38 Spcl. loads
The Alliant reloaders guide I have, dated 1996, shows 158g. LSWC:
3.4 grains of Red Dot max standard pressure 38 Spcl. at 793 fps.
3.8 grains of Red Dot +P 38 Spcl at 846 fps.
All loads with Speer brass and bullets, CCI primers, 1.440" OAL.
Barrel length not listed.
Granted, most modern published 38 Spcl loads are very mild.
I have no doubt 4.0 grains is safe, unless the gun is very old or poor quality. What gun do you want to shoot these with?
I've seen 4.0 grains or somewhat more listed from some other sources, Speer No. 11 is much higher.
Red Dot is a very fast powder, similar to Bullseye.
I would use a slower powder if I wanted to push the limit of this cartridge.
I have used lots of Red Dot in 45 acp and 44 Spcl with great results.
My powder measure is not very consistent throwing less than 4.0 grains of Red Dot, so I usually use 231 for my 38 Spcl target loads.