Lead Bullet Sizing For Revolvers

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WrongHanded

WrongHanded

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I'm delving back into .357 Magnum with some hardcast gas checked 160gr and 180gr bullets.

If a bullet won't quite go through the throat of a chamber, but it's close, I presume it just swages down. But what effect does this have on pressure?

Let's say I have two revolvers. One will barely allow a bullet to pass through all throats. The other won't quite allow it. What am I looking at here with regards to pressure issues? Is it better to just go smaller and let the gas check do the work?
 
WrongHanded said:
I'm delving back into .357 Magnum with some hardcast gas checked 160gr and 180gr bullets.

If a bullet won't quite go through the throat of a chamber, but it's close, I presume it just swages down. But what effect does this have on pressure?

Let's say I have two revolvers. One will barely allow a bullet to pass through all throats. The other won't quite allow it. What am I looking at here with regards to pressure issues? Is it better to just go smaller and let the gas check do the work?
Click to expand...
Check the throats against the forcing cone. The throats need to be .002-.003” larger than the forcing cone and bore. Otherwise they will enter the barrel undersized and possibly not even straight. If the throats are too large, then the bullets will over pressure the forcing cone and could cause damage. Remember, chambers can always be enlarged, and bullets can be sized smaller or larger pretty easily, but chambers are really a pain to try and shrink.
 
GeoDudeFlorida said:
Check the throats against the forcing cone. The throats need to be .002-.003” larger than the forcing cone and bore. Otherwise they will enter the barrel undersized and possibly not even straight. If the throats are too large, then the bullets will over pressure the forcing cone and could cause damage. Remember, chambers can always be enlarged, and bullets can be sized smaller or larger pretty easily, but chambers are really a pain to try and shrink.
Click to expand...

That's some handy information to have.

I don't think there's more than .0005" of difference between the throats from gun to gun. I've never bothered checking anything else. The GP100 will allow .3580" to pass, but not .3585". I couldn't get a .3580" bullet into the throats of the new 686+. I will check some Speer GDs and XTPs to see how those fit. I believe they are .357".
 
WrongHanded said:
That's some handy information to have.

I don't think there's more than .0005" of difference between the throats from gun to gun. I've never bothered checking anything else. The GP100 will allow .3580" to pass, but not .3585". I couldn't get a .3580" bullet into the throats of the new 686+. I will check some Speer GDs and XTPs to see how those fit. I believe they are .357".
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Supposed to be 0.3585” throats with a 0.3575” forcing cone is ideal, with a 0.3570” bore. That way everything seals tight and there’s no gas blow-by. For a .38/.357 shooting cast or jacketed. I’ve seen Ruger revolvers with .002 variance in the throats and under size bore. Ruger will fix it free, of course but only if you catch it.
 
Personally, I would try .357 diameter and see how it does in both guns. I’d rather have the base bump up, than the whole bullet squashed down. I surmise, it causes lube to go places it shouldn’t when an oversized bullet goes through a cylinder throat. Though I only have limited anecdotal evidence.

I think it’s worthwhile testing both .357 and .358 in guns chambered in 38 and 357.

I’ve found that .430 sized bullets do better than .431 in my Blackhawk 44 special, even though the throats are all .431+ to .432+, with a .4292 bore. Why, I don’t know. But each gun likes what it likes and sizing to cylinder throats is not always the answer for accuracy or leading issues.
 
First slug barrels to find barrel groove diameter. A bullet sized to .3575" to .358" should work well in both guns.

A lead gas checked bullet thats snug in the throat, will be easly sized . .0005" of sizing is not an issue.


Barrel Forcing cones are larger in diameter then cylinder throats.

The face of the barrel, forcing cone-
"When cutting a chamfer, you normally do not want to have the internal di-
ameter of the rear-most portion of the chamfered area to be over .020" larger
than the diameter of the bullet of the cartridge that is being used. In other
words, in a .38 Special revolver, which utilizes a bullet that is normally .356"
to .358" in diameter, the maximum diameter of the chamfer should be
.376" to .378".
 
