Cylinder throats - what's the deal?

Carmady · March 31, 2017, 02:47 PM

While searching and reading about leading I learned that tight/undersized throats can shave lead and generate a mess.

On a .357/.38, should a .358" lead bullet pass through the throats with thumb pressure?

I was getting a lot of leading with a 642, and a .356" .380 ACP bullet wouldn't pass through, so it was returned to S&W.

I checked a LCR and the .358" bullet would pass through, but the timing was a little off, and it was returned to Ruger because of excessive leading.

I checked a third revolver, and the .356" .380 lead bullet would pass through, but the .358" .38 bullet would not.

That's three guns, two .38s and one .357:
.358" bullet goes through one
.356" bullet goes through one, but .358" bullet will not
.356" and .358" bullets will not

Any insights?

RickB · March 31, 2017, 03:26 PM

I'm no revolver expert, but I did do quite a bit of research on cylinder/bore relationship when handloading for an old, blackpower six shooter.

Colt .45s were known to have very oversized chambers, as large as .456" even after gun manufacturers standardized on .452" bores.
If you wanted any accuracy, you had to load to the chamber, not the barrel.

My gun is a .44-40, and though bores have been standardized at .427", old Colt cylinders can run as small as .425.
I lucked into a gun with chambers that allow a .427" bullet to pass, though the gun might be more accurate with .428" bullets.

Not to get too far afield, but when Colt started chambering sixguns in .44 Russian and then .44 Special, they used the same .427" barrels that they had been using in .44-40, even though the two Smith & Wesson cartridges used .429" bullets.

In your case, I'd want chambers no larger than .357" in a .38 Spl/.357, but, you could load .358" bullets.
For the gun that won't pass a .356" bullet, you might have it reamed to match the others, rather than have to load rounds that will work best in only one gun.

dahermit · March 31, 2017, 04:56 PM

Quote:

While searching and reading about leading I learned that tight/undersized throats can shave lead and generate a mess.

The problem in shooting cast bullets in revolvers lies in the difference between the chamber throats and the bore diameter of the barrel. If the chamber throats are too small, the bullets are squeezed down smaller than the bore of the revolver and you will get leading (and inaccuracy), in the barrel. It is preferable to have the chamber throats larger than the bore of the barrel. Such larger bullets will swage down in the forcing cone of the barrel and within the limits of the bullet alloy, shoot accurately and will not lead. So, what you need to do first is to slug your barrel to determine its bore size and then slug each of you chamber throats to see if they are too tight. If they are too tight, a gunsmith can open them up for you.

DaleA · March 31, 2017, 05:48 PM

If you think your cylinder throats are not all the same or too small you can try reaming them.

Here's a video I thought explained the process pretty well.
https://www.youtube.com/watch?v=YZK1GRUR3xE

And here's where you can get a reamer from Brownells
http://www.brownells.com/gunsmith-to...-prod7700.aspx

Disclaimer: I've never done this.

Here's a couple other videos of reaming cylinders. But note that they don't show the actual reaming.
https://www.youtube.com/watch?v=FTb9cNKNavQ
https://www.youtube.com/watch?v=V9ySs13OinA

reddog81 · March 31, 2017, 10:26 PM

Any 38 caliber I've had will let a .357 through. I've had a couple reamed out to .358 for shooting lead. .357 works but .358 is better. Anything tighter than .357 and I'd contact the factory or pay someone to ream it. I'm willing to try a lot of things but I'll pay someone who knows what they're doing for that.

Carmady · April 1, 2017, 08:14 AM

Thanks for all the replies, much appreciated.

The 642, with the smallest throats, was returned. S&W emailed me yesterday and said it's "being processed."

Ruger called Thursday and said the LCR can't be fixed, so they'll send me a replacement gun. I asked her to please have someone check it out before shipping it because the gun I returned is a replacement gun. Maybe LCR's are easier to replace than repair.

Thanks for the DIY reaming info and links, but I'd probably end up with funnel shaped charge holes. I try to limit my gunsmithing to changing grips and painting sights.

jrothWA · April 11, 2017, 08:27 PM

the gents' shooting would ream all cylinfders to same diameter and cast bullets to match to get scores that were possible.

