Keep in mind the functioning Stens today have had many decades of vetting that ensures they work properly. When they were originally made there were certainly problems with mass produced parts not always working well together.I've not shot a Sterling, but I have shot a Sten a few times and found it much better than its reputation had me expecting. I expect the Sterling would be more polished and even better.
The Sterling has a different feel from the Sten because the pistol grip is located in the middle of the gun rather than at the back end.
I highly doubt the forward bolt lock was installed by field armourers. It required a new cocking handle as well as a hole to be drilled into the receiver in a specific spot. That would require a jig and a drill press.While this is true, remember that the push-through safety was a retrofit. I don't know what year it was adopted but the majority of Sten guns were made without that feature, and it was added later by field armourers. It wasn't always available, and many men trained before it was there.


















































