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Old March 21, 2001, 10:58 AM   #1
Timothy
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As I understand it, OAL is a major factor when loading for a firearm with a magazine or clip for obvious reasons ( if the OAL is too long they will not function properly in the magazine). When I load for single-shot pistols and rifles, OAL is determined only by where I want the ogive in relation to the lands. With this in mind, I take the OAL suggestions in loading data only to be guidelines to insure proper functioning in clips and mags. It seems to me that bullet manufacturers must place the cannelure or crimping groove at a place on the bullet, that when crimped there, will produce the correct OAL. Am I correct?
If the OAL (a measurement from the base to the most forward point of the bullet) is so critical, then why do OAL recommendations vary depending on bullet design? Is it not only the actual overall length of the load that is critical or are there other factors or dimensions involved here?
Since bullet dimensions within the same design vary by manufacturer if you detemine powder charge by bullet weight and design using load data not specific to your bullet's manufacturer and utilize the cannelure or groove you may very well end up with a different OAL than stated in the load data you are using. Now how do you know whether or not you have achieved the correct OAL before you try it out in your gun....where is the "Bible" to go by?
Last scenario, I promise. If, by whatever guideline, you determine you must shorten the OAL and in doing so crimping takes place forward of the cannelure or groove, what do you do?
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Old March 21, 2001, 06:51 PM   #2
Chris McDermott
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OAL is critical for another reason - it helps determine what maximum pressure is reached. With the same powder charge, if the bullet is pushed into the case and takes up more room, a higher pressure is reached than if the bullet is seated farther out. I think that this effect is more apparent on small pistol straight wall cases than big magnum rifle bottle-neck cases, but it does matter for both. That is why the reloading manuals list an OAL for the cartridge with their loads, and you should stick fairly close to that listed OAL. Yes, small differences to put the bullet where you want in relation to the rifling lands can improve accuracy, but be prepared for the max pressure of the load to change.
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Old March 21, 2001, 08:12 PM   #3
labgrade
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The overpressure bit, by seating bullets in further, comes into play more so with pistol cases because they have a smaller volume. A similar decrease OAL (by actual bullet seating depth may cause a 3% decrease in the 06 volume but 15% in the 9. (#s are just a WAG, but illustrative)

This next more for rifles than handguns ....

Too, starting bullets so that they touch the lands causes a higher initial pressure than would if the bullet is seated off the lands .010" or so. The latter method allows the bullet a bit more running start before it engages the rifling.

Different bullets have different shaped ogives (that curved side-part at the front of the bullet before the tip). A bigger ogive (less-curved) allows the bullet to be more streamlined (longer bullet) which also means that the bullet can be seated out further before it contacts the rifling.

Forget all about the canalure unless you're going to crimp & you'll not need to do that with a bolt action rifle.
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Old March 22, 2001, 01:05 AM   #4
Michael Priddy
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Timothy, I have found in my 270 and 30-06, that the oal which gives me the most accuracy at 100yds are too long for the rifle's magazine. I hunt with an accurate round in the chamber and shorter less accurate ( less accurate for the bench, not hunting ) rounds in the magazine. In reloading, I have found the oal to be the most critical factor for accuracy. I pick one of Ken Waters' accurate loads from his Pet Loads. Load up several( three to four ) three round groups with different oal. Five round groups keeps the barrel too hot. The first group is .005-.008" inches shorter than the maximum oal.( length where the bullet is touching the lands ) Each group after that are about .005" shorter. Generally, it is the second longest group that gives the best accuracy. I let Waters pick the powder and I determine the oal. This saves me a lot of time,powder and bullets in finding a powder/oal that will work well in my rifles without too many trips to the range.
Of course you will have to do this for each different bullet shape and weight. Lots of luck ...Michael
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Old March 22, 2001, 08:45 AM   #5
Chad Young
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Well, I have a follow-up question: why is the recommended minimum OAL different for the same bullet/caliber combination when the only variable is the powder? For example, I have noticed when I am loading .45 ACP cases, the minimum OAL when using W231 under a 230 grain FMJ load is considerably shorter than some other powders.

