Need a very easy explanation on using Sinclair Seating Depth Tool


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Jcinnb
June 25, 2013, 11:08 PM
Ok, I have the tool and have used it a few times. I am struggling with a 2 O'clock in the morning thought, that I have been unable to reconcile.

Here goes (from the how to I found on the Sinclair Blog):

I get dropping the bullet in chamber, using rod to push against lands and locking down the stop to get a distance.

I also get the next step where a case is dropped in, pushing until the shoulder seats tightly, and again locking down the stop.

I get making the measurement from the outside edge of the two large collars.

So far so good. I am good to go.

Now I am told to add the length of the bullet to the length found on the tool, to get "total overall length." I know what those words mean.

Here is where I have trouble.

1. Measuring the bullet and then the cartridge does not appear to take into account the depth the bullet is seated and how seating depth affects OAL. Help!

2. The next sentence in the instruction tells me to measure bullet from base to ogive using comparator. OK, then what?

I am sure it is me, but I am fine on the take off, the flight, the approach, but crash on the landing.

Please be patient and if you are able/willing to explain, please understand I am pretty new at this, just trying to learn.

Thanks, as always, in advance, and I did a lot of searching and though I found a lot of similar threads, did not find this issue addressed.

jcinnb

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higgite
June 26, 2013, 12:29 AM
1. The tool doesn't measure the length of the case. It measures the distance from the base of the bullet (the first marker) to the case head (the second marker). So, you add the measured difference (the length from case head to base of bullet) to the length of the bullet from its base to tip, and the result is the distance from case head to bullet tip, i.e., cartridge OAL with bullet touching lands.

2. Most bullets are more consistent in size from base to some spot on the ogive than they are from base to tip. A comparator measures each bullet to the same spot on the ogive.

Then what?
Then you know the max "OAL" from case head to bullet ogive with THAT bullet touching the lands of THAT rifle. If you want to seat THAT bullet and others from the same box .020" off the lands of THAT rifle, seat it to where it measures .020" shorter than the max "OAL" measured with the comparator.

Hope this helps. It is sorta confusing until you grasp what's really being measured.

Jcinnb
June 26, 2013, 07:25 AM
Thank you, I figured it out last night with a lot more thought. I do appreciate your response.

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