Bump Dies

[alamogunr]

Someone in another thread mentioned using bump dies to increase nose diameter. Bump dies have been part of many posts over time but despite the explanations, I am still somewhat in the dark as to what they actually do, what situations call for them and what the benefits are.

Can some of you enlighten me?

[felix]

A bump die is a swage die. ... felix

[Bent Ramrod]

A bump die is typically a specialty item supplied by the gunsmith who chambered the barrel, or a specialist who can work off a chamber cast. It takes a cast boolit (generally from a custom mould) and squeezes it slightly so the nose is an exact fit to the chamber leade. Last I paid any attention, the Cast Bullet Association's official position was that bumping wasn't swaging, but of course, as Felix says, it is. The boolit is changed in shape through pressure, which is the definition of swaging. It isn't completely changed in shape, just slightly in the nose, which is where the "bumping" designation came from. Swaging was illegal for CBA competition, but bumping was permissible, at least in the old issues of Fouling Shot that went into the argument in depth.

Mostly, this is an operation for the advanced experimenter and the hard-core benchrest competitor. The rest of us can get a crude approximation of bumping (if necessary) by selecting a relatively soft alloy and putting a little judicious extra pressure on the sizer/luber lever. Too much pressure and there will be "slumping" as well as bumping. A custom nose punch that covers the nose completely might mitigate this, if someone wants to take the trouble to make one.

I think in the average rifle that seating the cast boolits out into the leade would suffice. Subject to correction by the more experienced here, I've never seen any particular advantage to the kind of bumping that can be accomplished in a sizing die, and I'd rather spend the money on a good mould than a real bump die.

[Le Loup Solitaire]

It is/was a practice used by many handloaders to increase the nose section of cast bullets to make them fit the bore...specifically to better the land(s) riding qualities. I first read of it in an article by a gentleman names R. Sears a well known member of the Cast Bullet Association and an exemplary marksman. He discussed using the bullet luber/sizing machine to do this, but pointed out that he himself had broken a number of his own machines by "overdoing it". This means that a lube/ sizer although it can do the job , is prone to breakage if pushed. It would logically be better to use a regular press if possible as the press would handle the stress better. Mr Sears also would test his bullet noses first by inserting them into the muzzle-nose first. He did also advocate having a separate die made to do the bumping in. The article he wrote appeared in the NRA Loading handbook/supplement. LLS