If that's a Double Heat Treated receiver (High Number?), they can be still very tough to cut. Some more than others.
Kind of like trying to engrave a Colt SAA frame w/o annealing it first. It can be done, but the results aren't usually as nice as you'd want.
The double heat treat retains a case hardened surface, though not as hard and deep as the Low Number receivers.
Low Number receivers if original condition are like a glass rock.
If you get a L/N that you can cut (or file) it,,chances are it's been annealed somewhere along the line IMHO.
Wether that makes it more or less shootable is unkn.
The shootability of the original is the forever unanswered question it seems.
But I like to shoot my Sedgley L/N Sporter....
