Pretty amazing how the FPE drops when the majority of the mass is the air, isn't it?.... Bob
I don't know what range you used to calculate the BC from the LabRadar data, but the 100 yd. data is very poor, and even the 75 yd. data has some questionable velocities.... As you said, maybe only 2/3rd of the 75 yd. data usable.... What do you get for the BC if you average the MV and the 50 yd. data (throwing out questionable data from shots 9 & 16)?....The VanDerWaals effect will not give you the extra shot count above 4000 psi that you would expect using Boyle's Law.... The higher you go above 3000 psi, the fewer extra shots you get for each 100 psi....Bob
The difference in fill out on those slugs looks like the difference between a pressure pour and a regular pour.
... What temp do you use to burnout the pla?
Scott- Of all of my TJ's barrels, for some reason the 2 that I've had in .257 1:14 have been the roughest I have seen. Don't be afraid to get aggressive with it. I made a lead lap, then fire lapped, then polished with JB's and Mother's my most recent one and it is still so tight it prefers .256 slugs. After all of that the bore still shows inclusions when viewed with a borescope, but engraving on slugs is like a mirror... My .300, .357, and .457 TJ's all cleaned up much better than I could get my 25-20 liners.....
I like that 2000cc bottle, how much does it weight? Those bullets look like the BT version of 257420, in my gun they group best at slightly lower velocity (920ish fps). We measured them at 0.17-0.18 BC with Timo's labradar.