I have not even received my new 25/223 and I am already planning the next one. I copied this from another site and it looks very good to me. So it will probably be next of I do not succumb to the 25 Grendel I secretly am drooling after.http://www.ar15.com/forums/topic.html?b=3&f=121&t=382761
The 7.62x40mm is a .223 based wild-cat offering for the service rifle family of weapons and was created by Kurt Buchert of Lake Charles, Louisiana.
First thoughts began in September of 2005 as the result of many sleepless Hurricane Rita nights huddled around lanterns thinking and talking about the use of the 300-221 as a medium-sized game hunting cartridge in a service rifle platform. The thought or goal was to wild-cat an improved .30 caliber cartridge that would take advantage of as much of the .223 parent case capacity with a 125 grain bullet and still load and function in standard service rifle magazines and mechanism components. The selection of the .30 caliber projectile in this weight class was based on the calculated velocity window of 2,400 to 2,500 fps and decades of industry wide reloading, hunting, and military experience. The compiled information showed that the 110 to 125 grain projectiles performed well at these intermediate velocities while delivering modest recoil and a high degree of controllability and accuracy in manual and gas operated weapons.
Following the intermediate cartridge concept of the 7.92x33mm kurz, 7.62x39mm Russian, 7.92x40mm CETME, and 7.62x40mm CETME from the 40’s and 50’s the 7.62x40mm is a culmination of firearms industry, wild-cat, benchrest, and personal experience and information. The chamber dimensions went through several revisions in an effort to produce the best all-around compromise of feeding, case capacity, velocity, accuracy, and chamber release. The intersection of these efforts has come to what individual owners and industry leaders spoken with have called a “makes-sense” cartridge for intermediate power in a service rifle platform.
Case length: 39.76mm / 1.565”
Case rim: .378"
Case rim thickness: 0.045"
Case base: .373"
Case taper: 0.011” total
Case shoulder angle: 30°
Case Capacity: appx 30 grains of de-mineralized H20, varies slightly by brass manufacturer.
Maximum loaded overall length (OAL) in AR15 magazines: appx 2.250", varies by manufacturer of magazine.
Usable case capacity with a 125gr flat-base bullet seated magazine length is appx 26.5 grains of Accurate 1680 powder, varies slightly by brass manufacturer.
Rifling twist rate varies from 1:8 to 1:14
Average Performance Data
110 Hornady V-MAX =2,575 fps
110 Sierra Varmint = 2,550 fps
125 Speer TNT = 2,450 fps
125 Nosler BTBT = 2,450 fps
123 Lapua FMJ = 2,475
110 Hornady V-MAX =2,700 fps
110 Sierra Varmint = 2,675 fps
125 Speer TNT = 2,600 fps
125 Nosler BTBT = 2,575 fps
123 Lapua FMJ = 2,625 fps
Cartridge and System Information
The 7.62x40mm is derived from the 5.56x45mm (.223 Rem.) parent case. The low cost and availability of mil-surplus and commercial brass was one of the core reasons for the development of this cartridge.
Primarily designed to use 7.62mm (.308) projectiles in the 110 to 125gr range, but has been loaded and tested up to 220gr in sub-sonic applications. The range of bullet weights and designs in the .308 family make this a very flexible cartridge.
The user selectable ballistic performance makes it an excellent choice for varmint control, medium sized game hunting, or personal defense. As illustrated below in a comparison of the .223 and 7.62x40mm.
.223 load of a 55gr FMJBT at 3,000 fps will produce an average of:
1,100 ftlbs of energy at the muzzle
885 at 100 yards
710 at 200 yards
565 at 300 yards with a 5.4” high flight path
7.62x40mm load of a 125gr BTBT at 2,500 fps will produce an average of:
1,730 ftlbs of energy at the muzzle
1,430 at 100 yards
1,175 at 200 yards
960 at 300 yards with a 7.6” high flight path
The 7.62x40mm makes the most of standard rifle components, usually only requiring a barrel change while still offering the end user the ability to customize the rifle with their choice of buffer and gas systems. You can still tune the rifle for timing and felt recoil which makes the whole system more user friendly and reduces wear and tear on the rifle, does not require any proprietary parts to function.
For current 300-221 / 300 Whisper users it is a natural progression if looking for more velocity. Simply have the barrel re-chambered, cut and form new brass, adjust your reloading dies for the longer round, reload and head to the range.
The information in this document is not inclusive of all that has gone into the 7.62x40mm cartridge, the thousands of rounds reloaded and fired, experiments with magazines, chamber revisions and results, or the performance of barrel and gas system length…..
This is meant to serve as core information, a conversation starter, and a holding area for those who wish to share their experience with the 40...
line-up of 300-221, 7.62x39mmRussian, 7.62x40mm, and 5.56x45mm