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Freebore… how do you measure it?

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BROWNELLS CERROSAFE® CHAMBER CASTING ALLOY | Brownells

There are various products on the market which can be used to make a cast of a gun chamber. To be certain that the product we are offering you is the best and most practical, we contacted the basic manufacturer. They recommended Cerrosafe because ...
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Freebore is that part of the chamber beyond the neck that has no rifling. It does not include the lead.

Randy, you beat me to it.
 
I guess I'm assuming there is NO reamer print to get numbers from so the next best way to get your measurement. The reamer print is a no brainer. With it, I wouldn't think the OP would post how to get the measurement.
 
If you have
Medic505 said:
OK, so I watched the video. The video addresses the measurement of cartage base to the lands, or basically a reference point. It in no way gives you an actual measurement of the "freebore" as listed on the reamer print.
Click to expand...
Correct, the thread went off on a tangent with base to ogive measurements, not what the OP asked.

If one has acces to a lathe, make up a plug the same diameter as the bullet. Make sure is flat on the end that will touch the rifling. Size the neck on a case so it's snug but not real tight. Load the plug in the neck long and chamber the round. The plug should stop at the beginning of the lead/the end of the freebore. Measure from the end of the plug to the end of the neck.

No lathe? Take a flat base bullet, make sure the base is perfectly flat. If not, emery, sandpaper or file it flat.
Load the bullet, bottom up, long, chamber the round, measure.

This will NOT give an exact measurement to the .001 but should be within .005.
 
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284winner said:
Freebore is the distance between the ogive of the bullet and the rifling. Measuring it can be done by the OAL gauge. I'm not sure a better way to measure it but there's better ways to find the OAL of the cartridge while it's chambered.
Click to expand...
No, it isn't, not even close. On a reamer drawing there is a dimension indicated from the forward edge of the 45 degree chamfer at the end of the neck to the point where the throat angle begins. Typically, on a custom reamer the freebore is less than a thousandth over nominal bullet shank diameter, but this can vary. For instance the first design of the Wheeler 6BRA calls for a FB diameter of .244.
 
fatelvis said:
I know it is a rudimentary question, but I would just like to make sure.
Click to expand...
Maybe you already know, but you didn't ask why is it important? The reason you want the correct FB for the bullets you intend to shoot is so
1. the bullet doesn't have to seat too deeply in the case (FB is too short for your need) or
2. the bullet can't be seated out far enough to provide the "jump" you want (FB is too long for shorter bullets)
 
hogpatrol said:
Can you post the bottom of the print? There are dimensions missing.
Click to expand...
Can be found here. SAAMI Link

FREE BORE​

A portion of the chamber, usually cylindrical, forward of the casemouth of a diameter larger than the projectile in which rifling is not present. See Bullet Jump. See Throat.​



THROAT​

The tapered portion of the bore of a barrel, immediately ahead of the chamber which is sized to provide clearance for the bullet of the loaded cartridge. Also referred to as Leade or Ball Seat and is associated with Free Bore. See Free Bore.

Screenshot_20210926-135339_Drive.jpg
 
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BoydAllen said:
No, it isn't, not even close. On a reamer drawing there is a dimension indicated from the forward edge of the 45 degree chamfer at the end of the neck to the point where the throat angle begins. Typically, on a custom reamer the freebore is less than a thousandth over nominal bullet shank diameter, but this can vary. For instance the first design of the Wheeler 6BRA calls for a FB diameter of .244.
Click to expand...
Interesting
 
hogpatrol said:
www.brownells.com

BROWNELLS CERROSAFE® CHAMBER CASTING ALLOY | Brownells

There are various products on the market which can be used to make a cast of a gun chamber. To be certain that the product we are offering you is the best and most practical, we contacted the basic manufacturer. They recommended Cerrosafe because ...
www.brownells.com www.brownells.com

Freebore is that part of the chamber beyond the neck that has no rifling. It does not include the lead.

Randy, you beat me to it.
Click to expand...
AT least two people got it right....
 
243winxb said:
Can be found here. SAAMI Link

FREE BORE​

A portion of the chamber, usually cylindrical, forward of the casemouth of a diameter larger than the projectile in which rifling is not present. See Bullet Jump. See Throat.​



THROAT​

The tapered portion of the bore of a barrel, immediately ahead of the chamber which is sized to provide clearance for the bullet of the loaded cartridge. Also referred to as Leade or Ball Seat and is associated with Free Bore. See Free Bore.
Click to expand...
Freebore, .1774
 
pirate ammo said:
All you people are doing is confusing me, I am surely a lost soul for sure.
So, in a smooth bore it would be from the case mouth all the way to the end of the barrel. Hopelessly lost.
Click to expand...

Agreed. All I really care about is the measurement that the video I linked above shows because that allows me to get significantly under half moa and that's good enough for me. ... 0.2 - 0.4" @ 100yd.

The discussion above is just a bunch of people telling everybody else they got it wrong. Lol.

I'm sure I got it wrong too but I don't care. What I'm measuring works for me and gets me the accuracy I need.
 
garandman said:
Agreed. All I really care about is the measurement that the video I linked above shows because that allows me to get significantly under half moa and that's good enough for me. ... 0.2 - 0.4" @ 100yd.

The discussion above is just a bunch of people telling everybody else they got it wrong. Lol.

I'm sure I got it wrong too but I don't care. What I'm measuring works for me and gets me the accuracy I need.
Click to expand...
Agreed 100%
 
cartridge base to ogive does NOT tell you anything about freebore.

You are making 2 assumptions with this, the ogive on the bullet and your comparator are the same, usually they are not; and assuming the length from base to case mouth is the same in the chamber as your brass, 99.9% the chamber is cut deeper.

So using the CBTO measurement and case length, you are probably overestimating freebore.

The only way to measure it is as mentioned above, using plugs. One plug for case mouth. This measures the true case length allowed by the chamber. Most trim their brass to SAAMI length, this is often quite short. This also allows carbon to build up at the case mouth, this is another topic.

The 2nd plug is the diameter of the bullet.
Why plugs? They give you a flat finite surface to accurately measure vs a bullet ogive.

Using a case and the plugs, you compare the measurements of both plugs seated in the chamber. The difference is the freebore + the throat angle distance. If you wanted to get exact freebore, youd need a plug the diameter -0.0005" of the reamer print freebore diameter.
 
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