Re: 300 BLK powder funnel on RL550
Give Dillon a call and you'll have the correct powder funnel in hand in a couple of days. Dillion is SERVICE. You pay extra for that so you might as well use it.
The way to buy caliber changes for a Dillon RL550B is to keep a chart of what you have (Shell plates, powder funnels, pins). When you get a new caliber that you want to reload for, find out what it needs and compare that to what you have. Only buy, as separate pieces, what you don't have. But also list on your chart of shell plates, powder funnels, and pins, add a column for where each part is stored (which Dillon Caliber conversion box if you have any). I reload for over 30 different calibers and only have a dozen or so caliber conversion boxes and several loose powder funnels and shell plates.