Freebore

[tenring]

Bought a used BR barrel. Freebore is unknown. I am not a gunsmith. Is there a practical way to measure freebore? If freebore is zero, and I want to put more bullet shank in the neck, can I go minus zero?

 

[NorCalMikie]

IMHO, zero freebore is a good thing. Start off with the lightest bullets you can get your hands on. Stuff them .010 into the lands and build your loads from there. What you really need to know is where to seat your bullets. A "modified case" will let you see where the bullet is in relation to the lands. Sinclair makes plugs that tell you how long the case can be before it needs to be trimmed.
Get both and you'll know just about everything about your chamber.

All my barrels (except my gas guns) have zero freebore and all loads are built with bullets seated .010 into the lands.
Freebore too short for your liking? PT&G makes a reamer to lengthen the freebore.
If it was me, I'd be working with what I had. Work it till you can't work it anymore before you make any changes.
Loads built with the bullets .010 from the lands will start showing pressure signs at one point.
That same load with the bullets stuffed .010 "into" the lands won't show pressure at that same point and you can go higher in charge before you start seeing pressure signs. YMMV.

 

[Texas10]

Took my recently purchased 6mmBR barrel to a GS with a dummy round and 105 gr bullet seated just above the neck/shoulder junction and had him ream it to fit. Now it loves the 105 A-Max.

 

[dkhunt14]

Bought a used BR barrel. Freebore is unknown. I am not a gunsmith. Is there a practical way to measure freebore? If freebore is zero, and I want to put more bullet shank in the neck, can I go minus zero?

I believe zero freebore means no freebore and you can't go shorter. Very few rifles are zero freebore, especially fast twist barrels. The faster twist means bigger, longer bullets and you need freebore to make them shoot great. If it has freebore and you want to shorten it, you can rechamber with a shorter freebore reamer. MATT

 

[Alex Wheeler]

With some very short bullets (mostly .224) you may want to change lead angles. A 2 degree lead with zero freebore will put more shank in the neck than a 1.5 degree with zero freebore. So far as measuring what is your barrel, no easy way. One way to estimate it is make a dummy round at touch, then polish the bullet and set a caliper .002" under bullet diameter. Spin the bullet in between the jaws to scribe a line at the start of the ogive. Measure from the neck to the line, subtract .020-.030" for trim length and the chamfer in the chamber. This will give you a rough idea. By no means exact.

 

[Shynloco]

I believe zero freebore means no freebore and you can't go shorter. Very few rifles are zero freebore, especially fast twist barrels. The faster twist means bigger, longer bullets and you need freebore to make them shoot great. If it has freebore and you want to shorten it, you can rechamber with a shorter freebore reamer. MATT

+1. I've not seen a "zero freebore" barrel before and personally wouldn't want one because of the restriction it creates in the bullets you can use. But like Matt says, rechamber that baby using a reamer of your choice with a known freebore as you probably already have a bullet/load in mind for that particular rifle. And to avoid guessing, call Dave Kiff @ Pacific Tool and Gauge and tell him what you have in mind so he can recommend the right reamer and you can request the freebore. I've done that on a variety of rifles and have had fabulous results downrange.

Alex

 

[Webster]

Bought a used BR barrel. Freebore is unknown. I am not a gunsmith. Is there a practical way to measure freebore? If freebore is zero, and I want to put more bullet shank in the neck, can I go minus zero?

You don’t really need to determine the freebore. With the bullet or bullets you intend to shoot determine the overall cartridge length to touch the rifling. Then you have a reference point to try COAL longer or shorter with various powders. Once you determine touch load ammo up 5, 10, 15 thou shorter with various popular powders. Think of it as how long to make the overall length to touch the rifling. I like 8208 and Varget powder. You should find something that works. I don't jam since I don't want to stick a bullet in the bore if I eject a loaded round. I have a 6BR 14 twist and shoot light bullets for bench rest and gh hunting. I think they said the freebore was 0.065"? It was verbal 9 years ago. 58 -70 grain bullets are seated only half way down the neck in my rifle. When the barrel was new I loaded everything .005" jump. 3500 rounds later I still use the original COAL. It still shoots small groups even though erosion would indicate I am now at 0.015" jump. This Summer I'll try longer by .010" and 0.15".

If the rifle was setup for long distance with 105 gr. bullets you have freebore around 0.100" and a 8 or 9 twist. For 60-70- gr bullets the freebore is usually somewhere around 0.020- 0.-030" and 14 twist. I would need a 12 twist to shoot 75-85 gr bullets. The twist will tell you if the barrel was intended for light or heavy bullets. 8-9 twist for heavy bullets. You need to determine the twist, it will tell you if the barrel was intended to shoot heavy bullets. It should then have the longer freebore. All 6BRs are accurate. Have fun.

 

[Zero333]

It's hard to find the exact figure with out the reamer print, but a chamber cast helps.

You just need to find your lands with any bullet and you'll know more or less what you have.

 

[jrod1101]

Would the freebore on the below diagram be .233 or .253? Would this be ideal for berger 200-20x bullets in 30 cal.? Could 185's be used?

Jimmy

 

[Webster]

It's hard to find the exact figure with out the reamer print, but a chamber cast helps.

You just need to find your lands with any bullet and you'll know more or less what you have.

Even if you know the free bore you still have to determine the COAL to touch or jam. So why not just determine the to touch rifling distance with your bullets and forget about freebore? The most important thing is to determine the twist as a starting point.

 

[Zero333]

Even if you know the free bore you still have to determine the COAL to touch or jam. So why not just determine the to touch rifling distance with your bullets and forget about freebore? The most important thing is to determine the twist as a starting point.

I agree and that's along the lines of what I meant to say.

 

[dewey7271]

That same load with the bullets stuffed .010 "into" the lands won't show pressure at that same point and you can go higher in charge before you start seeing pressure signs.

Ok. I'm not trying to be argumentative here, but that just defies physics.
After looking at quite a few pressure curves, pressure trace etc, jammed bullets have a higher initial pressure than non-jammed in the ones I've seen. Maybe there's something I'm missing here? Or perhaps a trick I've missed?

 

[OKyote73]

I'm with dewey on this!

Ok. I'm not trying to be argumentative here, but that just defies physics.
After looking at quite a few pressure curves, pressure trace etc, jammed bullets have a higher initial pressure than non-jammed in the ones I've seen. Maybe there's something I'm missing here? Or perhaps a trick I've missed?