That's all well and good... but doesn't actually fix the problem.
There can be two (or more) potential issues if the slide is sticking / hanging up and then snapping forward.
One is that it's very easy to over tighten the two screws that hold the primer tube assembly to the press. The threads are *very* close to the inner surface, and the housing that holds the tube, and that the slide runs thru, is fairly soft aluminum. Overtighten those screws just a little, and you can warp the interior surface of that housing just enough to where it causes additional friction on the primer slide as it passes through. On mine, I could literally feel a little bit of 'wave' on that surface with a finger tip, once I knew where to go looking. A few licks with a small, fine file fixed that easily enough. This fixed about 90% of the flipped primers for me, but there were still a few that were driving me nuts.
Another is that the very design of the 550 primer slide and the way it is supported and the way the return springs bear on it are a little questionable. Basically when the primer slide is out all the way, well over 50% of its length is unsupported... and the return springs attach to a pin on the bottom side. They don't just pull it forward, they pull the back end *down*, ever so slightly. This can bind the slide up just a little, just enough, that it will hang for a fraction of a second as you lower the ram and the pressure holding the slide back eases. Then the slide snaps forward, catching up with its operating rod and stopping suddenly, which can flip the primer in the cup... or completely out of it. The solution here is not a replacement OEM primer slide 'bearing', but an extended plate that keeps the slide more fully supported all the way out at full extension, never letting it be levered down by the return spring. Some version also include a roller bearing to help keep the slide better aligned side to side.
Like I said, there are a number of places on the Internet now where you can get this little 'fix-it' part nowadays. The guy I bought mine from years ago had made his by hand as he was testing the design. Trust me, it works *amazingly* well. Not everyone experiences the same problem(s); I know people who swear they've *never* had the primer slide hang on their 550. Mine... went largely unused for a number of years because having to grab the primer slide every single time and ride it forward to keep it from snapping and flipping a primer made it effectively useless to me. So for me, it turned the 550 from a POS collecting dust, to something that has become my primary loading press.
YMMV,
Monte
