This brings us to the barrels. Another issue I had to confront was the condition of the Yugo bores. I wasn't until the 1980s that Zastava put the chrome plating process for barrels into place. As a result, many of the M70 kits imported into the USA do not have chrome bores, and almost all saw heavy combat use. Because of this, many Yugos have what are called "dark bores" — the bores have been shot out and are so corroded/worn that they literally look black.
To test the bores, people take a 7.62x39 cartridge or just the bullet and see how far it can be inserted into the bore. If it falls down to the shoulder of the cartridge, then the barrel is pretty much a sewer pipe and will more or less shoot like a smoothbore, resulting in fairly poor accuracy — we're talking feet, not inches, at a 100 yards in these cases.
By using CLP's Foaming Bore Brush and bore cleaner plus extensive wire brushing and dozens of patches, I was able to clean up the chamber and bore. After all the crud was gone, I could then test my kits and find which barrel the bullet went down the least meaning it presumably had more rifling.
The kit selected had a barrel where the bullet would only go a little over 3/4 of the way down the length of the bullet itself before stopping. Now, for the sake of argument, if that were my only kit and it failed the bullet test, then I would need to decide whether to change to another surplus barrel, perhaps purchase a new U.S. barrel (and their reputation is spotty), or even just use the worn out Yugo barrel as-is. If you have a fried barrel, you can either use it as-is or at least have potential options.