9mm barrel dimension & sizing question

[John in AR]

I'm a long-time reloader but am completely new to casting. I slugged seven different 9mm barrels today (four factory and three aftermarket threaded), and was surprised at the measurements. If it matters, I was using Rainier 124-grain plated bullets. All measurements on all bullets were taken with both analog and digital calipers, as I'm one of those overly-conservative types.

All factory barrels I checked (glock 19, glock 26, M&P full-size and M&P compact) all slugged out at exactly 0.3560"; every one of them. But the aftermarket barrels all measured tighter. An M&P threaded barrel from Storm Lake measured 0.3545, which seemed tight but not ridiculously so. The surprise was with two KKM threaded barrels. One for glock 19 and one for glock 26; they both measured out at 0.3530"; both of them, exactly. I was surprised enough by it that I did both of them twice. All four bullets came in at the same 0.3530".

Is that normal for 9mm dimensionally? All of these barrels are well-used (mostly with jacketed bullets and some plated), and I've not had any problems with any of them; so there's no functional problem. Just not sure how it will translate to use with lead projectiles.

I plan to cast my first bullets this week, making up some .356 124's and .358 125's; all lee six-cavity aluminum molds. The plan is to tumble-lube with Ben's Liquid Lube. I know that only after casting, measuring, and even loading & shooting them will I know for sure, but am just wondering what likely issues (if any) I'm liable to see with barrels that tight.

I'm frankly hoping to avoid the need to size. These are intended for close-in pistol use, not hunting or long-range paper punching; and I know that based on how the molds cast with my alloy (probably 80% coww & 20% scrap salvage lead), I'll have to experiment & see which barrels like what bullets at what size.

Just looking for feedback & thoughts from those who have gone there before me, trying to reduce my learning curve as much as possible. Am I likely to need a .355 sizer for the .3530 barrels (or am I over-worring about it); things like that are what I'm wondering at this point.

Thanks in advance.

[runfiverun]

you need a slug that squeezes down into the barrels diameter to get the real story.
many of the 9mm barrels i have measured have been more like 357, and the one taurus i done was real close to 358.

many of the newer guns don't have a throat so design becomes more important, and correct sizing makes a huge difference.
i size to 358 for my pistols.
some size down to 356 just so the round will chamber.

i would start with one gun and work with it, then introduce the others to what works in that gun and see how it goes from there.

[454PB]

I own four 9mm pistols, and they all slug between .355" and .356". I size to .357" for all of them......but you have to consider that the loaded round may not chamber if the boolit is oversized.

[John in AR]

you need a slug that squeezes down into the barrels diameter to get the real story...

Not sure what you mean..? I used a plated lead bullet, driven thru from the chamber to muzzle end. Are you saying that a pure lead (non-plated) bullet would give a different measurement?

[wv109323]

I would use one of my cast bullets to slug the KKM barrels again. I would also try to determine if there is a tight spot in the KKM barrels. It is odd that the smaller diameters are in threaded barrels.
Soft lead is usually used to slug.

[jcren]

Not sure it will make a difference, but soft lead (finishing weights or bp balls) are the standard for slugging, so you might double check just to be sure. Size wise, if you aren't loadi g to max pressures, 2 or 3 thou won't hurt.

[JeffG]

Not sure what you mean..? I used a plated lead bullet, driven thru from the chamber to muzzle end. Are you saying that a pure lead (non-plated) bullet would give a different measurement?

The cast bullet will need to need larger than groove diameter and typical jacketed are smaller than groove diameter by a couple thousands. I have never used plated bullets but expect they may also be smaller than groove diameter. By using a pure lead slug that is larger than groove diameter, you get a more accurate measurement.

[mdi]

Not sure what you mean..? I used a plated lead bullet, driven thru from the chamber to muzzle end. Are you saying that a pure lead (non-plated) bullet would give a different measurement?

I would say so. Plated bullets are not necessarily soft enough to form into the grooves as well as plain lead will do. Plus, even though the copper plating is soft, it's harder than soft lead, which swages to groove diameter easily. That's why nearly everyone suggests soft lead slugs at least .010"larger than the groove diameter...

I have three 9mm pistols and the groove diameter runs .355", .356" and .358" (an old Tokerev). I find micrometers give a more consistent measurements than calipers (calipers have long, often springy jaws).

[John in AR]

I would use one of my cast bullets to slug the KKM barrels again. I would also try to determine if there is a tight spot in the KKM barrels. It is odd that the smaller diameters are in threaded barrels.
Soft lead is usually used to slug.

