What does "zero" freebore mean

S

S/S

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What does "zero" freebore mean.
Have heard the term zero freebore used when chambering a barrel. Not sure just what it means.
S S
 
In the typical target chamber and some factory chambers, starting from the part that is designed to accommodate the case neck (For example, in the case of a .262 neck 6PPC this is a cylindrical section that is nominally .262 ID.) forward of this, the ID of the chamber funnels down (typically at a 45 degree angle) to just over bullet diameter where a new cylinder begins. This is the so called the freebore. My 6PPC reamer cuts a chamber that has a .060" long freebore that is a few ten thousandths over .243". At the front of the freebore the rifling starts. This is where the lands ramp up from zero to to full height and the groove diameter begins. In this section, sometimes referred to the as the leade, the typical taper of the rifling, referred to as the throat or leade angle, (again, for a typical target chamber) is 1 1/2 degrees. Zero freebore means that the leade begins right at next to the chamfer at the front of the neck part of the chamber. in this chamber drawing, the throat or freebore length is .105.
http://www.the-long-family.com/images/223 Ackley new.jpg
 
Nicely done Boyd :)

Another way to put it (dare I presume??) is the distance between the end of the case and the beginning of he rifling. In a zero freebore the bullet barely sticks out of the neck before it hits the rifling, in a long freebore, the bullet hangs way out before it touches the rifling. A REALLY long freebore like an old Weatherby and the bullet actually falls out of the case before it ever touches the rifling.

(I'm trying to be less scientific than Boyd :) dunno if it's working)

al
 
Thanks guys,
So if someone has a zero freebore chamber there's a chance that in order to chamber a round you may have to seat a bullet deeper into the case depending on the taper of the bullet, and one with say with .105 freebore you would have to seat the bullet out farther if you wanted to touch the rifling.
That's about what I thought it meant but was not really sure.

What I have is a 30 BR chamber that is supposed to have zero freebore, I tried loading some Sierra 125 Spitzers thinking that I would need a short bullet because of the zero freebore but I cant get the bullet to touch the rifling no matter how long I seat it out of the case so thought that maybe zero freebore meant something else. I think a bullet would touch if I used 150's or heaver but not sure if the 1-17 twist would work with them, any ideas on how to handle a problem like this would be appreciated.
S S
 
S/s ...

S/S said:
What does "zero" freebore mean.
Have heard the term zero freebore used when chambering a barrel. Not sure just what it means. S S
Click to expand...

It means that in this picture [I like pictures] the area that's marked Freebore would be nonexistent. ;)
 

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Freebore

SS: I've gotta ask: do you know the history of the rifle, since the barrel was installed? If you bought it used, it could have originally been chambered with zero freebore, and the barrel ident marked accordingly, then somewhere along the way, the throat was lengthened/deepened to chamber longer/heavier bullets. I can't imagine that much erosion from firing causing that much freebore. A borescope inspection would tell you a lot. If the bullet "jump" is more than you can accept, then the only answer would be to set-back the barrel and re-chamber, assuming there is enough shank dia. left at the receiver end.
 
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S/s ...

S/S said:
What I have is a 30 BR chamber that is supposed to have zero freebore, I tried loading some Sierra 125 Spitzers thinking that I would need a short bullet because of the zero freebore but I cant get the bullet to touch the rifling no matter how long I seat it out of the case so thought that maybe zero freebore meant something else. I think a bullet would touch if I used 150's or heaver but not sure if the 1-17 twist would work with them, any ideas on how to handle a problem like this would be appreciated. S S
Click to expand...

Do you have enough neck tension on the bullet to feel confident enough to say that the bullet is not being pushed back into the case every time you close the bolt? Any marks, even the slightest, on the bullet, from the lands?
 
Thanks abintx,
I also like pictures, and that one is exactly what I thought freebore was.

f d shuster,
I should have been more clear. This is the first time I ever had a barrel put on a gun so am green on what to say or questions to ask,

This is a new 30 Cal. 1-17 Krieger barrel that a gunsmith just cut with a new PTG 30 BR reamer. I was told it was a zero freebore chamber reamer, it was installed on the action with a no-go and go gauge to check headspace but I haven't shot it yet, made up some 30 BR brass by expanding some new 7 BR Rem brass to 30 cal, brass fits the chamber real nice, just tried to load up some dummies to see just how deep I would have to seat the bullet, turned out that the Sierra 125 Spitzers loaded all the way out of the case wont touch the rifling ?. Something is not right but not sure if it's me, the bullet, the reamer, or the gunsmith.
S T
 
Have you measured the base to ogive or OAL of your rounds before and after you chamber the round? Just bullet and case, no primer or powder, obviously.

If they are a shorter after you chamber them, they are getting to the lands.

Greg J.
 
You need to talk to your gunsmith.... you are right, something's funkywakk if you can't touch the rifling with a 125.

