This past Christmas I received a 550C. I was using the Lee pro 1000 for 223 and 45 for 4 or 5 years.I was always frustrated with the machines priming system problems. After a batch of 223 with no primers, variations in powder charges, etc. I said no more!! I then asked for the 550. It is now very enjoyable to not only make hundreds of bullets without any "tinkering", but caliber changes are very quick and easy. I really enjoy the 550!!