[BackWoods Billy]

I came across this last night and I would like to know if this sounds right. I Just started casting a few months ago and I thought it was the bore that I slugged and went with that size. This seamed to come from a good source but i'm not sure about it.

"Revolvers: The chamber mouth of the cylinder dictates the size of the bullet, not the groove size of the barrel! The bullet must be sized for a tight push fit through the cylinder. Example: Some 44s have a groove size of .429 and the cylinder mouths are .432 or more. In this example, size the bullet to .432+ and don't worry when the big light hits the bullet, it will fit the barrel!! If the mouth of the cylinder is smaller than the groove size of the barrel, the pistol will never shoot worth a hoot. Send it back to the factory or have it reamed to .001over groove size. Remember a hard linotype bullet will lead faster if it doesn't fit."

Thanks Guys.

 

[unclenick]

That's not bad advice. He is correct that a chamber smaller than groove diameter will never shoot cast bullets. Cast bullets have some spring, especially if hard, but it's not real fast, for some reason, so passing through any sort of constriction on their way to or through the tube usually results in gas blowby. That causes barrel leading and some resulting degree of base unevenness that spoils accuracy.

It is also correct that the bore can swage a cast bullet down several thousandths with no problem. Even jacketed bullets can stand some of this. It does raise pressure, but if you develop the load by working up and watching for pressure signs, it's OK. It's less than you'd think.

His advice to size to the cylinder may have a point of no return in some guns, where distortion by swaging may outweigh a little of the blowby he is trying to avoid by sizing to fit the throats. A .45 Colt with 0.456 throats and a 0.451 bore, for example. I would be prepared to try some different diameters for that.

It goes without saying that your throats all need to be the same. Note that you can still have an accuracy issue if your barrel has any constrictions. That's what we slug to learn, among other things. Cylindersmith.com has a service that will take cylinder throats to SAAMI max for about $40 if you send them the cylinder (they don't accept complete firearms; apparently no FFL holder there).

 

[cukrus]

The info you quoted sounds reliable. Think of the cylinder mouth, not the forcing cone, as the "leade or throat."
A rule of thumb says to size to groove (not bore) + 1 thou.
(A typical .30 bore may have .308 groove diameter, +.001 = .309 for size die;
a typical .35 bore may have .357 groove diameter, +.001 = .358 for size die.)
My practice is to make a chamber cast and size to fit the leade or throat for rifles or automatic pistols and seat appropriately to feed.
The only time I consider bore fit is for bore riding noses and paper patch cores.

 

[zb338]

Didn't Elmer Keith say you should size the bullet to the groove diameter?
He did a lot of cast bullet shooting.

Zeke

 

[ribbonstone2]

I do believe, with full power loads in magnum handguns, that the bullet is going to get kicked in the rear hard enough to slug up to whatever size is just ahead of the case. In a revolver, that would be the chamber throats.

If possible, would prefer that bullet start off nice and round and nearly that size (whatever it measures in your gun) than to rely on the powder burn to bump it up to that size.

Probelm comes in where the cylinder throat size does NOT match the barrel size.

If the Cylinder throat too big, shooting full powered magnum loads, the bullet is going to bump up and run into the barrel at that larger size. Starting with a smaller diameter won't really cure it.

If the cylinder throat is too big and you use a load with a smaller sized bullet that doesn't bump up the bullet, then the bullet has that extra space to both get a bit cooked before hitting the barrel and to let a bit of gas escape around the bullet (often gas cutting the lead and causing leading). Get leading in the chamber throats and the barrel.

If the throat is smaller than the bore, will also often get that gas cutting type leading, but usually leading in the bore with non-leaded or less leaded chamber throats.

