I use a product to detect cracks on newsprint roll robotic vehicles and find it works very well. It comes in a 3-can kit for I think about $20.00. It contains a cleaner, penetrant and developer. You spray the suspect area with the 3 chemicals and in a matter of minutes, the crack shows up like a sore thumb. Albeit there should be no excuse to let a gun go out with a cracked frame. Anyway, the product is called " crack check " by Dynaflux. I know they sell it through UZ Engineered Products out of Cleveland or just call Dynaflux at 800 334 4420
