OAL gauge Vs. Factory ammo

[Rh0dz]

Novice reloader here. Couldn't find the the answer to my question on here so posting. I used the Hornady OAL gauge to get my chamber size to lands measurement in my 300 prc. The average was 2.626 and the four measurements were within 3 hundredths. I then measured a factory hornady 212 precision hunter CBTO and got a measurement of 2.821. Is the factory ammo seating .200 in the lands? I've shot the ammo and it's under a minute and shoots pretty decent.

I'm lost on whether this is normal or not. If so, where should I start my seating depth for a velocity test? .02 off my OAL chamber measurement?

 

[Southernspeed]

Did you use the same projectile to measure your OAL as the precision hunter uses?

 

[Rh0dz]

Did you use the same projectile to measure your OAL as the precision hunter uses?

I did not. I used Berger 215s

 

[morningsun]

If it shoots under an MOA what's not normal about that?

 

[Southernspeed]

To see where the ogive meets the lands you need to use the same projectile as they vary so much. You can't compare the two unfortunately.

 

[Rh0dz]

To see where the ogive meets the lands you need to use the same projectile as they vary so much. You can't compare the two unfortunately.

10-4 thanks for clarifying.

 

[Rh0dz]

If it shoots under an MOA what's not normal about that?

Factory shot well but I'd have a random shot drop 40 fps slower. Gonna give reloading a shot. It's by far the deepest rabbit hole I've traveled down...

 

[Southernspeed]

10-4 thanks for clarifying.

Measure with what you are going to load with. As for where to start off the lands, some barrels work well with little jump, my 6.5 RPR likes .090, my .308 works well with .120. It's just about finding what works once you've developed a good load.
Good luck!

 

[r.tenorio671]

...each brand and model of bullet is different, you should measure each you intend to use to determine WHERE the ogive contacts the lands of YOUR barrel before you begin reloading those bullets. Once you have the measurements you can proceed to determine the charge weight and seating depth for that particular bullet to meet your desired result.

Edited: simplified explanation, Tanget bullets contact lands earlier at shorter COAL, secant bullets contact lands at longer COAL, hybrid bullets somewhere between the tangent and secant COAL's.

 

[Im2bent]

Doesn't the hornady gauge measure at the ogive?

 

[straightshooter1]

Doesn't the hornady gauge measure at the ogive?

Hmmm??? I didn't think the Hornady gauge measured anything and thought it was a caliper with a comparator insert that did the measuring at the ogive.

 

[straightshooter1]

...each brand and model of bullet is different, you should measure each you intend to use to determine WHERE the ogive contacts the lands of YOUR barrel before you begin reloading those bullets. Once you have the measurements you can proceed to determine the charge weight and seating depth for that particular bullet to meet your desired result.

Edited: simplified explanation, Tanget bullets contact lands earlier at shorter COAL, secant bullets contact lands at longer COAL, hybrid bullets somewhere between the tangent and secant COAL's.

Yes, COAL's are different as well as the shapes and sizes of the ogives. But, when measuring the CBTO for the distance to the lands, it doesn't matter what bullet you use; the measurement will be the same (if one is using the same comparator insert).

 

[Rh0dz]

Yes, COAL's are different as well as the shapes and sizes of the ogives. But, when measuring the CBTO for the distance to the lands, it doesn't matter what bullet you use; the measurement will be the same (if one is using the same comparator insert).

This was exactly what I thought. Now I'm confused.

 

[salks]

Your not measuring something correctly. Warning Danger.

 

[MakeSawdust]

Yes, COAL's are different as well as the shapes and sizes of the ogives. But, when measuring the CBTO for the distance to the lands, it doesn't matter what bullet you use; the measurement will be the same (if one is using the same comparator insert).

It is true that the measurements should be close. There are a lot of things that can effect distance to the lands. For them to be exactly the same, the comparator needs to be made from a chunk of the same barrel with the same reamer and the barrel needs to have very consistent bore and groove diameter throughout. Also, the work by the smith needs to be very concentric. Sometimes bad setups with floating reamer holders egg things out.

The reality is, with proper technique, the normal tools most of us have are just fine. When using the wheeler method or the Gordon method to finds the lands, I get really good repeatable results. For different bullet styles to measure the same to the ogive, the comparator would need to exactly match your bore diameter and the angle of the inside chamfer would have to match the angle of the freebore on the reamer used to chamber your barrel. Otherwise, there will be variation caused by the difference archs in the ogives of different bullet shapes and where the chamber vs the comparator touch that shape. This means that a 115 DTAC and the 108 Berger do not always have the same length to touch with the comparator, but it is usually very close.

I'm reality, none of this makes a damn bit of difference. Watch Erik Cortina's video on chasing the lands. I started out doing it this way based on some forum back and forth with Dan Newberry when I started reloading. I had really good results with minimal effort. When I started shooting long range, I started looking for more info and got dragged into chasing the lands. I did it for 2 barrels and it was a fucking nightmare to keep the gun in tune chasing the lands. Went back to a little larger jump and didn't chase the lands and the 4 barrels since have stayed in tune for the life of the barrel.

