Bought some Speer 148gr Hollow base wadcutters. Loaded them in .357 Magnum cases. Used 3.5gr of Universal Clays. Seated bullet just below flush. Very light crimp. With two guns they were okay. Not exceptionally accurate compared to full house magnum jacketed loads, but maybe 3.5 or 4"@ 25yds. But shot another 357 today and they were all over the target. 9" groups with wild flyers. Jacketed were still tight; sub 2.5"

I'll try 700X or Unique (don't have Bullyeye; might have some 231 though) and reduce the load I guess. Any other suggestions?

I just loaded up some 148 solid wad cutters to try with 4 grains of Trail Boss out of my AMU 1911 pistol.
The load cycles the slide with no issues.
I used a roll crimp to allow flayless loading and a little pressure build up for a more consistent burn.

i don't think powder will change a thing for this one -- sounds like the bullet/barrel combo just hate each other ..

as the benchrest crowd has PATIENTLY (haahhahaha) explained to me, a couple times (that helped the patience) they usually measure, not weigh charges, but are (insert hyperbole here) faithful to get the OAL right ---

translation -- generally OAL has more impact on accuracy than a slight variation in charge -- i don't recall i've ever improved something but (9-2.5 = 6.5, 6.5*4=10.5) TEN.. wow.. TEN moa by powder change..

i could be wrong, but i'd say this barrel hates this bullet

Fouled bore and/or forcing cone/chambers. Not powder, but might run some over a chrono to be sure ES is not bonkers.

Other stuff. Crud build-up in the seating die, as mentioned.

Not enough case bell, shaving lead.

A sizer/soft lead bullet diam mismatch has the same effect as not enough bell. In that case you might notice some brands of brass seem to produce better accuracy. Had that problem with .45 S&W brass and my .45 LC sizer - shaving badly no matter how much bell I used.

I cast 148WC from a secret proprietary formula (pure wheel weight). They shoot very well in my 6" 357 and 2" 38. I use 700X, I think it is 3.6gr?
Could be a sizing problem as stated above. S&W Mod 25's were famous for O/S chambers but usually sizing bullets larger solved that so could be you need to up the charge in order to obdurate the bullets more.

It's the lead shaving issue.

Don't know if I can increase bell enough that the wadcutters will slide in without seating (it's set up to where jacketed bullets almost fall through and the wadcutter still won't even start into the case).

Might be better to try with the 38 Special cases (thinner brass in the same sizing die should allow the wadcutter into the case with same bell, right?)

What you need is a larger, custom, expander plug. So your bullets don't get distorted whilst seating. I can make you one for a Lee die; others take too long....