Driftwood Johnson · April 11, 2017, 10:30 PM

Howdy

Here is the deal with cylinder throats.

It all starts with the rifling groove diameter of the barrel.

Ideally, cylinder throat diameter will be the same as rifling groove diameter, or ever slightly larger.

Say you have a 45 Colt revolver. Current standard rifling groove diameter for 45 Colt is .451. (we''ll talk about the old Colts in a minute.)

Standard logic with lead bullets is they should be .001 larger in diameter than the rifling grooves. That is so the rifling will bite into the bullet and get a good grip on it. So for a .451 barrel, you want a .452 lead bullet. You do not want the chamber throats to be much larger than the diameter of the bullet. If the chamber throats are too large, the hot, expanding gasses of the burning powder can squirt around the bullet, melting its outer diameter. If the outer diameter of the bullet melts, the lead will solder itself to the barrel. This is called leading.

So, working backwards, a .451 barrel will want a .452 bullet. And the chamber throat should be the same size, or ever so slightly larger than the bullet, to prevent leading. .001 over bullet diameter is a pretty good size for chamber throats.

A good test for the proper diameter of a bullet in relationship to chamber throat diameter is to pull the cylinder (or open it if a DA revolver) and point it down at the ground. Drop a prospective bullet into the chamber. If it falls right through, it is too small. If you have to shove it like the dickens to push it through the chamber throat, it is too big. If light pressure with a pencil will push the bullet through the chamber throat, it is just right. This of course presupposes that the chamber throat is the correct diameter for the barrel.

The deal with the old Colts was rifling groove diameter was .454 min, .455 max. But chamber throats could vary a bit. So hollow based, soft lead bullets were used in the old guns. The hollow base would expand to fill up the rifling in much the same manner as a Minié ball. After WWII, 45 Colt rifling groove diameter was standardized at .451 to match the rifling of 45 ACP.

Carmady · April 13, 2017, 05:42 AM

Quote:

Here is the deal with cylinder throats.

Thanks for all that.

I've recently checked three more revolvers with the .358" bullets. Two S&W J's, a 60-9 and a 60-10 from around '98, and the LCR which is the subject of the .005" end-shake thread.

The bullets passed through all three. More of a snug fit in the Smiths; and suspiciously easy through the LCR, as in a little loose. On the Ruger a sharp tap was enough to pop the bullet through the throats, whereas as it took more of constant nudge on the Smiths.

Carmady · April 13, 2017, 05:43 AM

Quote:

the gents' shooting would ream all cylinfders to same diameter and cast bullets to match to get scores that were possible.

They may have known better than to trust factory tolerances.

rodfac · April 13, 2017, 06:20 AM

I've slugged the cylinder throats on all of my revolvers and size my home-cast bullets to that dia. or 0.001" larger. When first setting up, I size a half dozen, load them, then see if they'll chamber properly in all cylinders. Brass necks, especially in pistol calibers, may differ in thickness, even in the same lot; and that's the reason for checking a small sample as you don't want to run 500 through the press only to find that they're all too big.

In .357 and .38 Special, I size all of mine to 0.3595" as that's what my Lyman 0.359" sizer works out to. All makes of cases (Federal, R-P, Winchester & Starline) will accept a bullet that dia. and still chamber in all of my guns, with throats that vary from 0.357" to 0.359". For comparison, I'm loading for a pair of Smith Model 19's, two Model 60's, and a couple of Ruger Blackhawks.

I'm gradually switching over to all Starline brass for my guns for its uniform quality. BTW, I've found that nickle plated brass not only neck cracks earlier and is thicker at the case mouth; enough to be felt when seating a bullet. This is important since it indicates that it's re-sizing my wheel weight alloy home casts to a smaller dia....and that's not conducive to accuracy. I use the nickle ones for snake loads or at most low vel. defensive carry practice loads from the 5-7 yd line. They just won't preform to my satisfaction from the greater distances.

