An update:
Back from water jug testing and I’m pleased to report that the Speer 135gr Gold Dot Hollow Point Short Barrel worked EXACTLY as advertised. The Hornady 125gr XTP worked pretty well too.
I was using Speer’s max load for 38 Spl +P (7.0gr AA #5) which felt surprisingly light to me, much lighter than I expected. The book advertised 1052 FPS (although significantly didn’t mention test barrel length) but with my 4-inch barrel I only got 800-850 FPS. However that was enough to get the bullet to open up nicely.
Hornady lists 6.8gr as the max load for their 125gr XTP (calling it a +P load) But AA lists 7.5 max, and 7.8 with Remington 125gr. Since it’s a 357 magnum I felt comfortable starting off with 7.8, and that delivered 900-950 FPS, and just a tidge more recoil, still very light. That bullet expanded too but not in the same fashion.
The 135gr bullets weighed 133.8 afterwards, while the 125 weighed exactly 125.0, remarkable.
Speer doesn’t have any 357 Mag data for AA#5 for their 135gr bullet, as they only tested seven powders. But they list a million powders for their 140gr bullet, including AA#5. They list a starting load of 9.1gr, so I’m going to load up a batch of those today (using 357 Mag cases this time).
Knowing water jugs are an imperfect testing medium, and given the fact that I have been wholly unsuccessful in finding human volunteers to cooperate in my bullet performance testing
I am planning on producing some ballistic gel and formalizing my testing a bit more.
This will also allow me to shoot at milk jugs one at a time, purely for their great entertainment value.
Photo of the two Speer and one Hornady bullet attached. Again, thanks to everyone for the great advice and support!