.338/.378 and .300 Weatherby question

[ARM28]

Hi

Please allow me to introduce myself. My name is Rob I am in the US Army stationed in Europe. I have a .50 BMG (Barret M82) and a .375 Cheytac that are my long range Working Tools. I have yet to fire the .375 Cheytac as it is not yet completed. My Gunsmith is using 300 grain Barnes X bullets at 3500 FPS in it as the Sierra 350 Grain bullets turned out to be sub par

When I was in Iraq for the last rotation (MNC-I 05/07) I got hooked on your forum and found it to be a mountain of knowledge in the longrange Craft.

Now for my question. I am having my .338/.378 and .300 Weatherby Mags Rebarreled and would like to know what kind of velocity increases I should expect when I increase the barrel lengths of these two weapons?
The .338/.378 is a Accumark and the .300 is a Vanguard. I shoot 250 grain pills from the .338 and 180 grain pills from the .300.

Thank You for any info you can give me

Very Respectfully
Rob

P.S Any Cigar smokers on this forum?

 

[screech]

I get about 2800 in my 30in improved 338-378 with a 300smk. I might get some more velo if I switch to H1000 or retumbo though. I just havent had time to play with it.

 

[Hired Gun]

I'm speculating near 2900 +or- 50 fps with the 300 SMK in a 30" barrel. A 180 in a long barreled 300Wby will probably hit an easy 3400 to 3500 according to our local Gunsmith. You may have heard of him. Darrel Holland. I shoot 200grain Accubonds out of my 26" Accumark at a real easy 3100 fps with IMR-7828. In testing I got 3200 but brass life was not as good. At 3100 is just goes and goes. 180's out of my 26" barrel go 3308 on the button with IMR-7828.

 

[BLASERMAN]

300 Wby

How many Grains of 7828 are you using behind the 180 gr bullet

 

[Hired Gun]

It is 88.5 grains in real Weatherby brand head stamped brass. It has to be a 26" or longer barrel or you won't get the speed. It is possible to get this speed in Remington brass but back off and work up. It will be a stout load in the smaller capacity brass.

IMR-7828
CCI 250 primers
180 Partitions
3.6" OAL

This load closely mimics Roy's original load for the 300Wby. Only use in Weatherby barrels with spec free bore for factory ammo. Like factory ammo it will leave the very slightest of extractor marks that can only be seen with keen eyes in good lighting but they will be present. Brass should still last at least 10 firings. I loaded many at this level more than 20 times. This load has proven to be a sub MOA load in many different Mark 5 rifles. My best ever 100 yard group with any 300Wby was shot with this load out of a very thin barreled German made Weatherby.

Due to the primer shortage If you can't find genuine CCI-250 magnum primers you can substitute Federal 215 with no other adjustments.

As with any load data back off and work up in your own rifle.