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Throat dimensions

This is a discussion on Throat dimensions within the Reloading forums, part of the Firearm Forum category; Okay. As you folks may know, I'm getting ready to reload for 44 Magnum. I've gotten most of my supplies on order (or backorder...) except ...

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Old February 3rd, 2011, 10:21 AM   #1
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Question Throat dimensions

Okay. As you folks may know, I'm getting ready to reload for 44 Magnum. I've gotten most of my supplies on order (or backorder...) except the bullets.

I was in the process of ordering some 0.430" cast bullets, when the supplier, Beartooth Bullets, recommended that I check the cylinder throat diameters before ordering as they generally recommend a 0.432" bullet for the SBH. I did, and my Ruger Super Blackhawk 44 Mag has throats sized at 0.432" based on slugging I did and my handy brand new dial caliper. It was dead on 0.432".

So, now I'm torn as to what size to get. It seems to me that 0.432" would make the most sense, but I simply don't know from a practical standpoint. I haven't slugged the bore, ASSuming it's around 0.429 or 0.430".

I really need some advice. Like I say, if it were left to me right now, from all I've read, the bullet needs to be the same diameter as the throats or maybe 0.0005" smaller, meaning 0.432" diameter would be the best fit.

(Can you hear my pain, Iowegan?)

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Old February 3rd, 2011, 12:00 PM   #2
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Tater, yup, I do feel your pain. If your throats are indeed .432", then you want a bullet just a tad smaller (.4315" max). Why? Because when you chamber a round in your cylinder, the bullet must fit in the throat or the cartridge will not chamber without force. I have my doubts when measuring a round hole with a caliper because all it takes is a wee bit of pressure on the caliper to corrupt the reading. A pin gauge or even a factory bullet is a much better test. The normal throat diameter for Ruger 44 Mags is .4305~.4315 (.431" +or- .0005") so it would not be normal to see .432" throats. Ruger bores are very uniform and typically run from .4295 to .4305" (.43 +or- .0005")

If your bullets are larger in diameter than the throats, they will get swaged down to actual throat diameter as pressure forces the bullet through, however they may not chamber easy. If the bullet hardness matches chamber pressure, and the bullets are about .001" smaller than throat diameter, pressure will bump up the diameter to actual throat diameter. So either way, the bullets will be delivered to the forcing cone slightly larger than bore diameter. This is good.

Where you run into problems is when throat diameters are too tight or bullet diameters are too small. This will result in a poor bore seal and will lead foul the bore. It also increases chamber pressure considerably when bullets are larger than the hole you are trying to push them through. Any bullet measuring .430" should work just fine in your gun, assuming the lead hardness matches pressure in your intended load.
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Old February 3rd, 2011, 12:54 PM   #3
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Well, one of my original "tests" for throat diameter was to put in a jacketed bullet, taken as 0.429" and a lead bullet, taken as 0.430". I took the whole cartridge and slipped the bullet into the throat. The "feel" was that the .429 bullet had a bunch of play and the .430" bullet had, what seemed, to be about half the play, which I had originally estimated as being a .431" throat.

I think I'll get a small order of the 0.430" and assume that the gun is built per spec, a good assumption with Ruger, and see how they work out. I'm guessing just fine.

I intend the pressures to match hardness well by the time I finish working up my loads.

Thanks once again, Iowegan!
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Old February 5th, 2011, 08:03 AM   #4
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Go with .432", if that's what your cylinder throats measure. My SBH measures pretty much the same as yours and I try for.432" size as .002" over groove dia seems right for my gun...
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