H&R 929 – .22LR – Why is the inside of the barrel threaded at muzzle?

My model 929 – serial #AT0912XX – .22LR caliber – 2.5″ barrel – is threaded inside at the muzzle for about 3/8″ of an inch. Does anyone know what the purpose is? Thanks!
This isn’t rifling – I know what rifling is – this barrel is threaded inside at the muzzle as if you could screw something into it.

If you’re talking about real threading, as in coarse or fine thread (see this link http://www.barnhillbolt.com/specifications/index.php?catid=75) some Nimrod ruined your pistol. Are you sure you’re not looking at the rifling in the barrel? By the way, here’s an interesting link to the 929 pistol. Read before firing. http://www.thehighroad.org/showthread.php?t=72276
EDIT:
As you have unquestionably determined that this is threading, as opposed to rifling, I would suggest you check with BATFE and find out which part of their many regulations have been violated. You have a gun that has been altered to accept something, and that something is probably on their sh!tlist. I’m hopeful you bought that gun with a BATFE Form 4473. If you bought it from “some guy”, the gun’s history may get you cooked. Might be time to either grind it into powder or voluntarily turn it in.

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