"Sure you can increase the muzzle velocity without necessarily increasing the peak chamber pressure for a given rd."
AFAIK you can't. Any increase in burn speed will burst the breech open (it can even happen with a too small load!) and the increase of driving substance will do you no good if the barrel length is not enough to contain the projectile for duration of that extra acceleration. Of course if the initial load was small to begin with there is room for increase but why would they do that?
The breech is designed to correlate with the load and the load correlates with the barrel length. The brake does not lighten the explosive load expressed on the breech but to the carrier aircraft in this case. A lighter projectile will have higher MV but it will also decelerate faster. Thus the heavier standard AP will retain its performance on longer ranges, where as the lighter projectile will have to be fired closer to regain its advantage in added MV.
Bk37 AP energy 13486J
Bk37 APCR energy 16837J
Mk103 APCR energy 8513J
To me the breech looks quite slim.
(Image removed from quote.)
-C+
Yes you can. But unless the current powder charge is low and can be increased without over pressuring the chamber (which I doubt it was on the BK37), then it would necessitate a change in powder and/or ignition source. What blows the breech apart is PEAK chamber pressure. This peak pressure correlates directly with the hoop tension in the walls of the chamber. Provided you stay below the tensile yield point in the elastic range you're ok (your barrel fatigue life is gonna suck though).
The total impulse applied to the round is the AREA under the Pressure vs Time curve, NOT the pressure itself. The trick is to stay BELOW the limiting max pressure, but to INCREASE the area under the P vs T curve. This can actually be done by varying the powder type (maybe a SLOWER burning powder) and varying the amount of powder. A blend of powders (yeah, I know
) can also help. Changing the energy of the ignition source (primer) lets you fine tune it even more if needed. Refinements in powders over the years have actually allowed this. The improvements have been small, but significant. (~5%)
Once again, the muzzle brake has absolutely nothing to do with the primary recoil at the bolt or breech block. The purpose of the muzzle brake is to reduce the secondary recoil effects due to muzzle blast impingement on the face of the muzzle. The total recoil is primary & secondary recoil combined. And yes, the gun attachment structure has to be designed for this cyclic transient load.
You're correct that lighter rounds decelerate more quickly, but armor penetration is affected more by kinetic energy than momentum. At higher velocities the armor fails in a totally different manner (think brittle shear fracture) because at very high loading rates the stresses in the armor material don't have time to redistribute, and subsequently the armor fails at a lower load than if loaded more slowly. There's a reason why modern anti-tank rds are small sub-caliber projectiles moving at ungodly velocities.
And yeah, the whole chamber and breech look VERY slim.
I don't think I'd feel too comfortable standing next to this thing when it was being fired.
