As a shooter who is always trying to improve the accuracy of my rifles, an idea came to mind that I would like to throw out for your comments.

My bench rifle is a Ballard Rifle Co. (Cody) action, barrel is a 30” Badger, 14” twist, no.5 weight, .321 groove diameter, standard factory chamber 32-40 with 4 degree leade (8 degrees included). The bullet I’m shooting now is a David Mos tapered spitzer, .002 over groove diameter at the base that I breech seat. It’s quite accurate BUT (see my initial statement)

All the previous is actually just data but does put parameters around the bullet mould I’m thinking of having made. The bullet would be a spitzer with front bearing band .314, to just kiss the rifling lands, with the succeeding bands each a couple thou larger. The last three bearing bands is what I would like to get feedback about.

What-if, the base band is right at groove diameter but the two bands ahead of it are .001 or even .002 over groove diameter? This would ensure a good tight fit in the bore without having long fins drawn off the bullet base during its passage down the barrel. To object being to have bullet exit the muzzle with the base edges as square and sharp as possible. With those two bands only being a thou or two larger diameter than the base band, I don’t foresee any problems in pan lubing them. This bullet would, of course, only be breech seated.

Comments, please -

I am with Frank in regards to using a wad and I would recommend using 30 thous. vegetable fiber not only to provide an additional gas seal but to also protect the base of the bullet. 
In regards to the base being groove dia. to reduce the possibility of creating fins I have been chamfering the bases of my bullets for years with excellent results to allow for any lead being pushed back that would then fill the void I created. In regards to the bands ahead of the base being 1 or 2 thous. larger I think 1 thous. would be ideal from my past experience.

Before I spent any money for a new mould due to a fining issue and or concern taking place at the base of the bullet I would try chamfering the base first. I do this with a RCBS inside outside chamfering tool and simply cut off that little tit on outside chamfering end of the tool and I take a couple of light cuts by turning the tool by hand which creates a small bevel and due to the design of the chamfering tool the base of the bullet self centers and will appear to be per say perfectly round. This process also removes any lead that might be pushed towards the outside edge by the sprue plate on base pour bullet moulds of which I found to be quite typical that I always felt had a tendency to make it somewhat unbalanced?

J.Louis

Crash, I believe you might have a viable idea. Seems to me that in order for there to be gas cutting there would have to be a flow of gas past the bullet. The sealing band ahead of the base band should work just fine.

Bill

Thanks guys for the feedback. It all gives me good food for thought.
J Louis
My base-pour bullets have nice sharp bases but chamfering that edge may have some merit although bullet fins are not currently a problem. I do wander about consistency in chamfering the base bullet-to-bullet. Seems like an opportunity to introduce another variable. If for nothing but to satisfy my curiosity though, I will definitely give it a try. 

I agree that a thou over groove diameter is the best rule of thumb. My current bullet is actually about a thou-and-a-half over. That mould was purchased off-the-shelf and shoots significantly better than my previous bullet which is why I’m still shooting it.

frnkeore
Maybe I’m missing something but I don’t see how a bullet with groove diameter base band would make it susceptible to gas cutting as the bore would be tightly sealed by the breech seated bullet. Plus there is a slight additional amount of metal displaced by the rifling lands which further expands the bullet diameter to seal the barrel.

Those bearing bands ahead of the base band could well be useless, that’s why I’m asking, in hopes that someone else may have tried it or if it’s just another of my hair-brained ideas.

I have not used wads with smokeless loads and breech seated bullets since the late 70’s. The why is too long a story for here but my choice to eliminate wads when shooting smokeless was on the advice of ol' 7 groove.
Chuckster
I can image such a bullet design would be a mess using a lube pump or lubrisizer, that’s why I would pan lube if I have such a bullet made.

Using tapered the Mos spitzer previously mentioned, this rifle is a reliable 3/4 minute performer. My end-game is to consistently squeeze my 200 yard groups by 1/4 inch so I can turn more of those 248 and 249 targets into 250’s.