Crane carbine vs midlength test results

[Vicious_CB]

http://soldiersystems.net/2018/05/14/nswc-crane-carbine-mid-length-gas-system-testing-shows-increased-performance/

 

So in Crane's testing of the URG-I vs M4A1, the numbers make sense except for this one. Maybe you ballistic gurus can answer this because I have no idea.

 

 

 

How can you have 2 significantly different mean muzzle velocities at 100 yards when they both started off with nearly the same muzzle velocity, out of the same length barrels with the same twist rate? It cant be stability since that is based on starting velocity and twist rate.  Is there some kind of magic that the midlength gas system imparts on the bullet that causes it to have less velocity decay or is this just a statistical artifact? 

 

[Ramlaen]

I'm not a ballistics guru but I would speculate it has to do with the gas being siphoned off farther down the tube keeping the pressure higher for longer.

[Collimatrix]

How many barrels total were tested?  Barrels of the same caliber and length will often show consistent muzzle velocity differences of tens of feet per second for no apparent reason.

[D.E. Watters]

On 5/15/2018 at 2:42 PM, Collimatrix said:

How many barrels total were tested?  Barrels of the same caliber and length will often show consistent muzzle velocity differences of tens of feet per second for no apparent reason.

Don't know.  The 2018 presentations haven't been posted on DTIC's webpage yet.

When they go up, it will probably be at this link:

https://ndia.dtic.mil/2018/armament/2018armament.html