Weatherby 338-378 grouping issues

[Long Time Long Ranger]

My best load with the 225 grain bullet in a 338-378 wby with a 28" Hart barrel is 128 grains of H-870 at 3440 fps. This is a 225 accubond. Since you can't get H-870 any more try Retumbo. Powders faster than that will get max pressure before you hit top velocity. I wouldn't go faster than H-1000. The 338-378 is better with bullets over 200 grains. The 225 Barnes may not open well on little whitetails. The accubonds may be better for that purpose. My brother got a nice mule deer at 650 yards hunting with me last year shooting the 225 ttsx out of his 338-300 RUM I built for him. The 225 performed very well on that deer so it may work but that would be way less velocity than the 338-378 shooting close range smaller whitetails.

 

[extreme]

I own four 338/378 wby accumarks .They all shoot well under a inch.. If it were me i would buy one box of weatherby ammo with the 225 gr.barnes tsx not ttsx ..shot a 5 shot group and if they group 1.25 or better you have a different problem..you can work up differnt loads until your blue in the face..large calibers like the 338/378 in a accumark like the 225 gr. barnes...that being said a custom 338/378 by a good smith usually can handle other lighter or heaver bullets but the heaver are prefered ..I have two customs both have longer barrels 1@28 inch 1@30 inch. and i use 300 smk,s in both mostly because neither liked 180 gr. or other lighter bullets..keep in mind if you would that this just another suggestion and even though i own a lot of 338/378,s each case is different and there are a lot of people on this site that are both custom smiths and just great shooters who are smarter then me ,and iam just telling you what my rifles do.

 

[enigma]

I shoot out of my weatherby 338-378 accumark Hornady SST 225gr bullets and IMR 7828 102 grains power and a fed 215 primmer and the total length is 3.770 and once fired brass is what I load.And I get 1inch 1/2 groups at 200 yards. Avg FPS 2854. This is my whitetail deer load.

 

[extreme]

I do not use my 338/378,s for whitetail deer..I only use them on bear,elk,moose,etc. I try to break the front shoulders if i have the shot snd 225 gr. barnes have never let me down if i do my part..I also use hornady and sierra and berger ,,,not real fond of bergers in this cal. maybe there new 300 gr. that just came back out will be better ,,,time will tell.