Rifling groove depth

[Ken Rummer]

I was looking at Colerain barrels in 50 and 54 cal. Groove depth is .016. My T/c, Lyman and GM all have grooves approx. .010 deep.

Is there any advantage/disadvantage to using this deep groove?

 

[ApprenticeBuilder]

If your prone to shooting a loose patch/ball combination (.010 under bore size ball with a .010 patch) then yes there are dis-advantages, many of them.

The round bottom rifling cleans up easier as there are no sharp corners to trap fowling, it loads tight ball patch combinations easier as it gives the extra patching material some place to go.

YMMV

 

[Rifleman1776]

This could touch off a firestorm debate. There are proponents for both.
However, I believe the deeper rifling is prefered by experienced shooters.
Shallow grooves are generally found more on factory made rifles. The manufacturing process of pulling a 'button' through a barrel to make the rifling is faster and cheaper than the traditional cutting. Button rifling is much shallower. However, with the right ball/patch combo good results can be had with either.

 

[Ken Rummer]

I was thinking about the patch thickness needed to get a seal in the groove would increase the interferrence at the lands. It should require more effort to seat the PRB. My concern was "How much more effort?"

 

[CoyoteJoe]

I find most T/C's run only .005" groove depth but I've heard they made a special round ball barrel with .010" deep grooves. Most Lyman and Pedersoli barrels run .006-008" deep. Rice barrels are listed as being .010" deep. Green Mountain grooves run about .012" deep. Round bottom grooves measure deeper since they are measured at the middle of the groove, the deepest part of the round bottom.
While the common practice is to select a ball size and adjust patch thickness to achieve the desired "tightness" of the load, there is something to be said for selecting the patch thickness to correspond to the groove depth and select a ball size based on the desired tightness. Any way you go about it there is no exact science, lots of trial and error experimentation. Generally speaking however, it is best to use a larger ball and thinner patch combination for shallow grooves and a smaller ball, thicker patch for deep grooves. And, generally speaking, best accuracy comes with the tightest combination you can load without pounding it down.
:grin:

 

[hanshi]

The groove depth on my US M1841 rifle is stated as being .006"; I have no idea if this is the same as the originals or not. Still the rifle was designed to fire prb and indeed was the last rifle issued to the military designed specifically for prb. Prb accuracy from my particular rifle is nothing short of phenomenal.

My flintlocks have much deeper grooves, .010" to .012" at least. I have a round groove rifle coming with rifling that should be at least as deep if not more so. I prefer deep grooves as it makes it easier to use thick patches.