Lotsa good ideas and theories on injections. I inject all my butts and briskets, and full or half loins. I also inject my shoulder clods(beef) and chuck rolls.
I use the regular injecting needles on butts and loins,but for my beef I use veteranary syringes with a 16 gauge X 1 1/2 inch needle. Nice and small, keeps the hole small and retains the baste better. I also use little bits in alot of areas,instead of heavy doses. The only thing with the vet needles, you have to run the marinade/baste through a paint screen, or coffee filter to get the big particles out or the needle will clog!
Hope It helps. Injections can be tough to figure out, but fun to experiment with.
Don't over do it on strength of your solution though. !