Anyone Have Advice for Using Hornady's OAL Gauge?

[MNtadpole]

All,

I'm in the process of trying use Hornady's OAL gauge to measure the max CBTO for my AR-10 in 6.5CM. My prior load development sessions showed possible signs of higher pressures for the given powder charges. My previous COAL was 2.818" which allowed it to feed properly in the P-Mag. It was suggested to go ahead and investigate possible occurrence of the cartridge chambering on the lands.

Anyways, my current issue is using Hornady's OAL gauges. While using the the gauge in conjunction with the correct modified case, I was unable to consistently find the rifle lands at the same measurement. I am using 140gr SMK as the bullet selected. I went ahead and cleaned the chamber and bore, after having initial issues with consistent measurements. Even after cleaning the chamber and bore, I am still having inconsistent measurements. Does anyone have any suggestions to get more consistent measurements with this tool? Thanks in advance!

 

[padom]

All,

I'm in the process of trying use Hornady's OAL gauge to measure the max CBTO for my AR-10 in 6.5CM. My prior load development sessions showed possible signs of higher pressures for the given powder charges. My previous COAL was 2.818" which allowed it to feed properly in the P-Mag. It was suggested to go ahead and investigate possible occurrence of the cartridge chambering on the lands.

Anyways, my current issue is using Hornady's OAL gauges. While using the the gauge in conjunction with the correct modified case, I was unable to consistently find the rifle lands at the same measurement. I am using 140gr SMK as the bullet selected. I went ahead and cleaned the chamber and bore, after having initial issues with consistent measurements. Even after cleaning the chamber and bore, I am still having inconsistent measurements. Does anyone have any suggestions to get more consistent measurements with this tool? Thanks in advance!

Are you using the Semi-Auto Overall Length Gauge?? The curved one, not the straight one for bolt guns?

If so, attached the modified case and drop your bullet in, adjust the depth stick so that the bullet is 1/2 or 3/4 down into the case so you dont have the bullet touching anything when your inserting the case. Now, insert the case into the chamber until it is fully seated and stops in the chamber. While holding you finder on the bend of the gauge with forward pressure to ensure the case doesnt move.. Press the seating stick/rod till the bullet stops and wont go any further...Tighten the set screw at this point before you move anything. Now pull everything out (may have to tap bullet out) and put back in case and measure. Remember, this is a way to find where the bullet is touching..... There is tolerances, this isnt a scientific way to get exact measurements... And it doesnt need to be for this purpose..

You should not be loading anywhere near the lands on a AR/Gasser.. I dont know what barrel, chamber you are using.. But Ive built and measured 20+ 6.5cm AR barrels to lands and with a 6.5cm SAMMI reamer, distance to the lands with 140 ELD has always been in the 2.85 range.... Nowhere near where you can even reach with a PMAG.... I run my 6.5cm AR loads in the 2.83 range which is where accuracy is the best and Im still .02 off lands.. I also dont use PMAGs.... KAC, Larue or ASC all allow you to use rounds in the 2.86-2.87 COAL....

If youre getting pressure due to be close or into the lands at 2.80-2.81 in a 6.5cm gasser, you have bigger problems...

 

[TheBoctor]

I'll run a cleaning rod in from the muzzle end and use that to kind of "float" the bullet into/out of the lands. You insert the OAL gauge/bullet and run the bullet into the lands with the plunger on the tool. Then, while still holding some pressure on the plunger of the OAL tool, use the cleaning rod to gently push the bullet out of the lands. You want to keep gentle pressure on both ends of the bullet while moving it in/out and you'll get a better feel of where it contacts the lands. Once you're happy, lock down the thumb screw and pull the tool/case/bullet out and measure. Be careful though, you always want to use a light touch when doing this, first because it's a pretty delicate process to begin with and doesn't require much force, second you REALLY don't want the tip of the bullet to get between the bore and the cleaning rod. Always remember to pull the cleaning rod a good ways up the barrel before you go re-insterting the OAL tool, too. Trust me on that one.

 

[padom]

I'll run a cleaning rod in from the muzzle end and use that to kind of "float" the bullet into/out of the lands. You insert the OAL gauge/bullet and run the bullet into the lands with the plunger on the tool. Then, while still holding some pressure on the plunger of the OAL tool, use the cleaning rod to gently push the bullet out of the lands. You want to keep gentle pressure on both ends of the bullet while moving it in/out and you'll get a better feel of where it contacts the lands. Once you're happy, lock down the thumb screw and pull the tool/case/bullet out and measure. Be careful though, you always want to use a light touch when doing this, first because it's a pretty delicate process to begin with and doesn't require much force, second you REALLY don't want the tip of the bullet to get between the bore and the cleaning rod. Always remember to pull the cleaning rod a good ways up the barrel before you go re-insterting the OAL tool, too. Trust me on that one.

