When I shoot 2018's out of my bow in my sig, and put on 175 gr. field points instead of the 145's, they porpoised a bit to the target at max 17-18 yards. I thought with a heavier tip they would settle down but they didn't. When I put 125 gr. field points on them, they porpoised even worse! Why would an arrow porpoise at 125 & 175, but not at 145? Or am I missing something?

28" Easton 2018 Gamegetter I,
   5" feathers,
   145  gr.  field point
   20  gr.  point insert
   10  gr.  PDP master universal adapter
   50  gr. PDP weight
   51 lb. draw  =  11.7  gpp
   FOC  =  17.0 %
   Dynamic  Spine  =  57.1
   Total weight  =  593  gr.  
   Total point weight:  225 gr.

I would try a adjusting nock point 1st .

Check that your knocking point isn't to low

Sounds like the 145 is the right weight  for that shaft size and your setup. The 125makes the shaft too stiff and the 175 not stiff enough. If the 145 flies good I'd shoot it .

QuoteOriginally posted by lpcjon2:
Check that your knocking point isn't to low

The guy at the archery shop lowered my nocking point 1/16" to get my 5575's tuned. Now you got me wonderin'.

Check the how to section for the adjustable knocking point and then just experiment.I had to move a nock point a few times to get the best flight a few weeks ago.It's trial and error.

Yeah, I'm wondering if I move the nock down, if the 2018's will take the 175 grain points without porpoising. If it doesn't throw off my 5575's, that might be the thing to do. Kinda scared to go to 175's, I'm already down to about 150 fps with these.

If it will kill use it.Aim is more important than speed.

Thanks.

consistent porpoising is almost always about nock point location.

QuoteOriginally posted by Rob DiStefano:
consistent porpoising is almost always about nock point location.

Yes, but I find it strange that it seemed to be porpoising with 125 & 175 gr. tips, but seemed to settle down with 145 gr. tips. That to me is puzzling.

it's a nock point problem

Rule of thumb.... it's easier to have a nocking point that's too low than one that's too high.

Odds are that you need to move it higher and that the 145 grain heads aren't flying as good as they could.

Point weight would show a change in fishtailing (wagging back and forth)not in porpoising (flagging up and down).

If your nocking point is above the arrow nock then simply shoot an arrow with the nock above the nocking point.

It was set to (5/8) above the Nap flipper rest when I did paper tuning. The pro shop lowered it to (9/16) above the arrow rest lever.  I'm thinking lower it (1/16) and try again.

When I have nock point issues,it is rarely solved by lowering.I think that is what Charlie is trying to tell you.My bet is that you need to put the nocking point back where it was.Changing point weight changes dynamic spine.Porpoising is a nock height issue not spine.You just lowered your nocking point and now have porpoising.Think about it.

I think you're right. I'm gonna try it.

Correct-a-mundo! I put the nock back to 5/8" and they didn't porpoise. Not only that, but the 175 grain points actually flew better than the 145's. The 145's did fishtail a bit.

In fact, I put 200 gr. and 250 gr. points on them and they still flew great! How's that for ya?

Good to hear your on target.  

I'm starting to figure out how to do this. I moved the rest 1/16" left and the 145's fly straight and no more fishtail.

I still have to work on my 5575's. The feathers float right coming off the bow now, but at 17 yards they go in as straight as the 2018s. I'm a thinkin' I should try a tad heavier point on these.

well sounds like its unanimus and i agree i just fixed the same problem and moved back to 5/8 above and problem solved ...good luck