This. Reloading recipies are not meant to be prescriptive. They are starting suggestions for an exercise in experimentation.
That's a little more loose than I think you intend. Yeah, there's some fudging room. But when reloading sites and manuals give you a max weight for the charge they typically mean it.
FA, just take note that the COAL makes a relatively minor difference. For example at Hodgdon's online reloading page they list the min to max range for Titegroup as 4.0 to 4.8 grains for a cast LRN (similar shape and length bullet) for a 1.20" COAL. Campro lists 4.4 to 4.8 for their longer 1.25" length.
When I loaded some Campro bullets a while back I opted for the 1.25 length simply because at 1.20 it was starting to look like it was going to end up crimping onto the beginning of the ogive nose shape. And that's not a good thing. But since you posted that your barrel won't "plunk test" nicely unless the rounds are down around 1.230 1.25 is going to be too long for your gun. Given that I'd aim at 1.220 and call it a day... unless you find that it's something else causing the issue. Be sure you're not crimping too tightly. If you do it'll bulge the bullet and that may be what is riding in the chamber and preventing a nice "plunk". I see that Campro gives you a crimp measurement. I'd try that and I'd also try for a crimp where the mouth rim is about .005 smaller than the skirt diameter half way to the end of the bullet (not the head, the bullet). You want the crimp to be there but not to be too radical.
It's especially important if you are not seating and crimping in different dies. If you're doing a combination in one die such as a Lee set then it's more important to really minimize the crimp. Otherwise it's crimping while still pressing the bullet into place. And that could possibly bulge the bullet and cause it to ride against the leade of the chamber. The "leade" being the groove diameter section just ahead of the lip that catches the casing mouth to headspace the cartridge. If the bullet is bulging to that size or larger it won't "plunk" correctly.
If you don't have room on your press for a fourth die so you can crimp separate from seating I'd consider seating with only enough crimp to close the flare of the mouth. Then run it through the crimp die after with the seater drawn up about 3 or 4 full turns and the die body screwed in an 1/8 to 1/4 turn to give you a proper crimp without touching the bullet. Separating the operations will aid in avoiding a pressure bulge from crimping while seating. Or learn to set the crimp VERY carefully for just a minimal amount.
The other issue is how well the gun cycles ammo of a given length. The rounds have to slide up from the mag and turn the corner into the chamber easily. So try some at 1.25 and a few slightly shorter
All else being equal moving in .05 will end up with the muzzle velocity going up around 5%. So it does make a difference. But it's relatively minor.
