On steel ... NO! As in NEVER! and most certainly NOT in your nice gun.
On opening a choke &/or getting a tube or tubes .. I would spend the money on a MEC loader instead and and play with some loads that allowed you more variety of patterns. Homemade spreaders can be VERY open. Its been a long while since I have posted this, but taking a cookie sheet and pouring the shot to be loaded out on it and then just flatening it with a suitable bludgeoning devise [hammer/brick/hard stone/etc.] and then loading the flattened shot into any of several spreader loads can REALLY open the patterns up. I use a thick steel plate on top of the shot and a few good sound blows with a sledge hammer to do a lot of it with minimal labor. Prolly ought to go buy your own cookie sheet, brides take use of theirs for flattening lead as a step too far. In between the home made plombe disco [flattened shot] spreader loads and your factory full chokes is a whole world of good fun developing some loads that will deliver patterns suitable to your need[s]. Just screwing in a choke tube marked such & such tells you nothing about the patterns being delivered. You don't need to count holes, just use a good plate with some white lithium grease or whitewash that can be re-coated quickly with a few swipes from a paint roller.
One of the members here, I don't remember who, suggested using a plastic soda straw inserted into the shot column to effect an open pattern and another the use of golf tees to the same effect. Both methods work. Keep to published recipes for powder and weight of ejecta and you are on firm enough ground. FWIW, high pressure & velocity loads [not the same thing, mind you] tend to produce more open patterns.
Hope that something here assists you. And of course, "Welcome to the board!"
