Well, I loaded up some 162g loads and some 147.5g 357 Magnum loads, with progressively higher Trail Boss charges ranging from 3.5g to 4.1g, and fired a ladder test at the range with my Uberti Competition rifle at an estimated 25 to 30 yards. Conclusions:
- Both weights of bullets worked reasonably well with this range of powder grains, but accuracy improved as the charge increased. I attribute this to more powder = less air space in the cartridge case below the seated bullet.
- Point of Impact did shift upward with increases in powder charge, but only a total of up to 3/4 of an inch at most, and at CAS ranges this is not going to be an important factor.
- My Labradar failed to trigger until right near the end of my load testing, when I thought of calling a buddy who also has a Labradar, and got his help troubleshooting. It was a simple error on my part: I had somehow unintentionally changed its setup from being triggered by its own Doppler radar, to requiring an external trigger, which I obviously did not have. So, I got velocity statistics only for the very last 5 shots fired with the 162g bullets. This gave the following results:
Stats - Average 861.44 fps
Stats - Highest 884.73 fps
Stats - Lowest 808.58 fps
Stats - Ext. Spread 76.15 fps
Stats - Std. Dev 32.36 fps
So, the SD and ES were both fairly awful. The velocity was more than needed for CAS (861 fps average for the 5 shots), but the recoil was so unnoticeable that the 861 fps average seems just fine. I suspect the 147g was likely faster, but again, the recoil was ridiculously low.
- Both bullets, the 147.5g round with flat nose, and the 162g round nose, fed just fine. Not a single issue with either one.
- The accuracy of the 147g was superior. Its average group size was 88% of the size of the 162g average, and the best 147g group size was 75% of the size of the best 162g group. This is what I had hoped for, as the 147g also has the flat head and is therefor at least theoretically safer in a tubular rifle magazine.
So, the 147.5g cast lead round with flat nose bullet at 4.1g of Trail Boss is my new 357 Magnum load for CAS. My buddy apparently has a bunch of them that he is willing to give me, so that is great.
An interesting result was the condition of the CCI 550 Magnum Small Pistol primers after firing. Below are photos of both the 147.5g and 162g primers after firing. Note the absolute lack of ANY flattening at these 3.5 to 4.1g load levels. But also not how DEEPLY the Uberti firing pin depressed the primer outer shell. That firing pin must be striking deep and hard.
Jim G
