There is no standard for what wall thickness "should" be. Thickness varies with every gun. Based on the amount of metal was removed in factory striking, and also if they have been refinished or not. The critical spot it around the tip of the forend, this is where pressures are greatest. Check out the couple threads that have been linked in above for more info. Wall thickness must be measured with special tools. Simply checking the muzzle end will not do it.

Are you sure about that?

Pressure reaches peak in the chamber.

anybody ever see a gun that just the chamber area or the first 4 inches of chamber that they would deem unsafe to shoot... i have not...charlie

Is it not generally accepted that the critical spot for checking wall thickness is 9-10 " from the chambers?

I measure the entire length of the barrel in several radials.

Having the forward hand at about 9" from the breach makes it a good place to check, assuming fingers are important.

Pressure is highest in the chamber.

Jent,

What pressure was the ammo that bulged those three #1 Frame Damascus barreled Parkers?

The term "Light Target Load" seems to denote low recoil and a lower weight of shot rather than low pressure.

Be it high or low, pressure and recoil are not necessarily the same.

That may or may not be generally accepted, a barrel could have a thin spot anywhere along its length. A thin spot could have been caused by a myriad of reasons such as repairs to bulges, dents or even when it was originally manufactured. Here's a generic drawing of a 12-ga. barrel showing wall thickness contour along its length (all barrels are not created equal and any other barrel is likely to be different than this example), a thin spot relative to the pressure exerted at that spot anywhere along its length could cause bulges or bursts.