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Posted: 12/19/2009 6:55:11 PM EDT
I got a Hornady oal guage today, red the instructions and tryed it out on my rifle, Useing a light touch I got a readiny 3.265, then I tryed another bullet from the same batch and get 3.285.  I tryed about 10 differant bullets from the same lot and get differant measurments, What gives?   308  168gn Barnes TSX bullets
Link Posted: 12/19/2009 7:35:48 PM EDT
Well, bullets do vary themselves.  Are you using a Bullet Comparator so that you are measuring off the ogive, or are you just measuring the COAL?
Link Posted: 12/19/2009 7:49:06 PM EDT
Originally Posted By rn22723:
Well, bullets do vary themselves.  Are you using a Bullet Comparator so that you are measuring off the ogive, or are you just measuring the COAL?

+1
Stoney Point is my choice.  If you measure the LOA of your bullet of choice.  You'll find few that have the same length, from the same box.
458
Link Posted: 12/19/2009 8:06:04 PM EDT
Originally Posted By rn22723:
Well, bullets do vary themselves.  Are you using a Bullet Comparator so that you are measuring off the ogive, or are you just measuring the COAL?


No I'm not useing a bullet comparator, I just ordered one.  It is amazing how much differance there is just measuring the COAL.

Link Posted: 12/19/2009 9:41:39 PM EDT
The OAL gauge works in conjunction with the bullet comparator gauge, your bullet hits the lands and then you lock down the OAL gauge and measure the COL using a bullet comparator to give you the base to ogive measurement which is the measurement you go off of when seating a bullets on/off the lands.

Measuring from the base to the tip still gives you the same fluctuation in length as measuring to the tip without the OAL gauge, once you get the bullet comparator so you can measure from the base to the ogive you will see that indeed your bullets are of constant length to that point and all reference measurements should be done from this point of measurement.

Hope this makes sense
EWP
Link Posted: 12/20/2009 9:49:26 AM EDT
[Last Edit: 12/20/2009 9:51:55 AM EDT by Mike_Mills]
There is one more thing to know about using those gages.  It used to be written up in the instructions but only as a recommendation, however, it really is required if you want repeatability.  

Use should use a wooden dowel rod in the barrel to push back against the bullet as you try to seat it using the OAL tool. The control you get, the sensitive "feel" you get, will allow you to get reliable, repeatable measurements to within 0.001".  Without the use of this technique, you are lucky to get repeatability of less than 0.010".

Be sure you are careful in tightening the screw when you lock in the measurement.  You can bend the push rod, changing the measured value.

The other thing to watch out for is the sensitivity of the measurement to the rotational angle at which the gage is inserted into the chamber.  I always put it in at the same angle to insure repeatability.  I use 12:00, as indicated by the set screw.
Link Posted: 12/20/2009 3:27:11 PM EDT
Here's what I do and I do it or four or five different calibers.

There will be fluctuations, even measuring the same bullet 5 times, you could get 5 different measurements, so it's not a hard and fast singular measurement.

I take 3 or 5 bullets, depending on time, from a single box.

I take the rod and make sure the modified case is cinched down tightly.

I then insert the case into the chamber, making sure it's butt up against the chamber shoulder.  I make sure the first measurement has the 'thumb screw' in the 12:00 clock position.  I tap the bullet gently, but firmly into the rifling and carefully tighten the thumb screw making sure the inner sliding rod does not back itself out, which it will.  There's a finesse to this one handed procedure and you'll get the hang of it.

After I measure this first try at the 12:00 position, I'll reinsert the case into the chamber, but this time the thumb screw will be in the 9:00 position, that is to say that it will be opposite the ejection port on a RH action.  I repeat the procedure and measure, careful to keep the rod/bullet snug against the rifling while tightening the thumb screw.

Finally, I'll repeat this process a third time, with the thumb screw at the 3:00 position, facing me and take that measurement.

I'll average those 3 measurements together and then start again with a second bullet at the 12:00, 9:00 and 3:00 position relative to the ejection port/action.  After I'm done averaging bullets 1, 2 and 3, I'll average those three numbers together, call it a day and crack open a cold beer.

You'll be surprised by the variation you'll get.  Sometimes you'll feel the bullet is against the rifling and you'll get some small ass measurement, way off the others you'll be getting.

Just try and vary the case in the chamber and cover you bases, you'll also see variations in COAL with the modified case in different positions, as all chambers are different and those cases are generically sized on most likely Hornady dies (now at least.)

Doing it this way, gives you a fairly uniform range in your measurements, due to this encompassing technique.

Chris
Link Posted: 12/20/2009 10:59:06 PM EDT
Chris, you are driving yourself crazy making all those measurements.  And then what do you do?  Average them out and possibly lose the important data.  

Have you tried the dowel down the bore trick I mentioned?

Using your comparator, measure the variation in length of those five bullets?  How much variation do you get in just those five?  Is it a lot (>0.002")?  If so, what does that imply for the larger population of bullets left in the box?
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