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seating depth by oal guage or chamber method?

 
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Old 07-29-2005, 05:54 AM
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Join Date: Mar 2005
Posts: 13
seating depth by oal guage or chamber method?

I have an kimber 22-250 rifle that I used a oal guage on and measured the cartridge at 2.487 inches to the lands...upon chambering a fire-formed, neck turned only case, with the same bullet pressed at the oal setting of 2.487, I then unchambered the cartridge and remeasered, and it miked out at 2.458 inches...what should I think of this? obviously the bullet is being pushed back into the case a bit...what should I do? still use the oal guage measurement or use the chamber method? I understand that the bolt will force the cartridge down and to the right and maybe give a "false reading"? Please give me some insight on the "correct" way of determining the best way to go...I'm interested in the best possible accuracy...also there have been no pressure signs at all...thanks
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Old 07-29-2005, 07:03 AM
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Join Date: Oct 2004
Location: Northamptonshire England
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Re: seating depth by oal guage or chamber method?

Hi nelsonic,
I use the "Ranging Rod" method i read about in a handloaders digest many years ago. This consists of a 30" length of 5mm brass rod ( for 22c/f and 243, 6mm, etc,7mm for 308) too which i have attached a locking collar approx 1" diameter and 1/2" thick.

Firstly i lift the bolt to cock the firing pin, i then slide the brass rod down the muzzel until it stops against the bolt face. i hold it in place and move the collar to contact the muzzel and look it in place.
With my Vernier i measure the protrusion of the rod from the face of the collar 3 times and record the mean reading.

The same process is then repeated but this time with the bolt removed and i have an assistant wedge my chosen bullet into the lands and hold it there with a suitable piece of dowel. The rod is then slid down the muzzel untill it touches the tip of the bullet, the collar locked and a reading of the protrusion taken and recorded as before.

Subtract the smaller dimension from the larger dimension and this will give you the exact C.O.A.L. for that bullet.
I then make up a dummy round to this exact C.O.A.L., take a bullet comparator reading and use this dummy round to set up my dies.

In my opinion this the most accurate way of finding your C.O.A.L and it may be a bit of a chore to do this with every different bullet you use, but in the quest for accuracy i think it is well worth it.

Ian.

"I mean't to shoot the pike but the duck got in the way"
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Old 07-29-2005, 07:15 AM
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Join Date: Feb 2004
Location: Virginia
Posts: 61
Re: seating depth by oal guage or chamber method?

For hunting rifles, I just seat bullets out farther and farther until:

1. It won't fit/feed in the mag...or...

2. I can't fully close the bolt reliably from hunting positions (sitting, off-hand, etc)...or...

3. When I try to extract an unfired round, it pulls the bullet.

Once I have found the max length without on of those bad things happening, I begin load development at that length and work back if velocity/pressure/accuracy tells me I need to.

Rick
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Old 07-29-2005, 06:16 PM
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Join Date: Aug 2004
Location: utah
Posts: 302
Re: seating depth by oal guage or chamber method?

nelsonic,
I assume that you are talking about the stoney point oal guage, it is for ballpark measurement (at best) I have done exactly what you are doing and it is frustrating, the best way that I have found is to use a magic marker from just above the ogive to just below the ogive and close the bolt carefully to not get false readings,once you have found the lands just use lighter fluid or solvent to clean off the marker.
B
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Old 07-31-2005, 10:16 AM
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Join Date: Sep 2004
Location: Southwestern Montana
Posts: 294
Re: seating depth by oal guage or chamber method?

CP - The ranging rod method sounds like it takes the reading from the tip of the bullet. Bullet length can be quite inconsistant. Have you seen the groups tighten up when you started using this method? I'm also looking to find the best way to measure overall length. The chamber method and measurement from the ogive sounds about the best to me, but your method sounds easy.

Any other ideas?
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Old 07-31-2005, 01:36 PM
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Join Date: May 2004
Location: MD.
Posts: 225
Re: seating depth by oal guage or chamber method?

Nelsonoc
The stoney point OAL will get you close. I also stand the rifle straight up and down, I feel it gives a better reading and doesn't bind. To remove another factor, I fire a round in my chamber and thread the case.
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Old 07-31-2005, 06:11 PM
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Join Date: Sep 2004
Location: Southwestern Montana
Posts: 294
Re: seating depth by oal guage or chamber method?

rimfire - what does thread the case mean? How is it done? What factor does it remove? Thanks!
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