Basically, if the cylinder throats come out at 0 to .001" larger than bore size, i'd be pretty pleased. If the throats are much larger than the bore, would size to the throats and reduce the power charges a bit. If the throats come out smaller than the bore, i'd spend the $ have them opened up to match (or just shoot jacketed bullets).
------------
Have managed to get the unfortunate combination of too small a cylinder throat and too large a barrel to shoot, but it's a lot of work finding a load that will work AND stay in pressure limits. If the pressure is high enough when the bullet is fully in the barrel to slug it up to bore size, then it can sometimes shoot well... but it's a careful balance between pressure and bullet hardness.
(But it is what BP does very well, and it's a combination often found in percussion revolvers)

 

[BackWoods Billy]

Thanks a lot for the info..As soon as I get my SBH back from Ruger I will size the cylinder throat. I've been sizing my bullets to .430 and thought I was good. I cracked the forcing cone on it and thought it was from the soft WW lead and the heavy loads. I'm pretty sure from what I have heard on here that could be the case. No leading with the softer lead,but a little with the harder stuff ( about 18 BHN )Thanks to you guys , I might get this right...

 

[scott0116]

The Lyman cast bullet handbook suggests sizing to groove. In another book i have an article, can't think of the book or author at the moment but the author tested 3 or 4 revolvers with bullets that dropped right through the cylinders against bullets that fit the chamber mouths and accuracy was equal and with some powders if i recall correctly was even better with the undersized bullets.

 

[scott0116]

Correction to the above post. In the article i referenced the author was using jacketed bullets in all tests. Any way i have asked the same question before and received the same responses. I do know that if using cast bullets that drop through the cylinder chambers you will need a lot of spare time to get the lead out!

 

[BackWoods Billy]

Thanks all. I tell you,I've asked all my friends that reload and a couple of the guys at the gun store and they all say to size to the groove. It all sounds good but i'm right back where I started.

 

[ribbonstone2]

OK..going to get real old-school. You haven't mentioned what revolver, so cant' be specific as to diameters or weights.

So am going to go though the process that was used back when I had no caliper or micrometer, no measuring tools at all.

Take 10 or 12 UNSIZED cast bullets, just as they fell out of the mold. Open the cylinder. Try to drop the unsized cast bullets through a chamber. Chances are, they hang up in the cylinder throat. When one hangs up, hold the cylinder up towards a strong light, and look. Is there a rim of light nearly all the way around that hung up bullet and just the edge/seam of the bullet is hanging it up in the throat? IS the bullet n a total pug in the throat, no light creeping in around the sides?

If there is light around at least part of the bullet, think of it as PASSING. If it is a total pug, no light showing around the edge, think of it as FAILING.

Either way, hand lube the unsized test bullets. Are going to get greasy, but you can just smear lube into the grooves by hand.

IF it passes the above, then load your 12 test bullets.

IF it failed the above test, then you'll need to dismount the cylinder from the revolver, clamp it in a padded vice, and push each bullet through a cylinder and out the throat. YEp, are using the chamber and throat as a sizing die. YOu will find (in most cases) the chambers/throats are not identical, and while it may be by a tiny amount, one of them is going to be smaller. Will take a lot of testing bullet fit into the cylinder (and a grease pencil to number the cahmbers helps a bunch), but find the smallest throat and use that as your sizer.


Shoot for accuracy.

NOW that's as LARGE a bullet as you can produce from that mold and alloy and still fit into the cylinder. Consider that your base line for comparison.

 

[BackWoods Billy]

Thanks. I"M mostly loading .44mag for Super Blackhawk and .38/.357 SP101 and a SW442. I will try that and see what they come out at. Thanks again, all of you, for your help.

 

[GBertolet]

Here is one solution for somewhat oversize cylinder throats. Coat the unsized bullets with Lee Liquid Alox. You could even coat them twice, provided you have room in the case to accept a bullet that large and will still chamber. It will increase the diameter of the bullets, sealing the cylinder throats off from the hot gasses, like a gasket, and the excess is scrapped off in the forcing cone, when it's not needed anymore.

 

[unclenick]

I am surprised by the advice to size to groove diameter. It is done with precision rifle bullets that are being breech loaded ahead of the charged case, but in revolvers it is odd to hear. Most factory lead bullet are made 0.001" over expected groove diameter as a mater of course. Marshal's technical manual has an experiment he did with a revolver firing different bullet diameters. 0.002" over groove proved most accurate, IIRC. Either more or less was less accurate in his gun. A lot of folks also find about 0.002" over does best in lever action rifles, as well. My 1895 likes them that way.

I think the general pattern I see is the tighter and more precisely made the gun and bullet alignment, the tighter you may be able to size bullet. If the gun is not so tight, the bigger diameters seem to do better. Like anything else involving guns, though, YMMV in your particular weapon. You just have to try it and see?

