First off I am just curious if anyone has noticed any gained accuracy by using 209 primers? I have tried them before as I set my knight up with a scope to use during modern deer season many years ago when I first got it. All I can say is I have better accuracy with regular #11 caps than I did with 209 primers.
What you found is entirely possible! Especially when you add in the different possibilities that exist. For many years on well know ML individual suggested that the pressure created by 209 primers would/could push the projectile and even some of the powder up the barrel before ignition of the powder. Depending on the powder and the condition of the powder you are/were using it really could happen. Moving the projectile off the powder could certainly effect POI.
I am guessing that testing I did was about 10 years ago. I remember back then reading that the 209 primers could cause your bullet to jump ahead of your powder charge and cause poor accuracy? So does that or can that still happen?
Today I think that is of far less concern, especially if you are using BH-209 which is a smokeless based powder with Potassium and Sulphur added to qualify as a BP sub. Even T7 or real Swiss the problem would be less likely - EXCEPT - both of them can absorb moisture and slow ignition. I think one of the real keys is to use the mildest 209 primer you can and still be confident of ignition. That thought is still controlled by the design of the breech plug.
This is an old chart of the approximate pressures created by different primers...
Shotgun Primers
Winchester 209ML ........................221 f.p.s.
Winchester 209 Triple Seven ML......244 f.p.s.
Remington 209 Kleanbore ML .........318 f.p.s.
Std. Winchester No. W209A ...........336 f.p.s.
Remington STS.............................338 f.p.s.
Std. Remington No. 209 ................341 f.p.s.
Cheddite No. 209 .........................347 f.p.s.
CCI 209M.....................................379 f.p.s.
Federal No. 209A ..........................381 f.p.s.
Rifle/Pistol Primers
Winchester WSP "Small Pistol" ….......116 f.p.s.
Winchester WSR "Small Rifle" ..........143 f.p.s
I normally use a W209 in most of my Knights - I have made the shift to the W209 because I can not get the old Remington 209-4 (410 shotgun primer) any longer.
With the Lehigh/Knight or Lehigh breech plug I have never had a problem shooting even BH with the shotgun primers designed for Muzzleloaders. BUT! I have tried them in sub-zero weather with BH - with T7 not a problem.
I am a little hesitant of trying them again just for that reason. Although it seems like they are supposed to be the best way to ignite powder now? Or at least most of the muzzleloaders are designed for those to be the ignition source.
Thank You Buck
Buck what rifle are you shooting and which powder might you be using?