large cylinder throats - why

[rays44]

With calibers that I'm familiar with, it seems the .45 colt chambering is a frequent offender. It's not uncommon to find cylinder throats way off spec (on the large side), often measuring .455 to .457 with a .451-.452 bore. Pick your maker: Colt, S&W, Ruger. The are all guilty at one time or another.
I have an opposite problem with my Magna Classic. An absolutely stellar machine with a .429 bore and .427 cylinder throats. Undersized throats can be fixed, but what do you do on those oversized .45 colt chambers? Why is there even a problem in the first place? Matching the cylinder with the bore dimensions should be in chapter 1 whether it's a Uberti or S&W armorer. This always perplexed my feeble mind.

 

[k22fan]

Early .45 Colt cartridges were loaded with bullets that were larger diameter than .45 ACP bullets. The classic .45 Colt factory cartridge had a 250 to 255 grain lead bullet that was .456" to .457" diameter. You could say S&W formerly reamed .45 Colt throats for that ammunition. Groove diameters were cut too tight for the cylinder throats so the revolvers could also fire modern .452" bullets. The Small Arms and Ammunition Manufacturers' Institute (SAAMI) .45 Colt bullet diameter still is .456" -.006". SAAMI .45 Colt cylinder throat diameter is .452" + .0075" so .455" to .457" throats are not "way off spec." They are well within the SAAMI .452" to .4595" range so you could say S&W formerly reamed .45 Colt throats to SAAMI specs rather than reloaders' preferences.

Similarly SAAMI bullet diameter for .44 Magnum is .432" -.006" and SAAMI .44 Magnum cylinder throat diameter is .4325" + .004". The .429" or .430" throats that reloaders prefer are "way off spec."

It's easy to understand why SAAMI will not make .45 Colt cylinder throat specs too small for factory cartridges as they were made for over a century. Why they will not reduce .44 Magnum throat specs is a good question.

Fortunately when Thompkins PLC bought S&W in the late 1980s one of the first things they did was reduce .44 Magnum and .45 Colt cylinder throat diameters.

 

[jack the toad]

Not to drift but is it typical for rifle bullets to measure larger (.458) than handgun (.451-.452) and if so, why???

 

[Fishinfool]

The older the cartridge, the more it seems to be an issue. The .45c has been around for over 130 years. A lot of manufacturers have chambered for it using multiple generations of machines and reamers. Standardization was sometimes spoty in earlier days, with some manufacturers deciding on what worked best in their guns, even if it wasn't "spec", which sometimes itself wasn't ideal. A lot more chance for variations than say something newer, like the .327 magnum, that is chambered by fewer manufacturers, and on modern equipment to recognized dimensions.

A good trick with oversized throats in a gun like the 45c is to use hollow base lead bullets. The base will squeeze up and down as needed, providing decent accuracy. For what its worth, my experience has been that, within reason, chamber mouth fit is more important than bore fit for good revolver accuracy. Like was said above, its a lot easier to fix undersized throats than oversized.

Larry

 

[steelslaver]

I fixed my 25-5 by taking a model 29 cylinder and reaming it to 45 colt with .452 throats. But there is no reason not to load larger bullets to fit your throats. A .002-.004 oversized lead bullet will become groove diameter as soon as it enters the forcing cone with no problems. Your loads would have to be near the guns limit to to any harm and the loads for 45 colt are way lower pressure than the gun will handle.

I have made several 45 colt cylinders for 45 colts from both 357 cylinders and 44 mag cylinders. 2 of my 45 colts started life as 629-1s and I have fitted colt cylinders to 45acp guns also. I regularly fire loads in mine that are well above factory loads, but not in the realm of the high er end Ruger only loads. I think with a modern S&W 45 colt that 21,000psi is a more appropriate upper limit that the old 14,000psi limit designed for 100+ year old colt "Peacemakers" and the like. No harder on the frame than a 36,000psi 44 mag load with the weight bullet and the cylinder will handle that. Except for length the chamber is the same diameter as 45 acp and it has 21,000 with +p at 23,000. Nobody is blowing up model 25 acps, and nobody will blow up 45colts at the same pressures. I certainly have not. Now with an .456, 260 gr bullet, .452 grooves and 25,000psi you might be pushing the line. One of the reason mine all have close to .452 throats and I only use .452 bullets.

 

[series guy]

I did exactly what steelslaver did to my 25-2. I used a .44 Magnum cylinder and had it reamed for .45 Colt with .452 throats. Now it is a very accurate gun. On the subject of .44 Magnum every performance center gun that I have measured has had .4285 cylinder throats (around 12 to 15 guns measured) and I shoot a cast Keith style bullet sized to .430 and accuracy is fantastic. Pressure is still pretty high as the bullet enters the forcing cone and it will obturate to engage the rifling after being slightly squeezed by the cylinder throat. I have found that cylinder throats have more affect on accuracy than the rifling.

 

[k22fan]

Not to drift but is it typical for rifle bullets to measure larger (.458) than handgun (.451-.452) and if so, why???

As introduced in the 1870s .45 Colt and .45-70 bullets were pretty darn close in diameter. You'd have to research old army records for any logic in reducing bullet diameter for their new automatic pistols. For the commercial market manufacturers continue to use the army's bullet diameters.

I have no experience reloading 19th century .45 Colts but trap door rifle groove diameters varied quite a bit and are more likely to be over .460" than under. Consistent groove diameter did not matter because the black powder bumped the bullets' diameter up to fit what ever the individual trap door's groove diameter was.