Just don't be trying new sizes with maximum loads to start. Find your best accuracy load. Don't believe all the loads listed in manuals will be safe in your gun—they are suggestions at best—so work up and back off if you get any sticky extraction.

 

[BackWoods Billy]

Thanks all. I tell you,I've asked all my friends that reload and a couple of the guys at the gun store and they all say to size to the groove. It all sounds good but I'm right back where I started.

Thanks Nick. I meant to say .001 over grove.

 

[ranger335v]

Cast bullet obturation, or up-set, in hot handgun loads is far more than most people would believe without seeing it even with "hard" bullets .

Dug a few hundred hard cast .357 and .44 SWC loads out of a distant defunct sawmill's sawdust pile back stop many years ago. At first I thought I wasn't finding any of my bullets because what I was finding had a much different nose configuration than mine. Finally realized the odd, near 1/2 wad cutter shapes I was digging out WERE my bullets! It just took them hitting a "soft" back stop at long range for me to recover undamaged slugs and see what was happening at firing. (Accuracy was great.)

So, by accident, I had found why my earlier bullet tweaks with tiny sizing changes had meant nearly nothing on my targets, they were slugging to fit the bore no matter what size they had been at ignition.

 

[digisol]

The revolver has a forcing cone, so named for good reason, but having correct size has squat to do the cylinder size, i've never had lead bullets that did not drop into any cylinder, in 38, 357 or 44, I would say the cases will have expanded to be near too tight if the lead was that large to be tight in the front of the cylinder.

 

[unclepaddy]

The revolver has a forcing cone, so named for good reason, but having correct size has squat to do the cylinder size, i've never had lead bullets that did not drop into any cylinder, in 38, 357 or 44, I would say the cases will have expanded to be near too tight if the lead was that large to be tight in the front of the cylinder.

I have a .38 special model 36 S&W that, when I slugged the bore and went .001 over that with lead bullets, the bullets would not chamber in the cylinder. Nothing wrong with the brass, just that the bullet was too fat to settle all the way into the chamber. In order to fire these bullets, I would have to have machine work done on the cylinder.

 

[digisol]

S&W are pretty good with faulty engineering / construction, you should have to do nothing but send it back for a new barrel.

I did this with a model 14 38, came back one of my best guns.

Should cost ya nothing.

 

[unclenick]

Sounds like the Smith had throats smaller than, or as small as groove diameter. That is fatal to revolver accuracy. Revolver accuracy smith's almost always start their work by reaming the chambers to SAAMI maximum. You can get that done for under $40 at cylindersmith.com. If you look through their throat sizes, you'll see they are either lead bullet size (.38) or one and a half thousandths over the groove diameter. So, lead bullet diameter or lead plus half a thousandths. That zero to half thousandth over will peak accuracy for most lead by offering tight bullet alignment as well as a good gas seal. For jacketed bullets, gas cutting is not an issue and they seem to be able to align themselves in a bore well enough that for most handgun accuracy levels you don't notice error from extra bullet tilt. But not so for lead. And even jacketed bullets won't shoot well from an undersized throat.

I think the ideal situation for lead would is a bullet 0.001" to 0.002 over groove, with throats half a thousandth over for ease of chambering. If you look at Beartooth Bullets shopping cart and select a bullet, you note that Marshal typically offers a number of diameters so you can pick one for your chamber. The best way to do that is to try different ones up to the size of your throats to see what works best for you.

It will still be the case that if your chambers have throats below groove diameter that, like a bore constriction, it will promote leading and reduced accuracy even if you pick a nominal bullet for the chambers. A friend of mine has a Ruger Redhawk that would not hold 6" at 25 yards with any kind of ammunition. It was returned to Ruger and came back with a slip stating the chambers had been reamed. It then shot sub-inch groups at 25 yards. Ruger did not charge for this, but today you can rack up $75 in air shipping charges for moving a handgun to the factory by common carrier. Removing the cylinder and sending only it would be a lot more economical. I don't know if the manufacturers will let you do that or not, but that's how the site I linked to works, so they may be cheaper for you in the end.