Chamber throats in LCR cylinder?

[JohnKSa]

What's wrong with that?

Unless the gun is actually not performing the way you want it to, it's a waste of your time and effort and their time and effort and money.

Ok, forget all that and let's just assume that you feel like you need to pursue this based purely on measurements--without verifying that the gun actually shoots accurately or not.

1. You need to do the measurements properly. For accurate inside diameter measurements you need a pin gauge set. Get that (or find a gunsmith/machinist that has a set) and verify the throat measurements. It would not be smart (or ethical) to send the gun off for work based on measurements that may not be accurate.

2. You need to slug the bore. If the throat measurements are about the same size or a bit larger than the groove diameter then there's no reason to expect accuracy issues.

3. Keep in mind that since you have no data to verify that the throat issues (if they really exist) are actually causing accuracy problems with the ammo you are using, nor have you verified that there is not some other issue that could cause accuracy problems, you could get the gun back after the work (assuming Ruger agrees to do it) and find that it's not accurate.

[jski]

I checked on the cost of a single “go” plug/pin gauge: $17.46 + shipping. Buying multiples of these would get quite expensive.

[JohnKSa]

Maybe, just maybe, (and I must admit that I'm surprised that no one has given you this advice so far) you want to shoot this gun to see if you're happy with its performance.

Because if you are happy with how it shoots, then the cost of pin gauges, the hassle of shipping, dealing with trying to get Ruger to modify the gun, all of it, is moot.

[jski]

I never said I hadn’t fired it. I did when I first got it. Took it to the range twice now. Put about 200 rounds thru it at 7 yards. My first snubby so it’s difficult to say if it’s me or the gun. The gun has a good feel in my hand but I’d like tighter groups. Just thought I’d consider all possibilities.

[jetinteriorguy]

Snubs are not easy to shoot, they definitely take practice. You could try slugging the chamber throats similar to the method used for bores. It would be a bit of a chore to remove the cylinder and properly support it in order to drive slugs through, but I think you’d get a more accurate measurement. If you have some round nose lead bullets that are bigger than the throats that would work good.

[JohnKSa]

I never said I hadn’t fired it. I did when I first got it.

Nice of you to avoid mentioning that for days even though the subject has come up repeatedly over the course of this thread, starting with the very first response.

Put about 200 rounds thru it at 7 yards.

So what started this was accuracy issues at 7 yards? Again, that would have been nice to know. Whatever is causing your accuracy issues at 7 yards, it's almost certainly not undersize throats.

https://www.singleactions.com/files/...derThroats.pdf

This guy did an extensive test before and after reaming undersize throats in a Ruger revolver. They did see an improvement in group size after reaming. Accuracy was tested by firing four five shot groups from the bench with each of several loadings at 25 yards and then taking the average size of those 4 groups for each loading.

After reaming, the average groups shrank by 0.6". That would be equivalent to shrinking 7 yard groups by about 0.17".

You could see improvements greater than that, but the people who ream throats for accuracy improvements are typically trying to shrink groups to under 2" at 25 yards or are concerned with 50 yard accuracy. You might see a 1" or 2" reduction in group size at 25 yards if your revolver has tight throats. That would be expected to reduce group sizes at 7 yards by 0.3" to 0.6"

[Carmady]

Maybe, just maybe, (and I must admit that I'm surprised that no one has given you this advice so far) you want to shoot this gun to see if you're happy with its performance.

See post #5.

[JohnKSa]

Yup. And post #2. I was being sarcastic.

[Carmady]

I missed that. Thanks.

[Double Naught Spy]

I could simply request they make all the throats .314", according to the SAAMI spec.
What's wrong with that?

Because you didn't use the correct calipers for the job, you don't really know if the throats are off or not.

[jski]

Well, there’s another variable involved here too. These 200 rounds were my own brew, so to speak:

32 H&R Starline brass ,
85 gr XTP bullets , and
either 11 gr of H110 or 7 gr of True Blue.

The True Blue load is hot but still comfortable. The H110 loads are relatively mild in comparison.

[Aguila Blanca]

Originally Posted by Double Naught Spy

Because you didn't use the correct calipers for the job, you don't really know if the throats are off or not.

Yes, he does. That was stated in the opening post.

Originally Posted by jski

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.

That's a qualitative assessment rather than a quantitative measurement, but it's certainly a "clue." Whether or not it makes a difference worth fretting over is a separate question.

Shooting some additional groups -- from a rest, at a distance longer than 7 yards -- might be useful if done in a scientific way. It would need a spotting scope. Mark the chamber with the tight throat, and always make that the last shot. Fire groups, using the spotting scope to look at the group after each shot. If the first shots make a good group and the tight chamber always produces the flyer that ruins the group, then you have substantiation for thinking that reaming that throat might make a difference.

As has been commented, though, any improvement is likely to be minimal.

[jski]

This whole journey into 32s began with:
Why the Best Snub Nose Caliber is .32

[JohnKSa]

That's a qualitative assessment rather than a quantitative measurement, but it's certainly a "clue." Whether or not it makes a difference worth fretting over is a separate question.

