You should not be getting that much powder coming out of your vent. It is obvious that your vent hole is too large. I have no idea why it would change from one week to another but it is obviously too large. If you want to see for yourself if it is too large, get a 1/16 inch drill bit and use it like a gauge to see if the hole is too large. If the bit is very loose in the hole, your hole is too large. It should be no larger than 1/16 inch. Having a vent hole that is too large is a pain and can easily effect your accuracy. If it is too large, replace it. I prefer using Jim Chambers "White Lightnin'" vent liners (http://www.flintlocks.com/parts.htm) but if you want to use his, you will have to order one of his vent liner drill bits and tap because his liners are not a standard thread that will allow you to simply screw one of his liners into your existing vent liner hole. They are, in my opinion, the best liner you can get and are worth the trouble of re-drilling and re-tapping the hole. You will need to drill out the flash hole when you get his liners because they are too small. Just use a 1/16 inch bit and carefully open the hole up. Quick and simple.