I thought I would add this, I stole the post from another site where they were discussing the 25/223. I am posting it only because the poster summed it up so well as to the round's potential. It was posted by.......
Mike from Dtech
There are a couple of things that take place when you go to a larger diameter bullet. The same grain-weight of bullet in a larger diameter, you will have less surface area on the bore. This is not why a larger bore bullet of the same weight is faster. In fact, when you lessen resistance, it will lower the velocity. The reason you will get more velocity out of the larger diameter bullet of the same weight is the area of the base of the bullet.
Pressure is your limiting factor in how fast you can propel a bullet. If there were no pressure constraints, you could propel a 100 grain bullet out of a 6" barrel at 4000 feet per second! The problem is we do have to live with pressure limits. That's why when you apply the same (maximum) pressure to the rear of a larger diameter bullet, you will get more energy.
Diameter is a funny thing: It works in the inverse square. In other words, when you increase your diameter by double, you quadruple your area. So, when you make a small change in diameter, you make a noticeable change in area. This is nothing new, look at ANY set of cartridges and see what happens when you change diameter. Take the .308 case: Neck it down to 7mm and then to 6.5mm and then to 6mm. You've got the 7mm-08 the .260 Remington and the .243 Winchester. As you move down in size, you move down in energy.
Back to the .25.223, it follows all of the laws that I just mentioned. You will get more energy out of it than a .223 or a 6 x 45. Magazine length is an issue. There are things that can be done to work around mag-length to a certain degree, but in the end it is a limiting factor.
Bottom line: I was talked into the reamer when I was ordering a bunch of others. I don't know from personally shooting this round what it will do. You would probably get about 20% more energy than the 6 x 45, but it would be in bullets that would either be light, or have a poor ballistic coefficient (round nose or something to that effect) I will no doubt sell a 25/.223 to someone, but probably not because it's better than the 6 x 45. It just has more energy. Probably just about right for short-range big-game hunting.