Tumble Lube "Mini" grooves

Old Ironsights
Posts: 4
Joined: Mon Jun 30, 2008 1:53 pm

Tumble Lube "Mini" grooves

Postby Old Ironsights » Mon Jun 30, 2008 1:58 pm

I've been working on a 9.3mm bullet for a 9.3x72R. Fairly low pressure, no GC Needed.

However, I tumble lube. SO, I worked the program and came up with this:

Image

Very pretty, and almost exactly what I want.

But the system won't let me order it.

Is this type of small groove somthing the system/lathe just won't do?

(Pertinate data for people to try: 205gr .367dia, TAN, .070 front band, .375 nose, .100 base, no crimp, 70% Meplat, 4 bands, 4 grooves, band length .04, OAL .775)

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mtngun
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Re: Tumble Lube "Mini" grooves

Postby mtngun » Mon Jun 30, 2008 5:46 pm

There is a minimum for the band length, because 1) the band has to be at least as big as the boring bar and 2) itty bitty bands will not cast well, especially as weight and diameter and groove depth increase.

I could not get the online program to acknowledge your specs, nor should it.

The minimum band length for your bullet is about 0.056". The cutting edge on my boring bar begins life around 0.055" thick, so there is no way I can cut a 0.040" band.

Even a 0.056" band may cast poorly when combined with my relatively deep, angular grooves. Diameters become a crap shoot. I cannot guarantee a 0.002" tolerance if as-cast diameters vary 0.010" from one pour to the next.

Bigger calibers have a bigger minimum band length because filling small bands becomes more difficult as weight and groove depth increase (and remember, my grooves are deeper than Lee TL grooves, and also shaped differently).

Some mold makers may get away with a more petite cutting edge because they only cut aluminum and because they only cut shallow grooves. Such petite tools will quickly fail if used to cut a Keith bullet in an iron block.

Mountain Molds has no plans to spend thousands of dollars on tooling and programming to introduce a new product that competes directly with Lee. We do not wish to be associated with Lee. If you want a Lee design, Lee will gladly make it for you.

The other issue is, why do folks think that tumble lube requires a special design ??? Any grooved bullet can be tumbled lubed, particularly Loverins. Get a conventional bullet that leans toward the Loverin style, and lube it any way your heart desires.

Old Ironsights
Posts: 4
Joined: Mon Jun 30, 2008 1:53 pm

Re: Tumble Lube "Mini" grooves

Postby Old Ironsights » Tue Jul 01, 2008 9:47 am

Thanks much. Answers all of my technical questions.

FWIW I think the reason the microgrooves are popular for tumble lubing is that the bullet weight can be bumped up as the lube mass decreases without lengthening the bullet.

But that's only a layman's guess. :)


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