oal gauge?

[westernsky]

g'day all
as ive just got my rifle built and ready to start developing a load, im hoping someone could shed some light on bullet seating depth for me.
ive read a few ways of measuring seating depth and everyone seems to have a different opinion on what works and what doesnt.
ive seen that hornady make an oal gauge and it seems to be a fairly simple way of measuring seating depth but ive also read that its not very reliable or accurate.
i dont want to lash out on fancy gear if it doesnt do what i need.
also, having a barrel burner i cant waste shots. yes i know thats my own fault, and many people have questioned why i bought such a heavy case, but i have, and i like it.
its a 300RUM for those who have not seen my other posts
any info will be much appreciated
happy shooting

[Brad Y]

I use a neck sized case with a dremel slit in the neck. Seat a bullet long then chamber and extract it and measure with an RCBS precision mic. Do this a few times to check and make sure Im 100% happy then load from there.

Benefits with the precision mic set is that you can set your dies up to size correctly ie bump shoulder back 1-2 thou with it and measure your seating depth off the ogive not the bullet tip. There is a plastic insert bit that comes in the precision mic set that is supposed to be for working it out, but I couldnt figure out how to use it effectively.

[Barry Davies]

By far the most accurate way is to measure from the muzzle back. If you care to PM me with your private email address I will send you photographs of the set up required.
Barry

[NDOliver]

If you have a Lee Collet die, screw the die into the press just enough to resize the neck to barely hold the projectile. You don't want too much grip on the proj.

Seat the proj. long then chamber it. The proj will be pushed back into the case, gently remove it and measure base to ogive with the comparator on your caliper. This should give you the seating depth to the lands for the specific proj. you are using.

Do this a few times and average the measurements. I have found this method to be more accurate than using the Hornady tool.

If you want to seat your proj. say 20 thou off the lands, you set your die to seat 20 thou longer than the measurement taken as above.

[Triplejim]

have a read of:
http://www.triplej.com.au/pdfpages/LandsGauge.pdf

[AlanF]

have a read of:
http://www.triplej.com.au/pdfpages/LandsGauge.pdf

I'll second that James. Have been using these for a couple of years. I cut the slots carefully with a fine tooth hacksaw, and they work fine. On a new sharp throat you need to take extra care that the bullet doesn't grab slightly as its extracted and give a false reading - a little oil helps prevent that. Even if it does happen occasionally, I always repeat the process until several agree (to within a couple of thou).

Alan

[westernsky]

cheers for the info guys. im going to give both a try and see how they compare.
once i get that side sorted, i can begin ladder testing.
just hoping its as accurate as i expect

happy shooting

[Barry Davies]

The problem with the "split neck" method is one of case neck tension.
A certain amount of tension is required to ensure that the projectile does not get left behind or disengages itself slightly from the case on withdrawal, thereby giving you a false measurement.
This " required" tension also ensures that the projectile will most likely engage the rifling somewhat deeper, again giving a false measurement.
To satisfy yourself that what I say is correct try measuring the seating depth with different neck tensions and note the results.
In my own rifle comparing readings obtained with the split neck method as against measuring from the muzzle back, I was able to get, in one instant, measurements .025" longer and upon reducing neck tension .011" longer. ( neither being correct )
Longer being equal to jam of the projectile.
Of course none of this really matters except when somebody asks the question -- in which case the answer could be so much" jam' ( no pun intended) when in actual fact it is jump.
Barry

[macguru]

One thing I do lately, I make up a dummy round (no primer or powder) and chamber it, you can feel the bullet engage the lands and if you smudge a bit of brasso on it you can see the land imprint on the bullet, then back off 5-10 thou at a time depending on what you want to achieve. I generally get my best results when ALMOST touching the lands, so i crank the redding micrometer die 5 thou at a time until i am happy. Then I keep the dummy as a template with that projectile lot.
NEVER make up a dummy with a live primer unless you like tapping the bullet out of the barrel with a cleaning rod and hammer

javascript:emoticon(':shock:')

[Seddo]

i use the hornady system.

If you play with it at both ends (cleanign rod for the projie) you can move the projie back and forward and get a better feel rather then just pushing it in.

[AlanF]

The problem with the "split neck" method is one of case neck tension....

Its not perfect Barry, but there's a lot of other imperfections involved e.g. the shape of the ogive varies between bullets, the seater stem contacts the ogive at a different position from the measuring "nose-piece", which in turn is different from the lands contact position. I have been using the split neck method to record the measurements of several barrels as they age, and not once has it shown a throat getting shorter, so it'll do me.

Alan

[Barry Davies]

I always thought that the key to consistent accuracy was to eliminate " imperfections"
The imperfections you describe have nought to do with measuring the seating depth of the barrel -which is what this thread is about.
If you have variations in your measurement of barrel seating depth ( by whatever method ) then the relativity now and later ( as the throat wears ) has no meaning.
Again bearing in mind we are discussing barrel measurements --if the method you use can vary then the results are also variable--from time to time.
Barry

[Barry Davies]

I think some are missing the point I am trying to get across.
Because of the very small angles involved in both the chamber and the projectile at the point of contact of the projectile, it is very easy to actually force the projectile into the rifling -- moreso with a tangent ogive than a secant ogive.
Any forcing of the projectile such as with the " split case " method into the rifling will give some "jam " and it's very easy for this " jam 'to be in the vicinity of .025".
So it's conceivable that what you measure could actually be .025" jam when you think it is just touching the rifling ( or whatever )
Now you decide to give them .005" jam over that and they are actually .030" into the rifling, or you decide to give them .010" jump but they are actually still .015 jam.
However, like I said this does not mean much unless somebody asks the question. That being the case the answer should be "I have .010 " jam ( or whatever ) using my method of measuring.
The imperfections that Alan referred to have no bearing on measuring seating depth and only come into play AFTER the projectile has been seated in the case.
These variations can be verified with an ogive gauge, but with good quality projectiles should not be any more than .002" which has no measurable effect on accuracy.
We rely on the manufacturer to maintain consistency of projectiles but because of the manufacturing methods there will always be variations batch to batch.
For example I have two batches of Berger 155VLD's that have .034" variation from base to ogive with a similar variation in OAL BUT their seating depth , measured from case base to ogive is the same.
Is one more accurate than the other? At this stage I don't know, but will surely find out before Jan next year.
Barry