I've done some FOC experiments. I started off w/ stock Excal GT's w/ alum inserts, 5" vanes, they weighed about 357 gr. My choice today is same shafts and nocks, but brass inserts and 4" vanes for a total weight of about 431 gr. w/ about 19% FOC compared to about 10-11% on lighter version. I also used 8-32 tpi threaded stock [steel: 1"= 25 gr]. All w/ 100 gr points/bheads

The easiest way, imho, to add FOC is to simply use a heavier head. The alum inserts weigh about 32 gr, the brass 111 gr, say 80 gr diff. If you try a 170 gr point on alum insert carbons, you will be very close to what I have, w/in 10 gr. You can add a piece of 8-32 like a set screw w/ allen wrench to back of insert to make up or exceed the 10 gr. Use blue loc-tite on it, let set a day or two and then chase the threads to clean out excess loc-tite w/ a 8-32 bottoming tap. I believe their are other weights available between 170 and 100 gr, think there is a 150 gr out there.

Once I got to the 431 gr GT's, w/ 100 gr Slick Teicks, I pretty much hung up the experimenting, but am going to re-try the 2" Blazers w/ bheads and see if I can get same poi as field tips like I do w/ 4" vanes.

Sprouls advice to read on Matthias 72 tests on Italian xbow site is good, he's taken all of this to new levels and has some good data there.

One more note about the GT Lazar II's. Back in 2004 and 05, both Excal and 10 pt were using them. They seemed to have the least run-out of the carbons, had at the time tighter tolerances than the rest THAT I WAS AWARE of, and I've had great luck w/ them compared to the others [by no means all] that I've shot. not too happy w/ the move to Mexico, and somewhere along the line I've gotten some that have an o.d. on the shaft .007" smaller, lol, but got too many of them to look for new now.