I had my 20ga 3/4oz load tested with Cheddite cx 2000 primers and Unique 14.5gr. They came in a little hotter than I like so I dropped down to 13.7gr and I am having them retested.

That's a pretty consistent load Craig. It's interesting that the Alliant website calls for 15.4gr Unique at 1200fps and 8200psi. Somewhat alarming that Ched 2000 primer makes that much of a difference. I'm currently loading Universal Clays in my 3/4oz load just because I was able to buy 6lb of it and to save my 20/28 for my 28ga. I found a low pressure 7/8oz load and reduced the shot charge to 3/4oz which keeps it in a safe pressure zone. We have to think out of the box nowadays.

It seems like someone who knows the rst folks well would be able to discover whether they are using the cx 1000. Many of their other components appear to be what is conventionally available.

RST buys primed hulls so whatever Cheddite uses in them for primers is what they have.

I have only had five of my loads tested with the Cheddite CX2000 primers in 20ga 3/4oz Unique,12ga 3/4 oz Clay Dot, 12ga 1/8oz Red Dot,10ga 1 1/8oz Red Dot and 8ga 1 1/2oz Clays. I'm finding as a general rule I can reduce the powder by 1.5 gr to 2gr from published data (with WW 209 or Remy 209) and get very acceptable pressures and 1150fps. The smaller the gauge the more sensitive from my experience.

Followup on previous post
 

I previously presented some 20 ga test data using Cheddite primers and the results were concerning, at least to me. So, I did some follow-up testing. My initial test set did not include a load that matched published data. This test set does. As previously stated I have shot in excess of 50k shells loaded with published data and never thought anything of it as I trusted the published data. The Hodgedon site lists the following load

Remington STS hull
17.0 grains of WSF
WAA-20 wad
7/8 oz shot
Win 209 primer
1200 fps
10500 psi

I submitted this load for testing. The only exception is I substituted a CB-1078 wad for the Win AA wad. So, not quite apples to apples but close. The first data set listed are the results. Not quite a match. Well, not even close. The second data set is one I did earlier with Cheddite primer. I repeated it here so you can make a side by side comparison..

The following two data sheets are with Cheddite primers with much reduced powder charges. The 15.0 load is a full 2 grains below the published data above or nearly 11% and while the velocity is approaching the published load the pressure is still well above.

This data was intended to serve my needs and curiosity. It may provide some insight for those of you that are forced to use Cheddite primers.

Gary, as a new member of this forum, I would like to thank you for your work in testing the above 20 gauge loads. As a sub-gauge tube shooter, pressure excursions are important to me. I follow the reloading forums on SGW and Trapshooters.com. Your work is the first that I've seen in which a powder suppliers published load was tested. In the instance above, the results are way off from published data. This is a real eye opener, indeed. From the above 16.8gr data the w209 ave pressure of 12,138 psi and the C209 ave psi at 12,577 would in this case imply about a 450 psi difference in the primer switch and not 2500 psi that has been mentioned (at least in this case).

Gary, My Briley 20 ga tubes are 0.618 also and I agree that the test barrel 0.614 seems tight. The volumetric difference between the two bores is only about 1.3% which doesn't seem significant. What I wonder is how did Hodgdon measure the pressures of therir published reloads? How does their pressure test equpiment differ from what Precision is using to measure pressures? Your tests of identical WSF 20g loads except one used CX2000 and the other used W209 primers showed that there was about 440 psi difference in average pressure with the CX2000 being the hotter primer. The big question for me is how are the powder suppliers measuring pressures of their published recipes and how does it differ from how Precision does it?