I tested them on Sunday in my FT gun which is set up for JSB made superfield 8.4's
I checked chrono readings on saturday evening. The 4.50 size were coming out exactly the same speed as the sf, the 4.52 size chronoed 8fps slower. Very good tight chrono readings overall with both head sizes.
On the cards, using 25 yd as zero, I needed to dial 0.5 moa less at 55yd with the 4.50 and the same as sf's for 4.52 headsize - so not really any significant difference in better bc. My barrel with the sf's has a bc of 0.024
Group size, 4.50 head size were no good in my barrel, 4.52 were much better, but didn't match what I get with the jsb made stuff.
Some more testing to do with lube etc