Cheddite Primer pressure spikes
 

From trapshooters.com. A poster had some loads tested and this stood out.

The first load with a Win 209 and 15.7 gr of 20/28 is listed on the Alliant Reloading Guide as being 1200 fps and 9370 psi.

The second load with a Win 209 and 16.7 gr of 20/28 is listed on the Alliant Reloading Guide as being 1250 fps and 10,490 psi.

Hull: Win AA 20 ga
Wad: CB1078-20
Shot: 7/8 oz
Primer: Cheddite
Powder: 15.7 gr 20/28

Ave pressure: 12,685 psi
Ave velocity: 1306 fps

Same as above except 16.7 gr 20/28

Ave pressure: 14,022 psi
Ave velocity: 1354 fps

https://www.trapshooters.com/threads...esults.918249/

Cheddite makes several flavors of primer. I am pretty sure we can only get the 2000 kind, but wonder if rst has access to the 1000. It seems like this might result in lower pressures but im not an engineer.

Well this is fraught with all kinds of scientific holes. Did he measure the powder loads with a scale rather than just trust the bushing? I spent a lot of time measuring powder throws with an RCBS digital scale, and sure enough I varied quite a bit as much as I tried to be consistent. Chamber length compared to the manual? Hull? Temperature? How many times have we run a chronograph on our loads and we "average them" because they vary so damn much. I think we need a heck of a lot more detail before we say Cheddite cause pressure spikes. That's just MY opinion and I'm pretty new at this but I'll say we need more evidence.

What makes the test results of reloads sent for testing by a member of Trapshooters.com more suspect then reloads tested by the members of the PGCA?

It doesn’t. The list of things that affect pressure are the hull (how many reloads), powder throw, the crimp and we can go on. My point is how do you know it’s the primer that made the pressure higher or a combination of things?

On that Trapshooter thread; many replies but so far the OP has been reticent to reveal the lab or source that did the pressure testing. ?????

I will continue to watch the thread and hope the OP provides that info. I doubt he is making up a story. One way or the other it would be good to know the facts.

I asked Alliant a couple of years ago about primer swapping, specifically swapping primers in 20 and 28 gauge guns. I wasn't concerned about 12 ga. because my pressures were in the 6k to 7k range. I asked them if using their published components, would it be safe to substitute only the primer? They didn't have the specific primer I wanted to use but they said they tested all the popular primers in their published loads and the highest pressure spike they observed was 2,500 psi. SAAMI service pressures are 12,000 psi for 20ga. and 12,500 psi for 28ga.

So, if you want to substitute a primer into their published recipe, add 2,500 psi to their data and if it's below SAAMI limits, you can substitute. They advised me not to do it in 28 ga.

The poster on Trapshooters.com posted the following this morning.

"The testing was done at precision reloading. I didn’t post the pictures of the actual test results because I never posted pictures and need to figure out how. Just haven’t had time yet. Once I figure it out I will post on Georges thread once he creates it."

RST buys primed hulls. I can't answer whether they can specify which primer or if they only manufacture shells with one primer (2000 vs 1000). My guess would be whatever primed hulls Cheddite produces they use one primer to keep costs down.