Cylinder throat size

[peter nap]

I haven't ever had a revolver throated. I just shoot them the way they come but decided to measure the new Taurus.

The cylinder throats are running +- 428 and my groove diameter in the barrel is a tight .427.

Do I need to do anything to these?

[Scrapper]

I'm sure others will comment, as this is always pertinent to accuracy in a revolver.


Check this thread out: http://castboolits.gunloads.com/showthread.php?t=21598

A piece of the thread>>http://castboolits.gunloads.com/showpost.php?p=240707&postcount=2

6. The cylinder exit hole should not be smaller than the size of the bullet you are sending down range. Have a gunsmith open up the cylinder holes so your bullets are not swaged down before they enter the barrel. This is also something you can do yourself. The ultimate boolit size is that which requires felt finger pressure friction when pushed through the Largest cylinder exit. The size chosen should not be so large as to cause a loaded cartridge to have any felt friction when placed into the Smallest cylinder


Check out this Thread as they discuss this topic:
http://shootersforum.com/showthread.htm?p=83417

The Original Poster asks:I have a couple of revolvers that shoot pretty good, a 5 inch 629 classic and a 4 5/8ths stainless blackhawk in 45 colt.

The smith probably shoots as good of groups as I can shoot with a 5" barrel and the ruger while having shot some above average groups at 25 yards. I have not been able to get it to shoot as good as I would like at longer ranges.

I am considering opening the cylinder throats on both these guns because they are under size. the smith measures about .429 or .4295 and the ruger .451 plus or minus 5 ten thousandths.

My question is, and this might be heracy on this board but how does opening the cylinder throats affect accuracy with jacketed bullets.
For better or worse I have not convinced myself that cast are all I will ever want to use in my revolvers and want to know all the facts about bigger cylinder throats before I take the plunge.

Has any of you done before and after tests with jacketed bullets, if so I would sure appreciate some good data.
If no before and after just tell me how well it will shoot now with jacketed after haveing the throats opened.



To read more use the link below:
http://www.alphaprecisioninc.com/revolver/default.htm

Revolver Accuracy by Alpha Precision, Inc.

As with other firearms, accuracy of the revolver is dependent upon several factors. First, the bullet must be the correct diameter with relation to the cylinder chamber throats, and the interior barrel dimensions (the groove diameter is most often referenced, but bore diameter is important as well). When cast bullets are used, the bullet should be .0005 to .0010"larger than the barrel groove diameter. Ideally, the cylinder throat will be .0005 to.0010" larger than the bullet. To illustrate, Douglas .44 handgun barrels typically have a groove diameter of .429". The cast bullet should be .4295 to .4300". The cylinder throats should then be .4300 to .4305". Jacket bullets are more tolerant and can be groove diameter + .0010. Cylinder throats .0010" larger than bullet diameter.




Check out LBT Bullet Technology: http://lbtmoulds.com/measurebore.shtml
REVOLVER MEASURING

Because it is critical that revolvers be measured accurately before and during lapping AND when selecting a bullet mold diameter we developed push through slugs, which are listed and explained a bit farther along. For example, if one attempts to lap a revolver barrel while the cylinder throats are undersized, the effort is wasted. Same thing applies if bullets are fitted to undersized throats, or fitted undersized to oversize throats. Don’t guess about bullet fit or a guns internal dimensions. It’s as erroneous as not looking at the sights when trying to print tight groups.

To measure for a mold using push through slugs, only three are needed in most cases, and detailed instructions come with the push thru slugs. Barrel to cylinder throat relationship can be proven by feel as explained in the slugging instructions sent with the slugs.

It is crucial to accuracy with revolvers that barrel constrictions from barrel to frame threads and roll stamping on the outside of the barrels be removed, and any roughness smoothed up, which can ONLY be done by lapping. Push through slugs will make the necessary internal measuring easy, and our lap kit will fix the barrel and cylinder problems. Please read the following information about each carefully.



You may want to read this also to help in your understanding this, although it's about Rifles not revolvers:
http://www.mountainmolds.com/helpRifle.htm
This site has some diagrams. Check it out.
The throat is the part of the chamber between the case and the rifling. In a perfect world, the throat diameter would be 0.001" - 0.002" larger than the groove diameter. The throat serves to align the bullet so that it is pointing straight into the barrel. If the throat diameter is much larger than the bullet diameter, then the throat cannot align the bullet. Also, an excessively large throat diameter may make the bullet susceptible to gas cutting as it passes through the throat.

[S.R.Custom]

... Ideally, the cylinder throat will be .0005 to.0010" larger than the bullet...

This statement will get argument from a LOT of people here.

[felix]

Hopefully, he meant grooves, not bullet. ... felix

[Scrapper]

I knew this, lol...

SuperMag, This statement will get argument from a LOT of people here.


... Ideally, the cylinder throat will be .0005 to.0010" larger than the bullet...

That statement is off a web page that I found, if you see the link I found it on. Very controversial subject I know, nonetheless I wanted him to see for himself all the different things you can find here on the internet, mostly opinions IMO, lol. Ultimately it is what works for the individual. I have been able to hit things with a gun other people cannot, of course I did compensate for said guns that didn't shoot quite right regardless of the combination of components.

There is a-lot to be gained by getting this combination of Bullet, Cylinder Throat, and Barrel just right. I'm sure everyone will agree the bullet needs to just slip through the throat and still be big enough to seal it's way up the bore and all throats must be the same or as close to the same as possible.

My point being there are many variables, as an individual it's up to you to find what works for your particular abilities and equipment.

[MtGun44]

In my experience, I have had best results with boolits that are the same size or .001
larger (or even .002) than the cyl throats. The whole deal works best when the throats
are the same or a touch larger than the groove diam of the bbl. Generally, my S&W
revolvers have been fine. I have reamed up a Ruger BH that was way, way tight in the
cyl throats and us oversized boolits in a SBH that is wide in the throats.

Bill

[Scrapper]

I agree with MtGun44. I believe many experienced shooters will agree with that statement.