Variation in Cartridge OAL (overall length)

[Ben Nelson]

Hey guys, gotta question . . . I reload 9 mm and do not trim cases to the same length. Is the case length variance the sole factor on cartridge OAL variation? I am seeing OALs vary in the 0.010" to 0.015" range.

 

[Leo]

No Sir, tha case trim length has nothing to do with Cartidge OAL. That is simply according to the die set up and the press. When you say .010" to .015" do you mean total or do you mean .015" plus or minus where you could have a total of .030" from shortest to longest? .010" total is not bad in a handgun. .030" is somewhat excessive in my book.

Things to look for:

Are you setting your dies at the place where the handle on your press is at a Mechanical stop?
Does the seater stem in your die have a flat nose or a cup? I have seen cupped stems seat all the bullet ogive diameters the same, but the bullets have a little variation between the ogive and the point.
Is there wax build up in your seating die from loading cast bullets?
Is your case holder too tight to allow the base of the brass to rest flat on the bottom? I have seen tight shell holders hold the brass up by the groove, not letting the base sit flat, throwing off OAL.

 

[Ben Nelson]

No Sir, tha case trim length has nothing to do with Cartidge OAL. That is simply according to the die set up and the press. When you say .010" to .015" do you mean total or do you mean .015" plus or minus where you could have a total of .030" from shortest to longest? .010" total is not bad in a handgun. .030" is somewhat excessive in my book.

Things to look for:

Are you setting your dies at the place where the handle on your press is at a Mechanical stop?
Does the seater stem in your die have a flat nose or a cup? I have seen cupped stems seat all the bullet ogive diameters the same, but the bullets have a little variation between the ogive and the point.
Is there wax build up in your seating die from loading cast bullets?
Is your case holder too tight to allow the base of the brass to rest flat on the bottom? I have seen tight shell holders hold the brass up by the groove, not letting the base sit flat, throwing off OAL.

Leo: To clarify, my OALs in my current batch of hollow points range from 1.140" to 1.155".

 

[Vamptepes]

That's a pretty large difference if you think about it. Last batch of 9 I ran tried to keep within .005 of each other. No more then .01 off

 

[Grelber]

Leo: To clarify, my OALs in my current batch of hollow points range from 1.140" to 1.155".

So with 9mm you are at something like a 1.1475" average and your total variance is + - 0.0075" ?

Personally I'd be happy happy.

 

[Sling10mm]

I would agree with Grelber that +/-.0075 is acceptable, especially for a round nose pill. I tend to see more consistency (less variation) with flat nose/hollow point bullets.

 

[Grelber]

Nagging curiosity made me dig out the manual that came with my Dillon 550B.
On page 12 it says "Overall length (OAL) may vary up to .016", and this is normal".

Do not know how .016" was arrived at and etc. , just for what it is worth.

 

[Ben Nelson]

Knowing an acceptable variation in OALs certainly helps when loading near the min OAL for a load or the max OAL for the 9 mm . . . Sounds like my OAL variation is acceptable. Thank you.

 

[d30carls]

I have found on my single stage press if I pull it down easier I tend to get a little more changes in my OAL but if i smack it down pretty hard every time I get more consistency in my OAL I think it is the way I pull it down not usually hard but the slight changes in pressure seem to make differences