I had the same problem with decapping 9mm and tried all the usual advice floating around the internet without success. This problem has plagued my reloading for years. Recently I made a small modification to the standard Dillon size/decap die and it has worked wonderful for the last ~20,000 rounds. I have only had two or three primers get sucked back in over the course of these last 20k whereas before I would have 5+ suck back in for every 100 rounds I loaded. I experienced the same problem on my 1050 and my Revolution and this mod fixed the issue on both machines. I’ll try to post some pictures this evening with a description of the modification.
Here are some pictures of the modification I made to the standard Dillon decapping/sizing die. I essentially modified the assembly to allow the spring to compress approximately 0.100” before pushing the primer out. After the primer is pushed out, the spring snaps the assembly back by the 0.100” with a significant amount of force and it launches the primer off the end of the decapping pin. There is a very audible “snap” each time a case is decapped. The primer is shot off with such force that often the spent primer will bounce out of the primer catcher on the 1050. This modification has completely solved the problem for me!
I tried a version of this using the original snap ring design at the top of the assembly but I kept breaking the snap rings about ever 2,000-3,000 rounds. This is why the end of the assembly has been turned down to the base of the snap ring grove and then drilled, tapped, and reassembled with a threaded fastener and washer.
Also, I have found that the standard decapping pins from Dillon have just enough variability in the diameter that some are so large they get stuck in the flash hole and don’t snap back easily. This prevents the new design from functioning correctly. Therefore, I measure the pins and turn off a few thousandths from the big ones and problem solved. This could be done with sandpaper and a drill if you don’t have a lathe... it doesn’t take much and they don’t all need it.
A lathe is required to make the modification. If you don’t have access to one or have a friend with one, any machine shop could make these mods in about 5 minutes and would probably only charge about $20.
If you want a video of the modified die running on the Revolution, PM me your email address and I will send it to you (it is too big to post). Let me know if you have any questions.