Security Six serial # break

[MMCSRET]

Reading the thread about the T-grip on the Ruger brought to mind the question of; Just where in the serial # range did they change the grip frame? I have two later numbered guns and I have Herrett Shooting Star grips for them, but I also have a set of Herrett Shooting Stars that don't fit, too small!!!
Please fill me in, Thanks.

 

[kludge]

150- and down 151- and up, AFAIK.

 

[trickyasafox]

there was a break at 150 to 151- and I think again at 153 and up