A research letter will not do any good to explain this. The order books show two separate guns made, not a repair to replace the frame.

Thanks for your help. How do I tell if mine is the no radius frame or not?

Yours does have the radius.
The transition from the water table to the standing breech is the area we speak of. Yours has a small radius at that point. Earlier Parkers are a hard 90 degree angle at this point.
Parker made the switch before your gun was made.

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Brian,

Having seen photos of my Parker, what would you guess as to it's value?

Thanks, Bill

PM sent regarding value.

How common is this issue of nonradiused lifter frames cracking and are there any warning signs that are apparent by a visual inspection? I personally keep pressures and payloads low but who knows what these guns were subjected to in the past

Any gun of that age is likely going to be fired with care these days and with he right loads.
I would not think cracking of these frames today should be of any concern.

Though cracking in this area my well have been observed over the years, I am not aware if Parker made the change as a precautionary measure or as a reactionary measure. That topic is likely subject for speculation.

Read the "Parker Story." I have seen several. In fact one cracked frame lifter was at last years Vintagers in Rhode Island.

Thanks for the link for disassembling my shotgun. I have it taken apart. I don't think it has ever been cleaned. Now the trick is to put it back together... :)