We've been doing this for many many years. First time Ive ever heard of anyone using a cleaning rod "To guide the bullet in" and for what purpose?? There is no need for a cleaning rod when inserting the OAL gauge. Its only necessary to tap the bullet out if the lands grab it.... I would not want ANYTHING touching the bullet or in the chamber area when inserting the gauge. There is too much room for error or false readings doing this and completely unncessary. Your case centers the bullet in the chamber, you push forward till it stops without slamming it into the lands. Its that easy... We dont need to make this more complicated than it really is. This is not a delicate process, push in, it stops, tighten up set screw, pull out and tap bullet out with rod if needed. Do this 5x, write the number down 5x, use the avg.

 

[Howland]

When I first tried I got measurements all across a 0.040" range. I quickly figured out that stopping at the first sign of slight resistance was causing inaccurate measurements.

Slide it in until you meet firm resistance. You won't mistake the slight resistance of contact between bullet and anything with the firm resistance of a .308" bullet on 0.306" lands.

Then keep in mind that the actual contact points are 1). the case shoulder against the chamber shoulder and 2.) the ogive against the lands. If you're using the modified case, the case head to shoulder dimension is rarely exactly the same as the same dimensions on a fully expanded case from your chamber. You must add (or possibly subtract) the difference. That is why people send a fully expanded case from their own chamber in for Hornady to drill and tap through the primer flash hole. Or you can do that part yourself.

 

[MNtadpole]

Are you using the Semi-Auto Overall Length Gauge?? The curved one, not the straight one for bolt guns?

If so, attached the modified case and drop your bullet in, adjust the depth stick so that the bullet is 1/2 or 3/4 down into the case so you dont have the bullet touching anything when your inserting the case. Now, insert the case into the chamber until it is fully seated and stops in the chamber. While holding you finder on the bend of the gauge with forward pressure to ensure the case doesnt move.. Press the seating stick/rod till the bullet stops and wont go any further...Tighten the set screw at this point before you move anything. Now pull everything out (may have to tap bullet out) and put back in case and measure. Remember, this is a way to find where the bullet is touching..... There is tolerances, this isnt a scientific way to get exact measurements... And it doesnt need to be for this purpose..

You should not be loading anywhere near the lands on a AR/Gasser.. I dont know what barrel, chamber you are using.. But Ive built and measured 20+ 6.5cm AR barrels to lands and with a 6.5cm SAMMI reamer, distance to the lands with 140 ELD has always been in the 2.85 range.... Nowhere near where you can even reach with a PMAG.... I run my 6.5cm AR loads in the 2.83 range which is where accuracy is the best and Im still .02 off lands.. I also dont use PMAGs.... KAC, Larue or ASC all allow you to use rounds in the 2.86-2.87 COAL....

If youre getting pressure due to be close or into the lands at 2.80-2.81 in a 6.5cm gasser, you have bigger problems...
[/QUOTE]

Well I can't conclusively say what the high pressure signs are truly due to yet. The goal here was to eliminate my reloading's COAL as possible cause of the high pressure. I had assumed that the P-Mag wouldn't allow a COAL that was at or too close to the lands, but I wanted to make sure...so here I am. I'm running a Daniel Defense DD5v5 20" barrel 1:8 twist. I am using the straight one, as I was told that it tends to be more accurate. Although I do see the benefit to the curved gauge, I am able to make the straight one work with my particular application. I can't yet determine if it is ideal though...

 

[padom]

Well I can't conclusively say what the high pressure signs are truly due to yet. The goal here was to eliminate my reloading's COAL as possible cause of the high pressure. I had assumed that the P-Mag wouldn't allow a COAL that was at or too close to the lands, but I wanted to make sure...so here I am. I'm running a Daniel Defense DD5v5 20" barrel 1:8 twist.

And when you measured to the lands with the gauge 5x with the bullet in question what was your measurement?

 

[MNtadpole]

And when you measured to the lands with the gauge 5x with the bullet in question what was your measurement?

They were all over the place. I think was being too gentle with the push of the rod. I think I will try a more purposeful push as you said. My recorded measurements are currently at home. I will post them to you once I'm home, so you can get a taste of the non-sense that I was creating lol.

 

[padom]

They were all over the place. I think was being too gentle with the push of the rod. I think I will try a more purposeful push as you said. My recorded measurements are currently at home. I will post them to you once I'm home, so you can get a taste of the non-sense that I was creating lol.

Lol. No worries.. push them till they stop...do it 5x...give us the avg. With a factory chambered DD I suspect it won't be short....

 

[whatsupdoc]

This method works for me.

Clean chamber, push a couple of patches through barrel.
Tighten modified case onto tool, adjust center rod so bullet is inside case, lock the rod with the thumbscrew.
With the rifle horizontal push the tool/case/bullet into the chamber.
Take the rifle and hold it vertically with the muzzle resting on the floor.
Rotate the tool body slightly back and forth while pushing forward into the chamber.
While holding the center rod loosen the thumbscrew that that holds the center rod and slowly let the center rod come to rest on the base of the bullet.
Tighten the thumbscrew and remove tool from chamber.

Measure.

 

[Dthomas3523]

It doesn’t matter if you’re getting the measurement down to the exact point of the lands.

Just take the measurement a few times and go with averages.

