Budbowhunter

I saw where you guys helped Bobcat-10 with his question on KE. I think that' s cool. You guys seem pretty informed on this stuff so I thought I would pose my question.
My problem is that I live out in the boonies here in southern Iowa. I would have to drive an hour and half to Des Moines to get to a pro shop with a cronograph and an arrow scale. I' m lucky to have a pro shop that will glue on new vanes. So here' s my new setup and the info that I have.

BOW- Martin Phantom II set at 65 lbs and 29 inch draw (IBO rated at 310 fps 70lb max - 30 inch max draw)

ARROW - Easton Carbon Evolution 300 cut to 29 inches. According to Easton website, shaft weighs 294 grains cut at 29 inches with 5 inch plastic vanes.

BROADHEAD - Tru-Flite 100 grain fixed 3-blade broadhead.

Besides that, all I' ve done to the bow is add string wiskers and a peep sight to the string. Oh yeah, I' ve got a mechanical release clip on there too. So what would my arrow speed and KE be? Thanks in advance for all your input.

slicendice

Try going to www.bowjackson.com

There are several " calculators" there to help you figure up arrow speed, KE, as well as many other things. This is a very helpful site.

Slice

Matt / PA

You ready for all this........

Here goes:


Your arrow........
Shaft=294 (good job!)
Insert=23
Nock=13
Vanes=27
Point=100
Total FINISHED arrow weight = 457grs.

Your speed.........THESE ARE APPROXIMATES!! (But should be FAIRLY close)
***Max IBO 310fps @30" /70#***
Start at 310fps-10 (29" draw length) = 300
300-3 (peep)=297
297-5 (whiskers)=292

Here' s the biggie: You are shooting at 65# which now makes your IBO legal arrow 325grs. With a 457gr arrow you are 132grs OVER IBO rated weight.
Most bows I' ve seen these days lose about 1fps for every 2-2.5 grs of weight added over that number. I' ll call yours 2.2
Take 132 divided by 2.2= 60fps.

SO take your 292-60= 232fps
I' m also gonna scrub off a few more just because we are guessing against the MAX IBO speed.
I' ll guess your grand total speed at right around 230fps

Your Kinetic Energy.......
457grs at 230fps= 54 ft/lbs

And there you have it........plenty of KE for any fixed broadhead you choose, and if you try mechs stay with the proven penetrators with modest cutting diameters like the Rocket " Nail Driver" ," Steelehead" etc.

Budbowhunter

Thanks again guys. That helps alot.
Matt. You say my arrow weight is 132 grains over IBO legal arrow weight. Does that mean that if I want to increase my arrow speed I need to look for a lighter arrow? And would that lighter arrow also increase my KE? I' ve read on here where the heavier arrow delivers more KE. That' s why I chose the Carbon Evolution 300. It' s the heaviest arrow I could find. I would like to get my arrow speed up to around 250 if possible without sacrificing too much KE. You say my KE is at 54 lbs. I want to try and get it up closer to 60 if possible. Without changing the bow poundage what are your suggestions. Thanks again.

Matt / PA

Bud,
Without changing bow poundage, or draw length there is no way that you are going to get 60ft lbs or more of KE and 250fps at the same time. Not possible.

If you go to a lighter arrow, say 400grs that will put your speed up around 250fps+/- but your KE will not increase at all.........in fact it will decrease slightly.

If you want 250fps and over 60ft lbs of KE you need to be shooting that bow at 70# and probably need to grow another 1" of draw length.

Keeping the arrow weight at 457grs and moving the draw weight up to 70# should give you a few more ft lbs. and you' ll pick up around anouter 10-12fps
Losing the Whiskers will give a few more FPS as well and if you have a Peep tube that eats up speed also.

Without increasing your bows performance by raising draw weight, or draw length.........or lightening the string load, you can' t have a speed increase AND a KE increase at the same time.
You' ll have to choose one or the other.

If you could shoot it comfortably at 70#, lose the whiskers and lower your arrow weight to about 400grs you' d be close, but you will also have a harder to draw and slightly louder shooting bow. Is it worth it?

Budbowhunter

Good point. Losing the wiskers is not an option for me. Quietness is of the utmost concern. Turning up the bow to 70# is an option but when I' m practicing or shooting 3-d I sometimes fire it 50 or 60 times. 70# would get a little difficult with that many reps. With only 9 days until the season opener here in Iowa, I' m going with this setup this year. I was just wondering about getting optimum performance out of my rig. What I mean by that is the fastest, flatest, arrow flight that will still give me complete passthoughs out to say 20 yards. The arrows I shoot now hit my layered target pretty darn hard and there is some drop off but my first pin is good out to 20 yards so I' m fairly happy with that. I appreciate all your help Matt. Thank you.