Measuring Cylinder Throats

[Bob R]

Every time I see a thread that involves the 45 Colt and the S&W model 25-x (usually 25-5) I see a reference to measuring cylinder throats.

I have an Austin Behlert 25-5 that I am going to start reloading for, and I would bet the throats are just fine....but.. do I really know?

So, if someone could tell me (with pictures would be best, small words second best ) what I would need to do to measure the cylinder throats on my 25-5 to ensure I buy the right bullets so that I can get the optimum accuracy from the gun. BTW, it shoots factory 45 Colt fodder like a champ.

bob

 

[Skip Sackett]

Bob,
That factory ammo may have swaged bullets and not real cast ones. That could account for the good accuracy as they are more forgiving when it comes to size. I was at a range recently in Missouri when a guy let loose with a lever action rifle. I asked what caliber it was and he said: 45 Colt. Now this is no kidding, it sounded like a 38spl it was so light. They were Cowboy Action loads.

At any rate, a set of pin gages is the way to measure cylinder throats. Few of us have them. They may be available from Harbor Freight though. They are usually .0005" under a nominal size, such as, .452" would be .4515". Simply insert the largest on that will go all the way in, stop when you have to.

I use a simpler method, bullets. Of course, I cast. I use an as cast bullet, measure it. If it doesn't push through the throats, I size it, measure it and try again.

Fortunately, all of my 45 Colt guns are .452". M25 -7, Ruger 45 Convertible and a Puma rifle.

If you are going to shoot standard type loads, a .454" bullet is going to work in either commonly sized throat.

FWIW

 

[k22fan]

Use ball gauges.

Bob,

Using bullets as Smith Crazy suggested works but limits you to the diameters you can scrounge up which probably isn't very many diameters if you haven't been accumulating bullet casting and resizing tools for years.

Presuming you have a micrometer or profesional quality calipers all you need is an expanding ball gauge which is a common tool in machine shops. They were not expensive back when I bought my set. I don't have a camera but I know a few small words. Rotating a ball gauge's handle moves its tapered center shaft in or out between the two halves of the ball end. Holding the ball inside a throat you expand it until you feel light contact then pull it out and measure the ball.

A set of pin gauges looks more convient and precise enough for measuring throats but can not produce measurements in between the size difference between pins or measure how much out of round a hole is.

Whatever method you use be sure your throats are clean or you'll get a false measurement.

Smith Crazy is right about the factory cartridges. The factories have used a variety of .45 Colt bullet diameters in the last 140 years. The old fashioned Rem. 250 gr. and Win. 255 gr. round nose bullets with the small flats on their noses have not changed much if at all in that time. They are approximatey .456" soft swagged lead with follow bases so they squeeze down or bump up to fit.

Best Regards,
Gil

 

[dickttx]

Not an expert by any means, but this is discussed at length on one of the Ruger forum.
Use jacketed bullets and try to push them through each chamber from the front with your finger. If they will push through that chamber is OK, if not it is too tight.
I tried this on a couple of Colt 357's, a Redhawk 41, and a Blackhawk 45. No problems with any except the Blackhawk. Last friday I sent it to be reamed.

 

[acl864]

Small Hole Gage .300" to .400"

This is the expanding ball gage k22fan is talking about.

 

[Beans]

Bore size on the US .45 Cal weapons have been .452 since WWII.

Colt Cylinder throats according to the Customer service rep at Colt can vary from .454 to .460 and still be within thier specs.

I almost dropped the telephone when I heard .460 and ask him to repeat it. He Did :-(

My complaint was that my 3rd Gen Colt had cylinder throats between .456 to .457 as measured with a set of "minus" pin gauges.

They told me I could send the gun in and if the cylinder throats were with the above stated specs nothing would be done.

The only choice was to send the gun to a SAA specialish and spend another $600 to have a different cylinder bored with .452 throats.

I haven't done it yet as it would push my $1,300.00 Colts to almost $2000
USFA cylinder throats on their .45 Cal weapons on the 6 that I have measured are .452-.452.

