Finding col

bwsbama25 · February 2, 2010, 08:20 AM

So i was reading diffrent ways to find what the col should be for my rifle and i was woundering if this is a good way to do it.The guy took a 30-06 case and cut 4 slits in the neck of the case so the bullet would be just loose enuf that whene you chamber the round in the gun it pushes the bullet to where you should set the col of that spacific bullet.Is this a good way to know the best col or do yall have other ways that are better.

mongoose33 · February 2, 2010, 09:27 AM

I suspect for that specific bullet it's ok. A different bullet w/ a different ogive will present differently, and may require a longer or shorter COL. If I used this method, after identifying it as the COL, I'd make up a dummy round (no powder or primer) and be sure it chambers.

And that COL will be valid for that gun; another w/ different parameters may require a different COL, and different bullets may as well.

mrawesome22 · February 2, 2010, 10:16 AM

That is a great method for rifles.

Lilswede1 · February 2, 2010, 10:34 AM

I used a Dremel tool with the thinnest cutting disc and made several slits to start with but found that one single slit worked best (for .223).
Then I purchased the Hornady OAL tool and better calipers.
The new tools resulted in much more consistent and accurate readings. The slit case measurements were .005" - .007" shorter then the Hornady guage.
Its best to use a case fireformed from that gun.
Also, only slit the neck. Do not cut into the shoulder area of the case. This would allow the shoulder to shrink a little and would change the reading.
Keep a record of your measurements. It will help down the line to determine amount of throat erosion.

lemming303 · February 2, 2010, 11:28 AM

That is a fine method, and will work great. I use the marker method. It's a little more complicated. I take a case that is either new or resized. I start a bullet into the neck and color the whole bullet with dry erase marker. Then I chamber it, careful not to touch the bullet on the feed ramp or anything else. When it comes out you must also make sure not to touch the chamber or ramp or anything. It will show you exactly where each land is. I then measure it, seat the bullet to that measurement, test it again, and then set my seating depth to .015 less than the lands. I find this is pretty accurate, because there is no flex in the case, and the bullet is unable to move once pushed into the case by the rifling.

F. Guffey · February 2, 2010, 12:09 PM

I drill the flash hole to a diameter that will accommodate a dowel or cleaning rod, I first determine head space (or the effect the chamber will have on the case when fired), then seat the bullet and insure bullet hold (neck tension) then chamber the case with bullet (no powder/primer) with the bolt removed then use a cleaning/dowel to push the bullet out of the case until it stops, when it stops the bullet has hit the rifling, then I remove the test case and measure the length COL (Case Overall Length), then I adjust the seater die with the test case, with the die backed out to prevent the crimping portion of the die contacting the mouth of the case I adjust the seater stem down until it contacts the bullet, as an index that is .000 'zero off the lands, when seating the bullet off the lands a depth gage can be used to determine the difference between zero and the distance the stem has been lowered, to prevent waking up in a new world everyday, keep that case for referees for that particular bullet with that particular case for a particular chamber. If the bullet is changed, start over with another test case.

On more than one occasion I have pushed the bullet out of the case before it hit the rifling, on one 7mm Gibbs the bullet traveled (free bore) .225 thousands before the bullet stopped with a 170 grain bullet. It is a custom rifle, no telling what they were thinking when the chamber was cut, they could have got a little confused when someone told them about Weatherby chambers and the need for free bore. Or something like "get a neck reamer and throat the chamber so you can seat the bullet out further! that will allow you to get more powder in the case and that will get you to shooting right up there with the Magnums

F. Guffey

F. Guffey · February 2, 2010, 03:29 PM

....traveled .225 after it was pushed out of the case.....

"

sorry about that

F. Guffey

February 2, 2010, 08:20 AM	#1
bwsbama25 Junior Member Join Date: January 21, 2010 Location: Birmingham Al Posts: 9	Finding col So i was reading diffrent ways to find what the col should be for my rifle and i was woundering if this is a good way to do it.The guy took a 30-06 case and cut 4 slits in the neck of the case so the bullet would be just loose enuf that whene you chamber the round in the gun it pushes the bullet to where you should set the col of that spacific bullet.Is this a good way to know the best col or do yall have other ways that are better.

