I have a 45# hoyt gm2.  A beman ics 500 cut to 29" and a 125 tip bareshafts perfect. I want a heavier arrow but i dont want to tube the 500. So i'm figuring i can shoot a 400 and load up the tip. How much up front is gonna make the 400 shoot like the 500?  Maybe some of the experts can get me close before i start shootin.          Thanks, Ed

In my limited experience, keeping the arrow length the same, point weight can at least double - and many times go higher.

From my 51# Shrew I used to shoot .400spine carbons with 250grs up front.  Your 45#GM2 should be very close to 50#, to give you an idea...

Arrow length is not an issue. At least 29". I was thinkin 100gr insert plus 125 tip and probably have to shoot a touch longer 400.

use the dynamic arrow spine calculator to get you started if you do a search for it it will come up.

You would need 190grains up front. I suggest getting a point weight test kit from 3 rivers for around $5. 190 grains should be about perfect but you will have to fine tune.

If you don't mind extra length just leave one full length and trim back as you tune to shoot the same weight point.I shoot 600s.500s and 400s from the same bow with 125gn points.The 400s are just a little longer.If left the same length it takes me about 75 to 100gns more weight on the front to tune the 400s with a 29" shaft.

The pt weight kits only come with 2 of each weight. If your gonna bare shaft, I would say a min. of three bare and three fletched, and four each would be better. You need a half dozen pts of each weight to get a good picture of your arrow flight.

My 400s are cut 29 1/4" bop and I have a hundred grain brass insert, 100 grain steel adaptor, and 125 grain broadhead up front. They shoot well from my 50 to 55# bows. For my shooting style, the 400s would be too stiff from a 45 lb bow.

fwiw to ya, and in my personal opinion only ...

i spent a LOT of time messing with carbons and have found that what's consider weak spined (500's) works best for me, even with a huge up front loading.  this may or may not work for everyone, but it works perfectly for me and my bows.  i found the stiffer 340 and 400 shafts were harder for me to tune.

i start off with an ics 500 shaft cut to 29-1/4" bop, 100gr brass insert, 125gr glue in point (bh, judo, fp, whatever) and a 125gr steel adapter, 4" feather 4-fletch.  total arrow weight is 585gr, 350gr up front, 29% foc.  i shoot this arrow out of 52-55# mild r/d longbows cut 1/8" past centershot.  for lighter holding weight bows (45-48#) i drop the front end weight down to 300grs.

as always, ymmv.

I'd have to agree with Rob...no matter what I do I can not get the 400s to fly well from my 47-55# bows.  But almost no matter what I do with the 500's...they fly great.  I shoot 110 gr steel broadhead adaptors with 125 gr WW  or 275-300 grain tippit hand forged two blade.  Both fly perfect with 500 Axis or Beman ICS hunters 28 1/2 inches bop..Doc

I do about what Rob does too. For my 46 and 52# Kanatis I cut the ICS 500 shaft to 29-3/4", add a 100 grain brass insert and a 145 grain point for a total of 505 gr. and about 21% FOC. I am using 3x4" fletching. With the same setup and a 170 grain broadhead, I still get perfect arrow flight.

I have to leave 400s full length and add more weight to the front.