Thread: My Bow's FPS

Well that was interesting. In a quite, rough and ready, measurement, I got the FPS of the arrow out of my bow.

Using the method from here - https://www.youtube.com/watch?v=tazuavGL6g8

So to explain - Using my iPhone placed at exactly 1/2 way, between the arrow point as the string hits the string stop, i.e. 1'21"" from the front of the riser, and the face of the target, 20 feet total distance.

I recorded a "Voice Memo" which is the sound, of me loading up the arrow, aiming, releasing and the arrow hitting the target. I recorded 5 shots and they were all, almost the same.

Then I sent the voice memo to my mac and load it into an app called Ocenaudio.

Zooming into and selecting the bit, of the sound wave, that is, the string hitting the string stop and the arrow hitting the target, gives a duration in seconds, which is accurate to 3 decimal places.

The formula I use then, is 20 feet / 0.085 seconds = 235.294 FPS which I'm quite happy with.





The Bow I ordered, was specced at 329 FPS IBO and 30~70 lbs draw weight.

The one I received, from the research I've done, is 320 FPS IBO and 30~60 lbs draw weight.

I understand the following:

I've dialled the weight back to about 40 lbs for now, apparently I lose around 17 FPS per 10 lbs down from 60 lbs. So 34 FPS

Also lose around 10 FPS due to using a 29″ draw length rather than 30″

And lose around 22 FPS due to using a 425 grain arrow rather than the 350 used in IBO testing (I don't know my arrows grain weight so I'll take the 425 as read)

Lose around 5 FPS due to extra accessories on the string and around 3 FPS due to imperfections in human release mechanics.

Ideally my calculated reading should be 246 FPS, but it's close enough to the rough and ready, reading of 235 FPS I measured. So that's OK for me.

Once I've got the new sight and got good at the shooting side, with practise, practise, practise, I'll dial it up to 60 lbs and 30" and see if I can get near 300 FPS.

and here was me thinking going to a bow was going to be simplifying life Vs using rifle.....Im fast learning maybe not so much.

Originally Posted by MarkN

Once I've got the new sight and got good at the shooting side, with practise, practise, practise, I'll dial it up to 60 lbs and 30" and see if I can get near 300 FPS.

Your draw length should be constant, as that will determine where your anchor is. If you are 29" shoot at 29" the whole time if 30" shoot at 30 etc. To set up at a draw length different to your actual draw length will introduce inconsistency in your anchor.

Originally Posted by paddygonebush

Your draw length should be constant, as that will determine where your anchor is. If you are 29" shoot at 29" the whole time if 30" shoot at 30 etc. To set up at a draw length different to your actual draw length will introduce inconsistency in your anchor.

Yes that's true, I'd be wanting to try the 30" and 60 lbs to see if the bow will do 320 FPS, just for curiosity's sake, for the rest of my shooting I'll be sticking to the 29" and possibly 50~55 lbs.

I'm enjoying testing this bow to see wot it is, in the absence of a manual, or guide, or any real information from the seller, in my preliminary tests, I got 62.5 lbs max measured at 30", but there's a 31" setting, so I might revisit that.

I'm thinking that bows generally test lower than their stated poundage, so maybe this is a 70 lb bow, dunno yet.

Originally Posted by paddygonebush

Your draw length should be constant, as that will determine where your anchor is. If you are 29" shoot at 29" the whole time if 30" shoot at 30 etc. To set up at a draw length different to your actual draw length will introduce inconsistency in your anchor.

dumb question,from complete bow novice......if you draw to 29" and have your stance etc set for that 29" draw....and you have 30 or 31" arrow will it be an issue or will it still do what its supposed to do??? aware it may shoot to different POI....

As far as I know, the tip of the arrow should be at or just in front of the riser at full draw, I guess hunting broad heads should sit clear of the riser for safety.

So My 30" arrows seem about right with a 29" draw and I've got some 31" arrows just came today.

When I get to shooting after my sight arrives, I'll be comparing them to see which are more accurate, mind you the 30" are 500 spine and the 31" are 400 spine, so it's guesswork at this stage.