For all fellas out there who have done this before I got a few questions for you. I have kicking around a few ideas for my first custom. First is a 243AI. Is the cartridge really worth putting a 40 degree shoulder on. Also what is your main reason for putting a 40 degree shoulder on any cartridge, for accuracy or velocity? And also have any of you guys ever modified the shoulder on a 7mm stw, say to 40 degrees versus the 25.

Thanks
Big-un

quote:

Originally posted by big-un:
For all fellas out there who have done this before I got a few questions for you. I have kicking around a few ideas for my first custom. First is a 243AI. Is the cartridge really worth putting a 40 degree shoulder on. Also what is your main reason for putting a 40 degree shoulder on any cartridge, for accuracy or velocity? And also have any of you guys ever modified the shoulder on a 7mm stw, say to 40 degrees versus the 25.

Thanks
Big-un

IMO. NO. Not because the .243 is not a good cartridge, because it is. However, all the rounds based on the .308 Win., as well as the .308 itself, are pretty much "improved" just as they are-they have minimum body taper already, and their shoulders are pretty sharp also. The main improvement derived from most Ackley designs is increased case life and less stretch/case trimming! There are a couple of exceptions, like the .250 Savage AI which is way under bore capacity to begin with, so anything that increases its' case capacity is welcome.

You just won't attain enough gain in case capacity to get much higher velocities than you can with the factory design, and I have not heard enough complaints about short brass life with this series either-I know from personal experience that .308/7.62X51 brass is pretty durable!

quote:

Originally posted by big-un:
For all fellas out there who have done this before I got a few questions for you. I have kicking around a few ideas for my first custom. First is a 243AI. Is the cartridge really worth putting a 40 degree shoulder on. Also what is your main reason for putting a 40 degree shoulder on any cartridge, for accuracy or velocity? And also have any of you guys ever modified the shoulder on a 7mm stw, say to 40 degrees versus the 25.

Thanks
Big-un

Most of the rimless so called improved cartridges work fine if the barrel is set back. On the other hand there is not much real increase in case capacity and the mechanical advantages such as a straight case to hold rear thrust are canards and don't really matter as the case would hold anyway and in particular in the example you gave.

These blown out cartridges look cool howver and are fun if you have not done it before so go ahead and try it.

As to the blown out belted magnums they are not good cartridges at all as the case is not supported and the force pushes on the shoulder during fire forming and tears metal from the expansion ring. However if factory brass is available as in the 300 Weatherby then it's just another belted round.