First off the fallacy of perfect in the context to AK welding should be addressed. A perfect spot weld doesn't look at home on a real AK in my opinion. In fact the factory welds are never perfectly round, set to the exact same depth every time or even properly in line. Even if they were that still isn't a perfect spot weld. When I spoke at length with the guys over at Tuffalloy about there spot welding tips they were like " What? you actaully want the marks visible??." The best welds as far as the Pro's are concered hold properly while leaving as little of a mark as possible. It was funny for them to talk to someone who actually wants to displace the metal. Usually there customers are complaining about the spot welding marks and want to limit them as much as possible.
In the AK world we have other criteria and the more "real world" we build our projects the more satisfying the results.
When I built this rifle the receiver was sand blasted before the rails were welded in. While it was still in the white it looked as though the spot welds were'nt deep enough but after paint it actually came out more on par with the military FEG receivers depth wise. This depth also happens to be good for Bulgarian 74's but the shape a little to round for them. When I actually go into production I will dial back the pressure some more.
The next pics below are of the original receiver that was cut when the gun was demilled. You can see the welds are shallower also the paint is a lot thinner than Rustoleum appliance epoxy in the above build.
Ultimatly recreating the spot welds isnt about shooting for perfect it's more about shooting for imperfect. It would be a boring world if they all looked exactly the same. When the receivers were originally produced the huge quantities and unskilled labor resulted in all the variations we see today. The pressures were cranked up the weld tips were used a ricdiculous amount of times. Personally I'm glad for the variations and thats how I'll build them.