Educate Me Please

[Pirate69]

I am shooting Lee 358-125-RF cast in my Sig 9MM. They drop at about 0.361" and I size them to 0.358". I seem to have a nice load and no leading at 3.7 grains of Unique. I having been wanting to slug the Sig barrel just to have the data. Thought it might be possible to retrieve a fired boolits from a sand trap and get some data. I fired 5 rounds into a fine "play sand" trap at 25 yards. I got great expansion that was all slightly greater than 0.5". The bases of the boolits looked to be undisturbed. I measured the base of the boolits and they ran from 0.353-0.354". Is is possible the barrel diameter is that small or is something else going on that I do not understand.

[Winger Ed.]

Is is possible the barrel diameter is that small or is something else going on that I do not understand.

Of course its possible.

Over the years, there's lots of discussion about sizing 9mm anywhere from .355 to .358.
It basically comes down to what works best for you.

[gwpercle]

Slug your barrel and you will then know the size . Measuring the bases of rounds fired into sand may be misleading . If the slugs are expanding to 0.5" , and I'm assuming no hollow point , then that is a good load / alloy .
I load for 4 different 9mm Lugers and size all boolits to .357" , which works in all 4 .
The throat or lack of throat , is where some 9mm's hang up ... make sure they pass the plunk test and you will be good.
Gary

[Char-Gar]

Once a bullet leaves the barrel, it is subject to multiple forces that can distort it's dimensions.

[Cast10]

All my Glock 9’s (5) use .357.

[fredj338]

If you are doing fine with 0.358", no real reason to slug the bore. I have a bunch of diff 9mm & went from 0.356, 0.357 & 0.358. They all shot about the same, glock or what ever. So I settled on 0.357" coated, fewer issues with thicker mixed brass.

[bangerjim]

all my 9mm's are 357, so that makes it easy to cast for all! Some of my molds are 357 and others are 358. The sizing die takes care of any discrepancies.....after PC, that is.

Slug your barrel if you are concerned.

And........YES........barrels vary...........a lot sometimes.

banger

[Larry Gibson]

And.....if you are lubing the cast bullets then the bullets will come out of the barrel smaller than groove diameter. The bullets will be swaged down smaller because they will ride a layer of lube in the barrel.

[justindad]

The Poisson Ratio may be at play here, which means if a material is distorted by a force in one dimension (say, the x-direction) then it can contract or expand in other unrelated dimensions (y-direction or x-direction).
*
If I use the collet style LFC Die on my .357SIG case and overcrimp, the neck area under the crimp expands out a bit. I would not trust the base measurement of a fired boolit.

[johnsonian09]

Both my m17 and p365 use .357. The m17 has a sub compact module 320 with the smaller barrel, that liked 356 better. But that’s one barrel out of 3. Slug yours and that will tell you what you need to do


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[GregLaROCHE]

If you don’t want to slug the barrel, consider finding a swimming pool you can shoot several into.

[MrWolf]

And.....if you are lubing the cast bullets then the bullets will come out of the barrel smaller than groove diameter. The bullets will be swaged down smaller because they will ride a layer of lube in the barrel.

Never thought of that. Thanks.
Ron

[Messy bear]

Like Larry said- they are smaller after they leave the barrel. Have many that show that

[Ziptar]

To slug a 9mm get some Size 9 or 1/4 ounce lead egg sinkers. For $5.99 and shipping you can buy enough to last you a lifetime.

You'll also need a solid brass rod that's a least two inches longer than and is as close to the internal dimensions of your barrel as possible. You can use steel rod but to minimize scratching the bore I'd recommend going just a tad smaller, polishing it, adding several single wraps of masking tape at intervals, and pounding a empty .25 ACP or .22LR case onto the end. DO NOT USE A WOOD DOWEL!

You'll also need a hammer, a micrometer (borrow one?), piece of carpet or neoprene rubber (optional).

The closest size brass rod your local hardware store is most likely to stock is 5/16". You can order a foot long piece of 11/32" (.34375") of brass rod from Mc Master-Carr for $15.20, that's about as close as you can get.

Once you've got your egg sinker, brass rod, hammer, and micrometer lightly oil the barrel by running and oiled patch through. Push the egg sinker into the chamber as far as you can with your fingers. Then grab your rod and hammer and tap the egg sinker through the barrel. I place the muzzle down of a piece of carpet and tap until the bullet is a 1/2" to 1" from the muzzle. When it reaches the end hold the barrel up as you tap so it doesn't hit the bench surface and mushroom . Tap until the egg sinker drops out and measure it with your micrometer.

The 1/4 ounce egg sinkers measure .367 going in. The barrel in the picture is from a well used Israeli surplus FEG PJK-9HP. I also have two well used Israeli surplus FN Hi-Powers and an Iver Johnson 9MM M1 Carbine. They all work great with the Lee 358-125-RF sized to .357.

[Pirate69]

And.....if you are lubing the cast bullets then the bullets will come out of the barrel smaller than groove diameter. The bullets will be swaged down smaller because they will ride a layer of lube in the barrel.

In this case, they are powder coated. I am not having any leading problems; just curious about the readings I saw.

[waco]

Just fire the biggest diameter that will reliably chamber in your gun. All my 9mm's get .358"