I know the others will jump on me for saying this, and it is just my own opinion, but if your friend doesn't have the right sized powder measure he could use the "eyeball" method of measuring the powder.
In a .36 caliber gun, like he has, if he fills the chamber to within about 5/16 of an inch from being full in a open-top Colt or 7/16 of an inch from being full in a Remington, that should be about 22 grains of powder (or a little less).
This depth of powder will allow the ball to seat below the chamber mouth in the colt because the powder is compressed during the ramming step.
By the way, Black Powder is rather inefficient (compared with modern smokeless) so a little variation in the amount of powder will not be noticed in a cap and ball pistol. This is the reason such crude measurements are completely safe to use.
I have long believed that in a cap and ball pistol which is in good condition , it is impossible to "overload" a chamber.
As your friend found, if the chamber is overloaded, the ball cannot be rammed to the proper depth.
With Brass framed guns, I cannot recommend this method because the brass guns are inherently weak.