WrongHanded said:
I couldn't get a .3580" bullet into the throats of the new 686+. I will check some Speer GDs and XTPs to see how those fit. I believe they are .357".
Click to expand...

Both the GDs and XTPs fit the 686+ throats just fine.

And I did shoot it for the first time today. I was checking zero, and off the bench with a light load using the 158gr LSWC of .358" diameter, I put 8 shots inside 2". 6 of them at about 1". So those bullets appear to be accurate enough from it.
 
Bazoo said:
But each gun likes what it likes and sizing to cylinder throats is not always the answer for accuracy or leading issues.
Click to expand...
This is very true. My four tuned Rugers - .45Colt, .44Mag, .357Mag, and .32H&R - have very different personalities and preferences, despite being made consistent. They got personality. Try pins and see what they tell you first. But @Bazoo is right that it’s not a foregone conclusion.
 
WrongHanded said:
I'm delving back into .357 Magnum with some hardcast gas checked 160gr and 180gr bullets.

If a bullet won't quite go through the throat of a chamber, but it's close, I presume it just swages down. But what effect does this have on pressure?

Let's say I have two revolvers. One will barely allow a bullet to pass through all throats. The other won't quite allow it. What am I looking at here with regards to pressure issues? Is it better to just go smaller and let the gas check do the work?
Click to expand...

Go large. I shoot .358 bullets out of my S&W 627. Pressure signs do not show up and I've shot thousands of 180 grain LRN out of it.

I use the same size in my 929 9mm. After shooting a number of 9 millimeter bullets I found that my barrel was .357 so the larger bullet sealed the gas better and swaged down to just the right size for my gun.

I always go 1 - 2 thousandths above bore, preferably 2.
 
RealGun said:
I think you are tweaking the bullets only because you can. When I have had throats too tight for lead bullets of pretty standard diameter, I had my gunsmith open them up. He did a number of revolvers for me, both Ruger and S&W.
Click to expand...
Same here. The biggest hurdle is getting all of the throats the same - or at least within a couple tenths of each other. It’s a lot easier to remove material than add it.
 
Alright, I'm going to do the load workup with the GP, as per usual. Then try a few in the 686 and see if there's a difference. If I'm not getting similar results, I'll try a .357" diameter with a gas check and hopefully that will do it.
 
The bullet diameter should never be smaller then barrel groove diameter, as I am sure everyone knows by now.

What I have never seen, till lately, the same bullet sizing die can produce different bullet diameters. Softer alloys, smaller diameter after sizing.
Harder alloys, larger diameter, more spring back. Same size die.
 
243winxb said:
The bullet diameter should never be smaller then barrel groove diameter, as I am sure everyone knows by now.

What I have never seen, till lately, the same bullet sizing die can produce different bullet diameters. Softer alloys, smaller diameter after sizing.
Harder alloys, larger diameter, more spring back. Same size die.
Click to expand...

Ah, well here's another component to the story. I believe this sizing die variance may have happened with these 160gr and 180gr hardcast bullets I ordered. I ordered them both to the same diameter of .358". That's what they said on the box. The 180s fit the throats of my GP. The 160s wouldn't quite go.

I measured them and came up with .3575 - .3580" for the 180s, and .3580 - .3585" for the 160s. I'm using some $26 digital calipers, so accuracy with them isn't great. They measure to the nearest .0005", and they're often +/- the same just from opening and closing. But the go/no-go in the throats tells the real story.

I'm more concerned about overpressure with the longer heavier bullet, just due to there being more surface area to create additional friction as it moves through the throat. So it's good those came to me fitting the throats of the GP. They don't fit the throats of the 686+ however. And as I'm working up powerful woods loads without a whole lot of data to go by, I'm being cautious and considering as many factors as I can.

