9MM & OAL, does it matter?

k9cougar · April 28, 2010, 07:51 PM

I've loading for only a year primarily for a glock 19 using 4.4g W231 with 124 gr plated rn. I really didn't pay that much attention to OAL. I simply grabbed whatever 9mm was on hand from a store, dialed that length into my die, and loaded. I've been doing a bit of reading in this forum and find wide variance recommedations in the OAL for 9MM. As long as you are within the min-max why does it matter? Do you get greater accuracy or stopping powder with longer or shorter OALs? Do you usually load toward the minimum, maximum, or in between and why? Just looking to learn.

Brian Pfleuger · April 28, 2010, 08:13 PM

It matters because different lengths can DRASTICALLY change peak pressure.

As in blow up your gun drastic.

Plus, maximum over all lengths are intended to insure that your finished ammo will fit and feed in a SAAMI spec magazine and chamber.

Minimum lengths are intended to insure that the bullet is properly gripped by the case and that pressures do not become excessive. Shorter lengths decrease the space that the powder has to burn, which increases pressure.

Different bullets, even of the same weight, have a different profile and your die will not touch all bullets in the same place. As such, setting your die using factory ammo does not insure either a consistent or safe final product.

In short, the process that you describe is potentially extremely dangerous.

32dgrz · April 28, 2010, 08:42 PM

Suggest the best OAL for our 9-124 Gr. HBFP is 1.050.

NOTE: Please take notice of our shorter than normal OAL - and if you are using other data for the same weight bullet - with a longer OAL - you will need to reduce the powder charge slightly, so you do not increase pressures too much.

Stay Safe,

Bud Watson
Berrys Mfg Inc

Coffeeshop123 · April 28, 2010, 09:38 PM

What Peetzakilla said. The cartridges headspace off of the case mouth, but OAL is important because of the distance the bullet jumps before engaging the rifling and the amount of free space left in the case when the bullet is seated. The "jump" before engaging the rifling affects both accuracy and chamber pressure.

You can safely use a factory round to set your seating die...if you're using the exact same components the factory uses. Case and bullet dimensions are critical, powder and primer type are important too. That's why a lot of loading manuals specify different OAL's for different loadings; the OAL's listed account for space left inside the cartridge but also ensure the cartridge fits inside the magazine, feeds/chambers properly and the bullet isn't too close to or too far from the rifling. If you're not 100 percent sure about your OAL then just work up your loads slowly, looking for signs of high pressure (excessive recoil, flattened/cratered primers, difficulty extracting/ejecting, etc). Be safe and have fun!

April 28, 2010, 07:51 PM	#1
k9cougar Member Join Date: February 21, 2010 Posts: 74	9MM & OAL, does it matter? I've loading for only a year primarily for a glock 19 using 4.4g W231 with 124 gr plated rn. I really didn't pay that much attention to OAL. I simply grabbed whatever 9mm was on hand from a store, dialed that length into my die, and loaded. I've been doing a bit of reading in this forum and find wide variance recommedations in the OAL for 9MM. As long as you are within the min-max why does it matter? Do you get greater accuracy or stopping powder with longer or shorter OALs? Do you usually load toward the minimum, maximum, or in between and why? Just looking to learn.

April 28, 2010, 08:13 PM	#2
Brian Pfleuger Moderator Emeritus Join Date: June 25, 2008 Location: Austin, CO Posts: 19,578	It matters because different lengths can DRASTICALLY change peak pressure. As in blow up your gun drastic. Plus, maximum over all lengths are intended to insure that your finished ammo will fit and feed in a SAAMI spec magazine and chamber. Minimum lengths are intended to insure that the bullet is properly gripped by the case and that pressures do not become excessive. Shorter lengths decrease the space that the powder has to burn, which increases pressure. Different bullets, even of the same weight, have a different profile and your die will not touch all bullets in the same place. As such, setting your die using factory ammo does not insure either a consistent or safe final product. In short, the process that you describe is potentially extremely dangerous. __________________ Nobody plans to screw up their lives... ...they just don't plan not to. -Andy Stanley

April 28, 2010, 08:42 PM	#3
32dgrz Junior Member Join Date: November 29, 2009 Posts: 10	From Berry Bullets Suggest the best OAL for our 9-124 Gr. HBFP is 1.050. NOTE: Please take notice of our shorter than normal OAL - and if you are using other data for the same weight bullet - with a longer OAL - you will need to reduce the powder charge slightly, so you do not increase pressures too much. Stay Safe, Bud Watson Berrys Mfg Inc

April 28, 2010, 09:38 PM	#4
Coffeeshop123 Member Join Date: April 27, 2010 Posts: 20	What Peetzakilla said. The cartridges headspace off of the case mouth, but OAL is important because of the distance the bullet jumps before engaging the rifling and the amount of free space left in the case when the bullet is seated. The "jump" before engaging the rifling affects both accuracy and chamber pressure. You can safely use a factory round to set your seating die...if you're using the exact same components the factory uses. Case and bullet dimensions are critical, powder and primer type are important too. That's why a lot of loading manuals specify different OAL's for different loadings; the OAL's listed account for space left inside the cartridge but also ensure the cartridge fits inside the magazine, feeds/chambers properly and the bullet isn't too close to or too far from the rifling. If you're not 100 percent sure about your OAL then just work up your loads slowly, looking for signs of high pressure (excessive recoil, flattened/cratered primers, difficulty extracting/ejecting, etc). Be safe and have fun!