Is there a max accuracy COL for each brand of pistol?


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Cliph
September 13, 2009, 03:34 AM
I noticed that the factory (UMC) loads were noticably shorter than my reloads. For my BHP 9mm, a COL of 1.62 will still seat enough for the slide to go into battery. Optimally, I figure the COL should be sufficient for the bullet to almost engage the rifling. Can I get opinions on this, please?

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coloradokevin
September 13, 2009, 04:13 AM
Well, the way it was always explained to me is that the COAL used in factory loaded ammo is short enough to allow function in pretty much any commercially made firearm in that caliber. While it seems that your expierence shows that your firearm can use ammo loaded to a longer length, there are probably other firearms that couldn't shoot ammo that was loaded to that length; thus factory ammo is shorter.

I haven't tried it with pistol ammo, but I know that rifle ammo is often loaded beyond SAAMI specs, just to work with the specific rifle that it is intended for. In fact, some optimized rifle ammo actually comes out longer than the magazine for that rifle can fit, thus necessitating single round loading.

That's my understanding and view of it in layman's terms, but someone here could probably do a better job of explaining all of this than I could.

243winxb
September 13, 2009, 08:21 AM
I figure the COL should be sufficient for the bullet to almost engage the rifling. When hand loading for an auto, longer OAL can give better accuracy. The end play is taken out of the chambered round. But to far is not good as the action must close fully and feed while fitting into the magazine. All depend how the barrel is chambered/throated. Factory ammo must fit all firearms, so its shorter. http://i338.photobucket.com/albums/n420/joe1944usa/45seatingpossibilitiesxn.jpg

rfwobbly
September 13, 2009, 10:19 AM
Yes, I generally agree. Due to generous freebore dimensions, lots of common (especially US-made) autos will accept and safely shoot rounds longer than the SAAMI max COL, but....

1) In MOST common autos, the maximum feasible COL ends up being set by the magazine. While the chamber might accept a single cartridge longer than the SAAMI max cartridge length, multiple rounds of longer than normal length can't be loaded into the mag and therefore make exceeding the SAAMI COL numbers a mute point.

2) There ARE some pistols out there with exceedingly short freebore dimensions, CZ pistols being one of these. It is for pistols such as these that manufacturers sometimes set the COL shorter than the SAAMI max COL. This would especially be the case when loading bullets that bring the full barrel diameter closer to the nose of the bullet, such as FP target bullets, or conical nose HP bullets.

So it is the bullet's ogive shape that effectively determines the COL in any pistol.

Hope this helps!

rcmodel
September 13, 2009, 01:07 PM
Max OAL is determined by SAAMI using the "standard" bullet shape for the caliber.

If you look at the SAAMI cartridge drawings an a reloading manual, you will notice that it is a round nose bullet for most of the older auto pistol calibers, including the 9mm.
More recent calibers such as the .40 S&W & .357 SIG is determined with a flat point similar to most JHP bullet shapes.

If you load a standard profile RN bullet in the 9mm with a OAL of 1.169" it should fit & feed in any 9mm pistol.

But if you change to a different bullet shape such as a JHP or FP-FMJ, it will need to be shorter then 1.169" due to more full diameter bullet shank protruding from the case which will hit the rifling leade in some guns before the cartridge can fully chamber.

rc

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