design strategies for Freedom Arms revolvers

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mtngun
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design strategies for Freedom Arms revolvers

Postby mtngun » Thu Feb 21, 2008 8:01 pm

from the old forum, and by the way, I've never owned an FA (something about raising kids) so take my advice with a grain of salt:

FA's are great guns and I just wish I had one (or two). Due to their tight dimensions, some cast bullets with long, full diameter front bands may not chamber easily. Here's a few ways to deal with it.

Reduced diameter front band. Here the front band diameter is 0.450" so it should slide into the throat easily. The body is sized 0.452" or 0.453" to create a good gas seal.
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Short front band followed by secant ogive.
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Short front band followed by step. Use the bore riding option to step down to maybe 0.449" - 0.450". The 0.449" section will enter the throat easily yet still provide some guidance and support when the bullet enters the barrel.
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What I would do. Short nose, short but full diameter front band, and secant or truncated cone ogive. The short nose results in a deep seated bullet, with lots of bearing length and lube. Basically the same general design that I shoot in my Ruger 357 for all the same reasons.
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EdK
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Re: design strategies for Freedom Arms revolvers

Postby EdK » Wed Jun 25, 2008 4:42 am

I'm fairly new to casting and am very intrigued with cast bullet design. I do own a FA revolver in 454 Casull and would like to get a mold specifically for it. I'm now performing my own due diligence so that I'm not asking anyone to design my mold, will fully understand what I'm asking for/getting and hopefully don't wind up with a piece of scrap metal (my fault). I believe I've measured my revolver quite accurately but still am a little confused by the need to come up with designs to specifically accomodate front band diameters to properly fit FAs.

"Tight tolerances" are mentioned as the culprit. Is this the same as undersized throats? I've actually been hearing quite a bit of that in regards to FA revolvers and am a little surprised as the throats in my revolver are running pretty close to 0.4525" as best as I can measure using a combination of Starrett brand hole gauges, micrometer and bumped up slugs. So provided throat diameter is a little over bore diameter I do not understand the purpose of undersizing the driving band.

Thanks, Ed

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mtngun
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Re: design strategies for Freedom Arms revolvers

Postby mtngun » Wed Jun 25, 2008 6:05 am

Let us assume that we are sizing our bullets to throat diameter or up to 0.001" larger. In the case of your 0.4525" throats, that means the bullets are 0.4525" - 0.4535" . It may be that your gun would shoot undersize bullets equally well, providing the bullet obturated quickly, however, a properly sized bullet is a safer bet.

Let us further assume that your sizing equipment will size your bullets to exactly 0.4525". In reality, it is normal for sizing dies to be off by 0.001" - 0.002", and it is normal for sized bullet diameter to vary depending on as-cast diameter, hardness, lube, technique, etc., etc.. We will nevertheless pretend that our sized bullets are a perfect 0.4525".

OLD WIVES TAIL: A correctly sized bullet will enter the chamber throat with light finger pressure.

REALITY: For reliable chambering, clearance is required. At least 0.0005" and probably more like 0.002". If your bullet can be pushed through the throat with light finger pressure, then the bullet is too small.

AND FURTHERMORE: I don't want to PUSH my revolver cartridges in the chamber. Cartridges should DROP in effortlessly.

In mass produced wheelguns, there is usually a grossly oversized tapered section in the chamber just forward of the case mouth. I'm not sure what this section is properly called. It allows an oversize front band to be chambered, as long as the length of the front band does not exceed the length of the oversized tapered section. Thus our mass produced gun is usually content to chamber a 0.453" or larger front band.

In a well made wheelgun, like an FA, there may not be a grossly oversized tapered section in the chamber, just forward of the case mouth. The chamber's tapered section may be shorter, or it may be smaller in diameter. A conventional bullet with a long front band of exactly 0.4525" diameter may not drop into the chamber. Hence FA bullet designs may utilize either a very short front band, or else a slightly undersize front band.

To shed more light on your situation, you would need an impression of the chamber.

EdK
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Re: design strategies for Freedom Arms revolvers

Postby EdK » Wed Jun 25, 2008 11:41 am

OK - learned a little more today. I thought throats were a cylinder. Now I have learned many have a taper. Looks like I've got more measuring to do.

Thanks for the reply, Ed


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