Originally Posted by
Larry Gibson
Bass
The question here is rather straight forward;
Why is it the average reloader when he gets a regular mould from Lyman, RCBS, Lee or Saeco for his rifle can get accuracy at a certain velocity yet loses accuracy above that velocity?
With the 30-06 for expample he gets good accuracy in the 1700-1900 fps range but above that he gets poor accuracy. He casts the bullets of WWs or an alloy like #2 as mentioned in Lyman's or RCBS cast bullet manuals and uses normal loading techniques as per the manuals. I believe the reason is that above a certain threshold of RPM (the threshold is a range of velocity of 125-140,000 RPM not a specific "limit") accuracy deteriorates with such cast bullet loads as the increased RPM accentuates the inbalances in the bullet (caused during casting, by poor fit, excessive obturation during accelleration, etc.). The increased RPM causes the yaw, pitch and wobble to be increased and accuracy suffers as the higher the velocity the higher the RPM.
I'm attempting to answer that question; is that too hard to understand? I think it is not as you've already conceded that RPM does have an adverse effect on accuracy of cast bullets; " So your test to find best "average accuracy" with what's "reasonably" available off the shelf or steps that are taken is fairly useless. If you want to prove "easiest accuracy" that a slower twist is more .... "idiot proof" and minimizes errors as a reloader and shooter of cast, save your components, I'll give you that." BTW; the use of the slower twist is to keep the RPM under the threshold while attaining a higher velocity. Our example shooter is not going to get another barrel for his favorite '06, he wants it to shoot as is.
Now as to the rest of your last post; yes you can get around the RPM threshold by getting "anal". There are a number of things one CAN do, but the average cast bullet shooter isn't going to do them. He neither has the equipment, the knowledge nor the desire. He just wants to cast bullets, load them in the rifle that he has and go shoot them. He is not going to get a different rifle, new molds, a lot more casting equipment or make some exotic alloy. He just wants to know why his bullets won't shoot accurately above 1900 fps or so out of his '06. And by just casting and shooting regular bullets he is not going to get accuracy above the threshold, now is he. The reason he won't get accuracy above a certain velocity with his 10" twist '06 (or any other rifle of 12" twist or faster) is EXACTLY what we are talking about, isn't it?
The question isn't about getting anal is it, it is about why normal cast bullet loads almost all cast bullet shooters use don't shoot as accuately above a certain velocity as they do below at or below that velocity. THAT is the question I am preparing to answer by shooting over 500 rounds, using 2 different cast bullets, 3 different powders (4895, RL15, H4831SC) loaded in 1 gr increments to give velocties from 1800 through 2500+ fps with each powder and bullet. Identical loads will be fired through 3 accurate rifles of .308 Winchester and each 5 shot string of a particular load will be chronographed and the group measured. Each through a rifle with a with a different twist; 10, 12 and 14".
The test IS NOT to show which rifle is more accurate but at what RPM accuracy deteriorates. Thus the test I am doing is to show at what RPM accuracy deteriorates in each of the 3 rifles with the 2 different bullets loaded over 3 different powders. Given the different twists of the rifles the RPM will be different for each rifle at any given velocity. If accuracy deteriorates in the 10" twist at 2000 fps but doesn't in the 12 and 14" twists then that is an indicator that RPM is the culprit. If at 2200 fps accuracy is still worse in the 10" twist and deteriorates in the 12' twist also but doesn't in the 14" twist then that is even more of an indicator that RPM is the culprit. Then if at 2400 fps accuracy deteriorates in the 14" barrel and we compare the RPM when accuracy deteriorated in all three twist barrels and find that it is close to the same then that would be a good bet that RPM was the real culprit.
So Bass, if you insist my test is "fairly useless" then I challenge you to come up with a comprehensive comparable test to show us how "the HV guys are changing the stereotype." Please SHOW me/us how your '06 holds accuracy from 1800 fps through 2600+ fps and that best accuracy DOES NOT come in the RPM threshold with that 154 gr LBT bullet but at the higher velocity/RPM of 2500+ fps. The choice of alloy, lube, size, barrel bedding or any of the other "anal" things you want to do are ok with me. Pictures of targets and chronograph results please. Shouldn't take more than 10 five shot strings to cover 1800 to 2600+ fps. The guantlet is at your feet. All you have to do is pick it up.
Nothing like a friendly little shoot out, eh?
Larry Gibson