300 g. SMK Terminal Performance

[James H]

Weatherby made the 30-378 on a stainless action (I have one)but I am not aware of them ever producing the 338-378 in stainless. The Accumarks are on CrMo actions.

James

 

[Long Time Long Ranger]

bgouin, Like Broz said it is a very easy conversion to the 338-378 or Lapua if you have a mk 5 action. All the mk 5 magnum actions are the same. The ones off the 378 case just have the bolt face opened up more with the 378 magazine box in there and the bolt throw lengthened. I have seven 338-378's and one 338 Lapua imp (sold) and all of them started life as a standard mk 5 magnum action (257-340 wbys).

The 340 wby is a very capable round and I have taken elk beyond 1000 yards with mine. Back when the 250 sierra gameking came out it had the highest bc of any hunting bullet and that is what I took long range elk with early on. My 340 with a 28" barrel shoots them at 3056 fps with 7828 powder. Now the 250 accubond has a higher bc and when the 338's off the ultramag case only get in the 3100's with the 250 grain you see the 340 wby is very potent.

But if it were me I would do either the 338 lapua imp or the 338-378 wby off your action. My pet 338-378 shoots the 300 grain at 3050 fps, the 250 grain at 3300 fps and the 200 grain at over 3600 fps out of a 28" barrel. I have taken many trophy animals with it for many years.

 

[bgouin]

LTLR
Thanks for this information. I have spent months trying to find out the capability of my Mark V action. I have received more information in the past few days than I ever thought possible. I was planning to upsize right away after the post from Broz, but I think that I will start with my original plan initially and stay with the 340 WM until I can shoot it. If I can achieve resonable accuracy then I will look into upsizing to a larger head size and go for longer range capability. Much of this decision is financially driven. Short term I can probably count on 1000 yard performance with the 340 WM which will stretch the capability of my current scope (Lupy M4 3.5-10x50x. Also my McMillian stock is a sporter and will only take up to a Lilja #6 barrel contour. A new stock and scope would set me back about $2k more, and this is just not feasible right now. I would imagine that once one gets started on the path to serious upgrading that the sky is the limit. The barrel upgrade has already cost about $600, so it makes sense for me to take baby steps. I now have enough information to get more serious in the future. My marksmanship will tell me weather to upsize or stay put. My original goal was to reach out to in excess of 750 yards and possibly up to 1000 yards. It sounds as if this is possible with the 340. Now I just have to wait for the barrel to arrive and see if I can shoot well enough for the above ranges.

 

[Long Time Long Ranger]

The 338 ultramag will work perfectly in your action without any modification and give you more velocity at no extra cost. Then you can use cheap remington brass and save some money. I use remington brass in my 340 by necking up 300 wby brass. Also done it with 300 H&H brass and 375 H&H necking them to the 340 wby. With the 338 ultramag you can save all that work and get 338 Lapua velocities with no additional expense. Just use the 338 ultramag reamer instead of the 340 wby. I shot my elk this year at 740 yards with a 338 ultramag. It is a very good round. Maybe the best of the 338's if you figure economics into the equation. What you get for the cost of brass and shooting it.

 

[bgouin]

LTLR,
I have considered the 338 RUM as well. I have about 15 boxes of Weatherby and Norma factory loaded ammo plus about 300 empty Weatherby/Norma and Norma cases. It appears, from most of the load data that I have seen, that the 338 RUM is about 50 fps faster than the 340 WM, so this would be only a slight step up in performance. I have also heard that the Remington brass is not as good as the Norma which is not as good as the Lapua. I'd like to clear my current inventory of loaded ammo first. I believe that my gunsmith can remove a couple of turns off of the barrel shank, re-thread and re-ream with a 338 RUM for a clean chamber. The proof will be in the accuracy and my ability. This rifle is light (10-11 lbs. with scope) for a true LRH rifle, but should give me much better capibility than the original factory rifle which would not print better than 2-4 MOA. It had a non-concentric barrel to chamber alingment plus a thin wimpy factory barrel.

 

[Long Time Long Ranger]

I agree, with that many boxes of brass for the 340 that is a good choice. Just not much real difference in the big 338's. I have shot them since the 70's and built many of the latest and greatest as they became available such as the ultramag and lapua cases. For instance out of a 28" barrel with a 250 grain bullet the 340 wby will get over 3000 fps, The 338 ultramag, 338-300 ultramag and 338 lapua will get over 3100 fps. The 338 lapua improved will get over 3200 fps and the 338-378 wby will hit 3300 fps. That is real data averaged from many big 338's over a chrono at top velocity. A fast barrel or a slow barrel will get outside these norms a little but this is what you can expect on average.

Any of these will kill elk size game at distances well beyond where most hunters could ever hit one.

 

[bgouin]

LTLR,
Thanks for the response. What powders do you reccommend for the 340 for 250 and 300 grain bullets? Most of my handbooks indicate 2900 fps max. for a 250 grain bullet in a 26" tube. I estimate 30-50 fps increase for a 28" barrel. I can't find any data on Retumbo or US869 from Hogdon. My next best choice seems to be Reloader 19,22, or 25, or IMR 7828 for the 250's. Reloader 22 seems to be the choice for a 300 grain SMK. Is their another powder that I should look into? I may have to break down and buy quick load to get started.

Thanx,
Bill

 

[Long Time Long Ranger]

Try 7828 with the 250 grain. Start with the load your book lists and go up from there. My data over 40 years is far more extensive than the handbooks. I am listing top velocities you can acheive with most rifles without liability concerns they have to deal with. Most of there loads concerning weatherby cartridges in particular are not max with a freebore rifle. Many custom barrels are out there with no freebore in wby chamberings. So many max loads listed are not max if your rifle has freebore. You will gain 18-22 fps per inch of barrel with the 340 wby on average depending on the burn rate of the powder used.

I think the 340 wby and 338 win mags are best served with the 250 grain bullets at more than 300 fps faster than the 300 grain. Overall performance is better within the ranges these rifles are most capable. After a few hundred yards the 300 would catch up with it in velocity but the 250 shoots much flatter and will drop elk size game at beyond 1000 yards. If I was setting it up to shoot 1000 yards I would shoot the 300 grain. I am talking about most average hunting situations I feel the 250 would be a better choice.

 

[Ron Johnson]

It seems to me the 300 gr. Matchking expands faily rapidly, even in light game, as has been stated. Racing goats shot into the shoulder lose the other side, with a couple actually hanging on only by small amounts of skin. Hit thru the ribs game of that size is not damaged too much. Several goats hit at longer ranges (beyond 1000 yds) the bullets still expand quickly, sometimes sucking the lungs and/or heart out the exit wound. On elk at 650 yds much the same, with a ribs only hit, one cow pulled the liver out. One goat at about 1000 yds looking straight at me took a hit in the front of the chest, exited ahead of the hindquarter, then hit rear leg at about the knee joint. The jacket was in the hide on the first exit, so I assume that the core was what hit the rear leg and broke it. Gamekings in 250 gr. are also quick to expand, but I have only shot one deer with that load. The 200 gr matchking in .308 works well at about 2900 fps and has accounted for 9 elk and a good dose of antelope. One Matchking in an Idaho bull turn sideways and did not expand. All the rest did a good job, but wounds are not like a standard expanding bullets. I think with 300 grs. we just have plenty of bullet for most of the game we are shooting. What do you guys think??