Measured some magnum throats

[sasu]

I got a pin gage set today from eBay and ran to the safe straight away.

According to the pins I have the following throats in these revolvers:

S&W 29 Mountain Gun 44 Mag 0.429"
Ruger Super Blackhawk Hunter 44 Mag 0.432"
Ruger Super Redhawk 454 Casull 0.454"

I show the reading on the largest pin that entered the throats, so the actual size is more than the value shown but less than the next pin which is 0.001" larger.

I will post the measurements from the rest of my revolvers when I have the time to measure them.

Take the measurements with a grain of salt as I have no way of knowing the absolute accuracy of the pin gages and neither my technique of using them. But the relative values should be very accurate.

If I remember correctly tight throats are better for cast bullets so that hot gases would not burn the sides of the bullets. Wide throats require jacketed bullets which are not prone to melt on the sides and can be driven with such force that they can expand to fill the throat better.

The thumb rule was that the bullet should be 0.001" larger than the throat and the throat should be 0.001" larger than the barrel groove diameter.

 

[Protocall_Design]

Gage Pins (Pin Gages) are the easiest way to get an accurate reading of small hole sizes. The more common sets are minus, meaning the pin is .0002 (2 tenths of a thousandth) smaller than the size marked on it. That allows it to go into a hole of that size. If it were exactly on size, with a hole exactly on size, then it would be a light press fit. You don't want to press fit a gage pin into a hole, as that damages it. With practice, you can get a pretty good idea of the hole size depending on how much wiggle room there is for one pin but not the next size. Your measurements are correct to the nearest thousandth (.001). There are also plus sets that are .0002 over nominal. The box should specify + or - for the set and there should be a + or - next to the pin size on each pin.

 

[sasu]

I have a minus set. I inserted the gages very, very gently. If a pin would not enter the throat on its own weight and some gentle wiggling I would give up on that size.

 

[Protocall_Design]

That is the correct way to use them.

 

[DWalt]

There is also a hole diameter gauge which spreads or expands a split-ball tip by means of a screw thread. You set the gauge until it just fits the hole, then measure the diameter of the gauge tip with a caliper or micrometer. They usually come in a set of different sizes. Pin gauges are probably a little more reliable and precise, but I normally use the spreading ball type.

 

[sasu]

I have already tried the spreading gauge but I did not get consistent results, that is why I finally bought the pin gages. It is very nice to know the throat diameter, it should speed up the development of accurate loads.

 

[k22fan]

I believe I am more accurate with small hole gauges of either the expanding ball or T shaped type combined with a mic marked to .0001". While I'm not confident about the final .0001" even plus or minus .0002" is better than pin gauges. Also, small hole gauges will tell you if a hole is out of round. Pin gauges will not. The main advantages to pin gauges is they are fast and require no skill. They are however more than adequate for making guesses at which bullet will shoot most accurately.

 

[lebomm]

Just as an FYI, folks, the technical term is "plug gauge".

Cheers,
Larry

 

[Protocall_Design]

There are also threaded and tapered plug gauges. Gauge pin narrows it down a little more.

 

[BLUEDOT37]

I got a pin gage set today from eBay and ran to the safe straight away.

According to the pins I have the following throats in these revolvers:

S&W 29 Mountain Gun 44 Mag 0.429"
Ruger Super Blackhawk Hunter 44 Mag 0.432"
Ruger Super Redhawk 454 Casull 0.454"

My pin gauge set is the first thing I grab for, when I bring a new gun home, so I can document it's specs. It's surprising (sometimes not good surprises) the variations you get from gun to gun.

My 29-2 has the "typical for the time" .432" throats while my 396's are tight at .4285".

My Ruger SRH 454C had .454-.455" throats too, not good for .452" cast bullets. Ruger said to send it in for repair, then told me it wasn't repairable (?!?) & would send me a new SRH. The new one had the same sized throats. I sold it as new & bought a M460 (.452" throats) instead.

I like to use them to check the barrel's bore for size & constrictions too.

Pin gauge sets are good backdrops also.

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