Hi 7.62 Nato,
There are three variants/wildcats based on the 223REM/5.56x45 case. Some will fit in an AR15 mag better than others. The 25x40 has the shortest case. It goes by the name 25x40mm. It was designed be Kurt. His handle on AR15.com is 7.62x40mm, his first creation. He also post on occasion here on quarterbore. The 7.62x40mm is now being offered by Wilson Combat. Basically, it is a 223REM case shortened to 40mm and the shoulder pushed back. This reduces the case capacity to about 28-29 g of water. The 25x40mm designed is such that you can load bullets up to 115 g Bergers. The case mouth will not ride up on the ojive of the bullet and will fit the 2.26 length restriction of an AR15 mag.
The second 25 cal 223REM/5.56x45 based wildcat is the one I designed with advise from Kurt. It goes by the name of 25-223AR. It has the same shoulder as the parent case but the neck is shortened about 0.06" giving an overall length of 1.70". This cat was designed to 25 cal bullets up to 100 g without the case mouth riding up on the ojive of the bullet and still fit the 2.26 length restriction of an AR15 mag. I have been able to push 100g bullets to 2550-2600 fps (16-inch barrel). I have gotten up to 2650 with some combinations of bullet and powders, but as with all internet reloads… You are on your own Start low and work up..You must use your own judgement if the loads are safe in your gun/barrel combination. The heaviest bullet that will fit in 2.26 length restriction of an AR15 mag is the 117 g Hornaday round nose bullet. I have pushed this bullet up yo 2400 fps. It runs through my ARs like a hog eating sxxt. The 117 g Hornaday bullet is designed for the Winchester 25-35 so 2400 fps is right in the velocity envelope for this bullet.
If you want to read more about this cartridge you can find it here:
http://www.ar15.com/forums/t_3_121/4...23.html&page=1
It is over 30 pages of material. So if you want to read about it set some time aside.
The third 25 cal 223REM/5.56x45 based wildcat is the one described here. It's main advantage is that it is simple to make brass. Run it through a 25-223 Rem die and you are good to go. However you will have a lot fewer bullets to choose from.
Here is a list of the bullets where the case mouth rides up on the ojive.
Nosler 100 BT
bullet length=1.117
shank length=0.576
ogive length=0.541
case @1.7 COL=2.241
case @1.76 COL=2.301
Nosler 85 BT
bullet length=1.000
shank length=0.461
ogive length=0.539
case @1.7 COL=2.239
case @1.76 COL=2.299
Nosler 100 PT
bullet length=1.035
shank length=0.500
ogive length=0.535
case @1.7 COL=2.235
case @1.76 COL=2.295
Barnes 80 TTSXT
bullet length=1.012
shank length=0.456
ogive length=0.556
case @1.7 COL=2.256
case @1.76 COL=2.316
Speer 87 TNT
bullet length=0.916
shank length=0.369
ogive length=0.547
case @1.7 COL=2.247
case @1.76 COL=2.307
Horn 100
bullet length=0.986
shank length=0.459
ogive length=0.527
case @1.7 COL=2.227
case @1.76 COL=2.287
Horn 75
bullet length=0.867
shank length=0.339
ogive length=0.528
case @1.7 COL=2.228
case @1.76 COL=2.288
Sierra 100 MK
bullet length=1.074
shank length=0.516
ogive length=0.558
case @1.7 COL=2.258
case @1.76 COL=2.318
There is a full discussion on this here:
http://www.ar15.com/forums/t_3_121/4...3.html&page=28
Good luck with our project. Wildcating is a very fun hobby/addiction.
320pf
Threaded Mode