I'm not sure if you were also asking about other calibers. Offhand I can not think of another caliber for which rifle bullets are larger diameter than pistol bullets.

 

[jack the toad]

Yes, I was specifically referring to the .45 caliber. Thanks

 

[Patrick L]

We could agree that the oversize throats are technically "not off spec" but jeesh! it's been proven that having the dimensions that wacky does not contribute to accuracy. I tend to agree with the OP that the factories could get it right if they abandoned the old GM style approach of "We make guns the way we make them. Don't try to tell US how."

 

[rays44]

Early .45 Colt cartridges were loaded with bullets that were larger diameter than .45 ACP bullets. The classic .45 Colt factory cartridge had a 250 to 255 grain lead bullet that was .456" to .457" diameter. You could say S&W formerly reamed .45 Colt throats for that ammunition. Groove diameters were cut too tight for the cylinder throats so the revolvers could also fire modern .452" bullets. The Small Arms and Ammunition Manufacturers' Institute (SAAMI) .45 Colt bullet diameter still is .456" -.006". SAAMI .45 Colt cylinder throat diameter is .452" + .0075" so .455" to .457" throats are not "way off spec." They are well within the SAAMI .452" to .4595" range so you could say S&W formerly reamed .45 Colt throats to SAAMI specs rather than reloaders' preferences.

Similarly SAAMI bullet diameter for .44 Magnum is .432" -.006" and SAAMI .44 Magnum cylinder throat diameter is .4325" + .004". The .429" or .430" throats that reloaders prefer are "way off spec."

It's easy to understand why SAAMI will not make .45 Colt cylinder throat specs too small for factory cartridges as they were made for over a century. Why they will not reduce .44 Magnum throat specs is a good question.

Fortunately when Thompkins PLC bought S&W in the late 1980s one of the first things they did was reduce .44 Magnum and .45 Colt cylinder throat diameters.

I stand corrected with regard to my "off spec" reference. Speaking for myself as a hand loader and revolver guy for around 40 years, I would just prefer to see tighter throat/groove diameter relationships that match jacketed and lead bullet sizes. It's just conducive to a better shooting revolver. Just my 2 cents.

 

[steelslaver]

I stand corrected with regard to my "off spec" reference. Speaking for myself as a hand loader and revolver guy for around 40 years, I would just prefer to see tighter throat/groove diameter relationships that match jacketed and lead bullet sizes. It's just conducive to a better shooting revolver. Just my 2 cents.

Yes, that is 100% correct and not correcting the 45 colt chambers when the started come out with the 25-3 and then the first of the 25-5was a error on the part of S&W. Before the 25-3 S&W factory 45 colts were very uncommon.

Why the tight 44 mag ones is another puzzle.

 

[rays44]

My 25-5 matches up well. I have a Navy Arms Schofield and a U.S. Patent Arms SAA. Both are gorgeous, well made arms (by Uberti). In spite of both having oversized throats, they shoot very well for what they are. I get more leading than I'd like, even with gas checks, but that's the price of admission.

 

[Walter Rego]

My 25-5 matches up well. I have a Navy Arms Schofield and a U.S. Patent Arms SAA. Both are gorgeous, well made arms (by Uberti). In spite of both having oversized throats, they shoot very well for what they are. I get more leading than I'd like, even with gas checks, but that's the price of admission.

Interesting about your Uberti/Navy Arms Schofield. Mine has throats that measure .452". I also have a US Firearms Mfg. Co. made (not earlier Uberti made) single action that is chambered for .45 Colt with a spare cylinder in .45 ACP. Both cylinders measure a tight .451" and the .45 ACP cylinder will shoot cloverleafs at 15 yards with factory hardball so the long jump to the forcing cone apparently has no effect with those tight throats guiding the bullet.

 

[rays44]

Interesting about your Uberti/Navy Arms Schofield. Mine has throats that measure .452". I also have a US Firearms Mfg. Co. made (not earlier Uberti made) single action that is chambered for .45 Colt with a spare cylinder in .45 ACP. Both cylinders measure a tight .451" and the .45 ACP cylinder will shoot cloverleafs at 15 yards with factory hardball so the long jump to the forcing cone apparently has no effect with those tight throats guiding the bullet.

My Schofield and SAA both have throats that measure .456 using pin gauges. The throat is really a critical part of the equation as your pieces show. They're really great revolvers.

 

[Carrier]

My Ruger 45 Colt Bisley sure doesn't have large throats. It's at a smith getting them opened up as well as the forcing cone to 11 degrees.

 

[bgrafsr]

Not an S&W, but a Pedersoli .40-65 1874 Sharps rifle. The barrel is stamped .410" for bore diameter. Cast lead bullets leaded the barrel badly when using .410" bullets. Found out the chamber throat was approx. .416", so I had a custom mold made and size the bullets to .417" now. Practically no leading anymore and no adverse effects from using that large a diameter bullet, as far as pressures go.

 

[rays44]

Not an S&W, but a Pedersoli .40-65 1874 Sharps rifle. The barrel is stamped .410" for bore diameter. Cast lead bullets leaded the barrel badly when using .410" bullets. Found out the chamber throat was approx. .416", so I had a custom mold made and size the bullets to .417" now. Practically no leading anymore and no adverse effects from using that large a diameter bullet, as far as pressures go.

Amazing that you can go .006 over bore diameter and not have leading. It proves, once again that the throat is critical. I would still stay low of max loads. Not familure with the rifle, but it sounds pretty cool.