Too, I don't worry about the gun's groove dia. as lead alloy bullets I'm casting will form to that and with a good gas seal while the lubing process takes care of leading, but and this is a big BUT...that's with a barrel groove dia. that's equal to or slightly smaller than the throat dia. (say within 2 thousandth's) If you're dealing with a gun with cylinder throat dia's smaller than the groove dia., you'll need to open up the throats to get good accuracy.

That 0.359+" dia. gives me excellent accuracy with both plain base and gas checked bullets. BTW, if you're seating gas checks, at least on my Lyman 450 Lubrisizer, the Hornady crimp on GC's will not size completely down to the dia. of the sizing die. The copper check has enough spring back that they stay 1/2 a thousandth bigger. To get that last bit of sizing and have the check the same dia. as the lead alloy bullet driving bands, I have to anneal the check with a torch...a PITA so I don't bother. With a 0.359+" sizing operation as described above, that last 1/2 thousandth still allows all rounds to chamber in all of my guns.

I do own and enjoy shooting a Marlin 1894 CS in .357 Magnum that likes larger bullets, but only by 0.001"...for it I size them 0.360" and get good results with zero leading up to 1600 fps and accuracy that's down around an inch and quarter at 100 yds with a low power scope mounted (and weighing plus sorting the bullets!).

If you're buying commercial cast bullets, I'd order up a 100 ct box at 0.360" and try them in your guns. Larger is generally better and they need to fit the throat. I don't go for the method that says you need to be able to finger push them through the throats...I like 'em a bit bigger and the accuracy improvements justify that in my guns. Too, and this is an important caveat, I don't load any lead alloy bullets for top end velocity...I'm after good target rounds that have recoil similar to my carry loads, and use jacketed factory bullets for hunting etc. If you're loading lead alloy for top end velocity then the smaller dia. bullets are a safer choice...but I bet you'll get more leading and less accuracy that way. Using those diameters, and keeping my plain base handgun bullets to 1100 fps or less, I get no leading and great accuracy.

Lastly, if you're limited to commercial cast bullets only, and they all use that hard lube, try swirl lubing them with Lee Liquid Alox thinned 30% with mineral spirits. It'll help with leading issues if they're a bit small in dia. That hard commercial lube is useful for really high velocity rounds, but you need a softer lube for most handgun bullets.

HTH's Rod & YMMV

Carmady · April 14, 2017, 07:28 AM

rodfac,

Thanks for the thorough and detailed information. Sizing and making my own bullets would take more time than I have. I recently stocked up on some Missouri Bullet Company bullets and will stick with them for a while. I read on their site that they do offer their bullets without lube, and I may try that.

I never considered throats until I started a thread about leading in the reloading forum. I've always heard that leading was caused by the bullets being driven too fast, but found that's not the case.

It seems like my leading problems originated in the new revolvers, a 642 which had small throats, and a LCR which was out of time. The bullets were my first suspect, but studying up on leading help me figure where the real problems were.

Thanks again.

Driftwood Johnson · April 14, 2017, 09:21 AM

Quote:

I've always heard that leading was caused by the bullets being driven too fast, but found that's not the case.

Howdy Again

Yes, bullets being driven too fast can also cause leading. Think about it. I told you that hot gas escaping around the bullet can soften the lead, causing it to stick to the barrel. Heat is the key.

Remember, lead bullets are an interference fit in the barrel. So as the bullet goes down the barrel it generates friction. That's why there is lube on the bullet, to lessen the friction. What do you get when you generate friction? Heat. Drive a lead bullet fast enough and the heat of friction will increase enough to soften the lead where it is bearing against the barrel. So the softened lead solders itself to the barrel, just like my other example.

That's why high velocity bullets are jacketed. The copper guilding material the jackets are made from melts at a higher temperature than lead. So jacketed bullets can be driven faster than lead bullets without generating enough friction, and therefor heat, to melt anything.

Nathan · April 14, 2017, 09:40 AM

I think the issue here is we are only talking throats. What is your groove diameter?

Ideally, in a 45 Colt, bore groove diameter + 0.001 = throat diameter and ballet diameter, but the key is bullets are bigger than the bore and don't get squished undersized or allow blow by going through the throat.

