You can over come that design (the need to pull the bbls open to be able to load the shotgun) by modifying the cocking arm and
altering the cocking plunger can also aid in elliminating the feature.
What is happening is that the cocking arm is being pushed to it's limit (which is OK) by the cocking plunger on the underside of the bbls.
The cocking arm is pushing both hammers back much farther than they need to go for the sear(s) to drop into the sear notches in those hammers.
So the hammers being under mainspring tension pushing forward, push on the cocking lever,,pushes on the cocking plunger on the bbl and push the bbl closed on you to a point where the sears stop the hammers and end the main spring 'push'.

In the alteration you want to make the gun cock 'later' in the bbl drop.
That will place the sears into the hammer notches when the bbls are dropped down farther and at that point take the spring tension push off of the bbls. The bbls then stay in that lower dropped position.

Don't shorten the sear nose(s) that will only make it cock quicker and the bbls will set closed even more on you. Leave the sears alone.
You are not altering the sear engagements, angles,, ect.
Just where the bbls are in their arc when the sears drop into the hammer sear notches. You want it to happen later in the drop from where it is now.

Numrich schematic shows the parts pretty clear.
https://www.gunpartscorp.com/gun-manufacturer/savstevspgfld/shotguns-sav/5100?page=2

It's a cut and try operation. A little at a time and use both the cocking arm and the plunger to get to where you want so you don't thin down one part too much. It doesn't take too much alteration to change the timing anyway.