Hi there - the numbers on the auto injector is a depth guage....the actual syringe is 10 mm....so when you dial in 8 or 5 for instance with the injector, you are setting it so that the needle goes in 8 mm or 5mm or what ever setting you have selected.
Its seems for the most part,many are instructed to use 7mm or 8mm. I use 8 on my arms, hips and stomach, and 7 on my legs.
I find that if you are a bit gun shy, where by u do not hold the injector tight against your arm, it tends to bang around abit, or jump, etc.....and this (for me anyways) tends to cause the bruising, the redness, the swelling, etc. If I hold it tight to my area of injection, it tends to be more sucessful. I became gun shy a couple of times as I ended up hitting muscle, and ouch!~!!!
I also do my shots at night, usually just before I go into the shower, and while there, I end up massaging my arm, and usually by the time I get out of the shower the discomfort of the shot has diminished. Applying skin cream/lotion to the injection site seems to help as well. If after the shower ritual it still stings, etc - I go to the freezer and get an ice pack, and hold it to the injection site for awhile...
I do find, other than behind my arms, I have converted back to self injections, as it appears that I have more control of where I am going to inject the copaxone, the speed to which it will enter my arm, and the speed to which the copaxone enters my body.....I have had less problems doing it this way then relying on the injector.
Just last night I used the injector on my arm, and even this morning, I have a sore arm, and it is hard and swollen - guess I did a lousy job of it last night.
Go to the Copaxone web page and it provided guidance in the use of the injector as well as instructions as to the settings to be used. Also note that Copaxone has now a thinner needle, which may assist with this!