If proper technique is used to inject and the smallest gauge needles are used then scarring takes ages to form, truly. I'm tempted to make a video of how to inject properly. And do it using a spot I and medical staff have used 1000's of times.
Only old veterans who have destroyed their veins from digging around with poor technique from their early days and reused their own needles require larger and longer needles cos they've usually moved onto hitting deep veins in their thighs.
IM injections require, in my opinion, a minimum of a 23 gauge luerlock needle but we're talking about steroids, usually oil based androgenic or anabolic steroids. I've used a 19 gauge tip for that purpose cos I had run out of smaller tips but as long as you commit to the shot as in use sufficient force to have the needle instantly in your leg or shoulder to the hilt,, don't try to push it through the skin slowly cos it'll hurt and depending on where you're shooting you can get muscle spasms which can be off putting and painful. If you're using larger gauged needles for IM steroid injections then the 'Z pattern' injection is best, this prevents the oil from coming back out through the entry hole. So you push the skin to one side do your shot and when you release the skin it will cover the hole in your muscle with skin that isn't breached.