I reload for a number of cartridges that I shoot in the Contender, including the 357 Max. I do all of my Contender load accuracy trials at 100 yards and I've never seen stringing in any of the loads, but I thought I might offer an opinion anyway. As far as the grip goes, I have hands that are on the small side and I had to train myself to not scoot my hand slightly around the grip so that my finger would cover more of the trigger. I took me quite a while to remember to do that for every shot, but that really helped with the overall accuracy. If you've been shooting the Contender for any length of time then you've most likely settled on a grip that is right for you. Having said that, you might want to explicitly verify your grip before each shot the next time you take the Max to the range. In terms of the shooting rest, I make sure the contender is snugged up to the rest for each shot such that the trigger guard is close to, but not touching the rest.
I had been shooting the 357 Herrett in a 10 in. barrel for about 30 years when I let the enthusiasm of some of the members of this forum coax me into buying a 12 in. 357 Max barrel, which I picked up from MGM. I've had that barrel over a year, but I just got around to trying out some 158 gr loads this past summer. My goal is to see if I can get both a good 158 gr load and a 180 gr load working for this barrel. I started with the 158 gr XTP-FP loads and I haven't yet loaded any 180 gr loads. Although the 158 gr loads may not be of any value to you, I'll share some of the information about the trials. I used 4 different powders, including Lil'Gun, and one thing I noticed about Lil'Gun is that it didn't show the stability that I wanted to see - it is possible that I just didn't reach the right amount of powder with Lil'Gun or that perhaps it needs a hotter primer. I used Starline new brass trimmed to 1.596 in., Rem 7 1/2 primers, and a COAL of 1.962 in. with the XTP-FP. I also applied a moderate taper crimp to each cartridge. Note that I did not check for accuracy with these loads - I wanted to see which powder(s) would get me to the expected velocity (around 2100 fps) while producing a relatively consistent burn of the powder, as judged by the extreme spread. From these results I will select the top two powders and then begin accuracy trials. Anyway, I fired 5 rounds with each load, allowing the barrel to cool after each 5 rounds. Below is the full Lil'Gun data, followed only by the top load for the other 3 powders. The data is arranged as powder / extreme spread / avg. velocity. (The loads shown were safe in my Contender, but start low and work up.)
Lil'Gun 21.5 gr / 325 fps / 1939 fps
Lil'Gun 22.5 gr / 251 fps / 1945 fps
Lil'Gun 23.5 gr / 156 fps / 1957 fps
Lil'Gun 24.0 gr / 79 fps / 1929 fps
Lil'Gun 24.5 gr / 125 fps / 1953 fps
H110 24.5 gr / 26 fps / 2079 fps
300MP 25.5 gr / 18 fps / 2160 fps
Enforcer 21.5 gr / 64 fps / 2162 fps
The Lil'Gun just did not show any consistency in the 5 loads that I tried. I will continue the 158 gr trials for accuracy using H110 and 300MP, and then I'll start over again with the same 4 powders with the 180 gr XTP.
For your 180 gr XTP stringing load, I might suggest that you drop a couple of grains of powder (for the sake of safety) and at the same time seat the bullets deeper into the brass - you don't need to seat all the way to the first crimp ring. If that load proves safe but you still get stringing then I'd suggest to either continue to increase seating depth or slowly add a bit more powder. The increased seating depth may help the Lil' Gun to burn a little more consistently. The 10 in. 357 Herrett barrel I owned had such a long throat that I could seat 180 gr bullets so that they barely entered the brass, and they still wouldn't contact the lands. However, I always seated the bullets deeper into the brass and never had a problem with accuracy even though the bullets would take a fairly large jump just to get to the lands.