Arrow Spine and Length

Hi Guys,
Hope you can help, I've been shooting GT Hunter XT 5575 since I started archery 9yrs ago with 125grn heads, I shoot a Mathews Z7, 66lb draw weight with a 26 1/2" draw length, I've always cut my arrows 28" long, which has not been a problem. Now I want tune for broadheads I think I am way overspined. When i put on a VPA 125grn 3blade it was 12" from my field point, after adjusting, the closest i can get my broadheads to my field points is 6" and my HDX rest is nearly touching the riser. I have even tried 200grn VPA 3blade and 200grn field points which i got down to 3" apart, but could not get any closer and the broadhead was still 3" to the left of the field point, suggesting its still to stiff spined.

My Question is:- What spine and length should I be using to shoot 125grn and also what spine and length should I use to shoot 200grn from a 66lb draw weight at 26 1/2 draw length Mathews Z7

What are your arrow and bow specs, just so I have something to compare to.

Your help will be greatly appreciated.


PS I'm not hunting this year, this is all preparation for my trip to Colorado in 2018 #elkcamp

 

I do not think you are over spined. In fact I believe you are under spined. With your specs I would be shooting 340's not 400's. It's always better to be over spined than under spined. With adding more point weight you are only weakening the spine further. With your bow specs and a 125 grain head with a 28" arrow I would recommend 340's. If you want to add more draw weight in the future and also more point weight (like the 200gr you stated) you should be shooting 300's at that point. To be able to shoot both the 125 gr and 200gr head I would go with the 300's, because like I said I'd rather be over spined than under. I shoot Gold Tip Kinetic 300's and I shoot a 27 1/2 draw @ 70lbs with a 27" arrow, this works great for me though, as I stack a lot of weight (160 grains) upfront.

 

great minds think alike

 

Bare shaft tune for bh / fp grouping. Sometimes a 1/2 inch makes a big difference. Check FOC.

 

well crap according to this chart I should be shooting 340's and I'm shooting 400s

 

You may be able to cut your arrows down to 26" and reinstall new inserts. This will stiffen up your arrow and put you in the proper spine range. I have a 26.5" draw and my arrows are cut to 26" carbon-to-carbon. I have approximately 1" of shaft past the arrow rest.

 

Not been on the forums for a long time, but have shot a bow for many years, and used to tune bows for probably hundreds of folks... I believe you really are probably "right spined," if you'd use a more appropriate tip, say 100gr or 125 gr... I've tuned bows from 55 - 73# using 340 and 400 spined arrows, and depending on cam aggression (speed of bow) you can tweak a bow to do anything given the ability to put the time in... You may be a bit long on the shaft, but I think with a 100 or 125 gr shaft, if you were to do a walk back tune, and decipher where your centershot really is, and then do a BH tune, you should be able to get things where they should be... With BH tuning, tweak the rest to where the BH hits, not the FP, and make the two become one... I've shot 26 robinhoods with a conglomerate of bows, be they single cam, cam-and-a-half, dual cam, (even shot one left handed this past year) and what I've found in tuning is that YOU the archer, must tune the bow to YOUR shooting...

 

Thanks Guys, your right, according to the chart I'm weak spined, best get buying some more arrows ....... Damn!

Thanks again for the replies, let you all know how I get on

 

Thanks chief, good to be back, it's been a busy 12months, but now I'm back on it

 

You can help your 400s by trimming your shafts a little shorter, and try shooting some 100 gr. broadheads. Trimming the shaft will give you a stiffer spine.

 

That is what I was going to say - snip an inch off and see what that does.

 

i always go one chart stiffer then manufacture recommends

 

I shoot a Mathews z7 @ 65 LBS, 26.5 using Easton FMJ 400 @ 28" with a 100 gr broad head. According to the chart I should be a tad weak spine but I think they fly true for me. In the past, I use to shoot 125gr broad heads but I would get flight issues; when I went to 100 gr, the arrow leveled out. Regardless if you purchase new arrows, or not, I would recommend spin test the arrow and broad head together ensuring you do not have any wobble. Once you know your Broadheads and arrows spin true, you can shoot broadheads/ field points down range, then adjust accordingly. If your arrows and broadheads spin true, there should be little difference @ 20yrds where the two land.