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Old March 4, 2005, 01:38 PM   #1
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O.A.L. Question

When looking at the loading manuals, ie lymans and Sierra, Maximum over all length is alway given. Yet there are never any reference to tolerance ranges. Since i'm new to re-loading, Should I size my rounds to exactly this dimension or should I size the cartridge a few thousandths under. The books don't seem to discuss this and all rounds seem to vary slightly. How Do you Senior Powder/Lead head Guru's do it?
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Old March 4, 2005, 03:20 PM   #2
bill k
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Look in the archives under reloading I asked the same question and got great answers. If I tried to explane it I'm sure I'd confuse you. The COL is really just an industry standard and each rifle has its own sweet spot length. My Nosler manual gives instruction on determining a particular rifles COL. I'd suggest finding a manual that gives the instructions on this plus I'm sure someone will explane it better.
I can tell you from experience if you find the correct COL for your rifle you will shoot better groups. It might be longer or shorter than the published length.
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Old March 4, 2005, 03:29 PM   #3
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Old March 4, 2005, 06:32 PM   #4
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William IV-it depends upon the reloading manual. For example, Lyman's 48th edition specifies a particular bullet/Brass/Primer?overall length for what they list, rifle or pistol.
Caution tells you to use the starting load and setup unless you must shorten the overall length in order to fit a magazine-whatever. Understand that any time you change bullets, cases, primers, or overall length, you stand the chance of increasing pressure.
Decreasing the overall length, with all other components remaining the same, WILL increase pressure. At what rate depends on the case, caliber, bullet, powder, primer, and in some cases, even prolonged sunlight which may heat up your max winter load to a damaging level at 110 degrees.

There are times when you must deviate from book values for feeding or accuracy issues. Most of us do this to some extent. What the book tells you is if you load this cartridge with what we list and at the length we did, you will develop similar velocities and pressures. But, I would not load a max charge of anything over whatever and then shorten the length by .040"

Most of my deviation from the books is going the other way-at least so far as rifles go. All mine perform better with the bullets closer to the lands, and there is likely a slight reduction of pressure, but not enough to dump more powder in!
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Old March 5, 2005, 12:05 AM   #5
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I have struggled with the vagueness of OAL measurements for a long time. They really don't tell me anything that I need to know, except for how long my cartridges can be to allegedly satisfactorily function in a certain gun. I want to know what the OAL should be for each bullet. Let's take .40S&W as an example...if I seat a bullet that's .525 inches long to an OAL of 1.130", then a bullet that's .535 inches long to the same length, my case capacity is going to be .01 inch less with the longer bullet. This should raise pressures, and, to some extent, velocity. It might even be too much of each. By the same token, a shorter bullet loaded to the same OAL will increase case volume, thereby lowering pressure and velocity.

To get around this, I've usually purchased some new, premium factory rounds, like Golden Sabers or Hydra Shoks, pulled a bullet or two, and measured them. I then use those measurements against my own bullets in order to set OAL. I don't care what the OAL comes out to be, unless it exceeds the maximum allowed. My incentive is to maintain consistent case volume. So far, it's worked pretty well, but I'd still like to see OAL's for specific bullets, rather than just a cartridge maximum.
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Old March 5, 2005, 11:56 AM   #6
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I hear ya, Larry. And if what you are doing is working for you, I would see little reason to change. There are a lot of reloading manuals out there which give only the SAAMI max length.
The following in my library do give specific overall lengths:

Accurate Powder Loading Guide

I would suspect there are more out there that I have yet to see. For me, it depends. For my pistols, I load to the max length which will fit in the magazine and feed correctly.
For rifles, I got a Stony point OAL chamber gauge and sit the bullet out to .050" from the rifling for best accuracy. I highly recommend that tool for anyone loading for their rifle. The only thing you may have to watch out for is making the cartridge too long to fit in the mag.
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Old March 5, 2005, 12:48 PM   #7
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It is very important to understand that the load developed for an auto pistol should not be SHORTER than the Overall length in the manual, if one is given. The maximum load was developed for a specific OAL that should not be shorter than the load listed. I know it has already been stated, but it is a very important point.

Revolvers are not quite as sensitive as auto's, so long as minimum OAL is maintained. Pistol chamber and throat length varies by manufacturer in the same caliber, as it does with rifle chambers. What I do for autopistols is similar to the rifle OAL length technique and I measure the OAL at the point where the bullet ogive makes contact with the lands, if it can be loaded that long, and then shorten the OAL a minimum of .005" to a maximum of .010" making the loaded round specific to the chamber length of the pistol it is to be fired in. Naturally, you don't want it too long for the magazine and you don't want it any shorter than the loadmanual cartridge, or you will have to reduce the powder charge proportionately and the load manual will not tell you what that reduction should be. Make your reloads just like the one in the manual, or increase length to fit the chamber specifically, but make sure it still fits the magazine and has enough bullet shank in the case for adequate bullet "Pull".
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