In Hodgdon's burn-rate chart published in 2019, they rated 4227 slower than Lil'Gun and H110/Win296. It was rated just faster than CFE BLK.
4227 is a single-base powder. It is an extruded powder of nitrocellulose (gun cotton) and contains no nitroglycerin. The cylindrical extrusions have a single perforation in the center that results in a highly progressive burn rate. It starts to burn slow, and then as the grains burn from the inside-out, the surface area of the grains increases, and the burn rate accelerates.
If you don't give it enough time under pressure to burn thoroughly, it will eject "powder skeletons." This isn't necessarily "unburnt" powder, but it is incompletely combusted grains. Some of the cellulose has not been gasified. I suppose it is like ash.
One time I was shooting 357 loads of 4227 over snow. They were maximum loads in the sense that the case would not hold any more powder. I was shooting a single action with a 5.5" barrel. After about 50 loads or so, there was a fan-shaped debris field of black 4227 skeletons across the snow in front of me.
Hodgdon's data shows for a 158 grain XTP, the maximum load is 16 grains of 4227 or 16.7 grains of H110.
Quickload calculates 16 grains of 4227 will fill the case 119.8% under a 158 grain XTP seated to an OAL of 1.58" (Hodgdon's spec.) Hodgdon measured the pressure at 42,600 CUP.
68% of the load will be burnt before the bullet base exits the muzzle. The rest of the load will combust, but it will be in free air (at low pressure).
16.7 grains of H110 will fill the case to 106.6% under the same bullet at same OAL. Hodgdon measured 40,700 CUP.
77% of the H110 will burn before the bullet exits.
Hodgdon measured 1520 fps (4227) and 1591 fps (H110) in their 10" test barrel for these loads. For the 18.5" test barrel, they measured 1668 fps and 1757 fps respectively.
What this evidence indicates to me is that 4227 needs a larger case. I thought it might work well in 357 Maximum, so I looked at the data and it is very telling because Hodgdon also includes a CFE BLK load.
For 357 Maximum, H110 is measured at 1865 fps with an uncompressed load of 22.5 grains. Similarly, Lil'Gun is measured at 1911 fps with an uncompressed load of 22.4 grains.
4227 is measured at 1749 fps for a compressed load of 22.5 grains. Similarly, CFE BLK is measured at 1698 fps with a compressed load of 27 grains.
The problem with 4227 and CFE BLK is that they are too bulky for even 357 Maximum. They need an even larger case.
Browsing some data, it looks like 4227 really comes into its own with 375 Super Magnum and some 44 Magnum loads (look at 300 grain XTP loads). These are where the case and bullet combinations are allowing enough room for sufficient mass of 4227 to develop the pressure, and where H110 or Lil'Gun are exceeding the MAP with case capacity to spare.
My conclusion is that 4227 is too bulky and too slow in burn rate for most 357 Magnum use. Note that we see the same thing in 350 Legend -- compressed loads with low pressures, and velocities that just can't keep up with H110 etc.
