09-11-2013, 04:43 PM
The velocity of a projectile is a work function. Constraining the variables associated with the volume, expansion ratio and powder burn rate, velocity becomes directly proportional to the mean pressure during the bore time.
Faster from the same known standard loaded round can only result from more pressure. This is a bad thing.
Variables within a barrel can increase the pressure and it is well known for people to have barrels that are faster than others. This generally results from a tight major diameter, high aspect ratio or error in the throat.
5R rifling has by design a lower aspect ratio. It will typically lower pressures and directly lower velocities. This can be compensated by bringing the load up to the original pressure which will normally allow a slight increase in velocity. This same effect may be seen in the use of MoS2 on bullet jackets.
There are techniques that can be applied to gain velocity. The reduction of engraving forces by lengthening the throat or an increase in throat diameter can be used. They usually magnify the throat erosion and can create secondary detonations in extreme cold climates. It is rare to find a cartridge that has the volume to benefit.
By simple physics ( or complex pressure breach work) the 6.8 SPC will allow for an increase in velocity between 30 and 90 fps over a Grendel when both are loaded with identical projectile weight and constrained to the safe limits of the weapon. The SPCII throating drops the pressure slightly as above and can be compensated by the addition of charge weight. It will yield around 30 fps.
There is no magic in internal, external, intermediate or terminal ballistics. If you see something extraordinary hope that you can find the instrument error before something disassembles itself.
Faster from the same known standard loaded round can only result from more pressure. This is a bad thing.
Variables within a barrel can increase the pressure and it is well known for people to have barrels that are faster than others. This generally results from a tight major diameter, high aspect ratio or error in the throat.
5R rifling has by design a lower aspect ratio. It will typically lower pressures and directly lower velocities. This can be compensated by bringing the load up to the original pressure which will normally allow a slight increase in velocity. This same effect may be seen in the use of MoS2 on bullet jackets.
There are techniques that can be applied to gain velocity. The reduction of engraving forces by lengthening the throat or an increase in throat diameter can be used. They usually magnify the throat erosion and can create secondary detonations in extreme cold climates. It is rare to find a cartridge that has the volume to benefit.
By simple physics ( or complex pressure breach work) the 6.8 SPC will allow for an increase in velocity between 30 and 90 fps over a Grendel when both are loaded with identical projectile weight and constrained to the safe limits of the weapon. The SPCII throating drops the pressure slightly as above and can be compensated by the addition of charge weight. It will yield around 30 fps.
There is no magic in internal, external, intermediate or terminal ballistics. If you see something extraordinary hope that you can find the instrument error before something disassembles itself.