Spot Nails nail gun nail size

Hi Folks, I purchased a parcel of various tools at auction. Amongst them was a heavy-duty SPOT Nail pneumatic nail gun. It’s a heavy bit of kit and a bit of an antique but works fine for how often ill need it. I am trying to establish what is the correct nail to use. The magazine caters for a straight nail. Is there any way of measuring or does anyone have the same gun? The model number, which is difficult to read appears to be VL 813A (maybe no V). It says to only use driver number P 06059 ( i can’t find anything to this reference online) and the patent number is 3651740. If anyone could advise on what nails it would take before I go wasting money on “no fits” that would be great. Much appreciated

I see several references to a Spotnails 813 - but that is a pneumatic staple gun not a nail gun

You know, i did wonder this. Looking at the loading cartridge it certainly lends itself to staples. Thanks Fred.