Cylinder Rotation Binding With First 10 Black Powder Cartridges
When shooting Black Powder Cartridges in the Uberti 1872 Colt Open Top Revolver in 38 Special, the first five shots, and then most if not all of the next five shots exhibit dragging (jamming) of the cylinder upon cocking the revolver for the next shot. The cylinder starts to rotate then binds up shortly after commencing to rotate. It seems to be when the primer arrives at the loading gate joint even though the loading gate is flush with the recoil shield and no ridge is present. After the first or second cylinder with Black Powder loads (or Pyrodex), no binding occurs.
When shooting smokeless cartridges, no binding is experienced at all on any of the first five or ten shots.
I can only assume that the Black Powder pressure/time curve allows the cartridges to “setback” against the recoil shield and probably allows the primer to flow leaving an unnoticeable extrusion which drags on some area of the recoil shield between the twelve and ten o’clock position of the recoil shield as viewed from the front to the rear of the gun. I posit that this setback is also being allowed due initially to the clean chambers which do not grab the brass upon firing. The higher pressure of the smokeless propellants coupled with a different pressure/time curve allows the clean brass to grab the clean chamber walls with enough tension to prevent case setback.
Once the chamber walls are soiled, the subsequent black powder cartridges do NOT bind up even though they are the same load that initially binds.
When viewing the cases that experienced binding under magnification, no evident streaks or rub marks manifest. Other than a deep firing pin strike, no apparent cause of the binding can be seen. The deep firing pin strike is not the root cause since the binding occurs after the firing pin has been withdrawn from the indentation. If the loading gate were slightly higher than the recoil shield, I would have to say the primer is grabbing the gate at that point. Fortunately, the loading gate is at or lower than the recoil shield surface. No high spot can be felt there with a pick.
On my next range session, I will load up six rounds and alternate with Black Powder and then Smokeless. This will certainly test the theory that the clean chamber walls coupled with the pressure/time curve of black powder, cause case setback until the chamber walls get sufficiently dirty to grip the clean cases with enough force to prevent setback of either the primer or the case itself. Know too that the head space is within tolerance on this revolver.
Also noticed is that new or resized brass has an OD of 0.3763” while fired brass has an OD of 0.3785”. I will also try loading up some cartridges without resizing the brass to see if that helps the brass grip a clean chamber wall when loaded with Black Powder. The first cylinder full will tell.
Has anyone else observed this anomaly when firing the first few shells loaded with black powder versus smokeless powder?
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Originally Posted by John Boy
