Chamber throats in LCR cylinder?

J

jski

New member
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?
 
J

JohnKSa

Administrator
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/upload...FP-and-R-Approved-2015-12-14-Posting-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.
 
J

jski

New member
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?
 
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J

jetinteriorguy

New member
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.
 
C

Carmady

New member
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.
 
J

JohnKSa

Administrator
Measuring inside diameters with calipers is a little tricky. It's easy to get variations of around a thousandth of an inch or so.
If that's not true, what should the ideal throat diameter be?
Click to expand...
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.
 
A

Aguila Blanca

Staff
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/upload...FP-and-R-Approved-2015-12-14-Posting-Copy.pdf

The throat diameter is .314 (+.004). The barrel groove diameter is .312 (+.004)
 
F

FrankenMauser

New member
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.
 
D

DaleA

New member
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.
 
A

Aguila Blanca

Staff
jski said:
Where in the SAAMI spec does it define chamber throat diameters? I've never seen it.
Click to expand...
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.
 
J

jski

New member
Aguila Blanca and John KSa, THANKS!

I thought the SAAMI spec was strictly for the cartridges. I learned something very useful!
Again, THANKS!
 
J

jetinteriorguy

New member
jski said:
jetinteriorguy,

Why are you leery of measurements taken using calibers?
Click to expand...
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.
 
S

Super Sneaky Steve

New member
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.
 
J

jski

New member
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.
 
J

JohnKSa

Administrator
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.
 
J

jski

New member
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?
 
J

JohnKSa

Administrator
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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