Cone of grease gun neede tip must point straight into bowl shape of grease fitting socket.
Resulting matching surfaces restrict pumped grease from escaping off to side of needle tip.
Pumped grease can now build enough pressure to unseat tiny ball check valve of grease fitting thus allowing pumped grease into bearing assy.
I use standard generic size grease gun with flex hose and needle tip.
Take plenty Q-tips and rags under the truck with you, clean fitting first.
Start with easy slow partial pump. If needle tip isn't properly pointed, grease will immediately be visible escaping around needle tip.
Stop right there and use Q-tip to re-clean fitting.
Try again with slightly different angle of needle tip.
When you "hit it", feeling of grease gun handle is entirely different since you're now building a bit of back pressure due to unseating check valve of fitting and nearly zero grease leakage waste around needle tip.
About 5-7 full pumps, with no leakage around needle tip, should show bit of grease purging somewhere around bearing assy and that's where I stop.
I don't bother wiping away any little bit of purged grease, it'll take care of itself.
If you get frustrated when trying to get needle tip angle correct and just pump away thinking some of it's getting in there as you build big wad of waste grease around needle tip, I don't think any of it's getting in there 'cuz you've not unseated fitting check valve.
Keep repeating method of partial 1st pump and clean-up of waste grease until angle is correct.
I'm also going to bend the needle tip just a bit next time to help get the angle correct.
But first I'll use some small diameter rod or maybe wire and bend that into a template piece that looks about right then bend the needle tube to match.