I have a 340PD that has about 200 rounds through it now. I only have shot .38 special loads. The problem my gun is having is that after about 50 rounds, the trigger becomes harder to pull but I am attributing that to the cylinder seems to be locking up when it is being shot. When I eject the empty casings out, the cylinder seems to be free to rotate. I think it is either locking up because of dirty ammo or could the frame be expanding with heat and hitting the cylinder?

Any comments would be appreciated.

Have you cleaned your chambers... ?

...and under the extractor.

Yes. I clean my gun every time I use it. I do clean the chambers and under the extractor. I believe I do a pretty good job.

You may have a problem with the fitting of the hand, but I am skeptical of that because of the "after 50 rounds" bit. This post probably should be diverted to the gunsmithing forum where a couple fellows who are pretty sharp on this stuff show up from time to time.

I wish I could offer better advice but I have read your description several times and, if the gun is clean, a hand clearance problem is the only thing that comes to my very small mind. I am no intellectual deep sea diver when it comes to this stuff - particularly without the gun to examine.

Heres my guess... The cylinders are carboning up, and you can't insert the cartridge all the way into the chamber. Check to see if you ammo is sitting flush, when you reload.

I wonder what the B/C gap is, could the cylinder be dragging when it get dirty?

Doubtful on a Smith..B/C gap is usually too big! But anything is possible.

Same thing happened to mine, though after a few more rounds.

You likely have excessive end shake and the cylinder is slamming into the barrel and binding when the gun is fired.

Get a set of feeler gauges available cheap at any automotive parts store. With the cylinder closed, push and hold the cylinder forward and measure the gap between the barrel and cylinder. My guess is you won't even be able to get the .001 gauge in the gap. If not this is a problem.

Next pull and hold the cylinder back as far as you can and measure the gap again. The difference between the two measurements is the end-shake and should be as close to .001 as possible.

Brownells sells bearings to correct excessive end shake.