I'll probably try re-slugging them. I actually cast some of the Lee TL356-124 bullets last night, so it would be simple to re-do them (again).

On the tight-spot possibility, that was one of the things I tried to feel for when doing them the second time. While not scientific, I couldn't subjectively 'feel' any different/tight spots in the KKM barrels. They felt like pretty consistent resistance the whole way through.

Don't know what to expect (yet); that's what the learning curve is all about, I guess...

[amc401]

I agree with everyone here, a pure lead bullet or round ball will probably give the most accurate details of your barrel and maybe a little easier to push thru. What works great for me on the 9's is the Hornady muzzleloading round ball 36 caliber .375 diameter, these are pure lead. Welcome to the casting world, what a fun experience !

[ioon44]

Lots of good advice here, I might add some thoughts.

Your alloy maybe too soft for 9 mm, I stay close to 6-2-92 alloy for 9 mm 14-15 BHN range.

Most 9 mm barrels range .356" to .357", I size to .3575" this has given me the best accuracy with Hi-Tek coating.

Reloading 9 mm with .3575" bullets I have to use a .38 cal expander so the bullets are no swagged down to under bore diameter in the loaded case, there has been a lot of discussion on the forum about this subject.

I don't think any of us ever get out of the learning curve, hope you enjoy casting.

[rsrocket1]

My M&P 9 FS barrel and Shield 9 barrel slugged at 0.3545" and my Beretta 92FS slugged at 0.357". The important part was that the throats of the S&W barrels slugged at 0.356" and the Beretta at 0.358". This means I could either seat 0.358" bullets to where any part that wide had to be under the rim (0.27" seating depth) or else size to 0.356", load longer and hope the bullets would bump up for the Beretta. My slower powders would be able to drive the deep seated bullets fast enough to get good ejection (1100 fps) without going over pressure, but I just got an 8# jug of Titegroup and to get 1100 fps would put me right on the edge of P and +P which I did not like.

I later found that 0.356" bullets did actually bump up in the Beretta so long as I kept the pressure up for my alloy (reclaimed shot).

If your guns can cycle properly with slower bullets, you can load them unsized so long as you keep the driving band completely below the case rim. Here's an example of what I mean with a .40 cartridge:

[Moonie]

For 9mm I would take a spare 9mm case, leave the primer in, fill it with lead, let it cool. Remove it with a kinetic bullet puller, lube it up and tap it through the barrel, do not use a wooden dowel for this. Measure with an accurate micrometer (do not use a caliper).

Never heard of an accurate measurement being taken with a plated bullet, as they may not be big enough to get a true measurement to begin with. You want a slug larger than the largest possible groove diameter. Using the above method works well as it tends to be tapered on the end that was furthest in the case so it should start easily.

[.22-10-45]

surprisingly, it really doesn't take much additional hardening over pure lead to show springback. I have Corbin swaging dies that when made were based on pure lead..and pure lead samples sent back with dies proove it..but when sizing a soft 30-1 lead-tin alloy...bullets will be .0002" to .0003" larger in dia. You really need to own a quality micrometer for slugging..calipers just don't have the feel for precise measurement.

[DougGuy]

You need a dead soft (pure lead) ball to slug with. Any alloy will have spring in it and can throw off your measurement.

Also, you CANNOT measure accurately with calipers, no matter analog or digital or who makes them. You will get readings that are JUST close enough but not as accurate as you need them to be.

Measuring a soft round object throws it's own error in there because if you measure with a good mic that reads in .0001" with minimal tension on the anvils they introduce a flat spot every where you take a reading, however, this will prove to be the most accurate measuring tool of the bunch. I prefer a Mitutoyo that has the mechanical digital readout on the side of it and a ratchet stop on the adjuster as it imparts the least amount of distortion at the point of measurement, but it does this consistently time after time and this is what you need to measure a slug with. I think I paid about $40 for mine from fleabay and it arrived in good working order.

There is a sticky thread on slugging a barrel here that is a good read. Basically you want the barrel clean and very lightly oiled and there are several ways you can use to push the slug in, some drive it straight through, but the most accurate is driving it in part way and then swaging it by driving from the other direction against a stop, then pushing the slug out.

[ironhead7544]

I use the slugs from Lead Bullet Technologies. You dont have to hammer them down the bore. Well worth the money.

You can feel any restrictions.