Even if you’re a few thou off from perfect, it doesn’t matter. Regardless you’re going to adjust seating until it shoots well.

 

[Jordanwickham]

If I can get that thing to give 5 readings inside of about a .015 spread I feel I'm doing pretty damn good. Now I just find jam but I'm not sure that works like that on a gas gun.

 

[TheBoctor]

We've been doing this for many many years. First time Ive ever heard of anyone using a cleaning rod "To guide the bullet in" and for what purpose?? There is no need for a cleaning rod when inserting the OAL gauge. Its only necessary to tap the bullet out if the lands grab it.... I would not want ANYTHING touching the bullet or in the chamber area when inserting the gauge. There is too much room for error or false readings doing this and completely unncessary. Your case centers the bullet in the chamber, you push forward till it stops without slamming it into the lands. Its that easy... We dont need to make this more complicated than it really is. This is not a delicate process, push in, it stops, tighten up set screw, pull out and tap bullet out with rod if needed. Do this 5x, write the number down 5x, use the avg.

I don't do this to "guide the bullet" anywhere. You push the bullet into the lands with the plunger, you push it out of the lands with the cleaning rod, and you do it several times pushing it back and forth gauging how it feels seating in the lands. It is especially helpful in guns with tight freebore or when your modified case isn't perfect (sticky neck or too sloppy where the bullet can bind) and you can't tell if you're really in the lands. It's my go-to when i can't get reasonably repeatable result just shoving the bullet in. I figured, since OP is having freebore/seating depth issues, that we may be beyond normal OAL gauge operations and this has helped me get an idea of what was going on during my periods of head-scratching in this department.

 

[Suasponte]

More then likely seating the bullet to jam or touching the throat will exceed your mag length. Just seat you bullet to feed in your mag and tune your load with seating depth in from your mag clearance dimension. You will hit nodes from that point in that shoots, they all do. Don't worry about where the lands are, worry about where you node points are and you will be much better off. Bump in .003 and load five then repeat. your will find the group doing this that shoots.

 

[Jaxdialation]

Still a very touch sensitive technique. It will work with some actions.
But not with mine.

I don’t have any issue with the Hornady tool since I learned to use a dowel to push the
round out and to use a consistent pressure on the rod. Before I figured that out I had to use averages. Now I get identical measurements easily.

I was having some inconsistencies with my Hornady tool. I switch to this method.

 

[NighthawkCG]

I don't do this to "guide the bullet" anywhere. You push the bullet into the lands with the plunger, you push it out of the lands with the cleaning rod, and you do it several times pushing it back and forth gauging how it feels seating in the lands. It is especially helpful in guns with tight freebore or when your modified case isn't perfect (sticky neck or too sloppy where the bullet can bind) and you can't tell if you're really in the lands. It's my go-to when i can't get reasonably repeatable result just shoving the bullet in. I figured, since OP is having freebore/seating depth issues, that we may be beyond normal OAL gauge operations and this has helped me get an idea of what was going on during my periods of head-scratching in this department.

I do this. Helps to learn the touch and build consistency with it.

 

[Holliday]

I use this method

 

[padom]

I use this method

Hes measuring an AR. Not a bolt gun

 

[MNtadpole]

All,

So I think I got it all figured out. I apparently took the instructions of this process too literally, when they said "gentle". After feeling the bullet meet some resistance with the tool, I pointed the barrel down and provided reasonable pressure until there was no discernible movement left in the projectile in the lands. This seemingly gave me repeatable measurements. Thanks all.

 

[232593]

Are you using the Semi-Auto Overall Length Gauge?? The curved one, not the straight one for bolt guns?

If so, attached the modified case and drop your bullet in, adjust the depth stick so that the bullet is 1/2 or 3/4 down into the case so you dont have the bullet touching anything when your inserting the case. Now, insert the case into the chamber until it is fully seated and stops in the chamber. While holding you finder on the bend of the gauge with forward pressure to ensure the case doesnt move.. Press the seating stick/rod till the bullet stops and wont go any further...Tighten the set screw at this point before you move anything. Now pull everything out (may have to tap bullet out) and put back in case and measure. Remember, this is a way to find where the bullet is touching..... There is tolerances, this isnt a scientific way to get exact measurements... And it doesnt need to be for this purpose..

You should not be loading anywhere near the lands on a AR/Gasser.. I dont know what barrel, chamber you are using.. But Ive built and measured 20+ 6.5cm AR barrels to lands and with a 6.5cm SAMMI reamer, distance to the lands with 140 ELD has always been in the 2.85 range.... Nowhere near where you can even reach with a PMAG.... I run my 6.5cm AR loads in the 2.83 range which is where accuracy is the best and Im still .02 off lands.. I also dont use PMAGs.... KAC, Larue or ASC all allow you to use rounds in the 2.86-2.87 COAL....

If youre getting pressure due to be close or into the lands at 2.80-2.81 in a 6.5cm gasser, you have bigger problems...

Sorry to resurrect this thread but how do you get the modified case, projectile, and gauge to sit square in the calipers? That wire in the curved gauge keeps everything from being perpendicular.