In my opinion shoulder angle and neck length have very little to do with barrel life. The shoulder angle may have a little more to do with barrel life, just because a steeper neck angle probably keeps more of the combustion in the case.
However, neck length has no affect on barrel life. There is enough freebore in every barrel, that the area just in front of the neck is meaningless. What is meaningful is the rifling. The rifling starts far enough down the barrel that the neck length of cartridge is meaningless, as far as barrel life is concerned.
Longer necks may improve accuracy, if in your loading process everything is perfect, therefore holding the bullet straighter.
That being said, it is the powder that makes the difference. As far as barrel life goes with these 6mm's, the 243 gets exactly the same barrel life as the 6CM, but only if you load it the same way. (I expect 3000 rounds from every 243 or 6CM barrel, and more often than not I am able to stretch the barrel to close to 4000 with no degradation in my X count at 600) The benefit of the 6CM is the 31 degree shoulder angle, which has proven to increase accuracy. I don’t know why it does, but the proof is on the target.
The key with these 6mm cartridges is to have enough case capacity to utilize the very slow burning, single based, powders (H1000, N165, Retumbo, N170). This is exactly why the 6XC and similar cartridges are always going to wear out a barrel faster than a 243, 6CM, 6SLR or even the 243AI. (243AI, loaded with the correct powder gets great barrel life). Understand the smaller case capacity calibers, trying to achieve similar velocities to the 6CM HAVE to use faster burning powders. That, simply, is what wears out the barrel faster.
These smaller 6mm’s (6XC class) are incredibly accurate and are a good choice for many shooters. When I developed the 6CM, I realized the 6XC wasn’t going to give me enough barrel life to last a season of shooting. (I shoot over 3000 rounds per year). I knew the barrel life I could get with the 243, but the 6XC was more accurate. So I made the front of the 243 look like the 6XC. AND IT WORKED. I know get the barrel life, because I can shoot the slower powders, and I get the accuracy.
Depending on your needs, any of these cartridges work great. The accuracy difference between the 243 and the 6CM is only realized by the very best shooters. The fact is that the guy behind the gun has more to do with where the bullet goes than the gun does. That goes for all disciplines.
My advice to everyone is to get out and practice, dry fire, pay attention to your loading processes, and equipment and to learn to shoot your rifle correctly. Testing loads is required and fun, but in the end it doesn’t make YOU a better shooter. Pick the cartridge that meets your needs. Purchase the best equipment you can afford. And go have fun.
Joe H
