You can pin into any muscle.
You will get PIP in any muscle.
I have cycled for years; my first cycle I could hardly sit in a car seat after my first few jabs... Now years down the line I still get the odd bit if soreness here and there, even just from 1ml of pharma Test E...
Your body can get used to it and the pain can start to be less each cycle. Virgin muscles will most often really hurt and fast acting esters tend to be even worse!
My favourite is quads, no shaking, very easy and smooth, plenty of movement in the musle to get things absorbing and you can pin the quads all day long with slight adjustments to where you pin. Massage the area after pinning and man the fuck up.