So you seat a 125 way out, almost falling out of the neck, and insert it....... pull it out and it's still just sticking out there??? Not pushed back at all?

and abintx brings up a point. if your neck tension is really low, like finger-tight fit, the bullet can stick in the rifling "leade" and be pulled back forward only to be stopped by the pressure ring and stay in the neck....... this can give the illusion of the bullet not moving.

al
 
Freebore, part 2

S/S; Seems like we have a mystery going here, with some very good sleuthing. If you can get your hands on the PTG chambering reamer, (from the gunsmith?), the freebore should be marked on the back end along with cartridge ident and neck diameter. Black lettering, easy to read. All my PTG reamers are ident marked. I once had a 'smith give me more (a lot more) freebore than I requested, took my Stoney Point OAL gauge, modified case and the bullet and took a throat measurement in his presence, showing him that he gave me a deep throat. End of discussion: he had to go to work and set-back & re-chamber the barrel. My instructions for chamberings are always given to the 'smith in writing, so there is never any mis-understanding, only mistakes/screwups.
 
A couple of the earlier posts have a link to an illustration that shows the freebore extending to the far end of the throat, or leade angle, where the lands are full height. IMO this is incorrect.
 
"So you seat a 125 way out, almost falling out of the neck, and insert it....... pull it out and it's still just sticking out there??? Not pushed back at all ?"

Correct, not pushed back at all and no marks on the bullet.
S S
 
Or, the reamer could (heaven forbid) feature the old JGS (SAAMI?) Spec. for the 6MM Rem. BR - a whopping 1.570" OAL, which in combination with the SHORT Remington 7BR brass (which, when necked-up to thirty, shortens even more), could make for the equivalent of 0.050" + [counterfiet] 'freebore', which is actually, excessive and EMPTY chamber-neck - a worse senario than simply excessive freebore! :eek::( You'll need to determine the neck-length and thus, OAL of your chamber . . . 'something isn't according to hoyle'!!:confused: RG
 
I just checked some of the 7 BR Rem brass before I expanded it, it measured 1.505, to 1.507 after expanding it with the Redding tapered expander it comes to 1.503, to 1.505. I didn't think it shortened up that bad but really don't know. I was told that 7 BR brass would be just right for makeing into 30 BR ?. I know that brass should be trimmed so that it's all the same length.

Would it be ok to trim all of it to 1.500 ?
Are there two different 30 BR's, a PTG and a JGS ?.

I have a call in to the gunsmith as I want to know just how the reamer is marked.
Thanks Guys
S S
 
S/s ...

S/S said:
Are there two different 30 BR's, a PTG and a JGS?
Click to expand...

If you call Dave Kiff at PTG and ask for a print of a 30BR he can send you a handful of different ones. Mr. Robinett was kind enough to send me his original and Dave sent me four [4] others. Since I asked for a slight change on one when he was making up my reamer, I have one with my name on it, so there is another one added to the pile. I don't know how many JGS has. They won't send the Ronnie Long print because he apparently requested it not be distributed. There's SEVEN so far. :)
 
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it measured 1.505, to 1.507


Fix... Lapua 6BR brass.........


Still not sure the reamer used is really a ZERO F/B.....
If that 125gr is being held by good solid neck tension, you should still hit the lands with the shorter Rem brass.... Weird.

The zero f/b gives little room to the leade.

You may also find that the Rem brass wont handle the "accuracy" pressures like the Lapua stuff... Same ole, same ole.

cale
 
I understand that Lapua brass is better, but is it longer ?, and how much longer ?. At this time all I have to work with is the 7 BR brass. I was told by the gunsmith that if I used the Rem 7 BR brass all I would have to do was expand it and it would be good to go. Found 100 rounds of it, ordered the Redding expander and started expanding, no problems with it other than difference in length .505 -.507 then after expanding .503 - .505, Not really knowing just how long it should be is why I asked if I could trim it to .500.

Being I don't have a reamer print I don't know how long it should be ?.
How much longer is Lapua brass ?, and how much shorter will it get when I expand it ?, will it loose the same as Rem 7 BR ?. will it stretch after firing ?.

I know, I have a lot of questions and this may be like you say, " Same ole, same ole", I'm sure that's true for you but I've never done anything like this before.

I just got a phone call and I may have the PTG reamer print later today, will get back later and let everyone know just what it is.
S S
 
S&s

The Remington 7BR brass is junk compared to lapua.

Or, maybe I am overstating it. If you are just building a 30BR to shoot tin cans, then the Remington will work just fine. But, ifyour ultimate goal is to reach the accueracypotential that a 30BR poccesses, then Lapua is the only way to go.

You are correct, a Lapua 6BR is longer, (1.560), than a Remington 7BR. But, when the case is subjected to the rigors of the necking up proccess that most shooters use to arrive at a 30BR case, it gets shorter. That is why the trim to length of a typical 30BR reamer is around 1.500.

The reason shooters use a "zero" free bore is so they can take advantage of the short 112-118 grn 30 caliber bullets that have become so popular in Varmint for Score.

Like most others have said, something is obviously wrong. Are you sure your Gunsmith is in tune with the perameters that are involved in chamberings that are specifically designed for Extreme Accuracy use?? Many are not......jackie
 
alinwa said:
Nicely done Boyd :)

Another way to put it (dare I presume??) is the distance between the end of the case and the beginning of he rifling. In a zero freebore the bullet barely sticks out of the neck before it hits the rifling, in a long freebore, the bullet hangs way out before it touches the rifling. A REALLY long freebore like an old Weatherby and the bullet actually falls out of the case before it ever touches the rifling.

(I'm trying to be less scientific than Boyd :) dunno if it's working)

al
Click to expand...

AL
It worked just fine...
 
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