You want no ka-booms from powdering when running a single-stage press? Very simple.
1. Make absolutely certain your scale is set to the correct powder weight. Re-check occasionally and CAREFULLY if you ever bump it, hang a shirt-sleeve on it, etc. If your dropped charge does not weigh close to the same as the others, DO NOT suspect that your powder tube suddenly got "off" -- suspect you bumped the scale.
2. Watch the powder go thru the funnel into the case. SEE that it ALL went. Tap the side of the funnel with the scale pan you just emptied if the powder hangs up in the funnel. Remove funnel, look into the case and verify it looks to have the correct amount of powder in it.
3. DO NOT set that charged case into a block. Do NOT set it down on your bench. Do NOT do ANYTHING with it except to put it DIRECTLY into your press followed immediately by a bullet, and seat it. There is NO REASON to do it any other way.
About a year ago I was about 15 feet away from a rifle that KA-BOOMED. If the shooter had not had glasses on he would have been blinded in both eyes (from bits of brass). If his bolt had not had a third lug on it the bolt, which had both front lugs sheered off, would have come back into his mouth causing very serious injury. I am pretty sure it was a barrel obstruction, but he had been shooting for half an hour when it happened. I think he put a round in with NO powder, pulled the trigger and, with ear plugs in, did not hear the primer go off. When the bolt went "click" he opened it, saw the spent case and assumed he had forgotten to load and loaded in a new round. No problem chambering it because the primer had pushed the bullet a couple of inches into the barrel.
I saw this exact, same scenario play out just a few days ago. The guy was just about to load another round when the guy beside him told him to check his bore. Sure enough . . . And he just couldn't believe he had failed to powder-charge a case, until his next round did the same thing.
Everybody talks about over-charging a case to produce a ka-boom. Yeah, it could happen, but the far more likely cause is not charging a case at all. Remember, you will NOT hear the primer go off. If you EVER pull a "click" DO NOT think you somehow worked the bolt on a spent case -- assume you did not hear the primer push the bullet 2 inches into the barrel.