I've been using 125 grain hard cast CNBB bullets made by R&C Bullets for years in my .357 Magnum revolvers. I order these bullets sized .357, and I developed an excellent load with them.

Now I would like to try them in my 9mm S&W Model 915 pistol. Should I resize them to .355, or .356?

With cast bullets you can usually shoot up to around 0.003" oversize (assuming they chamber OK) before accuracy deteriorates. Sizing them too small is a much greater sin because it allows gas to leak around the bullet base as it goes through the gun. That erodes and melts the bullet alloy and it winds up plating your bore and requiring a lot of cleaning.

The industry standard is to size cast and swaged lead bullets 0.001" over groove diameter. In your case, that would be .358" if your groove is 0.357". However, I find greatest accuracy occurs when the bullet is another half to one thousandth bigger than that.

You need to measure your groove and chamber diameters for best results. If your chambers are smaller than the groove diameter, the gun will have a lot of trouble with leading from cast bullets. In that case you would get the cylinder chambers reamed. Otherwise I would just order .359" bullets myself.

With cast bullets you can usually shoot up to around 0.003" oversize (assuming they chamber OK) before accuracy deteriorates. Sizing them too small is a much greater sin because it allows gas to leak around the bullet base as it goes through the gun. That erodes and melts the bullet alloy and it winds up plating your bore and requiring a lot of cleaning.

The industry standard is to size cast and swaged lead bullets 0.001" over groove diameter. In your case, that would be .358" if your groove is 0.357". However, I find greatest accuracy occurs when the bullet is another half to one thousandth bigger than that.

You need to measure your groove and chamber diameters for best results. If your chambers are smaller than the groove diameter, the gun will have a lot of trouble with leading from cast bullets. In that case you would get the cylinder chambers reamed. Otherwise I would just order .359" bullets myself.

Thank you for your informative reply. :)

I've been using 125 grain hard cast CNBB bullets made by R&C Bullets for years in my .357 Magnum revolvers. I order these bullets sized .357, and I developed an excellent load with them.

Now I would like to try them in my 9mm S&W Model 915 pistol. Should I resize them to .355, or .356?

Unklenick covered the reasoning well.

With what you have on hand, would try 356" or even the non-sized .357". If working up a target load and n ot striving for max. velo, the larger size just might work out fine.

Have read of some WWII 9mm's having bores as large as .359" but I've not run across any that large. have had more modern 9mms refruse to shoot well until the bullets were .357 or .358", but while that's not real uncommon, it is rare.

Even a true .355" bore can shoot well with .357" lead bullets, just not usually at max. velocity...but for typical target/range use, not much difference in tossing them out at 1100 than there is at a full 1200.

Unklenick covered the reasoning well.

With what you have on hand, would try 356" or even the non-sized .357". If working up a target load and n ot striving for max. velo, the larger size just might work out fine.

Have read of some WWII 9mm's having bores as large as .359" but I've not run across any that large. have had more modern 9mms refruse to shoot well until the bullets were .357 or .358", but while that's not real uncommon, it is rare.

Even a true .355" bore can shoot well with .357" lead bullets, just not usually at max. velocity...but for typical target/range use, not much difference in tossing them out at 1100 than there is at a full 1200.

Thank you.

My one real concern is obtaining a safe and functional O.A.L. when using these rather long bullets in 9mm cases. Please take a look at the cast 125 grain CNBB bullets at: http://www.rserv.com/

I'm going to have to seat these particular bullets deeper in the pressure sensitive 9mm cases to achieve an O.A.L. that will function in my magazines, and not cause any F.T.F. problems.

For jacketed 9mm bullets I use HS-6 and PP. But for cast bullets I plan on using Unique.

The 125 gr CNBB at .357 doesn't look different than the 125 gr CNBB at .356 on that web site. With a CN design in 9mm my experience is that you just have to seat deeply enough that the front band will not prevent chambering. I doubt there will be a problem with fitting the mag or F.T.F. I usually use a 138 gr CN cast at .356-.357 in 9mm that is .582" long at 1.075" COL.
Do you use a chronograph when working up your loads?

The real challenge with a slightly larger bullet in the 9mm might be chambering, as the case is not that forgiving of longer or larger bullets (or both). You might see some bulging, and very often the throat is very short and steep. So, an oversized bullet might cause interference when feeding, or even when seating the bullets (I have some experience with this)

The 125 gr CNBB at .357 doesn't look different than the 125 gr CNBB at .356 on that web site. With a CN design in 9mm my experience is that you just have to seat deeply enough that the front band will not prevent chambering. I doubt there will be a problem with fitting the mag or F.T.F. I usually use a 138 gr CN cast at .356-.357 in 9mm that is .582" long at 1.075" COL.
Do you use a chronograph when working up your loads?

Thank you.

No, although I've often thought about purchasing a chronograph, I never have. Instead, I depend on my data manuals and develop loads that are safe to use in my firearms. It might be a slower process, but it still works.

The real challenge with a slightly larger bullet in the 9mm might be chambering, as the case is not that forgiving of longer or larger bullets (or both). You might see some bulging, and very often the throat is very short and steep. So, an oversized bullet might cause interference when feeding, or even when seating the bullets (I have some experience with this)

I'm not really concerned about the aesthetics of slightly bulged cases. But if the cartridges won't reliably function in my pistol, I'll have to scrap my little experiment with these particular bullets and use them only in my .357s and .38s.

