I have been using a standard RCBS FL die set. Reloaded ammunition has been shooting between .5 -.75" @100 yds with a very good rest. Just started checking the ammo with a concentricity gauge and have found 4-7 thou run out. Fired case have very little runout in the neck and the body (1-3 thou). FL sized case seem to have about 3 thou runout in the neck. The bullets are barnes tsx both 150 and 180 grain bullets. I am measuring the loaded rounds about half way between the meplet and where the ogive begins. My reasoning is that this spot would exaggerate any runout. I have a theory that the runout may be causing some of the dispersion in my groups. Am I measuring in the wrong spot? Does anyone have any suggestions? A new seating die or should I start over with a new/different die set (maybe a bushing die set)? Any help would be greatly appreciated. Is there a limit on the accuracy to expect from the factory Accumark rifle?
Those are EXCELLENT groups for a factory wby in that caliber. Try some longer range shooting (300yds min) and see how it groups. Some guns with freebore are not as fussy about runnout as guns that don't have it. Your gun has freebore. But you may get the runnout down by doing a couple of things and it might help your groups slightly. (And yes you are measuring fine). First off try fiddling with the expander stem in your die. Try and make some very small turns in and out and see if you can get the resized neck runnout down a little. You might get it down to .001-.002 consistantly. The when prepping for seating get a low angle mouth chamferer and see if that helps the bullet enter the case smoother. As you are seating the bullet give the case at least 3 180 degree turns and see if this kind of helps center the bullet. Lastly, I doubt that any ammo up to .005" runnout will affect your accuracy in that rifle. Take some of your loaded ammo to the range and shoot it at 300 yds and see if there is a difference between that of .002 and say .006. (I mark the primers with different colored magic markers) I'm betting it will be minimal.
Thank you for the advice. I have forgotten about turning the cartridge during the seating process. I will play with the sizing die and trying shooting at 300 to 400. In your opinion is the factory barrel or the cartridge the limiting factor in accuracy?
Well.....first of all we are just mortals here on this site. There are so many guys here with custom built rifles, dies, and experience at shooting fantastic groups at terrifically long range that it's almost embarassing to talk in terms of factory rifles and accuracy.
To answer your question with my experience level I would say it's a combination of both rifle and cartridge. The 30-378 hasn't gotten the rep for accuracy as I see often in the Rum. And a rifle with freebore probably won't shoot as good as a custom without it. However you have to consider yourself blessed to have a factory rifle that shoots as well as yours does. With a little fine tuning of your load charges and seating depth and runnout you might be able to get that gun down to a .5 moa rifle. If so and you can shoot 2" groups at 300 yds and 4-6" at 600 yds that gives you one heck of alot of hunting flexibility. But, the bottom line is do you have acces to that much range to practice and the time and money to get totally confident at those ranges. I'd say once you do and if you want to go farther you could be looking at custom rifles and great scopes (and great expense) to take the game farther.
Thay rifle is perfoming very well for a factory gun in that caliber. Have you tried any other bullets? I have two 30 378s, one a factory accumark and the other a custom. I use the Berger 185 grain moly, vld and Retumbo.
I tried some 180 scirrocco's at first, but I couldn't get the accuracy. I had some concern about the velocity and the bergers holding together. I have used them in a 308 with excellent results. What velocity are you achieving with the VLD's. Retumbo has proved to be an excellent powder for the 30-378. Do you think there is a velocity that is too much for the VLD's? The majority of my hunting for the moment is 150-350 yds.
FWIW--I had terrible luck with the early scirrocco's too. Supposedly the later ones are better but I haven't got the "good feelings" for trying them again. I have some ofthe 180 etips on hand. Man if those shoot we'd have the best of many worlds.....the near bc of a 200ab and the toughness of the tsx. Be careful with retumbo in the 30-378...in mine it seems to get temperamental at max loads. One day I was shooting loads with no problem and all of a sudden I saw big pressure problems. I don't know if I had built up fouling that day or what but I never had the same lot of brass/bullets do that in any other gun.