I've got a Starrett 1 inch micrometer. and I'm using one of them ( I call them tong's ) to run back in there pulling them back in fourth and open them up at the same time tell there's a little drag, squeeze them down take them out then lightly tighten down the micro on the ends of it.

And the one 12ga it does start off about 4 and 1/2 inches back from the end of the muzzle at 724, then at 4 inches from the end of the muzzle it just opens up all at once to 780, then over the next four inches it comes back down to 673,

it's a polly choked barrel.

So I didn't know how it would affect the pattern. as to one that didn't open up them come back down.

Thanks for the sizes of the chokes the shot guns were not marked so I just guessed at it but I had got it right.

Also I'll print off the different constrictions.. Thanks for them.