why so little difference in cup

marlin60

marlin60

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Pwdr Grn Vel Cup

H4227 20.0 1839 42,000 CUP
H110 22.0 1966 41,400 CUP
HS-6 10.9 1629 42,100 CUP

The above numbers are from Hodgdon web site, for a 125 GR. HDY XTP.

I am not into reloading yet, but will be, so I have been reading a picking up tidbits as I can.

In the specs above, the top two loads have tremendous velocity, without much increase in CUP. Especially when compared to this load;

TITEGROUP 7.5 1497 41,200 CUP

Can someone touch on the physics as to why?
 
They are much slower burning powders and are just about optimum for hi-vel .loads in that cart.......any slower burning and they would be lower in pres. and vel....and may not burn completely, leaving unburn't powder granules in the barrel.
 
The CUP reading is the peak pressure. A fast burning powder will get it's peak pressure quickly with less powder, but since it burns faster (most of the powder burned down as the bullet leaves the barrel), the pressure will decrease quickly as the bullet goes down the barrel. Hence the reduced muzzle velocity and milder muzzle blast

A slower powder (such as H110) will need more powder in order to attain the same pressure peak, but it will maintain it's pressure longer as it continues to burn longer in the barrel (and also continues to burn outside of the barrel), hence the higher bullet speed.

H110 it the stuff! I exclusively use it for my 44 Magnum loads (31.5 grains with 180 grains bullets). Tremendous muzzle blast and flash! H4227 will give a very similar performance, but ain't half the fun of H110 (no flames/flash)


I suppose yours are for 357 Magnum?
 
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