The 160s will be using 2400, but as they don't seat as deep as, say the 158gr LSWCs I shoot a lot, there's more case volume to work with. I'm hoping for 1300fps out of a 4" barrel, but willing to settle for less if safety becomes a concern.

For the 180s (because it's heavy for caliber) I'm going to try 300-MP, and there's just no data out there that I can find. The only reference I've seen is on a YouTube video, which is far from solid verified daya. So I'm being extra cautious with this one. I'll be running a ladder test over a chronograph first, and watching for pressure signs, cleaning the chambers and barrel between charge weights. If things look sketchy, I'll stop moving up and pull what I have remaining. I'm hoping this one will safely reach 1250fps. We shall see.
 
"I'm using some $26 digital calipers"

Inexpensive micrometer is better for measuring small, round things.
 
I'm a K.I.S.S. kinda guy now after years of overthinking the minor intricacies of reloading. For a new to me revolver I start with slugging the barrel. Then measure cylinder throats ("drop through", "push through", "tight" are not measurements and, IMO, not a lot better than a WAG. I have slugged cylinders, used pin/plug gauges and expanding ball gauges). This tells me that the cylinder throats are larger than the groove diameter. I then size the bullets to the same diameter as the throats. Tweeking bullet diameter is very rarely needed. This has worked quite well for my11 revolvers...
 
243winxb said:
The 2400 may produce higher pressures when using a magnum primer. https://castboolits.gunloads.com/sh...00-in-the-357-Magnum-with-6-different-primers

Best to use a standard primer?
Alliant
357 magnum 170 fr Speer GDSP Speer 1.59 10 Fed 100 300-MP 17.5 grs 1,620
Click to expand...

I wasn't intending to use magnum primers for 2400, and I never have. I've also never used magnum primers for 300-MP, but with the current scarcity and my dwindling supply of standard SPPs, I bought some CCI 550s and will be using those with the 300-MP.

I did see that data from Alliant. My experience with 300-MP in .357, .41, and .44 tells me that 100% case fill is common. So I measured the weight of a case full of 300-MP, then divided it by the internal case length, and multiplied that by that length minus the bullet seating depth. I came up with 17.3gr.

That struck me as awfully high for initial testing. So I set the top of the ladder at 16.5gr, as per the YouTube video, which coincided with my gut estimation prior to seeing the video. But my starting charge is 15.0gr. I'm heading out to do that testing now.

Edit: I was wrong about that starting charge. I began with 15.5gr and it was fine. I started a dedicated thread for those load workups.
 
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Walkalong said:
Oh, and calipers are nearly useless for measuring ID (throats) IMHO.
Click to expand...

I wasn't using them for measuring throats. And I understand why you say they're useless for it. I was using them to measure the various projectiles I have that either will or will not quite fit the throats.

Although, I may see if the little machine shop at work has something more appropriate for measuring the throats. Either way, I don't plan to have any work done to the guns I have. They seem to shoot fine.

All I was really wondering is, if a bullet is .0005 - .001" too large for the throats, whether it would cause notably higher chamber pressures. But perhaps that just not commonly available knowledge.
 
WrongHanded said:
I wasn't using them for measuring throats. And I understand why you say they're useless for it. I was using them to measure the various projectiles I have that either will or will not quite fit the throats.

Although, I may see if the little machine shop at work has something more appropriate for measuring the throats. Either way, I don't plan to have any work done to the guns I have. They seem to shoot fine.

All I was really wondering is, if a bullet is .0005 - .001" too large for the throats, whether it would cause notably higher chamber pressures. But perhaps that just not commonly available knowledge.
Click to expand...
As @Walkalong mentioned above, cast bullets sized .001" larger than throat diameter is a common practice. I've seen this recommendation for as long as I've been reading about revolvers (about 40 years) and don't remember ever seeing it qualified with any warnings about increased pressure. Anecdotal, but FWIW.
 
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