Okay so lets start again, since i think we chased /u/crankyshot off for now.

Primers are probably the smallest variable in your load, you can use them freely, but for safety sake you should reduce back to a minimum load and work up from there.

Next in the scale of variables i'd say is brass (as long as your talking about using the same load data, aka powder charge) Brass can vary quite a bit between brands. Internal volume can differ quite a bit. it's definitely something you want to approach gently. But In my experience as long as you once again start low and work your way up you wont run into any trouble.

Third is bullet, I've found bullets to cause the biggest swings in pressure for me, since different bullets will take up different amounts of internal case volume. I find that some load data isn't well suite for different bullets, due to differences bearing surface and construction. But once again start low and work your way up.

Just try not to change all three variables in 1 go, that's a recipe for a bad day.