Glutes can take a beating. Basically there is a 2 inch by 2 inch area that you can pin safely on each glute so if you are woried about it you can hit the upper part of that area one week and the lower part the next week. In other words the pin can be a full two inches from the last time no problem as long as you stay in that 2" x 2" area.
INTRAMUSCULAR INJECTIONS (IM) -
The above 2 photos indicate the injection locations for the glutes.
Inject directly into the middle of the upper outer quadrant of the glute.
Injecting anywhere else in the glute risks hitting the sciatic nerve.
23gauge to 25gauge1.25 inch (32mm) to 1.5 inch (38mm) long needles are adequate.