No worries, that's the beauty of using a fast burning powder. I was playing around with my chronograph yesterday reanswering the same question.
The load=6.5g ww231/hp-38 Remington LP primers Lyman 429421 245gSWC bullet (range lead) sized to .430" mixed brass (range brass)
The primers=Winchester, Remington, cci standard & cci mag large pistol primers.
The test pistol=TC contender 10"bbl
The test=10 shot strings with each primer I was looking for 2 things, any jump in the fps & any difference in the sd. 10 shots aren't a lot by any means to base a test on. I was thinning out my old/partial primers that I had lying around. I used to pick up any kind of primers at the gunshows if they were selling them at a good price (before the Obama scare 4 years ago). I still do the same thing with gunpowder; it will always burn in something.
Why the test= I initially worked this load up using Remington lp primers, the Remington primes are known to have the light/weakest flash (brisance) & I ran out of them. I don't want to go buy more of them since I have other brands of primers that I can use. I have a bunch (2000+) cci LP mag primers lying around. I don't use any powders that need mag primers anymore & thought "lets burn these primers up in the contender". So I'm going from the mildest LP primer made to the hottest LP primer made.
The results= It didn't matter what primer I used with the fast burning powder. The Remington, Winchester & cci primers all stayed in the 880 to 890 #'s. An ES of 10 for a 30 shot string, not bad for mixed primers & brass, recovered lead & a homemade bullet lube. When I made the test load with the cci mag primers (50 of them) I used 6.3g ww231/hp-38 of powder instead of 6.5g thinking that the mag primer would add more pressure/power to the load. The mag primers did nothing for the load & the fast burning powder. The SD was actually 20fps slower than the loads with the extra .2g of powder, what the mag primers did do was lower the ES even more, the first 4 shots of the 5 shot string (I didn't see any need to go any further) all read the same thing, 863. For a minute I thought the chronograph was broke until the 5th shot read 868.
I don't know why I was worried about the load changing, I thought about it & I knew better from doing the same testing 20+ years ago. It was just that this is a real good plinking load for that contender, it stacks the bullets on top of each other (all bullets touching @50ft for every test group that I've shot now, 10+ 5-shot groups).
After thinking about it I do know primers can & will change a load, but it more of a mechanical change than a pressure change. Consistent ignition is key to accuracy in any load & the hardness of the different primer cups will affect a load more than anything. Federal & wolf primers are a good example of this. A lot of revolver guys hate wolf primers because they're a hard primer. They get light fp hits, ftf's & good hits all in the same cylinder of ammo. Federal primers are the easiest to set off; they have the softest primer cup. So these guys turn the strain screws down on their revolvers to lower the trigger pull & it also lowers the power of the fp shit/strike causing inconsistent ignition.
The use of mag primers & fast burning powders. I used to do this all the time, the lp mag primers could be found easier than the standard primers & most times cheaper. They will give any load with a fast burning powder a better SD because there isn't much powder in the cases & the powder will lay flat in the case (sideways). The bigger flash of the mag primer will burn the small charge of powder more evenly creating more consistency.
I used to do this for my contender loads 20+ years ago, the difference would show up at the 100yd line. It's amazing the small details like these I can & have forgotten over time.
