Joe:

I tried the 2.5 inch Gamebores in my two VH Parker 16s (one a 0-frame, the other a 1- frame) and they were not low-recoil on my shoulder.

Then I went with RSTs and there was no comparison with regard to perceived pressure.

Russell, recoil and pressure are not related. Velocity and charge weight is what you feel in recoil.

The ARMUSA Vintage 2.5” are 420 BAR, not sure about the others. Both are soft on the shoulder and break clays just fine.

How does 420 BAR translate into pressure as we understand it?

Morris said they tested the BPS shells to see if they really were a lower pressure and he said they did test as BPS claims.

What exactly would cause them to be "way beyond safe"?

Let's just use 12g 2 3/4" as an example. If your barrels are good, whether they are Damascus, twist or fluid steel, there is no reason why you can't shoot 1 oz at 1200 FPS out of the gun. No reason at all except for possibly the shooter being "recoil sensitive". Most problems arise when shot charges get bumped to 1 1/8-1 1/4 and your velocity increases above that 1220 mark. Then you may cause damage to the old wood long before you see any problems with your barrels or action. In my 40 years of shooting and 20 years in the industry, I have only seen two shotguns blow up. One was due to a flaw in the steel, the other was contributed to a bore obstruction while using known low-pressure shells. I have seen many handguns blow up though. Most from high pressure from low powder charges.

6,092 PSI

1 bar = 14.503789 psi

A few of us had purchased the Shenk Shells. The perceived recoil on both the target and hunting loads were significantly more than what we recalled from RST loads. I had the loads tested independently and the shenk shells measured at beyond 12,500 psi.

Please refer to Steven's post. These shells are way above the advertised numbers. The felt recoil was the first indicator for many of us. They were tested independently and produced very high numbers. In my opinion, too high for any vintage gun. Especially the stocks. Just my two cents of course.