Rem 209p and Win 209 (is there a difference)
 

I noticed that some of the 20 ga recipes I have been looking at call for the Remington 209p primer while other recipes call for the Winchester 209 primer.
Is there a significant difference between the two? How interchangeable are they? Does it really matter which primer is used?
(by the way, I'm just loading Remington hulls)

I recently asked Alliant about switching primers between 20ga. and 28ga. loads using their recipes. This is what they said about the 20ga. switching primers.

At this time we are working off from two independent studies where only primers were changed in load data. From these studies, swings in pressure by as much as 2500 PSI were noted. Based on this we are using the guideline that if pressures fall between 6500 - 8500 PSI, a primer swap is allowed.
Looking at our load data and using your components (Remington hull, CB1034-20, Remington 209P primers (used in testing) and velocities between 1200 -1250 FPS, the charges of 20/28 propellant would be 14.4 - 15.4 grains. The pressures for these loads are 7200 - 8200 PSI. So in this case yes you could use the Federal 209A primer.
Thanks,
Duane V. /Technical Service Representative
2299 Snake River Ave.
Lewiston, ID 83501
Alliant/Blazer/CCI/Speer

So in this case you would be fine using Winchester 209's for the above load data.

I asked about switching primers in 28ga. and this is what they said.

Based on the same information I relayed to you on the 20 gauge loads, you would not be able to use the Federal primers. The one load we have for your components has a pressure in exess of 11670 PSI. This is well beyond the window mentioned in the earlier email.

So if you are using Alliant powder and use their recipe, and your pressures are lower than 8500 PSI, it's OK to switch to any primer. That's not the case with 28ga., use the primers recommended in their load data.

You might find this article by Tom Armbrust interesting in terms of velocity, pressures and patterns:
http://www.armbrust.acf2.org/primersubs.htm

Greg thank you for posting that it is very interesting.