Cartridge overall length minimum


PDA






MoreIsLess
September 4, 2011, 08:48 AM
Being new to reloading, I have the following question:

I know you should not exceed the maximum overall length specified in the reloading manual. What about minimum OAL. How far under the maximum OAL is OK. What kind of problems can arise from OAL too low?

If you enjoyed reading about "Cartridge overall length minimum" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!
Walkalong
September 4, 2011, 09:29 AM
With revolver rounds seat and crimp in the cannelure or crimp groove and that is your O.A.L.

With auto rounds there is no formula. As stated in any manual, pressure goes up as seating depth gets deeper. How much varies on the space in the case and the pressures the caliber runs at. Seat a .45 ACP bullet .010 deeper and no worries unless you are running hot. Seat a 9MM .010 deeper and it is definitely something to consider when getting towards max. Enough to back off the max a bit IMO.

Most folks find an O.A.L. that feeds well in their guns, and adjusts, if necessary, the powder charge to suit.

MoreIsLess
September 4, 2011, 10:53 AM
Most folks find an O.A.L. that feeds well in their guns, and adjusts, if necessary

It sounds to me like a lot of it is trial and error.Thanks for the info.

helotaxi
September 4, 2011, 11:02 AM
Handgun or rifle? Going too short usually becomes an issue of reliability with repeaters. The short round might hang up coming out of the magazine or pop loose from the magazine before the nose of the bullet is in the chamber.

As mentioned, a shorter round will increase pressure in a straight-walled case but in a bottle-necked rifle case, the pressure will actually decrease as the seating depth increases. This is because the primary cause of the pressure spike in a rifle case is the bullet being swaged into the rifling. If it has a "jump" to get up a head of steam, the bullet inertia will help with this process and will reduce pressure significantly more than the small decrease in case volume will increase it.

The drawback to this is an increase in effective freebore and an increased likelihood that the bullet will yaw ever so slightly from the case to the rifling (and do so in a random manner) and hurt accuracy.

sourdough44
September 4, 2011, 11:42 AM
With rifle loads I always measure my chamber to see where that specific bullet touches the rifling. Then I look at book & max magazine COLs. I recently loaded some rifle rounds where book COL was to long for that bullet/chamber. The bullet would stick into the rifling some, maybe enough to hold the bullet while unloading & render the gun unshootable.

When you get loading, just going by book COL, especially for a rifle doesn't cut it. I'm close to book COL for handgun, as long as they cycle & fit the mag. You may want to be more aware of COL changes if near max charges.

brickeyee
September 4, 2011, 11:47 AM
What kind of problems can arise from OAL too low?

Higher than desired pressure.

Really more of a problem with handgun rounds (they tens to be smaller) or any load near maximum.

You can exceed the book OAL, but need to be aware that pressures increases if the bullet is jammed into the rifling, and that feeding from a magazine (or even the rounds fitting in the magazine) can be compromised.

Many .223 competition shooters have rounds that must be single fed for long range and heavier bullets to improve accuracy.

rcmodel
September 4, 2011, 12:02 PM
General Rule of Thumb:
If it looks about like a factory loaded cartridge should look, it's probably about right.

If it looks too short & goofy, it probably is! :D

rc

gamestalker
September 4, 2011, 02:18 PM
Proper OAL is determined by the firearm. I don't even load at the published OAL because it is nothing more than the OAL that was established as the general seating depth. The only factor to be aware of is the minimum. Exceeding that depth increases pressures.
In my AL handguns I use the barrel as my determining factor, which has always been longer than the published minimum.
With bottle neck rifle I seat up to the lands or as close as I can get while still maintaining enough neck, an example would be a bullet that is .284" in diameter should have a minimum of .284" into the neck.
Revolver is determined by the canelure, where it should be crimped.

243winxb
September 4, 2011, 03:24 PM
SAAMI sets the standard. They list both a Maximum & Minimum COL. http://www.saami.org/specifications_and_information/index.cfm?page=CC For the 243 win. Max is 2.710" Min. is 2.540" See > http://www.saami.org/PubResources/CC_Drawings/Rifle/243%20Winchester.pdf :)

ranger335v
September 5, 2011, 10:18 AM
SAAMI min and max OAL is for factory loads; it has no real meaning to handloaders.

243winxb
September 5, 2011, 10:26 AM
:D General Rule of Thumb:
RC said > If it looks about like a factory loaded cartridge should look, it's probably about right.
Ranger said> SAAMI min and max OAL is for factory loads; it has no real meaning to handloaders. The factory & SAAMI knows nothing? :what: They only load/sell millions of rounds a year. :)

brickeyee
September 5, 2011, 10:51 AM
The factory & SAAMI knows nothing? They only load/sell millions of rounds a year.

You said that, no one else.

Factory loads are designed to operate in ANY gun of the correct caliber.

There are all sorts of variations that a handloader can take advantage of that would not meet SAAMI guidelines.

Loading so long that magazine feeding is one of them.

The loading manuals give a length since the pressure developed is influenced by the length.

Going longer or shorter may increase pressure (shorter from reduced powder space, \longer from getting closer to the lands)..

Either can be compensated for during handloading.

1SOW
September 6, 2011, 12:27 AM
I know you should not exceed the maximum overall length specified in the reloading manual


Just one correction here. Your load data gives the "MINIMUM OAL" for "that load". If you go shorter and use the load data given, pressures will rise---maybe dangerously. If you go longer using the load data given, pressures will decrease--usually not dangerous.

If you go to a shorter oal than the load data gives, you have to adj the load to compensate for less case volume.

ranger335v
September 6, 2011, 10:52 AM
When asking questions like this it's helpful if we know what cartridge is at issue.

The OAL in a loading manual is what the book makers used in their firearm to complile their data, it's no more a law for the rest of us than their powder charges are.

MoreIsLess
September 6, 2011, 11:06 AM
it's helpful if we know what cartridge is at issue

It's .45 ACP, sorry I failed to mention that

243winxb
September 6, 2011, 11:28 AM
Deeper=more pressure. Not a problem with a starting load. Watch out for "set back" on loading. http://i338.photobucket.com/albums/n420/joe1944usa/th_45acp-1.jpg (http://s338.photobucket.com/albums/n420/joe1944usa/?action=view&current=45acp-1.jpg) Click for larger view.

If you enjoyed reading about "Cartridge overall length minimum" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!