Tony was being overcome quickly; a vampire took a while to heal wounds if inflicted, though it was hard to really inflict the wounds because they were fast and strong. A lycanthrope, by contrast was faster, stronger and healed rapidly enough to stay in a fight, unless the wounds came faster than the healing. Give a lycanthrope wounds in beast form, put them down and they got back up once they were able to heal it.

But shoot them with silver and it was all over, the silver had to come out before they could do any of that. They were weak as a mortal once it happened, with the silver burning into them, disrupting the uneasy spirit barely contained in the weak flesh.

The best werewolf hunters of the ancient era used slings, because they understood that a ball from a sling, a silver ball whirled around on a rope and then released expertly, was the best way to embed silver into the werecreatures while making it very hard for them to extract it. Arrows could be pulled out, swords tended to stay in the hands of users. So on and so forth.

But firearms came along and made it possible to put silver into werecreatures with more ease than a sling, which took such immense skill that it was reserved for a few people who did it from a very young age. A firearm was a weapon a peasant could employ with a small bit of training. It's why the armies issued them. And as more weapons were made, faster loading, more accurate, longer range, the werecreatures became easier to kill; aim a silver bullet for the skull and take them out in one shot. Silver bullet to anywhere that entailed an instant fatality was bound to finish the were fast, if the bullet wasn't pulled out.

Or you shot the were and followed it up with a fast attack to rip them to shreds when they were writhing around or otherwise distracted by the silver. It burned like nothing else, even when it came out.

In the era of rapid fire ballistic weaponry, it was even worse, if one was willing to spend on such rounds. Hunters did, for example; facing multiple baddies, they might load silver, magnesium based tracer and steel-jacketed hollowpoints, the lead exposed, figuring that the mix of rounds gave them a fair chance of engaging different types of supernatural bad. Silver, fire, iron and, of course, lead. Shotguns were popular too -- #4 buck had 41 pellets; if they were silver, it was impossible to dig them all out of a werewolf and get them back into the fight fast. More was better; double-ought buck was a thing for mortals putting down mortals, but some hunters going after weres specifically loaded birdshot, just to have a huge number of small silver pellets going into a werecreature. 

It's why lycanthropes adapted and learned to fight in ambush, to get the hell away from anything that smelled like silver. They were cautious as a result of the way much of their own society figured out how to fight them and turned modernity against them.

In any case, it was also why some smart vampire grabbed a shotgun that was there in case of an emergency and shot Tony in the fucking back with it. 

And it's why he went down with something like just seven 21 grain pellets in his shoulder, but it was enough to turn a rampaging were-lion, tearing through, holding his own, into a vanilla mortal black man in a lot of pain just like that.