Bbl i.d.

[angle-0f-attack]

OK...I know this isnt a viable way of measuriing bbl id but I dont have a slug kit so heres what I did.

I hammered a Meister Bullets 115grn, 18 BHN, .356dia bullet through my s&w m&p 9mm bbl. It went in .356 +/- .001 and came out with od of pretty much .351 with calipers.

What say you?

[deltaenterprizes]

I say your measuring equipment or technique are faulty.

[sagacious]

Are you measuring the land or groove diam on the slug?

[angle-0f-attack]

Yeah..i know this a silly way of doing it...just seeing what results I got.

I cant measure straight across the bullet for groove to groove measurement I'm just measuring the OD before going through barrel and remeasured after by rotating the bullet 360deg and taking multiple measurements.

.356 then .350 (both +/- .001)

[Larry Gibson]

I'd say it's close enough for government work or an M&P anyways; size your bullets .357 or preferably .358 and load up some ammo and go shooting:-)

Larry Gibson

[Centaur 1]

The M&P has 5 groove rifling, you can't get an accurate reading with standard calipers.

[angle-0f-attack]

Ok..the bullet goes in .356 and comes out .350...however i measure it there's still a .005 difference.

Land to groove height difference is about .003...I think this close enough.

It tells me that bullet is swaged in my barrel sufficiently.

What it does NOT tell me is if .006 is TOO MUCH of a difference?

Should it have come outta my barrel with a bigger O.D.?..a little less difference?

Do I need to find a smaller dia. bullet or is that tight of fit what I'm looking for?

[sagacious]

Ok..the bullet goes in .356 and comes out .350
...
What it does NOT tell me is if .006 is TOO MUCH of a difference?
No, .006" is not too much. Remember, that's only six thousandth's of an inch-- a quite small measurement. The lead bullet will size-down safely, if that's what you're concerned about. Start at the recommended beginning powder charge, and you'll likely not run into any surprises.


Do I need to find a smaller dia. bullet or is that tight of fit what I'm looking for?
Tight fit is best, both in the barrel and for proper casemouth tension. You wouldn't likely be able to get sufficient casemouth tension in 9mm with a bullet less than .355", as that's probably what your dies are set up for. If .356" chambers properly, then start with that and see how it shoots in your gun. Good luck.

[angle-0f-attack]

Excellent.

I just read that bullseye powder burns more efficiently than Win 231 so I think I might try those bullets with 4.0-4.5 grains of the Bullseye for cup of around 22,00.

Lymans book states 3.5grns to start to a maximum of 4.8 grns for a jacketed bullet so I'm thinking the 4.0grns is a good place to start for a 18 BHN lead bullet....?

Opinions?

[RobS]

Since you used an 18 BHN slug then there is likely to have some spring back with that alloy hardness so your bore measurements could very easily be a bit smaller than what you are reading. If .358 will chamber that is the route I would go and if not then .357. Casting for the 9 mm, it's always better to start on the larger diameter side then to try the small/"dark" side as this can lead to headaches that will linger on for days, weeks, and even months before you figure out what is going on.

Next time if you can try and find some soft (plain) lead to slug your barrel with so you can get yourself a better reading. Egg fishing sinkers will work well, however if they are the hard ones that many companies are putting out there these days then simply drill the hole out to a bigger diameter so the sinker can give and fit to the bore better.

[lwknight]

It might be a bit of a trig challenge but , I think there might be a way to accurately measure the bbl. It would require precise measurements of the width of the riflings and grooves plus the rotating measurement.
For what I call ( for lack of a better term ) is the minimun setting on the micrometer
in which the bullet/slug will be rotated with only light resistance.

I think I might be overthinking if it but simple trig may not get it. And my calculator does not directly have secant functions.
I hope someone smarter than me picks up on this before I have to remember how to work secants. Then again maybe simple trig can work.

Maybe I should shut up before I get a headache.

On farther thought. just plain geometry might get close enough.

[sagacious]

Excellent.

I just read that bullseye powder burns more efficiently than Win 231 so I think I might try those bullets with 4.0-4.5 grains of the Bullseye for cup of around 22,00.

Lymans book states 3.5grns to start to a maximum of 4.8 grns for a jacketed bullet so I'm thinking the 4.0grns is a good place to start for a 18 BHN lead bullet....?

Opinions?
If Lyman lists 3.5 as the "start", you may wish to begin with exactly that. One good way to approach this is to load 15 rounds at 3.5grs, 15 at 3.7grs, 15 at 4.0, etc. You will learn something relevant about what the various powder charges are actually doing during your range session. That info is very useful, especially if you keep a reload log and keep range notes of each load. You will find that info useful years from now.

What you do not want to do is load up a box (or boxes) of one single load and then hit the range. You may find you now have 200rounds of 9mm ammo that does not function/isn't accurate/leads like crazy/etc. Testing a range of powder charges is much more informative.

Lyman #47 lists 3.8grs to 4.9grs BE with the #358345 115gr 9mm cast.
Also, 3.7grs to 4.4grs BE with the #356402 120gr 9mm cast.

Btw, beginning and mid-level loads of W231 and the LEE 120gr tc cast from ww's is very accurate in several of my 9mm's. I have loaded the 9mm 120gr lead up to 4.4grs BE with mixed results (some great, some not-so-great), so don't rule out W231 just yet. Good luck.

[nicholst55]

Wrap a thin piece of shim stock tightly around the slug, mike it, then subtract the thickness of the shim stock X2. That should give you a pretty good idea of the groove diameter.