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Omega47
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Posted: November 29 2007 at 5:20pm | IP Logged Quote Omega47

I have been working with a bullet manufacturer to get the most accurate loads with their product. They suggest seating the bullets .041 off the lands. What are some methods, or what is the best way to determine land depth without doing a casting of the chamber?

Thanks
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davemuzz
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Posted: November 29 2007 at 5:59pm | IP Logged Quote davemuzz

Omega,

There are several methods of getting the measurement of your gun's chamber length.

On way is to just use an unprimed brass (I say to use a piece of brass with no primer so it doesn't get confused with a loaded round)...don't size it or the neck may have too much tension....but you may have to give the neck a "tweak" with pliers so it will hold a bullet. Then push the bullet in the brass just enough so the brass holds it. Now, chamber the bullet\brass. You will feel the bullet press against the lands. Close the bolt...then open it and carefully take out the bullet. Now...just measure it! Do this 3 or 4 time so you know you have the correct chamber measurement.

Another way (and I have this product) is to use a simple tool like this It will give you the chamber measurement without all the brass\bullet stuff.

Dave

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Omega47
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Posted: November 29 2007 at 6:07pm | IP Logged Quote Omega47

Thanks. I tried that and get the following measurements in my new Rem 700 .243:
2.725, 2.735 and 2.745 - all using the same bullet. Tried another bullet three times and got the same measurement pattern as the first try. Thought I'd outsmart it and made 3 dummy rounds with 3 new bullets. The first measured 2.725, the second measured 2.735 and the third measured 2.745. Now I'm stumped.
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Slick
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Posted: November 29 2007 at 7:29pm | IP Logged Quote Slick

Omega47 wrote:
Thanks. I tried that and get the following measurements in my new Rem 700 .243:
2.725, 2.735 and 2.745 - all using the same bullet. Tried another bullet three times and got the same measurement pattern as the first try. Thought I'd outsmart it and made 3 dummy rounds with 3 new bullets. The first measured 2.725, the second measured 2.735 and the third measured 2.745. Now I'm stumped.


The measuring technique is sound..

Here's my "WAG" (Wild-A..-Guess) as to what's happening.

1st pass you get 2.725 (which is correct for a "new" bullet"). Each subsequent pass adds an extra 10-thousands. I believe the reason for this is the bearing surface of the bullet (when it meets the lands) is nearly "straight" and the pressure required to seat the bullet is ever-so-slightly "collapsing" the jacket where it touches the lands. As such, each subsequent seating crushes the bullet a tad more - which in turn lengthens the OAL (artificially).

Think of the mechanical advantage (of crush) when inserting a conical object into a hole (that is so close to the maximum diameter of the object).

I say try it 3 times - (each with a new "never-seated" bullet) and three pieces of brass and you should obtain the 2.725 measurement - then seat as much deeper as required from there when building your loads.

I think I am right about whats happening - but I want to point out that my analysis is purely my own opinion YMMV.

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STCM(SW)
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Posted: November 29 2007 at 9:19pm | IP Logged Quote STCM(SW)

Slick has it IMO...
But I could be wrong.....

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Cracker
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Posted: November 30 2007 at 3:33am | IP Logged Quote Cracker

Omega47 wrote:
I have been working with a bullet manufacturer to get the most accurate loads with their product. They suggest seating the bullets .041 off the lands. What are some methods, or what is the best way to determine land depth without doing a casting of the chamber?

Thanks
Borrow or spend a few bucks to buy a chamber length gauge.

Lee
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Cracker
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Posted: November 30 2007 at 4:03am | IP Logged Quote Cracker

Buy the gauge and take the guesswork out of it. While it seems silly to buy a gauge to measure the chamber of your only weapon in specific caliber, once you have one, all you need to do is buy additional cases for other calibers, not to mention the fact that different bullets in the same calibers will reach the lands at a different length.

For that matter, individuals bullets of the same make and design will probably give you slightly different readings. All men may be created equal, but all bullets aren't.

Lee
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davemuzz
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Posted: November 30 2007 at 1:11pm | IP Logged Quote davemuzz

Slick is right.

Lee is right as well, but it will cost a few bucks.

I would say use Slick's method while your guage is in the BBT to your house, then....go out and buy at least 4 more rifles of various calibers so you can use that guage and get your monies worth out of it!

Dave

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