Shooting primarily paper patch military single shot rifles, i utilize grease cookies under my patched bullets. Most of what I shoot are the .433-.446 calibers and they all perform well with a .125 cookie. I recently run Into an issue with a French gras I've been working up a load for and am getting wild groups. The rifle is stringing vertically by several feet, each climbing higher. I'm using a rest and the rifle is secure so my breathing shouldn't affect it. I ran out of cartridges before I could apply more lube to the outside to see if that was the issue.
   
Long story short, what do groups start doing when you have inadequate lube? Verticle stringing? Horizontal? Shotgun like patterns?? Never ran into this issue

FWIW, I shoot my Martini's the same way - PP and grease cookie.  However, my lube wads are considerably thicker - about 3 times yours, maybe more.  And I use a softish lube.
I still blowtube between shots, however.
This in No.2 Musket and .45 turk, 577-450.  Shooting mainly groove-diameter bullets.

Thabks for the replys everyone. I successfully shoot with orginal military loads several trapdoors, peabodys, 71 mauser, berdans, vetterlis WITH black powder only.

The rifle I'm having issues with is a French Gras. For 4 years I have not been able to get this sucker on paper. The rifle is sound, barrel bands tight and action screws secure. I fit the fattest bullet I can chamber, grease groove and pp alike in the case neck. The gras is finicky as it has two fixed rear sight settings. 

The only difference between the gras and the other rifles I mentioned is that the difference in the groove diameter compared to the bullet diameter is significantly bigger. The .446 bullet has to expand to nearly .454 to fit the grooves. I use the same bullet for all my 11mm rifles and it's proven to work....the French rifle has been keeping me up at night. I'm loading 80 grains of 1.5 swiss to give that bullet all I can to make it bump up to the rifling. No damage to the bore or crown to speak of.