I bought a new bow and went up from 45# to 50# with a 10 strand fast flight string. I shoot 3 under with a thick old bear glove.
My problem, it's burning a hole it feels like on the side of my middle finger where it meets my ring finger. I have to shoot a dozen arrows or so then take a break shoot a dozen take a break. Let it heal a day or two then start over.
I never had this happen with my other bow and the only thing that's changed is the bow, weight, and string. So is this something that happens often? Is it something in my form maybe that has changed drawing and releasing the extra weight? I have no idea what's going on, it's really starting to get on my nerves and making turkey season practice not fun at all!!!

Let's see just for fun.

Say your old string was 20 strands (twice the diameter of the 10-strand) 1/8" vs 1/16" diam., but since the strings are round, assume max. pressure on your fingers occurs on half its diameter. So, use half of both or 1/16" and 1/32", respectively. And use say 2" of finger-string contact across 3 fingers pulling equally.

Bow 1-Finger pressure (force/area)= 45#/(2"x 1/16") = 360 psi

Bow 2 - Finger pressure = 50#/(2"x1/32") = 800 psi

That's a gain of 222 % in finger pressure = blisters      

I was having a similar issue for awhile, using the same bow and string I had been shooting for a while. Found it was, for me, coming from a string pinch/string and grip issue.

I have that issue with shorter bows on my ring finger. I shoot split. I wrap masking tape around it when its sore. Seems to work well for me.

Try using a new glove, or maybe try a three under tab. You could also double serve the string where your fingers hold.

Did you stay with the same length bow?
If you went to a shorter bow, you could have a much sharper string angle that is causing your fingers to be pushed together tighter while drwing the bow and maybe not coming off the string as cleanly.
Just a thought.    

Happened to me as well.  Bought a used recurve, 58".  My old recurve, 60".  I got rid of the shorter recurve and my discomfort went away.  Who knew?

-Jeremy  

I didnt think about the length. I was shooting a 62" bow my new bow is 58"....I have a short draw length 26".

Good chance that shorter bow length is the culprit.  But drawing three under with a 26-inch draw, you really shouldn't have much finger pinch with a 58-inch bow, unless it's a fairly straight longbow.  Fingers should toughen up over time.

That's what I was thinking with my shorter draw that wouldn't be the problem shooting a shorter bow, but it probably is the reason. On the glove I shoot now, the index and ring finger parts are thicker than the middle finger. I dunno if it's supposed to be that way or just wore out. So the ring and index are a lot stiffer causing my middle finger to do the most work. The glove doesn't fit tight anymore like it use to I have to adjust my fingers deeper in the glove after every shot.

The part of the string where your fingers rest - the serving - should be the same size as your previous string if you are shooting the same arrows.

Are you using a deep hook, or drawing only on the pads of your fingers? If you're drawing on the finger pads, the heavier draw weight will probably be noticeable. If using a deep hook, your fingers should pretty well flip out of the way without the string dragging across them.

Something has changed for sure, is your nock fit the same with the new string? if so the diameter is not the culprit. My guess is to much tension in your draw hand/fingers at anchor or glove is problem. Best protection for a glove for me is the Big Shot Crossover.

Another thought to check is make sure your not torquing the string with the heavier weight bow.

My nocks fit just like before so I'm guessing the serving is the same. I shoot with a deep hook in the first joint. I have a tab that i play with sometimes and if I hook it deep real deep I don't get the finger blister, but I get erratic arrow flight cork screwing and fish tailing but no pain. When I use my glove I get perfect arrow flight but finger pain.

Sincerely, Confused

Just a thought - do you have 2 brass nocking points on this new bow, and something different on the old bow ?
Shorter bow sounds most likely.

I use a 3 under tab for 45# and 51#. No issues.

On both my old and my new bow I have a top brass nock and bottom is a tied on dental floss nock