De-finning A Beagled Mold

[calinb]

I beagled an RCBS .250-50-RN (57902) mold, which drops .251 in pure lead, for my Lothar Walther airgun barrel. With a single .002 layer of aluminum beagling tape on each side of the mold, I experienced a very fine line in temperature / pressure between good fill-out and finning and air vent fingering. Here's how I completely eliminated the problem. I don't know whether others have done the same, but figured I'd post about it here in the original beagling forum, just to be sure. In fact, the technique worked so well that I'm planning to increase the tape thickness and beagle the mold up even more for my barrel, which slugs .248 / .254. With only two .002 tape layers, I can't currently size the beagled bullets larger than about 252-3/4 thou, without sacrificing roundness.

I removed the mold from the handles and inserted two nicely beagle-cast bullets (no fins or fingers) to mask the cavities. I pressed them firmly into place in their original positions (with their faint seams aligned with the cavity edges). Next I used masking tape to cover the beagling tape, but I made sure I left the bare region around the cavities unmaksed. Finally I sprayed two or three thick and wet coats of Frankford Arsenal Drop Out to the mold faces from the rattle can. (I have finally found a use for Drop Out! ) I applied enough "paint" to pretty well fill the mold vent lines.

After the Drop Out dried, I carefully plucked the bullets from the cavities and removed the masking tape, being careful to not disturb the underlying beagling tape. Here's where I noticed an unexpected and pleasant surprise. Whereas I only expected to mitigate the fingering at the vent lines, I realized that finning elsewhere around the cavity would likely be reduced (up around the nose of the bullet), because the Drop Out created a small fillet at the edge of the cavity between the mold block faces and the masking bullets. When I removed the bullets, the fillet remained.

Finally, I cleaned up a little Drop Out overspray with denatured alcohol and Q-tips. I was careful to not disturb the small fillets or filled vent lines. I've now cast a few hundred bullets and the result is no finning or fingering at all--even at higher temps and pressure to fill the little 25 cal. mold reliably. I also found the beagled gap between the mold halves to be fully sufficient for venting.

Give it a try sometime and I hope it improves the results of your beagling!

[dondiego]

I understand "finning" but what is your definition of "fingering" in this instance?

[BNE]

Great idea.

[calinb]

I'm calling the spikey thin lines of lead that leaks into the vent lines "fingers," as opposed to fins, which are wider. On my beagled RCBS .250-50-RN mold, I tended to get "fingers" near the driving bands where the vent lines are located and, somewhat less often, a fin up around the nose where there are no vent lines. That is until I applied the Drop Out.

I have two layers of .002 tape between the mold halves now, but will soon strip them, clean the mold, and redo it with two layers of .004 tape. I'll report back here how well the de-finning process works with a total gap of .008! It would be wonderful if the extra width results in fairly clean castings that resize well to .254. I know I'm really trying to push the beagling envelope in going from .251 to .254+ and also expecting the bullet to be reasonably round after resizing (requiring a lot of extra beagled width).

[calinb]

After doing a bit more research , I think some people call the undesirable vent line leakage "whiskers."

[JBinMN]

Pictures?

[calinb]

My good closeup camera has a frozen iris. I unstuck it once before, but guess I need to try again. (It takes about two hours of fussing with very, very tiny parts.) Maybe I'll try a very small amount of dry silicone lubricant on the plastic iris this time.

But I digress. This isn't a digital camera repair forum so maybe I could try to use my smartphone to take some photos of the mold and castings, before and after, but my smartphone has never done very well with closeups. I'm about to remove the two layers of .002 tape and and replace it with .004 tape.

[JBinMN]

I just thought it would be nice to actually "see" what is being talked about. It helps me sometimes to get a better grip on what is being done.
Thanks!

[kbstenberg]

Another suggestion is to use Saran wrap between the mold halves.
I use High temp gasket sealer regular tinfoil (to add thickness between mold halves) put the Saran wrap between the molds. Clamp them together for 24 hrs and pull apart. Kevin

[Grmps]

I've been curious about this for some time, why beagle a mold and get out of round bullets, fingers, whiskers, fins when you can leement(polish) a mold and get a round larger cavity?

[calinb]

By the time you achieve two or more thou of additional width, you are "lapping" more than merely "polishing," if you enlarge a cavity with abrasives. I have lapped mold cavities too. They don't stay round beyond a small increase in size either--even with careful and painstakingly slow work. The lapping compound tends to build up at the mold seam and do more work there. Beagling is faster and reversible (or partially reversible, when you go past the "sweet spot")!

Finally, as others have noticed in various threads on beagling, beagled bullets aren't as far out of round as you'd expect. Yeah--across the seams it's "arithmetic" but across other points between the seams and square measurements, you typically get more width than you'd arithmetically expect.

[S.B.]

Aren't the fingerings lines,as you call them, meant to provide cooling to the mold?
Steve

[calinb]

Aren't the fingerings lines,as you call them, meant to provide cooling to the mold?
Steve

They are meant to provide venting, but they don't seem to be needed once the mold halves are separated with the beagling tape. (The beagling gap provides sufficient venting.)

[S.B.]

As your mold creates leakage? I always adopted the theory I didn't want to recreate the wheel.If your mold isn't big enough get a bigger one.
Steve

[calinb]

As your mold creates leakage? I always adopted the theory I didn't want to recreate the wheel.If your mold isn't big enough get a bigger one.
Steve

Sounds like beagling isn't for you! For many, it's proven to be a useful (and completely reversible) option. I'm just suggesting a method to solve a problem that sometimes may occur when beagling, for those who beagle molds. Some people like dippers while others like bottom pour. Some people like multiple cavity molds while other like singles. Some people like GCs whereas other like plain base,...etc.

[calinb]

I just thought it would be nice to actually "see" what is being talked about. It helps me sometimes to get a better grip on what is being done.
Thanks!

Here's the masked mold. The metal aluminum beagle tape is masked by the blue tape and bullets mask the cavities.


The final of several thick, wet coats.



After removing the blue masking and bullets. The cavities have no "paint" in them.


If you are a beagler and ever get fins or "whiskers," give it a try! It's easy to remove the paint with solvent later, if desired.

[KenH]

Your photos sure make it clear - GREAT job!

[JBinMN]

Your photos sure make it clear - GREAT job!

Yes! +100


Thanks calinb!

[calinb]

Your photos sure make it clear - GREAT job!

Yes! +100


Thanks calinb!

Thanks guys! Glad it helped. BTW, I used denatured alcohol and one of those nylon gun cleaning "toothbrushes" to remove the old "paint" and beagling tape residue when I re-did the process for the photos. I always try to use the least nasty solvents first and denatured alcohol worked great here. I even put my masking bullets into a little bottle of it and swished it around to clean them up before re-use.

[byrd45900]

Ive always called that "whiskers" too.