Most injection needles have a single port at the tip. This can work for smaller needles, like a veterinary syringe, but with larger needles, unless you're very careful, you'll just end up punching a hole and filling that hole. What you want for large cuts of meat like beef brisket or pork shoulder is to get the liquid dispersed throughout the meat. For that, the best bet is a needle with side ports, like example A, below.
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Many competition teams prefer to use veterinary syringes of about 50cc and about a 12 gauge needle. We don't sell these on account of the variety of restrictions in various states, but you can find them at Tractor Supply or any farm supply store that sells antibiotics and other farm-aceuticals (ha ha).