What does the min/max COL have to do with performance?

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raysteel

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Hi all, new to reloading and I see a difference in min/max COL. Right now I am loading up 9mm luger with nickel brass 1F. What performance difference would one see in a min COL compared to a max COL? Would anyone have a good load using sr4756 fr a 124g fmj Berry Bullet? Its coming out of a Thureon 9mm

Also a 2nd question Im going to resize 308 to fit 7mm-08. Anyone have any experience with this and what die(s) would I need? and be considered best for this.... RCBS/Lee etc

Thanks guys
 
COL is something I have played with alot. In rifles I load different for every single gun so I take the time to get my overall length proper for best accuracy. How the overall length affects accuracy is by changing the bullet jump distance. Closer doesn't always mean better generally I guauge my Max overall length for the gun then I back it off about 5/1000ths and start there. For pistols however I load for multiple handguns and have not noticed a large enough difference so I load them all about 10/1000 th's shorter then my shortest handgun. I hope that makes sence
 
ripitup911 said:
COL is something I have played with alot. In rifles I load different for every single gun so I take the time to get my overall length proper for best accuracy. How the overall length affects accuracy is by changing the bullet jump distance. Closer doesn't always mean better generally I guauge my Max overall length for the gun then I back it off about 5/1000ths and start there. For pistols however I load for multiple handguns and have not noticed a large enough difference so I load them all about 10/1000 th's shorter then my shortest handgun. I hope that makes sence
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Thanks, if its in a pistol carbine what do you think then for COL?
 
308 to 7-08 Any sizing die will do the job in a single pass. Use lots of lube, and adjust the sizing die so it bottoms out on the shell holder.

COL. The Min / Max in the book are suggestions. I would tend to take the MIN as gospel, unless that length still had the bullet hitting the chamber throat.

MAX, in practice, is determined by the shape and size of the magazine for YOUR pistol, and the shape and size of the chamber throat of YOUR pistol. If you seat a bullet to the max in your book, and then chamber it, you might find it hits the rifling. You then have to seat deeper.

To answer your question about OAL and performance, OAL is 99% concerned about "Will it chamber OK and will it feed ok?" Every gun has a length that is too long. The cartridge will either be too long to fit the magazine or the bullet will engage the rifling. I have 20+ 9mms (pistols, SMGs and carbines) and tend to load ammo to 1.125" because that fits all my guns. I find the Norincos and CZs have short throats, so I just test OAL in them.

With 4756 try 4.5, 4.8 and 5.1 and see which shoots best.
 
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Ganderite said:
308 to 7-08 Any sizing die will do the job in a single pass. Use lots of lube, and adjust the sizing die so it bottoms out on the shell holder.

COL. The Min / Max in the book are suggestions. I would tend to take the MIN as gospel, unless that length still had the bullet hitting the chamber throat.

MAX, in practice, is determined by the shape and size of the magazine for YOUR pistol, and the shape and size of the chamber throat of YOUR pistol. If you seat a bullet to the max in your book, and then chamber it, you might find it hits the rifling. You then have to seat deeper.

With 4756 try 4.5, 4.8 and 5.1 and see which shoots best.
Click to expand...

Thank you Thank you....Does firing out of a pistol carbine rifle change anything compared to firing from a handgun?
 
Berry's pistol bullets aren't jacketed. They're plated. Plated bullets use cast data.
You must work up the load for your pistol. There is data on Hodgdon's site for a 124 grain BERB HBRN TP and sr4756 though.
OAL is mostly about fitting the mag and chamber and not so much performance in pistol cartridges. Can help in a bottle necked rifle cartridge. The whole 'off the lands' thing is about rifle cartridges. Even those must fit the magazine though.
 
sunray said:
Berry's pistol bullets aren't jacketed. They're plated. Plated bullets use cast data.
You must work up the load for your pistol. There is data on Hodgdon's site for a 124 grain BERB HBRN TP and sr4756 though.
OAL is mostly about fitting the mag and chamber and not so much performance in pistol cartridges. Can help in a bottle necked rifle cartridge. The whole 'off the lands' thing is about rifle cartridges. Even those must fit the magazine though.
Click to expand...

Ahhh ok, got it. Sorry, newbie here I thought it was a FMJ. Now I know, thanks for that
 
COL in 9mm also affects the peak pressure. If loading to near max loads do NOT use the minimum COL. Most loading data books will give you a COL for their loads. And if you compare the data you'll find that those books or sources with shorter COL's will have slightly smaller max loads for any given powder.

Back when I played with COL in 9mm I found that varying the loads over a .020 inch range produced something like a 50 to 80 fps variation in muzzle velocity on a handgun. This is an indicator of how it causes the pressure to alter.

But if you're not dancing around with max or near max loads then the posts above about the COL mostly affecting how easily and smoothly the rounds come out of the mag and slip into the chamber are spot on. For example, for some reason CZ handguns have a slightly short chamber or a steeper leade into the rifling. So an otherwise longer but still within spec COL can cause the round to not seat fully and the slide jams while not yet in battery.

So it's not a bad idea to load one dummy bullet with a light crimp at the extreme length for COL then chamber check it in your Thureon. If it doesn't seat fully then press the bullet a touch deeper, measure it and chamber check it again. Keep going until you find a COL that works and gives about a .005 to .008 safety margin. That is the COL that is good for you to go into production with.

Or do what most of us would. Find the gun in your collection that needs the shortest COL. Make all your rounds about .005 to .008 smaller than what that maximum COL for that gun is and it'll fit everything you own.
 
COAL is essentially a worthless dimension because it varies from bullet to bullet. A COAL is only of any worth when dealing with a single make and weight of bullet. And that is really only for handgun ammo as rifle ammo should be measured to the ogive and not to the bullet tip.

With a handgun, COAL is really only important to ensure the bullet feeds and seats in the chamber properly. Other than that is is pointless.

I would want to know more about the claim that COAL can vary velocity. The 50-80 fps claim is well within the variation range of a typical load anyway.
 
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