Since the groove diameter is unchangeable, throats and bullet size is usually played with.

My Ruger 45 Colt has a .4508 groove diameter and .4510 throats. I run .451 jacketed and .452" cast with good results.

Carmady · April 26, 2017, 06:49 PM

Quote:

I was getting a lot of leading with a 642, and a .356" .380 ACP bullet wouldn't pass through, so it was returned to S&W.

I received the 642 today.
Before returning it a .356" lead 95gr .380 bullet wouldn't pass through the throats. Neither would the .358" lead 158gr .38 bullet.

S&W replaced the cylinder and repaired the yoke.
Now the .356" .380 bullet will pass through the throats, but the .358" .38 bullet still won't.

I haven't shot it, so I don't know about leading yet.

March 31, 2017, 02:47 PM	#1
Carmady Senior Member Join Date: February 26, 2013 Location: on the lam Posts: 1,735	Cylinder throats - what's the deal? While searching and reading about leading I learned that tight/undersized throats can shave lead and generate a mess. On a .357/.38, should a .358" lead bullet pass through the throats with thumb pressure? I was getting a lot of leading with a 642, and a .356" .380 ACP bullet wouldn't pass through, so it was returned to S&W. I checked a LCR and the .358" bullet would pass through, but the timing was a little off, and it was returned to Ruger because of excessive leading. I checked a third revolver, and the .356" .380 lead bullet would pass through, but the .358" .38 bullet would not. That's three guns, two .38s and one .357: .358" bullet goes through one .356" bullet goes through one, but .358" bullet will not .356" and .358" bullets will not Any insights?

March 31, 2017, 03:26 PM	#2
RickB Senior Member Join Date: March 1, 2000 Location: Boise, ID Posts: 8,518	I'm no revolver expert, but I did do quite a bit of research on cylinder/bore relationship when handloading for an old, blackpower six shooter. Colt .45s were known to have very oversized chambers, as large as .456" even after gun manufacturers standardized on .452" bores. If you wanted any accuracy, you had to load to the chamber, not the barrel. My gun is a .44-40, and though bores have been standardized at .427", old Colt cylinders can run as small as .425. I lucked into a gun with chambers that allow a .427" bullet to pass, though the gun might be more accurate with .428" bullets. Not to get too far afield, but when Colt started chambering sixguns in .44 Russian and then .44 Special, they used the same .427" barrels that they had been using in .44-40, even though the two Smith & Wesson cartridges used .429" bullets. In your case, I'd want chambers no larger than .357" in a .38 Spl/.357, but, you could load .358" bullets. For the gun that won't pass a .356" bullet, you might have it reamed to match the others, rather than have to load rounds that will work best in only one gun. __________________ Runs off at the mouth about anything 1911 related on this site and half the time is flat out wrong.

April 11, 2017, 08:27 PM	#7
jrothWA Senior Member Join Date: November 11, 2006 Posts: 2,519	When revolvers ruled the Bullseye course of fire.. the gents' shooting would ream all cylinfders to same diameter and cast bullets to match to get scores that were possible.

