Help me understand arrow penetration

[Hallaketrout]

I am new to crossbows. Exocet 200.
I was out yesterday practising on two pieces of blue flotation foam, duct taped together, about 16 inches thick, the type they use for dock flotation. ( don't use this stuff it sticks to the arrow shaft.)
I was shooting Firebolts with 150gr field tips = 418 grains on my scale, and Gold Tip Laser II , with brass inserts and 100gr field tips = 406 grains.
The GT laser II are more front heavy, but they are both very close on impact point and 1 1/2 group at 40yds.
At 40 yds the Firebolts would sink in to about 1 1/2 before the vanes, the
GT II's would penetrate to the vanes, and penetrate the tip through a piece of plywood that was behind the foam. I'm sure they didn't hit a previos hole.
Is this because they are front heavy?
I have to admit I am impressed with that penetration, I just have to find a different glue for the inserts, because they came loose before I could do more tests.
Anybody else found this?

[vixenmaster]

Better FOC is yer answer, although both will do the job.

[See4miles]

The better FOC is certainly a factor as your arrow probably had better downrange velocity as a result of less oscillation. The field tip design may have helped as well. Are they the same design and diameter?

They both showed great penetration at 40 yds though.

[Hallaketrout]

Thanks for the input, thought that must be the difference.
I am planning to try the Firebolts with 150gr Boltcutters, and the GT Laser II with 100gr X-Act this weekend, I'll see what happens.
I am starting to feel a sence of urgency as deer season opens October 1 . You think you have lots of time, then all of a sudden it's right on top of you!

[vixenmaster]

Don't rush you have time. I change set-ups during the season going from diff arrows & weights & BH's only takes me the time to sight-in fer new change