Tolerances on 9mm Loads

[johnw63]

I was loading some 9mm last night and felt pretty good about my work but was wondering how tight I really need to be with the tolerances. Specifically, the case mouth outside diameter is listed as 0.380 in all my manuals. Measuring after resizing but before flaring I was getting around 0.376 to 0.378 and I was getting 0.385 to 0.390 once they had been flared to accept the bullets. The bullets seemed to fit in perfectly with the flare I was using. Then upon seating with the taper crimp they were coming out around 0.378 to 0.381. Should I be concerned if they are not exactly 0.380 every time? Or is a .002 + or - close enough?
Also, regarding length, Three manuals listed COL at 1.100 with the FMJ round nose bullets and one had it at 1.090. So I was getting between 1.098 and 1.101. I felt pretty good about that range, but is that good enough? Or, should it be exactly 1.100 each and every time?
Thanks for any feedback.

[ScottRiqui]

You're not going to get repeatable accuracy down to the thousandths of an inch with consumer reloading equipment (I don't even know if commercial ammo is consistent to the thousandth.)

All of your tolerances sound fine to me - I don't think 1/100th of an inch setback is going to cause problems, and most of your rounds had nowhere near that much.

[Unclenick]

Originally Posted by Johnw63

Should I be concerned if they are not exactly 0.380 every time?

No. The actual cartridge spec is 0.3800" -0.0070". So .380" is a maximum for the loaded cartridge mouth only. The chamber spec is 0.3810" +0.0020", so if your chamber is in its middle range, you .381" rounds should still be OK, though I'm surprised you found cases with neck walls at maximum. With a 0.001" oversized cast bullet under such a case, it will, indeed, be 0.381". Take the barrel out and see if your rounds drop in? Push on one with a thumb. See if it still falls out when you invert the barrel? If so, you are fine. Also, unless you are using a thimble micrometer with 0.0001" resolution, bear in mind it is not unheard of for calipers to be off by as much as 0.002", and 0.001" off is pretty common. Use a micrometer for critical measurements. You can usually get one for around $15 from Enco.

Your cases should be small before you seat the bullet. Otherwise the neck can't grip the bullet adequately and it will be pushed back into the case on loading. That can raise pressure to unacceptable levels..

The length spec is strictly for ensuring your cartridges aren't too long for the magazine. Again it is a maximum, but this time there is no minimum involved. You can load as short as you want, as long as it isn't deep enough to raise pressure unacceptably. For round nose bullets, which are usually seated longest, most manufactures set their dies to be at least 0.005" below maximum to be sure they can't hang up in a magazine. Many go deeper than that. Get a seating depth recommendation from the bullet manufacturer for any particular bullet shape, if you can. Hornady lists theirs in their manuals.