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Old November 28, 2022, 11:18 PM   #1
jski
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Chamber throats in LCR cylinder?

I just purchased a new .327 LCR and was measuring the chamber throats. I first noticed that with all but one chamber I could drop my XTP bullets straight thru. So I measured the throats and got .3105”, .3140”, .3125”, .3130”, .3115”, .3140”. Those numbers aren’t anything I would think are acceptable for chamber throats.

Does this need to go back to Ruger or is it acceptable for a snubby?
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Old November 29, 2022, 01:43 AM   #2
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Bullets should drop through. The chamber throats shouldn't be swaging the bullets down in diameter.

I would expect all the chamber throats to measure pretty close 0.314" based on SAAMI's specs.

https://saami.org/wp-content/uploads...sting-Copy.pdf

That said, if the gun is shooting well, I wouldn't worry about it. If you were trying for extreme accuracy, swaging the bullet down before the jump to the barrel usually isn't ideal, but with a snubby, I don't think you'll be able to see the difference.

If it bothers you, you could contact Ruger about it, or maybe see about having a local gunsmith ream the throat on the tight chamber by a very little bit. Sounds like just a thousandth will do based on your measurements. The bullets are only getting stuck in the 0.3105" throat but are passing through the 0.3115" throat.
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Old November 29, 2022, 05:02 AM   #3
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I've always thought the throat diameter should narrow down to ~.001 less that the grove diameter? So for a 32 cal round with an canonical grove diameter of .312 the throat diameter should be .311.

If that's not true, what should the ideal throat diameter be?

Last edited by jski; November 29, 2022 at 05:26 AM.
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Old November 29, 2022, 05:53 AM   #4
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How are you measuring? If your using a calipers I’d be leery of those measurements. The best way to measure them would be with pin gauges for a more true measurement.
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Old November 29, 2022, 07:02 AM   #5
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Assuming your bullets are FMJ, I'd put a piece of tape on the chamber with the loose throat.

Then take it to the range and shoot at two targets, one target for the marked cylinder and the other target for the rest. Compare group sizes and location. If they look the same, call it good.
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Old November 29, 2022, 08:12 AM   #6
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jetinteriorguy,

Why are you leery of measurements taken using calibers?
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Old November 29, 2022, 09:19 AM   #7
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Measuring inside diameters with calipers is a little tricky. It's easy to get variations of around a thousandth of an inch or so.
Quote:
If that's not true, what should the ideal throat diameter be?
According to SAAMI, it should be 0.314".

The exact diameter isn't critical as long as it's reasonably close to spec and not swaging the bullet diameter down to any significant extent. That tends to be bad for accuracy.
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Old November 29, 2022, 11:14 AM   #8
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Ruger has long had a reputation for variances in chamber throat diameter in their revolvers. This was a long-standing complaint with the Blackhawks and Vaqueros. Supposedly Ruger changed the way they machine the chambers a few years ago to alleviate this problem, but perhaps they didn't make the change for the LCR line.

The problem with chamber throats being smaller than the barrel groove is that the bullet will be smaller than the groove diameter when it hits the barrel. After leaving the case and jumping the barrel-cylinder gap, there may not be enough pressure behind the bullet to expand it back out to fill the groove diameter. The chamber throat isn't supposed to squeeze the bullet diameter down that far -- that's why barrels have forcing codes.

Here's a link to the SAAMI specs for pistols and revolvers. The .327 is on page 51 of the PDF:
https://saami.org/wp-content/uploads...sting-Copy.pdf

The throat diameter is .314 (+.004). The barrel groove diameter is .312 (+.004)
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Old November 29, 2022, 11:46 AM   #9
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Ruger is not chambering the LCRs with six different reamers. They are using the "new" method with each chamber cut using the same reamer.

Those measurements are highly suspect, doubly so with the verification that it was done with calipers.

But if those are, in fact, the diameters of the throats, you need to send it back for repair.
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Old November 29, 2022, 12:26 PM   #10
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JohnKSa,

Where in the SAAMI spec does it define chamber throat diameters? I've never seen it.
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Old November 29, 2022, 12:59 PM   #11
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Thanks Aguila Blanca and FrankenMauser.

I kind of remembered there was something about Ruger and their chambers usually being on the tight side and the way they cut their chambers and you knew what it was and put it out there again.

There is a wealth of information on this web site.
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Old November 29, 2022, 01:26 PM   #12
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Quote:
Originally Posted by jski
Where in the SAAMI spec does it define chamber throat diameters? I've never seen it.
Click the link that both John KSa and I provided. Scroll to page 51 of the SAAMI PDF. The upper illustration is the cartridge. The lower illustration is the chamber.
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Old November 29, 2022, 03:32 PM   #13
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Aguila Blanca and John KSa, THANKS!

