I would think it depends on your level of BF. If your pretty lean then that should be fine. But regardless of your bf your not getting it very deep into the muscle itself. You are probably getting it in the calf muscle but not very far into it. I would suggest a 1/2" or 5/8".
I am lean and I do not want to order pins until I do a bulk order again. It is EOD injections. adding VERY small dose of tren in. Also, I never did this... but can I pin a flexed muscle? it is a 31g. I have no problem pushing it through by the way.
1/2"min although ive heard of some guys doing forearm shots with pins that small i would recomend goin by your pharmacy for some quick pins if they ask just tell them its for injecting your dog with vitamens works for me 21-25 g 1 1/2 "quads or glutes to be sure