April 13, 2017, 06:20 AM	#11
rodfac Senior Member Join Date: January 22, 2005 Location: Kentucky Posts: 3,623	I've slugged the cylinder throats on all of my revolvers and size my home-cast bullets to that dia. or 0.001" larger. When first setting up, I size a half dozen, load them, then see if they'll chamber properly in all cylinders. Brass necks, especially in pistol calibers, may differ in thickness, even in the same lot; and that's the reason for checking a small sample as you don't want to run 500 through the press only to find that they're all too big. In .357 and .38 Special, I size all of mine to 0.3595" as that's what my Lyman 0.359" sizer works out to. All makes of cases (Federal, R-P, Winchester & Starline) will accept a bullet that dia. and still chamber in all of my guns, with throats that vary from 0.357" to 0.359". For comparison, I'm loading for a pair of Smith Model 19's, two Model 60's, and a couple of Ruger Blackhawks. I'm gradually switching over to all Starline brass for my guns for its uniform quality. BTW, I've found that nickle plated brass not only neck cracks earlier and is thicker at the case mouth; enough to be felt when seating a bullet. This is important since it indicates that it's re-sizing my wheel weight alloy home casts to a smaller dia....and that's not conducive to accuracy. I use the nickle ones for snake loads or at most low vel. defensive carry practice loads from the 5-7 yd line. They just won't preform to my satisfaction from the greater distances. Too, I don't worry about the gun's groove dia. as lead alloy bullets I'm casting will form to that and with a good gas seal while the lubing process takes care of leading, but and this is a big BUT...that's with a barrel groove dia. that's equal to or slightly smaller than the throat dia. (say within 2 thousandth's) If you're dealing with a gun with cylinder throat dia's smaller than the groove dia., you'll need to open up the throats to get good accuracy. That 0.359+" dia. gives me excellent accuracy with both plain base and gas checked bullets. BTW, if you're seating gas checks, at least on my Lyman 450 Lubrisizer, the Hornady crimp on GC's will not size completely down to the dia. of the sizing die. The copper check has enough spring back that they stay 1/2 a thousandth bigger. To get that last bit of sizing and have the check the same dia. as the lead alloy bullet driving bands, I have to anneal the check with a torch...a PITA so I don't bother. With a 0.359+" sizing operation as described above, that last 1/2 thousandth still allows all rounds to chamber in all of my guns. I do own and enjoy shooting a Marlin 1894 CS in .357 Magnum that likes larger bullets, but only by 0.001"...for it I size them 0.360" and get good results with zero leading up to 1600 fps and accuracy that's down around an inch and quarter at 100 yds with a low power scope mounted (and weighing plus sorting the bullets!). If you're buying commercial cast bullets, I'd order up a 100 ct box at 0.360" and try them in your guns. Larger is generally better and they need to fit the throat. I don't go for the method that says you need to be able to finger push them through the throats...I like 'em a bit bigger and the accuracy improvements justify that in my guns. Too, and this is an important caveat, I don't load any lead alloy bullets for top end velocity...I'm after good target rounds that have recoil similar to my carry loads, and use jacketed factory bullets for hunting etc. If you're loading lead alloy for top end velocity then the smaller dia. bullets are a safer choice...but I bet you'll get more leading and less accuracy that way. Using those diameters, and keeping my plain base handgun bullets to 1100 fps or less, I get no leading and great accuracy. Lastly, if you're limited to commercial cast bullets only, and they all use that hard lube, try swirl lubing them with Lee Liquid Alox thinned 30% with mineral spirits. It'll help with leading issues if they're a bit small in dia. That hard commercial lube is useful for really high velocity rounds, but you need a softer lube for most handgun bullets. HTH's Rod & YMMV __________________ Cherish our flag, honor it, defend it in word and deed, or get the hell out. Our Bill of Rights has been paid for by heros in uniform and shall not be diluted by misguided governmental social experiments. We owe this to our children, anything less is cowardice. USAF FAC, 5th Spl Forces, Vietnam Vet '69-'73. Last edited by rodfac; April 13, 2017 at 06:42 AM.

March 31, 2017, 05:48 PM	#4
DaleA Senior Member Join Date: September 12, 2002 Location: Twin Cities, MN Posts: 5,313	If you think your cylinder throats are not all the same or too small you can try reaming them. Here's a video I thought explained the process pretty well. https://www.youtube.com/watch?v=YZK1GRUR3xE And here's where you can get a reamer from Brownells http://www.brownells.com/gunsmith-to...-prod7700.aspx Disclaimer: I've never done this. Here's a couple other videos of reaming cylinders. But note that they don't show the actual reaming. https://www.youtube.com/watch?v=FTb9cNKNavQ https://www.youtube.com/watch?v=V9ySs13OinA

March 31, 2017, 10:26 PM	#5
reddog81 Senior Member Join Date: October 16, 2014 Location: Iowa Posts: 1,634	Any 38 caliber I've had will let a .357 through. I've had a couple reamed out to .358 for shooting lead. .357 works but .358 is better. Anything tighter than .357 and I'd contact the factory or pay someone to ream it. I'm willing to try a lot of things but I'll pay someone who knows what they're doing for that.

