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Old August 29, 2005, 01:04 AM   #2
BigSlick
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Join Date: January 25, 2005
Location: Texas of course
Posts: 277
It's good to stay at or very close to quoted OAL measurements if you are at or near max loads. Seating deeper can cause a potentially unsafe pressure level. If you're trying to duplicate the performance in the published load data, of course OAL will be a factor.

For mid-range loads, being off from quoted OAL *usually* isn't a problem, within reason. As an example, you probably wouldn't want to go 30-40 thousandths deeper with a caliber like 40 SW. 45 ACP on the other hand is a much lower pressure cartridge and somewhat more forgiving in this respect.

The Lee reloading manual has a pretty good section about pressure. Pick one up and give it a read. Maybe the info there will help you make a better decision for the particular load you are working with.

From an equipment standpoint, most standard dies won't be able to hold an accurate, repeatable seating depth less than 2-3 thousandths. Some have much more slop.

Presses that use a floating shell plate, or a removable tool head will have some slop in them too. Either the dies, shellplate or tool heads having a minute amount of slop usually isn't a big deal for most pistol rounds for plinking.

For rifle loads where extreme accuracy is the goal, this variance can make significant difference.

For more precision and accurate seating depth measurement, a competition seating die with micrometer adjustment (or something similar) will help tremendously. The thing to make sure of with these is that your press and shell plate (or holder) is stable so you can recognize the effects of the comp seating die.

It can be tough finding published data that agrees from one source to the next. Some suggest a minimum OAL, others specify it exactly. The implications of this could be argued ad nauseum without resolution.

Best bet, is to start with a load well below maximum and work up in small increments, watching closely for any signs of pressure.

For 45 ACP, when working up a new load, I start at minumum published charge level, at an OAL that I know feeds well in my gun, and proceed with caution until I find a load that works well or see the first sign of a pressure problem.

Hope some of this helps...

BigSlick
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