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Old October 15, 2002, 01:55 PM   #1
Krautguns
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Help- Confused on OAL, seat depth meausement

Could someone please explain to me the tools and process nesescary to determine the correct OAL for a particuar rifle? I suppose this would be a chamber measurement? I am currently looking to custominze loads for a couple of rifles I own both bolt guns and semi autos. What exactly do I need to do this, and how is it done? Currently I am reloading for:

.223 - Semi auto
.308 Semi auto
.30-06 Semi Auto
7.5x55 Swiss Bolt (this is my main concen for proper exact OAL)
8x57 Mauser Bolt

Thanks!
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Old October 15, 2002, 02:31 PM   #2
sricciardelli
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Tools required? A wax candle.

Light the candle...
Make a dummy round...
Smoke the bullet with the candle...
Chamber the round...
If there are bright marks on the bullet, seat it a tad deeper in the next dummy round...

Repeat the above steps until there are not bright marks.

Load 5 dummy rounds exactly the same as the final one and make sure they fitin the magazine.

If they fit, that is your OAL, if they don't fit, then your OAL will be the maximum length that fits in your magazine.
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Old October 15, 2002, 03:11 PM   #3
Krautguns
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I was reading on he stoney point OAL gauge, etc. I thought I needed something like that!
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Old October 15, 2002, 03:35 PM   #4
kdubya
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The above instructions are correct.

If I may, let me expand somewhat on them.

A dummy round is one with no primer or powder - simply a resized case with bullet of your choice.

Seat the bullet out longer (.030 - .040) than the loading manual "OAL" (overall length) for a loaded cartridge. Smoke the bullet with a flame device - candle, match, anything that produces soot, but little heat. Coat the bullet ogive (the tapered part of the bullet and back to the straight part) with an even coating, but don't make too heavy of a coat.

Carefully insert the dummy round into the chamber and fully close the bolt on the case. CAREFULLY extract the round, trying to be careful not to let it rub too much on the sidewalls of the chamber and receiver. It will anyway, just try to minimize it. These result in scrape marks in the coating, so just ignore them.

You are looking for bright spots spaced evenly around the bullet ogive. These markings are caused by the lands of the rifling touching the bullet. There will be a mark for each land, usually. Sometimes, a land or two won't start at the same place as the others, so don't get excited if you find less bright spots than there are lands.

Seat the bullet .010 - .020 deeper into the case neck, recoat the bullet and repeat the process until the land marks no longer appear, or are very faintly seen. This will give you the maximum OAL of the specific cartridge. You now need to back off another .010 - .015 for safety sake. This establishes the desired OAL for THAT SPECIFIC BULLET. Each brand and weight of bullets must be set the same way as above.

Next, the magazine maximum length has to be addressed. It will do no good (unless firing single shot, loading directly into the chamber with each round) to do the above, unless they will also function through the magazine. I like to have approx. 1/8" to 3/16" clearance between bullet tip and magazine end wall. This normally controls the practical cartridge OAL, as this dimension is usually less length than when the round is chamber OAL'd.

Another method, without the smoking of bullets, is to take a very fine toothed metal saw (jeweler's saw, coping saw, etc), a resized and trimmed case and bullet of choice. Make two careful cuts down the case neck to the top of the case shoulder, quartering the neck. You will now have 4 petals of brass for the neck. Carefully squeeze the petals to reduce the diameter somewhat and push the selected bullet into the neck about 1/2 way. The fit should be firm, not loose.

CAREFULLY chamber the round, carefully withdraw and measure. The bullet should have pushed against the lands and seated the bullet deeper into the case. This establishes land contact OAL. Remove bullet, press petals together again for firm bullet fit and do again. Measure each time for at least 3 trial fits - this should establish the average of land contact OAL. Again, back off .010 - .015 for desired OAL for that particular bullet.

The beauty if this method is less mess, a bunch of different bullet types and weights can be quickly measured for OAL. Save the case for future needs.

I have a whole shelf full of such reference cases and can quickly determine proper OAL of any new bullets.
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Old October 15, 2002, 04:33 PM   #5
Krautguns
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So- Why all the expensive tools if this is all you need? I'll have to try this trick in my K31.
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Old October 15, 2002, 05:45 PM   #6
kdubya
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Krautguns -

They make those things for people with lots of money and need for new toys. Heck, they even sell "stock pads" to keep the oils and cleaners off the stocks - a piece of plastic sheeting or taped on plastic bag will do the same!
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Old October 15, 2002, 07:30 PM   #7
Krautguns
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Interesting indeed. If you get good results with this trick, then Im all for it. Not shooting ants at 300M. Just want nice handloads, espically for my new K-31 Schmidt-rubin.
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