Reply with quote #1
With the success I've had with my 6CM I have designed a new cartridge.
The goal is more velocity with the same accuracy.
The cartridge is based on the 6.5X284 case. I believe this be a good parent cartridge give the quality brass available. Also, given the fact the case is shortened and necked down to 6mm, no fire forming will be required. Neck turning may be required, even with the .276” neck diameter of the chamber.
I have shorted the case to the length of the 243 Win (2.055 inches). The new cartridge will have a 31 degree shoulder, and a neck length of 0.2486" (less trimming).
I am estimating a case capacity increase of 11% over the 6CM. I am expecting to easily obtain 3200 fps from the 115 gr bullets and possibly as much as 3300 fps. The 6CM currently is able to propel the 115 at just under 3100 fps.
If this works, and I will not know until next spring, this cartridge will be better than the 6.5x284 for long range and will be able to be shot in any across the course rifle that can fire a 308 sized case.
Furthermore, utilizing slow burning, single based powders, the barrel life should more than 3000 rounds as the 6CM is giving barrel life of up to and beyond 4000 rounds.
Any thoughts, ideas or comments are appreciated.
Reply with quote #2
The 6-284 is a barrel burner. Is shortening the case a little going to double barrel life or do you have more changes in mind for the case? I really like the idea if you can get any reasonable barrel life.
Reply with quote #3
6CM Max keep me informed.
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Joe, Sounds interesting,but I think you would need a longer neck. I think at that speed with the 115's the throat will burn out rapidly..........jim
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Joe, is anyone helping you in testing? Good luck hope it works out as good as the 6CM, if it does it sure will make some people grumpy. I've got faith in ya.
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I know people who use Joe's 6CM or Joe himself will pipe up, but as I understand it he was using a very slow burn powder, H1000, and maintaining the throat every few hundred rounds. He'll be able to explain it in detail. Sounds very interesting.
Reply with quote #7
For me it's all about consistent accurate velocity and proper balance and I don't really see that discussed here so far.
More capacity does not necessarily equate to more accurate consistent velocity.
Frankly with a 6mm, I think going much bigger in case capacity over a 6CM is a foolishness for anyone shooting across the course or prone matches where you need to put 22+ shots down the bore without a break (including perhaps rapid fire sequences).
Invariably the discussion seems to center on velocity as if that's the overriding issue when velocity (in my opinion) takes the third position in terms of priority, with accuracy and consistency numbers 1 & 2.
I have a 6CM and it's fine but I have had great results with my sightly smaller capacity 6mm Super X (and I am not trying to say the Super X is better or worse than the 6CM as they are not way far removed from each other in terms of case capacity).
Personally I think there are optimum balance points with cartridges, especially when factoring in bore size, the projectiles to be used, the powder that might be ideal, etc.. By that I mean it is possible to have things out of balance which would then have a tendency to sabotage any gains you think you may get by boosting something in the mix. An example is having a case capacity so large it is out of balance with the bore size and projectile to be shot. If that is not the case then why not just neck down a 50 BMG case to 6mm and shoot that? Then we could drive 115 DTACs at probably 5000 fps. People don't typically do that because it is counter productive and it is likely to lead to an out of balance situation that in turn adversely affects other important things (like accuracy and consistency).
Where the optimum balance point is with a 6mm bore size and the 105 - 115 gr bullets is hard to say for sure, but I bet much more capacity than the 6CM is pushing the outside limit and would likely be over the edge. The 6mm Rem AI and the 6mm/284 already exist as cartridges but they are not well used at all in competitive shooting.
Reply with quote #8
George over at GAP....
http://www.gaprecision.net has an improved version of the 6mm Rem that he is shooting in a repeater with AICS mags. It's called the "6mm Crusader. The case is blown out, but not all the wayt to ypical AI specs. The shoulder if I remember correctly is 32 degress . He is firing 115 bullets at 3300 fps +. No feeding issues and accuracy is superb. I believe single based powders are the way he goes too. I think RL25. Just go to http://www.snipershide.com and use the search menu.