9mm OAL question

[wiiawiwb]

I've been reloading MBC HiTek coated 125gr SWC for the past eight months for a Glock 17 and DW ECO. No problems at all. I decided to buy some RMR 124gr RN plated bullets and reload them.

I was trying the get the longest OAL that would reliably feed in both guns. I made a few dummy rounds at 1.159 and they passed the plunk test and fed and ejected from both guns. I then reloaded 5 rounds using HS-6 and they fired accurately and without incident. Just this morning, I finished firing 100 rounds and all were fairly accurate.

What is the downside to reloading 9mm with a lengthy OAL if the rounds are firing accurately and without incident?

 

[Havok7416]

No downside. Longer OAL just means a smidge less pressure, but if they are accurate and cycle reliably, who cares?

 

[ArchAngelCD]

I usually load any bullet for semi-autos as long as I can within SAAMI limits that will feed reliability. I see nothing wrong with loading them where you did. Why were you concerned?

 

[Walkalong]

Down side?

Might be a tight fit, or even a no go in some mags.

Might not plunk in other guns.

I load various 9MM 115 and 124/5 Gr RN bullets at 1.130 to 1.135 OAL. (Although I have one I load at 1.140/45) I bet it will feed 100% for you, and you will be assured it will fit any mag, and most chambers/leades.

 

[wiiawiwb]

Whenever I see my reloading parameters different than others I question it to make sure there isn't something that I've overlooked. Still new at this and I'd rather ask and make sure my approach is sound.

 

[rodregier]

I like to leave a few thousands short of the throat to allow for residue buildup.
(say .005 or so).

Omitting that could give you issues trying to extract a live cartridge in a pistol that has been fired a lot.

OAL varies a wee bit on a progressive press, so you want to also load short of absolute maximum to allow for that. Again .005 or so will give you that margin.

 

[rodregier]

The other consideration is enough bullet inside the case to ensure it's firmly held.
It also helps to ensure the projectile is being launched into the centre of the barrel boreline.
I like roughy 1/2 of the bullet diameter for that.

In the the case of 9mmx19, that is roughly 0.354" / 2 = 0.177"

Measure a case, measure the projectile and then seat it.
The difference is the seating depth.

 

[ArchAngelCD]

Whenever I see my reloading parameters different than others I question it to make sure there isn't something that I've overlooked. Still new at this and I'd rather ask and make sure my approach is sound.

That is a good way to go about learning. It never hurts to ask and be sure...

Welcome to this addiction called reloading lol.

 

[LiveLife]

What is the downside to reloading 9mm with a lengthy OAL

+1 to Walkalong/rodregier's comments.

Downside to loading 9mm long is reduction in neck tension and chamber pressure build, especially for 115 gr FMJ/RN bullet with shorter bullet base and particularly .355" sized plated bullets with rounded bullet base which leaks more gas and this problem gets worse with slower burning powders at lower powder charges.

Many reloaders complain 9mm is more difficult to reload accurate than other calibers like 45ACP. This may be due to smaller case volume that is more affected by reloading variables not so much noticed in larger case 45ACP.

When primer ignites powder, there are several factors to consider to produce more consistent chamber pressures which leads to more consistent muzzle velocities that results in lower SD number:

- Powder case fill/powder position in relation to primer flash
- Powder charge/load data vs powder burn rate
- Initial powder burn and chamber pressure build from neck tension/bullet seating depth
- Continued chamber pressure build from case neck/mouth expanding to seal with chamber
- High pressure gas leakage as bullet jumps through leade/freebore to start of rifling
- Max chamber pressure build from bullet's bearing surface engaging the start of rifling

With 115 gr FMJ/RN bullet, while longer OAL/COL will reduce gas leakage from shorter jump to start of rifling, it's been my experience that reduction in neck tension/chamber pressure build can overshadow gas leakage if using powder charges less than near max and/or using slower burn rate powders.

With 124 gr FMJ/RN bullet, this is less of an issue due to longer bullet base and I will often use longer 1.150-1.160" OAL to reduce gas leakage and to reduce powder charge compression but prefer to use shorter 1.130"-1.135" for 115 gr FMJ/RN bullets.

Atlanta Arms match ammo which is used by various match teams, including Army Marksmanship Unit/Marine Service Pistol team, uses 1.130" OAL for 115 gr FMJ match ammo that has accuracy of 1.5" group at 50 yards loaded to minor power factor of 125/1150 fps (BTW, 1.145" OAL is used for 124 gr FMJ) - http://atlantaarms.com/products/9mm-115gr-fmj-match-amu.html

To increase consistency of chamber pressure and muzzle velocities, for my carbine load development with 115 gr FMJ/RN bullets, I tested 1.130" to 1.160" OAL with different powder/charges and so far, shorter 1.130" OAL with faster burn rate powders at near max/max charges are producing greater accuracy - http://www.thehighroad.org/showthread.php?p=10245856#post10245856

With that said, sometimes you have no choice but to load longer as loading shorter will compress the powder charge. For my accuracy testing with 124 gr Berry's/RMR bullets, 1.160" OAL was used with WST/Titegroup/BE-86 to not compress the powder charge to produce sub 2" groups at 25 yards - http://www.thehighroad.org/showpost.php?p=9924922&postcount=137