For safety's sake, I am inserting a comment here. A chronograph is useful for looking at shot to shot consistency and identifying the point at which increasing powder charge causes little increase in velocity (a high pressure sign). It is not safe to use a chronometer to adjust powder charge to match a published hand load or commercial load velocity. The chronometer instructions will warn you strongly against this practice.

There are four reasons the above is true. First, many inexpensive chronometers are sensitive to lighting conditions and do not produce reliable absolute accuracy. One fine sunny day my dad had his Chrony out and I had my Oehler 35P out. He was working up .308 loads in one of his rifles. The Chrony consistently gave his load right around 2700 fps (which strained credibility), while the Oehler consistently gave about 2500 fps (much closer to QuickLOAD predictions and loading manual listings). Dad's Chrony will give him a good idea of % deviation and extreme spread, but good absolute accuracy is just not in the cards for that unit. You tilt it a little, and the light change alters its readings. YMMV, but you cannot trust any chronometer, not even a calibrated one, will necessarily match the one used by a load manual’s authors or by a commercial load developer.

Second, your gun doesn’t have the exact same internal dimensions as any other gun a load may have been developed in. Peak chamber pressure depends on the volume a case expands to in a particular chamber, and the dimensions of a gun’s throat and bore. A load reaching a certain velocity at a certain peak pressure in one gun cannot be expected to perform identically in any other, not even if it is the same model. I have, for example, seen the same lot of match ammunition's muzzle velocity vary from 2475 fps to 2620 fps from one M1 Garand to the next. Thus, making a load up to a particular velocity may underload one gun or overload another.

Third, many people don't realize that velocity is affected by barrel length. They see a load with a published velocity and think they should get that same velocity even if their barrel is shorter than the barrel it was developed in. Most people don’t realize that the complete SAMMI specification for each chambering includes test barrel dimensions. These barrels have a minimum size chamber, specific rifling dimensions, and a specific length. Any load fired in a bigger chamber or in a shorter barrel length or in a barrel with greater rifling cross-sectional area will achieve lower velocity with a given load.

Fourth, manufacturers use non-canister powders that have not been blended to closely match a standard burning rate as have the canister powders sold to reloaders. Some commercial load powders, like that used in Hornady’s Light Magnum line of ammunition, cannot have their velocity duplicated by currently available canister powders. Attempts to load to match the velocity of these loads with other powders will probably result in unsafe pressures.

Watch out for dangerous assumptions!

Greysky,

If your loads are a workable COL but won't chamber, get either a Lee Factory Crimp Die or a Redding Profile Crimp Die. These will force outside dimensions to be functional, even if it means squeezing the bullet down inside the brass.

Greysky,

If your loads are a workable COL but won't chamber, get either a Lee Factory Crimp Die or a Redding Profile Crimp Die. These will force outside dimensions to be functional, even if it means squeezing the bullet down inside the brass.

Thanks again for the information... You fellows have instilled some new confidence in me regarding the use of unjacketed bullets.

Excellent points Nick! I have experienced enough to reinforce all of your comments. With cast bullets I use a chronograph to check that my loads are consistently slow enough, preferring to avoid leading and pressure signs.

I choose the think outside the box, but that is the new paradigm so I may be a brainwashed lemming.

I choose the think outside the box, but that is the new paradigm so I may be a brainwashed lemming.

Speaking only for myself... NOT! :p

For my 357 Mag - I don't size as they drop from the mold at .358-9"! For my .380 I size them to .357 and they seem to shoot alot better!

I would try dropping a .358" bullet in each of your revolver's cylinders, and see if they get stuck. They should require a slight "shove", with a pencil or some other object, to force them through your cylinder. This is the easiest way to tell if a bullet is the correct size for your revolver. I suspect your .355" and .356" bullets will fall right through, meaning they're too small. Good luck.

ive allways had my best luck with .357s at 358 and 9mms at 357

Curiously, the SAAMI drawings I have in my NRA Handloading book shows the spec on the barrel's groove diameter to be .355" and the bore diameter to be .346" for the 38 Spl, .357 Mag, and 9mm! I never could figure out why the bullets are sized differently? :confused:

The .38's were all derived from the old .36 caliber black powder revolvers, as far as I know. The higher numerical designation was a kind of advertising hype to make it sound bigger. 0.38" is the case diameter rounded up to the nearest hundredth of an inch. Thus your chamber would be cut to fit that .38 case and you could say the gun was chambered for that diameter.

9mm is just an even number of millimeters that coincidentally falls quite close to the .36 when you convert it. 9 mm/25.4 mm/in = 0.35433".

I've never noticed the NRA published drawing you refer too. I'll have to look it up when I get home. It is certainly in error, as the .357 and .38 caliber guns I own are right at about .357. I also notice that Cylindersmith.com, which does cylinder reaming for accuracy by going about 0.001" above groove diameter, is reaming .357's and .38's to 0.358", so they must not be finding those 9 mm bore dimensions common in these chamberings either. So I don't know what to make of it?