No, I have not had any difficulty shooting cast bullets from a 336. But in this particular instance it was with a 1952 vintage ballard rifled gun, so your theory does not apply to this exact case. I have got 35 Rem, and 444 Marlin micro grooved barrels to perform very well for me. If you think about it, it makes sense too. There is a third more surface area a micro grooved barrel uses to grip and put the spin on a bullet. With the MG barrels the key you must pay particular attention to is bullet to barrel fit. If a cast bullet is fitted to a MG barrel they usually shoot better than say another comparable rifle. You said that they need to be really hard. To me what this really means is that to forego the work necessary and trying to fit the bullet to the rifle, a hard bullet will be more forgiving that a soft bullet. In essence it is the lazy mans way to get a 336 MG to shoot better. But a hard bullet is something that should not be shot at game for obvious reasons.
I cannot get a 94 to shoot as well as a 336 for instance. To me, it is the micro groove rifled barrel that is the key to this success. It is unfortunate that the old wives tale about the MG and lead bullets not going together was started in the first place, by some very, very, talented and knowledgeable writers and now is passed off as fact. The ebb and flow of popular cartridges, is interesting to look at. The way the gun writers and shooters percieve a particular cartridge sometimes has very little to do with how great a said round is. Take the 30-30 for instance. It is not anywhere near as good of a round as say 300 Savage is, one is as dead as a dodo, why? Making the 30-30 a better gun with bigger bullets is a right of passage for many folks. It is what it is, a round that has seen the test of time, it has been on the kill of so many critters my calculator does not go that high. But to me, heavy bullets is just putting lipstick on a pig as Palin said. If you can accept the 30-30 for what it is, and CAN do, which is lob a 170 grain bullet at game at moderate velocoties you will save yourself time and money. But since I did this, I cannot tell folks to not do this just based on my experiences. Like I said, it is a right of passage for some folks and will continue to be no matter what I have to say.
I have a 32 Win Special in a 336 MG barrel, that will shoot the pants off ANY 94 I have ever seen, and gives a good bolt gun a run for its money...all done with cast bullets.
The reason those big bullets dont work as far as I can understand, is because that big bullet is not balanced properly, and its nose is not flying true through the air. Centrifugal force is keeping it spinning of course, but it has trouble keeping its nose from making tiny circles. This is the keyhole issue. If you think about it long enough, you begin to see that this experiment can relate to other heavy bullet for caliber arrangements and can be extrapolated to other calibers in this way. The laws of physics don't really care how much you love a particular caliber and the fact that you really, really want to lob a big bullet down range. The longer it is, the faster it needs to be spun. This can be done by either using a faster twist barrel, or shooting it faster. Neither of these is condusive to lead bullets, and since whatever happens to lead is also happening to copper but to a lesser extent, you begin to understand why bullets do what they do, no matter the metal used. Copper is harder and more forgiving, but copper clad bullets are subject to the same analysis as a pure lead projectile. If you understand all this, you will achieve better accuracy, and a better chance of making game dead. This is the main reason I want to shoot and practice, its the time once a year (if I am lucky that I will get the chance to kill a nice bear or nice buck).
Anyway, if a bullet that is not flying true hits bone it will deflect. If it hits a twig before the target it will deflect. The exact opposite effect of the normal person who is shooting a heavy at game wants. To me, the old wives tale that needs to die is the fact that heavy for caliber bullets do better as brush busters than normal for caliber bullet weights.
FWIW, I have had good success with 311041 and 311407. Both are right around 175 grains. Its a good place to be with a 30-30.
What you said about the heavy 30 cal jacks is very true and something that ought to be taken into account. The jackets are built to withstand the force of hitting something at 300 Win Mag speeds. If you shoot these bullets at 1700fps it will act as a solid with minimal expansion.
I hope that I am not coming across as a know it all, just passing along what I know. I have far more to learn, that I do know.
