Freebore… how do you measure it?

[fatelvis]

I see everybody referring to their freebore in exact thousands of an inch. How does one determine the exact free bore of their rifle? Is that measurement from the mouth of the case to where the bullet engages the rifling? I know it is a rudimentary question, but I would just like to make sure. Thanks!

 

[garandman]

Hornady OAL gauge, modified case and your projectile of choice.

 

[garandman]

 

[fatelvis]

So you just jam the bullet into the lands and measure between the case neck and ????

 

[garandman]

Watch the vid.

 

[Bill Norris]

I see everybody referring to their freebore in exact thousands of an inch. How does one determine the exact free bore of their rifle? Is that measurement from the mouth of the case to where the bullet engages the rifling? I know it is a rudimentary question, but I would just like to make sure. Thanks!

If you have access to your reamer print it will be listed there as well.

 

[garandman]

So you just jam the bullet into the lands and measure between the case neck and ????

You measure from the case base to the ogive with a comparator.

 

[243winxb]

2 measurements- chamber http://bulletin.accurateshooter.com...-chamber-length-with-home-made-modified-case/

Then measure case head to ogive. http://bulletin.accurateshooter.com/tag/base-to-ogive/

Subtract chamber from ogive measurement. This would give length of throat/leade.

 

[Ranger188]

As Bill said. If this is a custom chamber done by a gunsmith, he will be able
to tell you what it is.

 

[Old Navy]

I see everybody referring to their freebore in exact thousands of an inch. How does one determine the exact free bore of their rifle? Is that measurement from the mouth of the case to where the bullet engages the rifling? I know it is a rudimentary question, but I would just like to make sure. Thanks!

I don't see the answer to your question yet.

 

[jnyfeler]

I don't see the answer yet either.
Jeff

 

[284winner]

I see everybody referring to their freebore in exact thousands of an inch. How does one determine the exact free bore of their rifle? Is that measurement from the mouth of the case to where the bullet engages the rifling? I know it is a rudimentary question, but I would just like to make sure. Thanks!

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.

 

[TrxR]

Maybe a chamber cast? Im not sure if that goes far enough in to the barrel for that thoug.

 

[garandman]

I don't see the answer yet either.
Jeff

And @Old Navy ....


Watch. The. Video. I. Posted.

You know how they say one picture is worth a 1000 words? Well a bloody video is worth 10 million words. Watch the video.

 

[kvd]

I think 243winxb answered the question posed by the OP. The video is good but it only helps with the OAL portion of finding the free bore. One needs to have a way the subtract the chamber length and for that cutting a section of case neck to fabricate a collar is required - or something similar. There is no direct way to measure free bore unless the reamer is available or one can read this dimension off the reamer drawing.

Just my 2¢ worth

 

[243winxb]

A chamber casting with Cerrosafe may show where chamber ends & rifling starts. Giving throat length?

 

[243winxb]

Help me find my throat on my 243 Winchester, where is it??

 

[jackieschmidt]

And @Old Navy ....


Watch. The. Video. I. Posted.

You know how they say one picture is worth a 1000 words? Well a bloody video is worth 10 million words. Watch the video.

Maybe in the next week everybody will actually watch the video.

that being said, the theoretical freebore of a given chamber is listed on the reamer print of the reamer that cut the chamber. But even that is not an exact figure. I have three “zero freebore” 30 BR Reamers that vary as much as .015 between what’s written on the print and what they actually are.

So, watch the video.

 

[284winner]

Help me find my throat on my 243 Winchester, where is it??
View attachment 1282084

Your throat is from the case neck to the rifling. The throat is part of the freebore by my definition. Your freebore is from the ogive to the rifling. The throat lengthens as round count increases therefore lengthening your freebore. Hence the term, chasing the lands.

 

[RGRobinett]

As stated, the free-bore length should be displayed on the reamer print - to understand variation, check the tolerances on the print. As Jackie pointed out, dimensions vary. Tolerances and potential "stacking" is the reason we cannot share "seating-depths" - not only can free-bore length vary, so can leade angle, which generally is +/- 1/4 of a degree . . .

The video shows one method of determining the contact point for a loaded-round using a specific bullet - related, but neither defines nor provides a measurement of free-bore.

Technically, free-bore is the un-rifled section of the barrel between the chamber mouth, and the origin of the lands, as defined by where the leade angle is tangent to the free-bore diameter. This section should be somewhat larger in diameter than the groove diameter - 0.0005" to 0.001" [larger] is a good range. Keep 'em ON the X! RG