Favorite 250 grain load is 120 grains of H-870 at 3360 fps. My best loads with the 300 smk are between 110-114 grains of H-870. Around 3050 fps in my 28" barrel. In my ruger #1's that have 31" barrels they hit 3120 fps. Also if your shooting is under 800 yards the 200 accubond is very accurate with 130 grains of H-870 driving it over 3600 fps.

 

[TXshooter]

Has anyone loaded this caliber with the 225 gr ttsx. If so what powder worked for you. I was thinking of trying RL-22 because I already have it but thought RL might be a good one to try

 

[trapperjohn]

Have been shooting 225gr Barnes TTSX with 105gr RE25 for a year or so in Weatherby Mark V. Great on elk. 3" group at 300yds. Just over 3100fps. Also started working up load on 300gr Berger for same rifle but didn't have initial accuracy of Barnes and stopped working it due to hunting season prep. Load comes from Barnes #4 manual.

 

[Long Time Long Ranger]

Only the slowest powders available make this cartridge what it is which is bad to the bone. You can get by with something as fast as Retumbo with lighter bullets but nothing faster will give you the velocity you look for in a cartridge this size. Thunderbird cartridge company sells powder and say the H-870 they sale is the same as the old H-870. If it is that is where I would go. H-870 is the powder I have always shot out of the 338-378 wby since 1979 to get top performance. I have tried virtually every new powder that has come out since then but nothing has beaten H-870. Everything else is just to fast for it to get top velocity. Accuracy yes because it is a very accurate cartridge with many 1 mile + kills recorded. But velocity and accuracy requires something slow like h870.

 

[340Shooter]

Has anyone tried US-869?

 

[Iron Worker]

I just acquired a MK V in 338-378 26" bbl is Re#33 to slow of powder to burn pushing 230 gr Hornady ELD bullets ?

 

[Lahunter76]

Any one have any new data? Would love to be able to get 2950-3025 out of a 28" barrel with a 300gr. Just looking may not be able to do this with a Sammi cartridge! One day!