banzaibird,

You bet! Here's a photo of just what you are wanting to see. This is a back action sidelock dressed up as a bar action. Notice the mainspring to the rear of the tumbler. Also notice the plate extending over the bar, but with no spring. This is a DR lock.

Here's the very same lock from the outside. A good eye will spot this as a rifle (with back action locks) because there is no pin on the sideplate near the front of the bar.

On the other hand, the next photo is a bar action sidelock off a shotty. Notice the mainspring out in front of the tumbler, mounted along the part of the sideplate that extends along the bar.

Here is a photo of the same shotty from the outside. Notice the pin toward the front of the bar. This anchors the mainspring at the apex of its fold. The existence of this pin is a dead give-away that it's a bar action.

Finally, here is a back action sidelock that is not dressed up like a bar action. It's an H&H .577 Nitro, and I got the photo from Lewis Drake's website. You can see that the sideplate is truncated and does not extend along the side of the bar.

I hope this adds something to the discussion.

Curl