[SL1]

under_dawg,

You said you were told to "use Speer data" for West Coast Xtreme plated bullets and you said you have Unique and Trail Boss powders. The Speer manual #14 lists Unique but not Trail Boss for 125 gr and 158 gr "Unicor" and "Gold Dot" bullets. Both are actually plated construction, but I don't know how they compare to West Coast Xtreme's bullets. Speer says it chooses different lead alloys with different hardnesses for different bullets, and builds-up electroplated "jackets" to thicknesses that vary from 0.007" to over 0.030" on different bullet designs. So, the loading data can vary quite a bit from one plated bullet to another of the same weight by a different manufacturer, or even different bullet designs of the same weight by the same manufacturer.

The issue is really one of pressure, not velocity. The softer the lead and the thinner the jacket, the lower the pressure that will cause the bullet to expand against the inside of the barrel and increase friction, which causes pressure to increase more than if the bullet acts solid. I am shooting some Speer Gold Dot bullets (but in a different cartridge) at 1400 fps without copper fouling the bore and with good accuracy. Those bullets were designed for that velocity and pressure (40,000 psi). Another example is the Federal "Fusion" rifle bullet, which is also a plated design that is used at about 3,000 fps and 60,000 psi in a .270 Winchester. But, some plated bullets have very soft cores and very thin plating. Those act like unplated soft swaged lead bullets with repsect to how much pressure they can withstand before deforming in the bore and causing rapid pressure increases with a little additional powder.

You should also be aware that unplated lead bullets are not all the same, either. Soft swaged lead bullets need to be kept below about 10,000 psi, but heat-treated, hard-cast bullets can be loaded up to about 45,000 psi. The first pressure restricts velocities to about 900 fps in a handgun, but the second allows velocities up to about 2,400 fps in a rifle.

So, here is the Speer data for Unique in the .357 mag case with Gold Dot bullets:
125 gr bullet: start load: 8.6 gr 1259 fps
max load: 9.6 gr 1343 fps

158 gr bullet: start load: 6.9 gr 978 fps
max load: 7.7 gr 1040 fps

The Speer manual says these loads stay below 35,000 psi. The velocities are for a GP-100 with a 6" barrel. Velocities from you 4" barrel will probably be 50 to 80 fps less.

For comparison, the same manual lists the 125 gr bullet (but not the 158 gr bullet) in the .38 Special case at normal (17,000 psi) and +P pressures (20,000 psi). The max load of Unique for 17,000 psi is 5.7 gr and for 20,000 psi it is 6.0 gr in the (smaller) .38 case.

One final comment: you gave Lee's load data for Accurate Powders for a 125 gr plated bullet. According to Accurate Powder's manul #2, those data are the start loads for a 125 gr Ranier plated bullet. The maximum loads in that manual are:

#2 Powder 6.8 gr 1390 fps 32,100 psi
#5 Powder 8.9 gr 1493 fps 32,200 psi
#7 Powder 11.2 gr 1578 fps 33,500 psi
#9 Powder 13.1 gr 1630 fps 32,200 psi

These velocities are for a 8" test barrel, and are a lot higher than you will get from a 4" revolver barrel with its gap between the cylinder and barrel. Comparing these loads to the loads for the same powders in the Speer manual, I see that Speer's max loads are more than a grain higher for the Gold Dot bullets of the same weight. That means the Speer bullets are probably harder than the Raniers. I do not have data for the West Coast Xtreme bullets, so it is hard to guess what their max pressure loads would be. Also, the Accurate Powders manual does not say that the Ranier bullets stayed accurate and did not foul the barrel with maximum pressure loads - - it just said they were still safe at those loads. Therefore, start with the start loads and go up until either (1) the load is as fast as you want, or (2) the barrel starts to foul, or (3) the accuracy deteriorates, or (4) you reach the maximum listed load.

Good luck, have fun, and be safe.

SL1