[spacecoast]

Are you sure that the rules specify a 158 grain bullet?

Yeah, quite sure. Below are the details from the NRA Conventional Pistol rule book, which also precludes the use of red dot sights (no issues, that's how I always shoot).

3.1.4 Distinguished Revolver - The revolver must be capable of chambering and firing a 158-grain round nose or Semi-Wadcutter .38 Special cartridge. It must be a factory manufactured revolver with no external modifications except for stocks which may be modified or changed because of the size of the competitor’s hand or to facilitate loading. Except for stocks and the honing of the sear or sear notch to make a more crisp trigger, and maintain a 2 1/2 lb. minimum trigger pull, no external or internal modification may be made to the revolver as manufactured and sold by the factory of origin. No parts may be removed from the revolver, either externally or internally, nor may any part be added, with the exception of milling the cylinder to accommodate moon clips. Specifically prohibited is any system of recoil control based upon compensators, barrel venting, barrel porting or weighted grips. Exposed holes that have been drilled and tapped for mounting of a scope are not considered to be an external modification.

(a) Trigger - Must have single and double action capability and must be capable of lifting 2 1/2 lbs when the revolver is cocked for single action firing. Triggers will be weighed. Any trigger, sold by the manufacturer of the revolver, without modification, may be used.
(b) Sights - Fixed or adjustable rear sights may be used. An adjustable front sight is not allowed.
(c) Barrel - Length not to exceed six and one-half inches (6 1/2").
(d) Stocks - Except as set forth above, the right and left stocks must be mirror images of each other.
(e) Ammunition - Any safe .38 caliber ammunition using the 158 grain round nose or Semi-Wadcutter bullet only.
(f) The following are not allowed. Trigger Shoes, compensators of any type or design; any external trigger stop device; any internal trigger stop not originally installed by the factory as original equipment in stock revolvers of the same make and model; tape on the stocks or stocks flared at the base.

However, my go-to load for the 158 grain semiwadcutter in .38 special is 4.3 grains of Unique. It's been my standard load for about 20 years and shoots very, very well in every revolver I've tried to use it in.

Thanks, I neglected to mention that I also had a box of 158s loaded with 3.7 gr. of Unique that I tried for a few shots out of desperation, but it was just as bad consistency-wise and recoiled more heavily (in addition to giving a higher point of impact). Recoil shouldn't matter much for slow fire, so I can try 4.3 grains, but if it's a good load I'll have to figure out how many clicks to move the sights up/down assuming I continue to shoot a much softer load in timed and rapid, where recoil makes a big difference. To this point I've been able to get away with the same sight settings in slow vs. timed and rapid, with only minor adjustments (usually left and right).

my K-frame Smith does VERY well with 3.7 grains of Bullseye, behind a 158 grain cast SWC.

Thanks, again worth a try (see notes above on sight settings).