It's a clue that there's likely no problem. If the bullets were NOT fitting through then that could indicate a problem based on the rationale that they might be getting swaged down to smaller than groove diameter which might cause some issues.

But if he's going send the gun to Ruger to have them spec the chamber throats, he needs something more than "bullets pass through" or some inside diameter measurements made with calipers.

He could slug each throat and the bore and measure the slugs with calipers, or he could slug the bore and measure the throats with pin gauges. Sending it off based on inside diameter measurements made with calipers doesn't make sense--there's a reason they make pin gauges instead of just doing inside diameter measurements with calipers.

[Aguila Blanca]

John -- I think you are overlooking a potentially important point from the opening post, which I quoted in post #37:

I first noticed that with all but one chamber I could drop my XTP bullets straight thru.

If the bullets WON'T drop through one chamber, that chamber is different from the others. More important (perhaps), if a bullet won't drop through it, then a bullet when fired through that chamber throat will be squeezed down to the diameter of that throat. If that's smaller than the groove diameter of the barrel, then bullets fired from that chamber will be sort of rattling their way down the barrel.

According to SAAMI specs, the nominal bullet diameter for .327 Federal magnum is .313 inches. The nominal groove diameter of the barrel is .312 inches, which is smaller than the bullet, but the nominal diameter for chamber throats is .314 inches -- which is larger than the bullet.

The chamber throat isn't supposed to squeeze the bullets to smaller than the barrel grove diameter.

[JohnKSa]

...then bullets fired from that chamber will be sort of rattling their way down the barrel.

If it's smaller than the bore diameter that would be true. If it's just smaller than groove diameter, it won't be ideal for best accuracy, but it will still be engraved by the rifling and should shoot well enough unless it is smaller than the bore diameter as well.

But yeah, it's not ideal for the throat to be smaller than the bullet.

[jski]

Aguila Blanca, thank you for making that point. It’s like having an engine with one of the cylinders misfiring. Also, I’d like to point out that all the XTP bullets measure exactly .311”. So that chamber has a throat diameter that’s somewhat less than .311” which is definitely less that the bore diameter.

[JohnKSa]

So that chamber has a throat diameter that’s somewhat less than .311” which is definitely less that the bore diameter.

Bore diameter spec for the .327Mag is 0.303". It is extremely unlikely that any of the throats are less than bore diameter.

As for whether the small throat is less than groove diameter (spec 0.312") that would depend on the actual groove diameter of your revolver. Which, it should be obvious by now, may or may not be spec. If you want to know what the actual groove diameter is, you can slug the barrel to find out.

It’s like having an engine with one of the cylinders misfiring.

It's not even close to that. It's entirely possible that the one tight throat will have no measurable effect on performance at all with the ammunition you're using.

[jski]

JohnKSa, I’d like to thank you for your thoughtful input. It’s been helpful.

*** Lest this be misconstrued, it was NOT intended as sarcasm.

[JohnKSa]

No worries--I could have even handled some sarcasm...

[1911Tuner]

After leaving the case and jumping the barrel-cylinder gap,

The bullet doesn't "jump" the gap. It's actually well into the rifling before the base of the bullet gets clear of the throat. You can see this by dropping an unfired bullet into the barrel and swinging the cylinder toward the bullet. The point where the bullet stops is where it's starting to engage the rifling. There's a good portion of the bullet left sticking out that will remain in the chamber throat.

While it's not desirable for the throat the swage the bullet below groove diameter for a number of reasons, I like for the throats to be at or very close to nominal bullet diameter.

[JohnKSa]

Very interesting observation, and not one I've ever heard anyone else make!

[1911Tuner]

Very interesting observation, and not one I've ever heard anyone else make!

I first made it in a gun shop years ago when I heard a guy behind the counter talking about bullets yawing as they jumped the gap and simply pointed out that the cylinder face is only about .006-.008 inch from the barrel face.

From his blank expression, I knew that he wasn't getting it...so, I grabbed a jacketed 158 grain .357 bullet from one of those loose zip-lock bags in the store and dropped it into the barrel of a revolver...then swung the cylinder to show how much bullet would remain in the throat. With that particular combination, the bullet is actually starting to engage the rifling before the base clears the case mouth.

Incidentally...for best accuracy with any bullet and less fouling with lead bullets...an unfired bullet dropped into a chamber should stick in the throat, and push through with light to moderate force, depending on whether it's jacketed or lead...lead bullets being typically .001 inch larger than nominal diameter.

So, "yawing" can't happen. The bullet is guided straight into the barrel from the instant it moves until it leaves the muzzle...first by the case, then the throat...and finally the taper in the forcing cone takes care of any slight cylinder to barrel misalignment long before the bullet base reaches the gap.

Sometimes the answer to a question has been staring us in the face the whole time. We only have to take the time to look.

[Jim Watson]

That is definitely a flaw, but I don't think I could shoot an LCR well enough to tell the odd chamber. The OP may be a better shot than me.

Back in the revolver era, a target shooter might select his best chamber and load it in single shot mode for the slow fire event. He would then select his worst chamber and leave it empty for the timed and rapid fire.