6mm CM COAL?

[rugby10]

As a new reloader, I am trying to figure out the correct COAL distance to the lands to properly seat the bullets.

I have a new Terminus Zeus action and 26" Bartlein barrel. I am using the Hornady comparator, a 6mm CM modified case, and a Hornady 108gr ELD bullet to do the measurements. I measured a bunch of times and took the average since it was a little bit different each time. The result was a BTO of 2.044".

I also used the comparator to measure a Hornady 108 ELD match cartridge just for reference and the BTO result was 2.225".

If I was to start testing with setting my bullet depth to .02 from the lands, that would give me a BTO length of 2.024" which is significantly shorter than my reference cartridge. I understand it might not be exactly the same size, but a difference of .201" makes me wonder if I am doing something wrong.

Any comments or suggestions would be appreciated. Thanks.

 

[Hohn]

So you’re saying that your factory 108 cartridge would be a very hard jam in your rifling at bolt close?

 

[rugby10]

So you’re saying that your factory 108 cartridge would be a very hard jam in your rifling at bolt close?

Nope, has no issues and shoots decently. I am just using it for comparison which makes me wonder if I am doing something wrong with the measurements.

 

[Richard Coody]

Yeah
Your measurements are wrong. You haven't measured to the lands in your rifle.

Google Search

www.google.com

Google Search

www.google.com

 

[RegionRat]

@rugby10 ... I agree you are probably doing something wrong.

If you can't get to where your measurement to lands is longer than that factory cartridge which you know is not jammed, then keep trying to debug your measurement or seek a second set of eyes, preferably a set with experience.

 

[rugby10]

@rugby10 ... I agree you are probably doing something wrong.

If you can't get to where your measurement to lands is longer than that factory cartridge which you know is not jammed, then keep trying to debug your measurement or seek a second set of eyes, preferably a set with experience.

Wondering if I am pushing the case in too far before I push the bullet in to touch the lands.

Should the case be pushed all the way into the chamber until it stops?

Not really feeling alot of resistance before pushing all the way in..

 

[Richard Coody]

Wondering if I am pushing the case in too far before I push the bullet in to touch the lands.

Should the case be pushed all the way into the chamber until it stops?

Not really feeling alot of resistance before pushing all the way in..

The case should go in until the shoulder of the case is against the shoulder of the chamber and stops.

I sent you a link to utube videos of how to use the Hornady overall length gauge. Watch them. I bet you can figure out what you are doing wrong. I lightly tap on the end of the rod to make sure my bullet is jammed into the rifling. The brownel video is the one I like best.

 

[rugby10]

The case should go in until the shoulder of the case is against the shoulder of the chamber and stops.

I sent you a link to utube videos of how to use the Hornady overall length gauge. Watch them. I bet you can figure out what you are doing wrong. I lightly tap on the end of the rod to make sure my bullet is jammed into the rifling. The brownel video is the one I like best.

Watched many videos already, but I will try again. Thank you.

 

[RegionRat]

I second Richard's advice.
Press the case into the shoulder and hold it there with a steady margin. I also run several "taps" to determine the bullet has been "wedged" into the lands. Play with one light tap then hold the case and bullet ramrod steady while you torque the clamp screw. Then try several taps etc, to determine how "soft" the measurement is.
Keep in mind, there are many factors at play and many of them have a dispersion behavior due to friction. Not every reamer uses the same angles or diameters, not every bullet jacket has the same shape or alloy. There are many reasons why there is a range to the measurement. Too many folks will claim their numbers repeat to less than 0.00XX but that is ego talking. There can be several technique driven differences in the measurements, but it doesn't matter. I tend to find some guns are reamed with a shallower angle and the number can spread more than 0.005" and ones with a steep angle seem to be less variable. YMMV.

Play with your technique till you are happy, but then don't sweat it too much since it isn't a hard number and throats will wear. Just make sure you have a decent starting value for your seating tests and then let the bullet seating measurements and targets determine your dimensions.

When you think you are done establishing the dimensions, go ahead and make a dummy sample with a high neck tension and seat a bullet 0.010 longer than you think your lands are, and mark it up with ink to see if you can find the land markings. You should very nearly have trouble closing the bolt and pulling it out without it making a fuss. Double check the dummy length when you pull it out for good measure.

 

[bozo699]

You will never be 100% spot on with that tool!... there nice and have there uses but if your trying to be exact and get the same measurements 10 different guys would get the strip your bolt and use Alex Wheelers method for finding the lands.
Wayne

 

[rugby10]

I second Richard's advice.
Press the case into the shoulder and hold it there with a steady margin. I also run several "taps" to determine the bullet has been "wedged" into the lands. Play with one light tap then hold the case and bullet ramrod steady while you torque the clamp screw. Then try several taps etc, to determine how "soft" the measurement is.
Keep in mind, there are many factors at play and many of them have a dispersion behavior due to friction. Not every reamer uses the same angles or diameters, not every bullet jacket has the same shape or alloy. There are many reasons why there is a range to the measurement. Too many folks will claim their numbers repeat to less than 0.00XX but that is ego talking. There can be several technique driven differences in the measurements, but it doesn't matter. I tend to find some guns are reamed with a shallower angle and the number can spread more than 0.005" and ones with a steep angle seem to be less variable. YMMV.

Play with your technique till you are happy, but then don't sweat it too much since it isn't a hard number and throats will wear. Just make sure you have a decent starting value for your seating tests and then let the bullet seating measurements and targets determine your dimensions.

When you think you are done establishing the dimensions, go ahead and make a dummy sample with a high neck tension and seat a bullet 0.010 longer than you think your lands are, and mark it up with ink to see if you can find the land markings. You should very nearly have trouble closing the bolt and pulling it out without it making a fuss. Double check the dummy length when you pull it out for good measure.

Thank you so much for your suggestion. I am now getting a constistent BTO of 2.230.

If I follow the videos exactly, they say to shoulder the case, then slowly push the ramrod until the bullet touches the lands. Well, by starting to push the ramrod a little BEFORE shouldering the case 100% and wiggling it around a little, it hits the lands and produces a measurement I would expect. Maybe the reamer did indeed have a different angle or whatever which causes the measrement to be off without some extra persuasion.

Thanks to all for your help.