338-378 questions

[backyardsniper]

I have been in the market for a long range hunting rifle I had planned to buy a lapua, however i came upon a deal i couldn't pass on a 338-378 in a synthetic Mark V with a brake already equiped, it will be wearing a burris 3-12x50 xtr. I am a proficient handloader and will be loading for this rifle. It is coming with one box of factory 250 gr I believe they are noslers on top. I have no dies as of yet so I would appreciate any info on what some good loads are and what level of performance i can expect from a mark V I know they are probably not as accurate as some of the rifles chambered in Lapua and I also do not know the factory twist rate in the weatherbys I can only asssume it to be 1/12 so I would imagine a 250 is as heavy as i will be able to stabilize. Any info or input about this rifle and sugestions on dies and accesories that i will need to get optimum performance from this rifle would be greatly appreciated

 

[James H]

It is a 1:10 so you are good to go with the 300s.
I load for both a 30-378 with RCBS Gold Match dies and 338-378 with standard RCBS dies and I much prefer the Gold match dies. I also have a 338 Lapua that I use Redding Competition dies for and I think I prefer the Gold Medal match dies. That bullet loading window sure is handy for these extra long cases. When you get to the big 378 case you are more limited on who makes standard dies for them.

James

 

[Long Time Long Ranger]

James is right on, they are 1-10. I use standard RCBS dies I got for $26 and neck size. First thing you want to do is freefloat the barrel, bed the action and adjust the trigger. All that is easy with the mk 5 and should get you very good accuracy. The 338-378 wby is an extremely accurate long range round. Most all mk 5's after doing this work will easily kill game at a 1/2 mile with proper loads. The 300 grain bullets kick so hard in light rifles I do not fool with them. The light rifle is best inside a half mile so use light bullets best suited for that range. 225 Accubonds with the .55 bc at over 3400 fps give very good ballistics with minimal recoil. I am trying the 185 Barnes ttsx .432 in mine at 3650 fps. I killed a big 6x6 elk about three years ago with a 200 grain nosler ballistic tip .414 at 914 yards. Muzzle velocity was just under 3600 fps. H-870 is the best powder I have used with it but Retumbo also does very well. The slowest ball powders you can find are best. You just can't get enough of the extruded type powders in there. Retumbo is the best of these. I use over 130 grains of H-870. My loads are with a 28" barrel. With this round you are stepping up quite a bit in performance over the ultramag and standard lapua chamberings.

 

[J E Custom]

I have been in the market for a long range hunting rifle I had planned to buy a lapua, however i came upon a deal i couldn't pass on a 338-378 in a synthetic Mark V with a brake already equiped, it will be wearing a burris 3-12x50 xtr. I am a proficient handloader and will be loading for this rifle. It is coming with one box of factory 250 gr I believe they are noslers on top. I have no dies as of yet so I would appreciate any info on what some good loads are and what level of performance i can expect from a mark V I know they are probably not as accurate as some of the rifles chambered in Lapua and I also do not know the factory twist rate in the weatherbys I can only asssume it to be 1/12 so I would imagine a 250 is as heavy as i will be able to stabilize. Any info or input about this rifle and sugestions on dies and accesories that i will need to get optimum performance from this rifle would be greatly appreciated

The barrel should be a 1 in 10 twist and will handel the 300 grain bullets well because of the
velocity.

The 300 grain bullets can be loaded to 2750 to 2800 ft/sec.

The 250grain factory loads are 3060 ft/sec and 5200 ft/lbs energy.

The 225s can be pushed to over 3300 ft/sec.

As far as accurate, the big Weatherby can be extremely accurate if loaded correctly(Neck sized
only) and with a head space of .0005 or less.

I have a 30/378 that has shot a .092 5 shot group @ 100 yards.

The powder I like is US 869 and H 50BMG with Fed 215 primers.

J E CUSTOM

 

[Autorotate19]

JE Custom, why with the weatherbys do you get better accuracy with just neck sizing?

Thanks

 

[signature542]

Hi

That rifle with some tweaks is highly capable and will produce the results just short of a full on custom rifle. You have a good action for future use.

We have had good results with RE25 and the groups are 1/4 moa from an accumark. In my down time hopefully we can get some H1000 to work out as our ES is a little bit to high.

Get the trigger sorted and bed it properly ..If the stock isnt up to scratch Bell and Carlson can help you for a reasonable dollar amount.

I would agree with JE and the 30/378 in my experience has been just that bit better in the accuracy department. Actually I whacked 3 in one hole with my mates 30/378... It was a good day! Mind you it shoots 2.5 inches at 500 yards! Not bad from a factory rifle with 210 Bergers.


Mind you I also have a 300 wtherby Mk 5 accumark!

 

[Long Time Long Ranger]

Ovastafford, I am not answering for JE and hope he answers but this is one of my reasons. All the big 378 cases I have worked with do best if you also get a good headspace off the shoulder by neck sizing only. Some top target guys I know even headspace more off the shoulder than the belt.

 

[backyardsniper]

thanks a ton fellas, I have one or two more questions. First the rifle doesn't match anything i have seen in the books. It appears that it has the accumark stock with a blued not stainless barrel. No flutes. It it matte not really high blue. I suppose the fella that had it may hve had a standard mark 5 and upgraded the stock. He traded it and a beauty of a 7mm ultra mag in on a 223 bench gun. I have a friend that works at the gun store. They said i was probably the only person in this area that would be interested in the beast so they offered it to me for 800 with the full box of factory ammo. They only want 530 for the ultra mag itis a rem 700 cdl i believe wood stock with midweight matte blue barrel they do not appear to have been shot much, only prob is i can't even find 7mm ultra brass on the internet, that being the case i would have a 530 dollar paper weight. If anyone is fammiliar with this configuration of the mark 5 i would appreciate some enlightnment

 

[James H]

Does it look like this?

Mark V® Synthetic | Rifles | Products | Weatherby.com

James

 

[backyardsniper]

no has spider web stock like accumark but matte blue barrel with brake

 

[signature542]

Does it have the alloy bedding block? If it does its a medalist stock. They do make stocks with spider ones that dont have the alloy block and just use a pillar sytem.
Interesting, possibly an upgrade at some point in time.

Have you shot it yet?

 

[backyardsniper]

also i can not find gold medal dies for 338-378 anywhere only for 338 lapua. does anyone know where to find them or do you use the lapua ones with a different bushing since it is only neck sizing

 

[James H]

Boy do I have egg on my face. I was certain when I got my GM dies for the 30-378 they were available for the 338-378 also, they sure aren't now though. I also looked up my second choice Redding competition dies, none there either. It looks like the choices now are custom or just standard dies for the 338-378, that sucks in my opinion.
One other thing, for my 30-378 I tried the neck bushing dies and switched to the FL bushing die. Since I started shooting long range competition I quit neck sizing everything and use FL bushing dies.

James

 

[J E Custom]

Ovastafford, I am not answering for JE and hope he answers but this is one of my reasons. All the big 378 cases I have worked with do best if you also get a good headspace off the shoulder by neck sizing only. Some top target guys I know even headspace more off the shoulder than the belt.

+1
That's exactly the reason.

With the belted cases once you fire form you have a perfect fit and if you neck size
only you don't have any head space and the shoulder holds the case off the belt.

When I set up a belted case head space I use .0002 to .0005 for accuracy and
after fire forming, by neck sizing the belt is held off the chamber by this amount so
it is using the shoulder to head space on.

Sorry it took so long to reply but I had to make a varmint hunting trip.

J E CUSTOM