since you are taking about primers .As far as blow by , the tighter the fit the less blow by , is that the biggest factor . ??? I notice in my muzzle loaders that if the primer is tight i get no blow by , no matter how hot the primers is . When i used the Winchester primers in my Traditions Pursuit , i had to slam the gun closed and i had no blow by whatsoever . But with the Remington kleanbore primers i got better groups, but they fit loosely in my breech plug and i got tons of blow by . Is there any Truth to what i think is happening here ???? The .25 conversion brass has to be form fitted in your gun by shutting you muzzy closed . Isn't that the reason they have no blow by , the brass is so tight fitting . Does a hot primer cause more blow by , or is the shape of the breech plug and the tightness of the primer the main thing ??? Am i way off on this ??