The RL 450 and RL 550 are functionally the same press. I bought my 450 in 1982 new, bought the 550 used in 2007. The structural difference is the removeable tool head on the 550. For several hundred dollars
, a 450 can be upgraded to everything a 550 does: auto prime, auto powder, auto eject, except the removeable tool head. To get the removeable tool head, Dillon sells you a new frame or does an in-house upgrade.
A RL 450 will reload any caliber a RL 550 reloads. All the parts and pieces are interchangeable.
The Dillon Square Deal reloads only pistol calibers using
SPECIAL Dillon dies. Standard 7/8-14 dies do not fit a Square Deal.