Cartridge OAL testing, what are good increments to test?

Suputin said:
COAL is an entirely worthless measurement. The ONLY way to do it is with a bullet comparator. Anything else and you are wasting time and components.
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I wouldn't say ENTIRELY useless. Me and some friends have shot some very very good groups going from the tip (just the tip).....but having said that I'm switching to the ogive.
 
Gunneegoogoo said:
I wouldn't say ENTIRELY useless. Me and some friends have shot some very very good groups going from the tip (just the tip).....but having said that I'm switching to the ogive.
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Having the correct COAL for a given reload will optimimize accuracy. No expensive tools are required as it can be accomplished with a simple cleaning Rod.

Insert a rod on a closed bolt and carefully mark the rod at the muzzle. Insert a selected projectile onto the rifling and mark the cleaning Rod at the muzzle again. The measurement between the two marks is the max length for the selected projectile. Just subtract a few grand and that will be you optimum COAL.

Repeat this with every projectile you are going to use.

Simple.
 
Sqr said:
Having the correct COAL for a given reload will optimimize accuracy. No expensive tools are required as it can be accomplished with a simple cleaning Rod.

Insert a rod on a closed bolt and carefully mark the rod at the muzzle. Insert a selected projectile onto the rifling and mark the cleaning Rod at the muzzle again. The measurement between the two marks is the max length for the selected projectile. Just subtract a few grand and that will be you optimum COAL.

Repeat this with every projectile you are going to use.

Simple.
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This is what I do but as stated earlier, with some bullets that have less than consistent tips, this will yield varying measurements. Like up to .025. This can get frustrating.
 
Sqr said:
Having the correct COAL for a given reload will optimimize accuracy. No expensive tools are required as it can be accomplished with a simple cleaning Rod.

Insert a rod on a closed bolt and carefully mark the rod at the muzzle. Insert a selected projectile onto the rifling and mark the cleaning Rod at the muzzle again. The measurement between the two marks is the max length for the selected projectile. Just subtract a few grand and that will be you optimum COAL.

Repeat this with every projectile you are going to use.

Simple.
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No offence whatsoever, but I'd do that for hunting ammo, no way for precision. The width of the pencil mark is wider than the tolerances we're talking here.

That method relies on the tip as well, another potential source of error.

The comparators are not terribly expensive. About 20$ per caliber.
 
A method I've read for the big blunt nose heavy cast bullets used in the straight wall stuff I'm mostly looking at shooting is to set up a casing and bullet sitting long and with a neck tension which needs a firm but not too heavy press of the thumb to move. Seat this testing setup and force the head in with finger pressure far enough to get the breech block to close (no bolts on that sort of rifle, Single shot breech loaders) Then when you drop the block don't let the case extractor pull on it. Instead use a cleaning rod or wood dowel to ease it out as you lower the block. Then read the COAL and allow a few thousandths for the amount of rifling engraving on the lead nose.

Doing the same thing with jacketed spitzers would not produce engraving marks. Just spot touches. And this, along with those ogive resting comparitors would/could provide some highly repeatable seating accuracy. Slight variations in nose shape that causes any differences in bullet OAL would no longer matter.

Thoughts?
 
Suputin said:
COAL is an entirely worthless measurement. The ONLY way to do it is with a bullet comparator. Anything else and you are wasting time and components.
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Not entirely, if for no other reason than most people want their ammo to fit in the magazine, and want to be able to eject a loaded round. Length to ogive isn't going to tell you either of those things.

Besides, COL to tip is a perfectly accurate measurement to distance to lands, for the individual bullet that was used to measure it in the first place. If the seating die is set using that same bullet its just as accurate as measuring to the ogive. In fact, if you wanted to get right down to nitty gritty hair-splitting a comparator measures to an arbitrary data point, somewhere between bore and groove diameter. There's no particular guarantee that the bullet hits the comparator at the same diameter as it hit the leade which is sure to have a different profile (Even if it started out the same erosion would make sure it changed), or that bullets with different profiles hit the leade at the same diameter. why would they? Then the measurement from the arbitrary point is thought to be transferable to other bullets of other shapes? Heck, when you consider that, the guy measuring to the tip is actually being more accurate just as long as he knows it only applies to the test bullet.

How's that for hair-splitting.;) What can I say, its a slow day.
 
I measure every round and reseat as needed, not just a sentinel test bullet.

COL, or COAL, is not a good measure to the lands. The ogive to tip distance can vary by .030 or more between bullets, so the jump from seating to lands is not truly measured with COAL.

This time 10 days ago I'd have said sure, but after learning some stuff CBTO now makes more sense.

Having said that, you can see what my rifles have done using COAL on other posts.
 
Gunneegoogoo said:
No offence whatsoever, but I'd do that for hunting ammo, no way for precision. The width of the pencil mark is wider than the tolerances we're talking here.

That method relies on the tip as well, another potential source of error.

The comparators are not terribly expensive. About 20$ per caliber.
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For precision you weigh and measure each bullet OAL and place them into lots. Then you do Rod for COAL measurement for each and every projectile. If you do test bullets only this method will get close enough to begin fine tuning with a bullet seating micrometer seat die.
 
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I'll agree that the rod method gives you a starting point. So does the jiffy marker on the bullet trick.

Others have stated that bullet OAL is not a good measure, but rather bullet base to ogive is.
 
Gunneegoogoo said:
I'll agree that the rod method gives you a starting point. So does the jiffy marker on the bullet trick.

Others have stated that bullet OAL is not a good measure, but rather bullet base to ogive is.
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Substitute stop collars for pencil marks and it is just as accurate as the stoney-point tool and doesn't require modified cases. Miles ahead of the jiffy marker method. This one was left set after determining the distance to lands on my Cooper 30-06 with 165 NBTs. Once that bullet is seated, a measurement can be taken with a comparator. I got those 20 years ago.

 
Evil_Dark said:
Hi all,
After having found the proper powder charge for my .308 with Hornady Match 168gr HPBT, I want to fine tune that load with playing with the OAL. I've started at 2.775" as the standard stated in my manual, but what would be goods increments to tests?
Five rounds of 2.785, then 2.795 (0.010" incréments) ? Or more? Less? Never played with that before...

Does this play with the pressure and the FPS?

Thanks

Dark
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I just recently did a seating depth test and i have my selected powder charge and seated 5 bullets for each 5 thou jump so 5, 10, 15, 20, 25 &30. It varied pressure/velocity ever so slightly. I did my seating depth test at 200m the longest distance at my range. I was looking for a seating depth with the smallest vertical group
 
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308BAR said:
I just recently did a seating depth test and i have my selected powder charge and seated 5 bullets for each 5 thou jump so 5, 10, 15, 20, 25 &30. It varied pressure/velocity ever so slightly. I did my seating depth test at 200m tho longest distance at my range. I was looking for a seating depth with the smallest vertical group
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Sounds right to me. 200 is good, 300 is better if it's not windy.
 
So what jump worked best for you? I usually go 20thou. Too many variables to test, not enough time in multiple lifetime to test everything.
308BAR said:
I just recently did a seating depth test and i have my selected powder charge and seated 5 bullets for each 5 thou jump so 5, 10, 15, 20, 25 &30. It varied pressure/velocity ever so slightly. I did my seating depth test at 200m the longest distance at my range. I was looking for a seating depth with the smallest vertical group
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Make my own from 1F shoulder bump 1-2thou. Order weird size tap from eBay for 6 bucks.
Dogleg said:
Substitute stop collars for pencil marks and it is just as accurate as the stoney-point tool and doesn't require modified cases. Miles ahead of the jiffy marker method.
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