Unexpected velocities

I've encountered two different issues in some of my reloads that I'm hoping the forum can help me with. 

#1: I just recently started reloading 38 Special for a new to me SW 52-2. I get very consistent velocities averaging 750 FPS using the Zero 148gr DEWC over 2.7gr WST.  I decided to try the Zero 158gr LSWC in my Colt OMM and upped the charge to 3.3gr WST. I'm getting velocities averaging 610 FPS... the spread being 538-656 FPS.  Thinking it might be the gun, I tried the DEWCs in the same Colt OMM and got the usual 750 FPS. I cut open a couple of unfired rounds when I got home and double checked the charge and all of them were right around 3.3gr WST. I'm perplexed as to why the velocities are so much lower... maybe not enough crimp?

#2: I get very consistent velocities shooting the Zero 185gr LSWCs in my 1911.  Standard deviation is ~15 and the ES is low. When I shoot the Zero 185gr JHPs, the ES has been up to 150 and the Standard Deviation shoots up to ~30. I'm still not good enough to really judge the effect that has on accuracy (doesn't look to be significant) but the real issue is it affects the cycling reliability. I have to drop down to a really lightweight spring in order to accommodate the few rounds that keep dropping well below the mid 700 FPS range I'm looking for.

Powder position in a case which has too much unfilled space is the issue with your 158 gr load. To prove point change nothing. Next time out with chronograph do fhe following, each with at least 3 - 6 shots:
1) Load, point muzzle upward before and between each shot. Do not let muzzle dip below horizontal. Note velocity.
2) Load, point muzzle downward before and between each shot. Do not let muzzle raise above horizontal. Note velocity.
3) Load, point muzzle as you typically shoot across chrono.

You will get the highest average and closest deviation with #1. Solution is to choose a powder which is less dense, or use more powder, or select a powder which is not as position sensitive in low power loads. Another option is to seat the bullets deeper, to use up some of the empty case volume.

I had not considered that but that makes a lot of sense. I wonder if the same thing is going on with my JHPs in #2.  I load them close to max COAL.  I'll have to look but the LSWC I'm guessing are seated much deeper.  In addition to your tests above, I'll seat some deeper to see if that resolved the issue.

Thanks!

As alluded to, the real reason is that the powder volume of a 38 with a flush seated wadcutter is significantly less than a typical 158 LSWC or LRN bullet,  hence the lower velocities with similar loads.  To get the velocity you need to increase the charge.  Hodgdon lists 3.7 WST giving 790 fps and 3.3 giving 700.  I’d load 3.5 and see if you get better velocity.

I'm curious how deep others are seating their 185s.

I think you’ll find most people are seating 185 Zero/Nosler JHPs at 1.200-1.215,” with crimp depending on cases and personal preference.

I remember as a kid back in the mid 1970s and my father and his shooting buddy loading their bullseye loads with little patches of toilet paper on top of the powder charge thinking it would help keep the powder closer to the primer and make the loads more uniform.  Don't remember if it helped but I thick that combo of bullseye powder and TP made a smoky mess at the range.  I am tempted to try it just for fun