Broadhead tuning

[the rifleman]

I'll start out by saying that I'm pretty well versed in bareshaft tuning via OL Adcock and Ken Beck's video.  I have had good results with tuning my other longbow---i.e. bareshafts, field points and broadheads all group together right down the line.

I picked up my 42# Whip the past couple of days and have been working on getting bareshafts and broadheads tuned.  I have the arrows tuned very well for spine (they fly right down the line, previously being too weak).  My nock height was the puzzle.  If I moved it down to 5/8" I would get occassional bounces off the shelf with the bareshaft sending the arrow high and nock low.  I finally got the fletched and bareshafts pretty close together up and down with a 23/32" nock height.  I am using 146 grain field tips.  I mounted a 156 grain grizzly broadhead on the arrow and they are flying very well, but hitting about 4-5 inches lower than field tips at 20 yards.  I know the grizzlys are 10 grains heavier, but wouldn't think that would make that much of a trajectory difference.  I tried coming down with my nocking point, but then would experience tuning issues most likely related to the arrow bouncing off the shelf.  I shoot using string walking and have no trouble adjusting to the difference in trajectory, just curious if anyone else has run into the same issue.

The arrows I'm using are carbon express heritage 75s cut to 28 5/8".  I like these arrows, but for some reason they seem to be a bit more sensitive to nock height than arrows that I'm using in my other bow.  It doesn't take much of a reduction in height and they take off high, which I believe is attributed to them bouncing off the shelf.  My form and release are not issues with my other bow, but may be showing up with this one for some reason.

From a hunting standpoint, am I good to go with the broadhead tune I have?

[Orion]

Hmmm.  Don't know if I can be of much help.  Agreed that 10 grains of difference shouldn't make that much of a difference in trajectory.  In fact, there really shouldn't be any difference, based on weight. 

If you're string walking, then you're also gapping. Are you're using the end of the arrow behind the point to set your gap?  If you're using the end of the field point and broadhead, the broadhead is longer, which would cause a lower hold and impact.  I expect you already know this.

The shafts should be OK, but may be on the light side spine wise and could be a bit sensitive for that reason.  Do you have some 90s you could try?

[YosemiteSam]

Check the orientation of the head.  I know most folks say it doesn't make a difference to them but it absolutely makes a difference for me.  For me, the blades must be perpendicular to the string.  My working theory is that the blades slice through the air when in paradox vs. paddling if oriented parallel to the string.  But that's just my theory.  All I know is that I hit with field points when I do it that way and I'm all over the place when I don't.

[the rifleman]

Thanks Orion.  I should have mentioned that my draw is 26.25" so im pulling high 30#s.  I had tried 600 s with this bow, but they needed 200 up front which gave me a heavier arrow than i wanted.

Im shooting .800s out of my Pika which is 35# at my draw.  I do gap at back of point.

[the rifleman]

I also like to orient 2 blades horizontal.  More for a sight picture, but i don't doubt your theory.

[Orion]

Hmmm.  At your draw length and weight, I agree that .600s may be too much (75s are .611 spine). Did you try the .800s out of the Whip?

Maybe it's just the nature of the beast.  I've always found lighter weight bows and arrows to be more sensitive to form flaws, at least my flaws. 

Even though the front end weight is nearly the same, the broadheads place that weight further forward.  May need to stiffen the broadhead arrow just a bit to get flight identical to your field points.  Can you reduce the weight of the adaptor or insert?  How about adding a 10 grain collar to the nock end?  Or perhaps shortening the broadhead tipped arrows a quarter inch or so.

 

[the rifleman]

I just noticed something this evening when i put a grizzly on one of the 800s and shot it out of the Pika.  The alum insert im using on the grizzlies stands a little proud of the shaft and really shines.  Since im aiming off the arrow i believe it is acting as a " higher front sight" on a rifle would--- causing a bit of a lower hit.

I agree that the lighter bows are more sensitive to form glitches.  That said, ive also been able to improve my form dramatically since moving down in weight.

Thanks for all of the input.

[Orion]

That could be it.  Hope it is, because I can't think of anything else.