I've been working up some loads with the MP Molds 357-125-HP using the Penta Pins in my 38spl revolvers. These are sized to .358" after powder coating. So far I have experience excellent accuracy from this boolit in everything I've fired it in. And decided I wanted some fairly strong loads for my SP101 and Taurus 85. So naturally, I decided to give this one a try. Having a lot of Unique on hand I decided to try this powder. The Lyman 4th Cast Handbook lists data for the Lee 125gr RNFP with Unique at 4.3gr-5.3gr. I rolled the dice and chose 5.0gr for my first load, and seating to 1.518", crimping fairly lightly into the front band. I was very surprised by the accuracy I was getting in a S&W 65 (sort of my test gun for hotter 38spl loads). Based on the data I estimate these to be in the 850-890fps range. One thing I noticed while shooting in the Model 65 was that I would occasionally get a decently sized muzzle flash. I also noticed while the rounds did have a decent recoil to them, they did not feel too overly powered.
After this I decided to try these loads in the Ruger SP101 to see how they performed. And this is where I hit a snag, so to speak. I experience good accuracy in the Ruger. And I noticed that if anything these loads seemed comparable recoil wise to my target load of 358311 over 4.0gr Unique. Meaning, either equal to in recoil, or slightly less in recoil. Not very scientific, I know. Definitely manageable in the pistol, no problem. I also noticed in both that the primers didn't show any signs of excessive pressure, and the cases ejected freely without any issues. However, what makes me start to rethink my load is the muzzle flash from this pistol. Where I got only an occasional light muzzle flash in the Model 65, I am getting a larger bright muzzle flash in the 2" SP101. Which leads me to believe that I'm possibly not choosing the right powder for this application, as I figured that 5.0gr of Unique would have more than enough time to burn completely in the gun.
I'd like to keep this boolit around, or above, the 900fps range. But I also don't want to be blinded in low light. It looks like the only other recommended powder that I have on hand is Bullseye. However, with the bullseye data it very quickly moves into the +P range for the same velocity. Reaching around 18000psi by the Lyman data. And while I have no problems with using that with the Model 65 or the SP101, I don't think the Taurus 85 Ultralight would handle it quite as well. So this brings me back to the drawing board, where I think I may need to rethink my powder selections for this load. I do have Red Dot, as well as a few less suitable powders such as 2400. But I think that of those Unique and BE are the best suited, as they're fast burning powders that should burn up completely in theory - though I've disliked BE in most 38spl loadings due to position sensitivity.
That said, I've also wondered if maybe a heavier crimp into the front band would work to slow down the bullet long enough for the powder to burn completely. But I think at best this is only a partial fix, and the real solution may be to use a different powder.
Does anyone have any thoughts on powder/crimp, or observations from their own tinkerings with this bullet they might be able to share? So far I do like the load, but I'm not looking to set my targets on fire. Though I can think of a few instances where that might be handy....