Cartridge Overall Length

[Graham Smith]

I know that this isn't rocket science, but all the variables do start to add up. Take overall length, for example. Different sources give different OALs for the same weight and type bullet. I'm guessing that this has something to do with bullet composition (e.g. lead, plated, jacketed, etc) and shape and cartridge pressure but I don't want to have to dig out my college calculus books when it comes time to work up a new load.

Right now, I am concentrating on 124gr 9x19 and have worked with the Hornady 124 FP and the 125 HAP bullets as a starting place. The recommended OAL for the 124 FP is 1.050 but there is no recommended OAL on the HAP bullets since they were "designed" for 38 Super. I'm also going to be looking at both Berry and Montana Gold bullets and they are not going to be in any of the regular load manuals.

So, within the range of the OAL such that fits, doesn't blows up and doesn't gets stuck in the barrel, there is a happy medium. How does one figure out what that is?

IOW, where do these recommendations in the load manuals come from in the first place? Is it purely a case of trial and error or is there some logic to it?

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P.S. Does anyone happen to know the formula for figuring out how many politicians will fit in a hole 10x10x50 without compacting? We'll need to find a place to put all the incumbents that don't get re-elected next September and it's never too soon to start planning.

[devildogmech]

Their OAL for the listed Powder type and bullet is the shortest you can "safely" go... The publishers do LOTS of testing with pressure barrels, and I realy wouldnt want to go shorter than the listed limit. Remember, making the OAL will decrease pressure, so you can always make it longer. But making the OAL shorter will increase the pressure.

I load my 9mm long... my BHP and S&W 915 like the finished rounds a little longer than factory...

JMHO

Billy

[Graham Smith]

Their OAL for the listed Powder type and bullet is the shortest you can "safely" go...

Well, that makes sense now that someone says it.

Perhaps the question should be, where do you find some if this information? I've read "ABC's of Reloading" and have the Lee Manual and extracts from a few other manuals, but I don't think I've ever read this.

Anyone have a recommended reading list?

[LPatterson]

Their OAL for the listed Powder type and bullet is the shortest you can "safely" go...

JMHO

Billy

This is not absolutely true but a value based on a legal standpoint. Some guns have chambers smaller/shorter than that in a test barrel so the length needs to be shortened to chamber a round without hitting the rifling. Almost every loading manual says to start at the lowest loading & reduce by 10% when working up loads. For most bottom feeders the magazine or the feed ramp will determine the OAL by how it feeds a loaded shell. A 45ACP loaded with a 200gr H&G #68 can feed perfectly @ 1.250 in a 1911 but choke consistanly in an XD.

[G-ManBart]

Some manuals will actually give both a minimum and maximum overall length for you to go by. In general, factory ammo OAL is a figure that will let the ammo work reliably in the majority of guns (fit the magazines and feed) while still staying within pressure limits and delivering acceptable velocity. You can vary the OAL a little bit from the figures in a book and still be safe if you follow the rule of reducing the starting charge and working up from there. Unfortunately, for a lot of USPSA/IPSC shooting we're already going outside of what the books publish so it's somewhat uncharted waters.

[revchuck]

Graham - FWIW, factory 9x19 hardball usually runs ~1.15" OAL. Max OAL for the cartridge is 1.169". Factory JHPs run ~1.12-1.15".

The Hornady 124 grain FPs have a really short nose, hence the short OAL.

The old way (which still works) to determine how long you can go is load a dummy round to the max length your magazine will accept. Note where the rim of factory ammo you know that works ends up in your barrel. Drop the dummy round in the chamber; if the rim ends up the same place, you have the max OAL for your gun with that bullet. If the rim sticks out farther, seat the bullet deeper until the rim ends up the same place as the factory round. It'll probably be a little longer than what the loading manual says. Adjust powder charge to make the appropriate PF, then load a couple hundred to make sure it runs in your gun.

After you do all that, you probably won't detect a difference in accuracy...but then you might, too.

[Carlos]

Their OAL for the listed Powder type and bullet is the shortest you can "safely" go... The publishers do LOTS of testing with pressure barrels, and I realy wouldnt want to go shorter than the listed limit. Remember, making the OAL will decrease pressure, so you can always make it longer. But making the OAL shorter will increase the pressure.

I load my 9mm long... my BHP and S&W 915 like the finished rounds a little longer than factory...

JMHO

Billy

I agree. I often see reloaders mistake the OAL number in the book for "recommended" when it should actually be read as "minimum safe OAL." Besides, most guns feed well with an OAL of 1.150" or slightly more (however, Angus & Matt use a much shorter OAL in their CZs. They know a lot more than I do about CZs. Nonetheless, my guns work w/ ammo that is 1.150").

What benefit is there to loading short? None I can think of. It presents less of a margin for set back, raises pressure, as a result it is harder on the brass, and puts your bullet further from the rifling.