JW

Change your target.

Use a target that shows life sized Turkey head that also displays the neck vertebrae, skull, and the eye.

You can find free downloadable Turkey head targets online.

Count only the hits in that area I mentioned above. Use the rest to move the mass centered on the beck head area. Develop a center using clamp on sites. Magnetic are a waste of money as you'll loose them.
Now the neck vertebrae, skull and Eye.
If you can consistently count 8 to 10 pellet hits in this area I described it will kill! And kill consistently.
Anything less tou are out of range.

That is why we pattern.

I start a 10 yrs with trap loads, easier on the shoulder. Then when I know where my point of impact is. I adjust how I hold on my target and ultimately on my bird.
I suggest a set of clamp on open tru glo sites as with today's tight extra full Turkey chokes you really are shooting a rifle.
I like the bottom center of my circular pattern to be my aim point which iis best aimed at the waddles.
That way I know I am circling the head with shot of the Turkey with my pattern.

Once I develop that at 10 yards. I take shots at 20, 30 , 40, even farther.
Doing all this with trap loads.
So when I think I have it. I take a Turkey load and will try shots at 20, 30 ,40 or further.
Using trap loads to develop your aim point is cheap and far easier on your shoulder.

Another method is to use a piece of paper big enough for a 30 inch circle and count only hits in that circle. Do note if you see pattern drift and center it, again by using clamp on sites. The sites must be adjustable for wind age and elevation

Then take that total number of pellet strikes and compare using a Tom Roster Table.
But in my years of Turkey hunting treating my shotgun like a rifle using Tru glo open clamp on , adjustable sights, and now because of age a scope. I just dont miss birds.

One last thing and this is my opinion

3.5 inch round is overkill and far too expensive.
Stick with 3"

LASTLYCladwell makes a life sized spatter Turkey target. Awesome to use for kids. It shows the beck anatomy I described above. And hits are color coded. Red means Dead.
Yellow means a possible Oh Oh.

Dont be an Oh Oh.

JW