 

[Skip Sackett]

Nonsense!

I haven't done it yet as it would push my $1,300.00 Colts to almost $2000
USFA cylinder throats on their .45 Cal weapons on the 6 that I have measured are .452-.452.

This is one reason that I refused to purchase a Colt 1911. The ones we had in the Corps were so sloppy that you could throw it at the enemy instead of shoot at them and do about as good.

Then I got out and found that you could purchase a really nice 1911 and to get it to feed some bullets you had to have it worked on. Of course, that was after you paid $1000 for the gun alone! Um, again, no thanks.


The first full size 1911 that I bought was a Smith & Wesson. It cost me somewhere in the neighborhood of $550 brand new and ate everything I fed it.

I own a Taurus now. PT1911 and had I purchased a Colt with all of the stuff on it that it has, the Colt would have cost me upwards of $2000! My PT1911 cost me $450 brand new and shoots like a dream.

Sorry for the thread drift.

 

[k22fan]

Sorry for the thread drift.

You're forgiven. Beans steered you off topic and I surely enjoyed reading both of your posts.

Colt Cylinder throats according to the Customer service rep at Colt can vary from .454 to .460 and still be within thier specs.
The only choice was to [...] push my $1,300.00 Colts to almost $2000

This kind of disregard for how their handguns shoot has led me to believe that Colt's marketing people think the best profit can be squeezed out of their historical brand by building pistols for collectors to look at or for inexperienced customers who choose based on their famous brand. Back in the 70's I learned by experience that active shooters generally get better value for their dollar in other brands including good old S & W. That hasn't changed and probably won't change in my lifetime.

Best Regards,
Gil

 

[Bob R]

Thanks for the replies, I think I will head on over to the local machine shop, chat awhile and have them measure the throats for me. I am 99.9% certain they are exactly where they belong. I can't see Austin Behlert sending out a gun other than perfect. Thanks again.

bob

 

[Hexer]

I second the small hole gauge and micrometer. I have a 25-2 Model of 1955 .45 ACP. I had heard there may be problems with that model and there was. The Chamber throats measured .456. As with my Colt SAA 3rd Gen. the throats are .457.

 

[k22fan]

25-2

[...] I have a 25-2 [its] Chamber throats measured .456. [...]

What vintage is your 25-2?

 

[Gun 4 Fun]

Grizzly Industries sells some really nice pin (plug) gauges in plus or minus sizes. They come in kits that contain 250 gauges that run from .251"-.500" which are best suited for most guns.
The plus sizes are .0002" over nominal, and the minus are .0002" under, which makes it possible to get very accurate readings. The minus are the best for checking throats.

Worrying about whether or not a chamber throat is out of round is a waste of time in my opinion, unless some, (or all), of them are noticably out of round. You can't size bullets for out of round, but you can size them to match throats as closely as possible. While a bullet can and often does obturate the to the throats they pass through (depending on pressures and bullet composition), the entire bullet doesn't, just the base, which helps seal of gasses and align the bullet with the bore. A bullet passes through a throat so quickly that is extremely doubtful that the entire bullet would have a chance to become out of round (provided of course that the portion of the throat that is out of round is not actually smaller than nominal bullet diameter).

Bob R-
whenever you read those posts, they're probably by me, or someone asking me about it. It is an issue that should never have been, since the factories all had/have the technology to make the throats in their guns corrctly match the bore. It is a real shame that so many fine .45 Colts can't shoot up to their potential because of the factories not wanting to update their equipment until forced to do so. The .45 Colt is my favorite handgun round/caliber, and just knowing that the factories did this really gets me going. I always try to point out to those who are asking what to look for, and how to work with one, if they happen to get one that has oversized throats.

 

[Chubbs103]

You can also slug your chambers and measure them this way. Slugging involves pushing soft, pure lead through each cylinder and then measuring what you get on the other end. Some people use fishing weights or other sources, but you can buy kits specifically for this purpose. You can also slug your barrel to find out the the minimum of the bore.

