reloading noob wonders about bullet diameter

[MrBorland]

ok, title says it all. Reloading noobie, here, but the question really was prompted by factory ammo:

I was at my bench tonight perusing my loading manuals. Out of curiosity, I pulled out a few (5) factory .38/.357 factory rounds, and took my caliper to them. I "calibrated" the caliper to a 0.44 rim diameter, and found they all had consistent (and correct) rim and case diameter as well as appropriate OAL.

What I was surprised at, however, was the variability of the bullet diameter when measured right above the crimp (but not within any visable cannelure). Though the specs say a .38/.357 bullet ought to measure 0.357 or 0.358" in diameter, the bullets I measured (all jacketed) ranged from 0.353" to 0.361". The empty brass from some 0.355" rounds even slid easily over the exposed portion of an unfired cartridge from the same box of ammo with room to spare. Is this normal? If I bought these bullets for reloading, how the heck would I set them? - seems they'd just fall down into the powder load.

Seems like the 0.353" bullet would rattle all the way down the barrel and ruin accuracy, whereas the 0.361" would be a pretty tight squeeze and increase pressure.

My questions are, then, is all this normal? When buying bullets for reloading, can I reasonably expect they're going to be 0.357" or 0.358"? And how much outside this size would be "allowable" before accuracy and/or pressure becomes an issue?

 

[ants]

Some bullets have a sharp step at the shoulder. The mold for my cast 45acp bullets does that. You seat the bullet so that the case mouth is right at the edge of the shoulder, then you crimp it. The only part of the bullet you can measure is smaller than the bearing surface. 'Bearing Surface' is the straight untapered portion of the body that engages the rifling in the bore. That's the part that will measure 0.357".

 

[ReloaderFred]

With a lot of loaded ammunition, you can't tell much by measuring the diameter of the seated bullet, as the ogive may start right where the crimp is. The only way to tell the correct diameter is to measure the bearing surface of the unseated bullet.

Hope this helps.

Fred

 

[rcmodel]

+1
No way a-tall to measure the bearing surface diameter of a seated bullet.

Don't even try.

rcmodel

 

[Mal H]

I agree with the above. The measuring method you're using leaves a lot to be desired and is not reliable.

I don't believe any manufacturer would be using bullets for any .38 caliber rounds that even approached .361" - even [*gasp*] A-Merc!

To answer your question: "And how much outside this size [nominal .38 sizes] would be "allowable" before accuracy and/or pressure becomes an issue?" I have found almost all manufacturers to be very accurate in their sizing of bullets. If they say it's .357, I haven't found variations much greater than .0005", and that's true for jacketed, plated, and lead. Now, you might find blemishes or small voids in some lead bullets where the true diameter is unmeasurable, but overall, stated bullet diameters are usually accurate. So, how much would I accept? No more than .001" in lead or plated (but I wouldn't buy any more bullets from that supplier), and no more than .0005" for jacketed.