Quote from Reloader on March 15, 2021, 3:17 pm

I never liked the primer seating on the 550. The feel was rough and it seemed like there was too much spring tension there and that the seating post was too wide so it would hit the bottom of the brass and not be able to seat past flush. I made a significant discovery today though. I dug out the Dillon and set it up after many years to make some ammo with my son. We managed to crank out a bunch of .45s after doing a lot of tweaking. We had it tuned pretty good after punching out all the joint pins and re-greasing/oiling it. After adjusting the primer holder so the primer post was perfectly aligned in the plate hole, I noticed how nice the feel was when pushing the handle forward for the primer seating stroke. The primer bar actuating rod that runs in the plastic rollers (I'll call it acutating rod) was disconnected. When I reconnected it, the priming stroke was rough again. The actuating rod was pushing back on the primer bar so the primer post is forced against one side. I then looked closer at the actuating rod and found when I inserted it at the top and let it drop, it was missing the rollers to the right. I flipped it up and bent it a bit at the top corner until it fell nicely in line with the rollers. This didn't fix the forcing problem. The rod was being sprung between the two rollers on the priming stroke. Next I marked the actuating rod just below the top roller (on the shell plate), took it off and put in bottom first into the hinge point hole so the mark was just showing and clamping the rod with a large crescent wrench, bent the rod downward a bit. Then after reassembling, the rod was no longer pushing on the rollers during the priming stroke, and the feel was good like it was without the rod. When the shell plate was adjusted properly I verified the primer post travel did go a bit into an empty primer pocket hole. Not a lot, but enough to fully seat one. The primer post still seems too wide in that the slop in the shell holder can cause the post to hit the shell bottom sometimes. I'm temped to turn down the top bit of the primer post to the diameter of the Lee primer system post. Then maybe I'll be happy with the Dillon. At least now the operation is much improved. I hope this works for many of you also.

Quote from Reloader on May 18, 2021, 1:25 pm

"I have examined my 550b carefully as to what appears to act as a "stop" when priming. I have become convinced that the coil spring (the primer cup spring) itself acts as a stop for the primer punch on the priming stroke. I have aimed a strong LED light in there from both sides and can see that the primer cup does not make contact with the primer slide...it appears to stop when the primer cup spring coils collapse and make contact with one another. If that be the case, I would suspect that grinding about .002 or so off the bottom of the spring would result in the primer punch seating the primers deeper. Can anyone concur that it is the spring closing completely that causes the ram to stop on the priming stroke (assuming that there is no interference from anything else)?"

5/18/2021 Addendum:
I did a lot of dissassembly and testing and have found that the "stop" on my 550b for the priming stroke is a contact point (very hard to see) between the right-hand leg of the Primer Housing and Shield (part # 20263) and the bottom of the Roller Bracket Assembly (part # 14280). I observed the leading corner of the Primer Housing and Shield had a small compression mark in it and I confirmed contact during the priming stroke by removing everything from the top of the main shaft including the Shellplate Platform (#13781), Return Bracket (13885), and Roller Bracket Shell Platform (14280).

With those structures removed, the Main Shaft was not restricted in its downward movement.

Therefore at this juncture I am persuaded that the "stop" on my (may not be typical on all 550b's), 550b, is the result of that contact and is a likely factor in the trouble I have had with seating Large Pistol primers. Time and observation of continued use with large pistol primers will tell.

I welcome replies.

Quote from Reloader on May 18, 2021, 1:27 pm

Note: I have slightly relieved the contact point on the Primer Housing and Shield using a grinding burr and a Dremel Tool to eliminate that (seemingly unintended) contact point.

Quote from Reloader on June 1, 2021, 1:02 am

Addendum: Large primers not seating deep enough.

I would like the Dillon staff to respond to this.

I found this article via internet search. On page five, the author gives a procedure for deepening the seating of large primers. In regard to the bottom of the primer cup being the mechanical stop, he suggests taking a few thousandths off the bottom of the cup (I am not going to address his taking a couple of thousands off the bottom of his shell plate). When looking at my large primer cup and the primer slide, logically if the bottom of the primer cup were making contact and stopping the downward travel of the ram, there should be a contact mark where the cup meets the Aluminum primer slide. I see no such mark, other than a wear mark that matches the diameter of the primer cup spring.

So, Dillon folks, will you comment on this particular part (large primer stop) of his article?
https://www.dropbox.com/s/fp72h0e4awobo65/6_19_Dillon-Prometheus-Article_v1.2.pdf?dl=0