While it is nice to have comparators to measure the consistency of your loaded rounds, you can start loading at any length. Seat a bullet long in a dummy cartridge and finish seating it by chambering. Measure that and shorten by .020 to .080 and start testing. Let the target dictate the final decision.

 

[straightshooter1]

Because different chambers have different lengths of freebores, knowing where the lands is is important so that one knows where to start. Loading to .001 from the lands, or anything closer than .010) is going to produce pressures that's very different than if one is .020 from the lands and can be a dangerous situation depending on the powder charge being used. I simply like to know where the lands is in order to decide where I want to start from (I like to start .010 off the lands and no closer). After a seating depth test and finding a load that's working well, I ignore whatever the jump there is and don't chase the lands. If any adjustment needs to be done down the road, what I see on paper will tell me if and when I might need to make any adjustments with the load.

Because I start at .010 or more from the lands, the accuracy of the measurement to touching the lands isn't very important to me for deciding on that starting point. If I were loading cartridges to touch or jamming the bullet, then accuracy for the measurement would certainly matter.

With my OCD approach to reloading, LOL, I do keep track of throat erosion by measuring after every cleaning just to collet as much data about what's going on with my loads.

 

[straightshooter1]

This was exactly what I thought. Now I'm confused.

The difference you found could be do to your technique for measuring or something going on in the throat area, like carbon ring or maybe some else??? This is where a simple borescope, like a Teslong, can help by actually seeing what's in there. Otherwise, you're just guessing. Maybe some aggressive cleaning in that area would help, where you'd get a uniform measurements???

 

[918v]

Yes, COAL's are different as well as the shapes and sizes of the ogives. But, when measuring the CBTO for the distance to the lands, it doesn't matter what bullet you use; the measurement will be the same (if one is using the same comparator insert).

no it won’t

 

[918v]

This was exactly what I thought. Now I'm confused.

Comparators are meant to be used to compare the results of die adjustment using one set of components. You can’t just find the lands using one projectile and turn around and use that number for another completely different projectile.

 

[918v]

I use the slit case method of finding the lands. I have found that when I find the lands using different projectiles the comparator readings are different.

 

[Rh0dz]

The difference you found could be do to your technique for measuring or something going on in the throat area, like carbon ring or maybe some else??? This is where a simple borescope, like a Teslong, can help by actually seeing what's in there. Otherwise, you're just guessing. Maybe some aggressive cleaning in that area would help, where you'd get a uniform measurements???

This actually makes a lot of sense. I have a little over 200 rounds down the barrel without it ever being cleaned. Thank you.

 

[Rh0dz]

Because different chambers have different lengths of freebores, knowing where the lands is is important so that one knows where to start. Loading to .001 from the lands, or anything closer than .010) is going to produce pressures that's very different than if one is .020 from the lands and can be a dangerous situation depending on the powder charge being used. I simply like to know where the lands is in order to decide where I want to start from (I like to start .010 off the lands and no closer). After a seating depth test and finding a load that's working well, I ignore whatever the jump there is and don't chase the lands. If any adjustment needs to be done down the road, what I see on paper will tell me if and when I might need to make any adjustments with the load.

Because I start at .010 or more from the lands, the accuracy of the measurement to touching the lands isn't very important to me for deciding on that starting point. If I were loading cartridges to touch or jamming the bullet, then accuracy for the measurement would certainly matter.

With my OCD approach to reloading, LOL, I do keep track of throat erosion by measuring after every cleaning just to collet as much data about what's going on with my loads.

Agreed. My main concern with the conflicting measurements was to not be in the lands and have potentially dangerous pressures. I may just try to find a local smith in Orlando to verify for me since this is my first reloading attempt. Would put my mind at ease and give confidence in my next step. Thank you.

 

[Rh0dz]

I use the slit case method of finding the lands. I have found that when I find the lands using different projectiles the comparator readings are different.

I will give this a shot too.

 

[straightshooter1]

no it won’t

You're right, I'm wrong.

I do find secant ogives to be substantially different measurement that what I get with tangent ogives. Here's some examples:

168 SMK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Berger 185 Juggernaut

155 SMK. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Berger 175 VLD Hunting

Berger 185 VLD Target

. . .another Berger VLD bullet added to this post at football half time .

 

[r.tenorio671]

...this may help the OP...

As shown, various bullet types and brands but have different Cartridge Overall Length (COAL). A closer look and you can see the ogive of each is at approximately the same point (blue line), which is the Cartridge Base To Ogive (CBTO). Although the bullet style and length differ, they are loaded to the same CBTO measurement. If you use a magazine fed platform, the internal dimensions of the magazine will restrict your COAL to what will fit and feed from the magazine. The CBTO measurement will ensure that your loaded cartridges will have the same amount of jump.