April 1, 2017, 08:14 AM	#6
Carmady Senior Member Join Date: February 26, 2013 Location: on the lam Posts: 1,735	Thanks for all the replies, much appreciated. The 642, with the smallest throats, was returned. S&W emailed me yesterday and said it's "being processed." Ruger called Thursday and said the LCR can't be fixed, so they'll send me a replacement gun. I asked her to please have someone check it out before shipping it because the gun I returned is a replacement gun. Maybe LCR's are easier to replace than repair. Thanks for the DIY reaming info and links, but I'd probably end up with funnel shaped charge holes. I try to limit my gunsmithing to changing grips and painting sights.

April 11, 2017, 10:30 PM	#8
Driftwood Johnson Senior Member Join Date: January 3, 2014 Location: Land of the Pilgrims Posts: 2,033	Howdy Here is the deal with cylinder throats. It all starts with the rifling groove diameter of the barrel. Ideally, cylinder throat diameter will be the same as rifling groove diameter, or ever slightly larger. Say you have a 45 Colt revolver. Current standard rifling groove diameter for 45 Colt is .451. (we''ll talk about the old Colts in a minute.) Standard logic with lead bullets is they should be .001 larger in diameter than the rifling grooves. That is so the rifling will bite into the bullet and get a good grip on it. So for a .451 barrel, you want a .452 lead bullet. You do not want the chamber throats to be much larger than the diameter of the bullet. If the chamber throats are too large, the hot, expanding gasses of the burning powder can squirt around the bullet, melting its outer diameter. If the outer diameter of the bullet melts, the lead will solder itself to the barrel. This is called leading. So, working backwards, a .451 barrel will want a .452 bullet. And the chamber throat should be the same size, or ever so slightly larger than the bullet, to prevent leading. .001 over bullet diameter is a pretty good size for chamber throats. A good test for the proper diameter of a bullet in relationship to chamber throat diameter is to pull the cylinder (or open it if a DA revolver) and point it down at the ground. Drop a prospective bullet into the chamber. If it falls right through, it is too small. If you have to shove it like the dickens to push it through the chamber throat, it is too big. If light pressure with a pencil will push the bullet through the chamber throat, it is just right. This of course presupposes that the chamber throat is the correct diameter for the barrel. The deal with the old Colts was rifling groove diameter was .454 min, .455 max. But chamber throats could vary a bit. So hollow based, soft lead bullets were used in the old guns. The hollow base would expand to fill up the rifling in much the same manner as a Minié ball. After WWII, 45 Colt rifling groove diameter was standardized at .451 to match the rifling of 45 ACP.

April 14, 2017, 07:28 AM	#12
Carmady Senior Member Join Date: February 26, 2013 Location: on the lam Posts: 1,735	rodfac, Thanks for the thorough and detailed information. Sizing and making my own bullets would take more time than I have. I recently stocked up on some Missouri Bullet Company bullets and will stick with them for a while. I read on their site that they do offer their bullets without lube, and I may try that. I never considered throats until I started a thread about leading in the reloading forum. I've always heard that leading was caused by the bullets being driven too fast, but found that's not the case. It seems like my leading problems originated in the new revolvers, a 642 which had small throats, and a LCR which was out of time. The bullets were my first suspect, but studying up on leading help me figure where the real problems were. Thanks again.

April 14, 2017, 09:40 AM	#14
Nathan Senior Member Join Date: July 1, 2001 Posts: 6,331	I think the issue here is we are only talking throats. What is your groove diameter? Ideally, in a 45 Colt, bore groove diameter + 0.001 = throat diameter and ballet diameter, but the key is bullets are bigger than the bore and don't get squished undersized or allow blow by going through the throat. Since the groove diameter is unchangeable, throats and bullet size is usually played with. My Ruger 45 Colt has a .4508 groove diameter and .4510 throats. I run .451 jacketed and .452" cast with good results.