February 2, 2010, 10:34 AM	#4
Lilswede1 Senior Member Join Date: September 8, 2008 Location: NW Wash State Posts: 216	It works with only 1 slit I used a Dremel tool with the thinnest cutting disc and made several slits to start with but found that one single slit worked best (for .223). Then I purchased the Hornady OAL tool and better calipers. The new tools resulted in much more consistent and accurate readings. The slit case measurements were .005" - .007" shorter then the Hornady guage. Its best to use a case fireformed from that gun. Also, only slit the neck. Do not cut into the shoulder area of the case. This would allow the shoulder to shrink a little and would change the reading. Keep a record of your measurements. It will help down the line to determine amount of throat erosion.

February 2, 2010, 09:27 AM	#2
mongoose33 Senior Member Join Date: June 23, 2009 Location: Wisconsin Posts: 228	I suspect for that specific bullet it's ok. A different bullet w/ a different ogive will present differently, and may require a longer or shorter COL. If I used this method, after identifying it as the COL, I'd make up a dummy round (no powder or primer) and be sure it chambers. And that COL will be valid for that gun; another w/ different parameters may require a different COL, and different bullets may as well.

February 2, 2010, 10:16 AM	#3
mrawesome22 Senior Member Join Date: November 9, 2005 Location: Ohio, Appalachia's foothills. Posts: 3,779	That is a great method for rifles.

February 2, 2010, 11:28 AM	#5
lemming303 Member Join Date: March 5, 2009 Location: Texas, best country ever! Posts: 42	That is a fine method, and will work great. I use the marker method. It's a little more complicated. I take a case that is either new or resized. I start a bullet into the neck and color the whole bullet with dry erase marker. Then I chamber it, careful not to touch the bullet on the feed ramp or anything else. When it comes out you must also make sure not to touch the chamber or ramp or anything. It will show you exactly where each land is. I then measure it, seat the bullet to that measurement, test it again, and then set my seating depth to .015 less than the lands. I find this is pretty accurate, because there is no flex in the case, and the bullet is unable to move once pushed into the case by the rifling.

February 2, 2010, 12:09 PM	#6
F. Guffey Senior Member Join Date: July 18, 2008 Posts: 7,249	I drill the flash hole to a diameter that will accommodate a dowel or cleaning rod, I first determine head space (or the effect the chamber will have on the case when fired), then seat the bullet and insure bullet hold (neck tension) then chamber the case with bullet (no powder/primer) with the bolt removed then use a cleaning/dowel to push the bullet out of the case until it stops, when it stops the bullet has hit the rifling, then I remove the test case and measure the length COL (Case Overall Length), then I adjust the seater die with the test case, with the die backed out to prevent the crimping portion of the die contacting the mouth of the case I adjust the seater stem down until it contacts the bullet, as an index that is .000 'zero off the lands, when seating the bullet off the lands a depth gage can be used to determine the difference between zero and the distance the stem has been lowered, to prevent waking up in a new world everyday, keep that case for referees for that particular bullet with that particular case for a particular chamber. If the bullet is changed, start over with another test case. On more than one occasion I have pushed the bullet out of the case before it hit the rifling, on one 7mm Gibbs the bullet traveled (free bore) .225 thousands before the bullet stopped with a 170 grain bullet. It is a custom rifle, no telling what they were thinking when the chamber was cut, they could have got a little confused when someone told them about Weatherby chambers and the need for free bore. Or something like "get a neck reamer and throat the chamber so you can seat the bullet out further! that will allow you to get more powder in the case and that will get you to shooting right up there with the Magnums F. Guffey

February 2, 2010, 03:29 PM	#7
F. Guffey Senior Member Join Date: July 18, 2008 Posts: 7,249	....traveled .225 after it was pushed out of the case..... " sorry about that F. Guffey