I thought the SAAMI spec was strictly for the cartridges. I learned something very useful!
Again, THANKS!
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Old November 30, 2022, 12:51 AM   #14
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SAAMI spec 327.png
The chamber spec is the bottom diagram and shows a .314" diameter throat.
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Old November 30, 2022, 05:47 AM   #15
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Quote:
Originally Posted by jski View Post
jetinteriorguy,

Why are you leery of measurements taken using calibers?
It’s not that a good quality calipers is inaccurate, but getting the jaws to read the ID of a hole is very difficult. If the jaws are slightly off or twisted even slightly the measurement will be wrong. With a pin gauge your using a round object to measure a round object, much more accurate.
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Old November 30, 2022, 07:34 PM   #16
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There are variances in 32 cal bullets. If you're shooting XTP's you're shooting .312" bullets. Others are .314. I like my throats to be .0005 larger than the boolit.

Ruger does suck at drilling holes, especially in their 45's. I had a Vaquero so tight it would strip off the lube and my target would have one hole and one blue splatter of lube near by. If you enjoy this caliber invest in a reamer and pilots. If you do one gun it will pay for itself. It's an easy job with the right tools.
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Old December 1, 2022, 09:33 AM   #17
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Sorry to disappoint BUT all the 32 XTP bullets I measured with my beaucoup bucks calipers are exactly .311". Both the 85 and 100 grain bullets.
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Old December 1, 2022, 09:36 AM   #18
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Cast bullets will probably be larger, but it doesn't really matter as long as the throat diameter is about the same as the groove diameter.

Even if the throats are too small, it's not a disaster--but it would be expected to affect accuracy. If you are getting acceptable accuracy from the gun, then I wouldn't worry about it.
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Old December 1, 2022, 05:03 PM   #19
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JohnKSa,

Here's a question: What should I ask of the Ruger gunsmiths? Besides making them all the same diameter. Is there a different answer depending on bullet type? .312" for JHP v. 314" for cast lead?
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Old December 1, 2022, 09:28 PM   #20
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I wouldn't ask anything of them unless you are seeing unacceptable accuracy from the gun.

If the accuracy is unacceptable, then you could tell them that (tell them what accuracy you are getting, how you assessed it and what you expect from the gun) and ask them to check to see if the chamber throats are in spec.
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Old December 2, 2022, 06:09 AM   #21
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Ruger will not fix tight throats. I've tried. They will shoot it, even with poor accuracy and say it's good.

These guys will make what you need.
https://pacifictoolandgauge.com/512-...gauges-cutters

Or Manson has a .32 in their product catalog.
https://mansonreamers.files.wordpres...-catalog-1.pdf

My advise is to get the pilot pack and some Drill Do from Brownells. They don't say what the final diameter is so call them first.
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Old December 2, 2022, 07:33 AM   #22
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Without any accuracy results posted, he should spend money on tools and permanently alter his gun?

How does it make sense to do anything at all until he establishes that there's a problem by checking the accuracy?
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Old December 2, 2022, 11:25 AM   #23
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Quote:
Ruger will not fix tight throats. I've tried. They will shoot it, even with poor accuracy and say it's good.
They replaced an "old method" Super Blackhawk cylinder for me. There was nothing wrong with it, other than differing throat diameters. They fit it with a "new method" cylinder, and much more, for free. Okay, not totally free. I had to ask nicely and then pay $13 to send it to them.


Regardless....
I don't think the revolver needs attention unless proven to have issues.
And that requires testing, not tools.
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Old December 2, 2022, 01:41 PM   #24
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Quote:
Without any accuracy results posted, he should spend money on tools and permanently alter his gun?

How does it make sense to do anything at all until he establishes that there's a problem by checking the accuracy?
The OP will have to make the decision. Personally I don't like sloppy work. These are mass produced guns made to a price point. I want mine to be the way it should be so if there's a missed shot I know it's my fault and not the gun.

There are other important dimensions when making an accurate revolver with throat size being just one.

The fact is he won't know how accurate it can be without anything to compare against. Getting the throats right may not make it more accurate, but I've never seen it hurt anything.
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Old December 2, 2022, 01:56 PM   #25
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I could simply request they make all the throats .314", according to the SAAMI spec.
What's wrong with that?

Last edited by jski; December 2, 2022 at 06:11 PM.
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