Chubbs

 

[cp1969]

It wasn't just Colt putting oversize cylinder throats in their guns. The S&W model 25 had 'em; so did my Ruger Blackhawk (.457"). I'm not sure what the thinking was behind this other than the fact that the standard .45 Colt factory load used a swaged, hollow-base design bullet that would swell up to fill any size of cylinder throat. They were also sized .454" for many years. Shooting .454" dia bullets through .452" dia throats isn't the best idea, either, so maybe they were thinking about people shooting OLD ammunition in their new guns.

Plug gages are the best way to measure throats. There is error, not much but some, in using ball gages or telescoping plug gages, there is also error in the measuring instrument itself. You can read a diameter to within tenths on a digital caliper, but that does not mean what you're reading is the true number. Micrometers are better, but have the same calibration and "feel" problem. The number you get with the plug gage is the number, within the tolerance specified for it--they rarely go out of calibration.

 

[Hexer]

To answer K22fan's question, my 25-2 is circa 1980 with 6 inch barrel. A beautiful gun, but unfortunate about the chamber throats. I'm experimenting with different bullets and loads to try to negate some of the problems.

 

[rodell]

Enco offers inexpensive, but plenty accurate, plug gauges. They are imports and work well. My set goes from .2501 to .5501.

 

[k22fan]

[...] Worrying about whether or not a chamber throat is out of round is a waste of time [...] /QUOTE]

I did not mean to imply that you would get useful information by measuring out of roundness in S&W throats. I only meant to campare tools.

Incidently, the information you have been posting on .45 Colt throats has been great stuff.

[...] I'm not sure what the thinking was behind this [oversize throats] other than the fact that the standard .45 Colt factory load used a swaged, hollow-base design bullet that would swell up to fill any size of cylinder throat. They were also sized .454" for many years. Shooting .454" dia bullets through .452" dia throats isn't the best idea, either, so maybe they were thinking about people shooting OLD ammunition in their new guns.

There is error, not much but some, in using ball gages or telescoping plug gages, there is also error in the measuring instrument itself. [...] and [the] "feel" problem.

The Win. 255gr. RNs with the small flat points have been .456" for well over 100 years and are representitive of common factory loads when Colt, S&W and Ruger started manufacturing .45 Colt revolvers. Compared to that load .458" throats are no more oversize than Model 24, 29, 624 and 629 throats were up until the British owners tightened S&W .44 throats. The gradual change to .452" .45 Colt bullets was primarily responsible for the problem.

Learning a consistant "feel" with measuring tools comes with experience. With plug gauges you can only say the diameter is somewhere between two numbers a thousandth apart. I can take a measurement with less uncertainty than that with ball gauges although it barely matters for throat measurement.

You can also slug your chambers and measure them this way. Chubbs

Thats a good idea that eliminates the need for any tools other than your micrometer or calipers. I didn't think of it simply because I've had my small hole gauges for so long.

Best Regards,
Gil

 

[Gun 4 Fun]

Gil,

I'm sorry if my post seemed to be taking a shot at you or sounded harsh. That was not my intent, and I realize that no one can hear the inflextion in another poster's voice on a forum, or know their demeanor. Again, no offense meant to you.

I have read many other posts regarding the out of round throat issue, and most guys don't realize that it is fairly common because without the right tools, there's no good way to check, and most of the time we are only talking about a thousandth or so at most.

I just don't worry about that issue, because the only way to correct it is to ream the throats, and then you can wind up with oversized throats (if you didn't already have them), and no one wants that.

 

[cp1969]

Weren't the throats reamed at the factory? In what little knowledge I have of machining, we would center drill & drill to remove rough material, bore to get location, then ream for size.

 

[Gun 4 Fun]

Weren't the throats reamed at the factory? In what little knowledge I have of machining, we would center drill & drill to remove rough material, bore to get location, then ream for size.

Yes, but like anything mechanical, reamers wear, and it only takes half a thou to allow 2-3 times that much wobble/wollow in the critical throat area. Reamer fixtures also delevope wear over time. On top of that minute differences in material hardness can play a hand in out of round throats.