Personally, I run my loads a bit longer than minimum in order to keep pressure low. I have no desire to have a KB.

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Old March 22, 2001, 10:30 AM   #6
labgrade
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Chad,

Can you rpovide a reference (loading manual, etc.) that mentions that? Not doubting you but I've just never seen that before - coulda been there all long ... Every manual I've seen (noticed) has the bullet listed with OAL & then all the powder charges listed below. Curious is all.
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Old March 22, 2001, 10:14 PM   #7
saands
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Chad could have been referring to two different powder companies' loads for the same popular bullet ... a 9mm Hornady XTP for example. That, it would seem just goes to show you that there is no particular "perfect" volume. The powder company tests loads and list max loads that are safe ... I assume that this is why all the "max" loads don't have the same pressure ... a combo of little more powder and a little more case volume could probably have eeked out a few fps more than that final load, but that would be a TON of work for them.

Another reason that OAL is more critical for straight walled cases than bottlenecks is that the volume reduction is proportional to the cross sectional area of the case where you are reducing the length. Most of the volume in a bottlenecked case is in the fat part, while the straight case is equally represented.

For pistol cases, I calculate the distance from the base of the bullet to the back of the case for a known safe load and back calculate the min OAL if I use the same weight bullet in a geometry that is not documented in my tables. The important part (for safe pressures ... not accuracy) is the case volume ... as assembled.

Be safe,
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Old March 24, 2001, 11:47 PM   #8
Nukem
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My general rule is to load all ctgs for magazine fed weapons as far out as possible and still maintain relaible feeding. Boltguns to the lands and just back off a few tho.

As for some of the loading data out there. I can relate one story,, I was using an older Sierra manual, loading some Sierra 9mm 115 gr JHP for years using the spec for OAL. Upgraded to a new Sierra manual and the same load data in the new manual showed .100" LESS for OAL! I called the Sierra tech line and questioned them about it. The reply was that the new manual and data was developed by their new ballistician and he stood by the numbers. I questioned the rise in pressure that had to go with a .100" reduction in OAL,,,no answer??? Needless to say, I kept using the old OAL data for that load.
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Old March 25, 2001, 03:56 AM   #9
a-bolt
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great string. many questions answered.

my question: what is the tolerable deviation off of the suggested OAL in the load book, 10%, 5%?

Better to be over or under the OAL value?

Does it matter according to pisol being auto or revolver? (i'm talking pressure levels and KB risk here not mag/feed probs).

thanks.

P.S. I usually try to hit the suggested OAL dead on just out of workmanship pride but I ask these questions for reference generally.



[Edited by a-bolt on 03-25-2001 at 04:14 PM]
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Old March 25, 2001, 09:56 AM   #10
jbent
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OAL

I assume that it was more a matter of reliable feeding. My son shoots a G35 in IPSC; I load .40s for him to 1.125 using montana gold which is sort of stubby. I shoot a Para in .40 in IPSC competition and load my rounds to 1.185. I use 0.3 grains more N350 and it gives me a pretty consistent power factor of about 178. If I shoot his 40s, I experience feed problems. Naturally, if he loads mine, they jam in the mag.

Dave Dawson told me once that 1.2 was a good target for my Para. I tried it with 180s, but got a lot of variation in velocity which I assume to be too much case space. When I backed it down a bit the deviations came way down.

I'm only a couple of years and 15,000 roundsor so old [new?] at reloading, but I gathered form this experience that it is a function of the particular gun/ammo combination. The montana gold ammo seems a little more squatty -- okay, I'm sure there's a correct term for it, but I don't know it -- than others like the Hornady which I've also used. That may also impact your choice of OAL.

Hey, has anyone used 200gr 40s? Any magic formulas?
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Old March 25, 2001, 10:39 AM   #11
WESHOOT2
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In my experience, ALL GUNS ARE DIFFERENT.

Just gotta try.....(gives me white hair, natch)
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