ridgeway
Silver $$ Contributor
I agree 100%. The terminology used here is debatable.
True Freebore ?
- Thread starter jamesdmock
- Start date
Maybe a picture is worth 1000 words. In this drawing, the FB is .115. The chamber length is 1.925. If .025 is added to the chamber, will that not increase the EFFECTIVE FB to .140? Just saying.
Last edited:
Alex Wheeler
Site $$ Sponsor
Increasing the chamber length will seat the bullet out farther, but the actual freebore doesnt change. I think its best to understand the actual spec's and their effect rather than muddling them together.
No, it won't.
After losing sleep over this (just a bit) last night I'm coming 'round to Chuck's and Bart's way of thinking about this.
Freebore is just that - the chamber's profile ahead of whatever the chamber's case neck ID is, to a point where the reamer's design indicates the lands are to begin.
Sometimes this dimension is minimal so the start of the lands can be achieved at a later time. Otherwise it's determined by what style and weight of bullets are to be used with this chamber.
The ID of this Freebore chamber section is usually just larger than that of the diameter of the bullets to be fired. 0.00025" clearance (or 0.0005" over bullet OD) isn't an unusual number. (This is where Alex's comment about bullet alignment in the chamber gets applied.)
In the drawing you've included it's a far more generous .0075" (something I'd expect to see for chamber neck clearance rather than freebore clearance) while the neck clearance here is .005".
Shortening the case neck's length - without having a new reamer shaped to effect a shortened neck portion in the new chamber to be cut with it, will otherwise have no effect on the length of freebore cut by the original reamer. It would simply reduce the amount of neck into which a bullet would be seated.
Unless I'm missing something really, really simple in all this...
(And I admit my suggestions in earlier posts were in contrast to what I've added here. It's happened before, probably will again, but I try hard not to have it happen too often.)
ridgeway
Silver $$ Contributor
James...where are you getting .025"? I think the area you are speaking about is a chamfer, not part of freebore.
chuck chuck chuck,
let new ASK YOU A SIMPLE question:
do you shoot a print, a reamer or a chambered rifle with brass and a bullet ?
"free bore" on a print is a number, period
"real chamber freebore" is a combination of:
the "design/print" free bore
actual case length
the amount of length growth for the case neck in the reamer.
SO YES there can be a large difference in "print" free bore, and ACTUAL mechanical free bore in the real chamber.
typical neck growth in a reamer is .020...that affects real free bore.
where you trim your brass also affects the real free bore.
as I mentioned earlier, I spec my reamers to only 0.007, and I trim back from that maybe 5-6.
where the bullet engages the THROAT does not change.
let new ASK YOU A SIMPLE question:
do you shoot a print, a reamer or a chambered rifle with brass and a bullet ?
"free bore" on a print is a number, period
"real chamber freebore" is a combination of:
the "design/print" free bore
actual case length
the amount of length growth for the case neck in the reamer.
SO YES there can be a large difference in "print" free bore, and ACTUAL mechanical free bore in the real chamber.
typical neck growth in a reamer is .020...that affects real free bore.
where you trim your brass also affects the real free bore.
as I mentioned earlier, I spec my reamers to only 0.007, and I trim back from that maybe 5-6.
where the bullet engages the THROAT does not change.
ridgeway
Silver $$ Contributor
Yes, it sure is a number and reading what you wrote I don't think you really follow the relationship between the chamber length and freebore and how it affects the freebore. Trimming brass does not in no way shape or form change freebore. Two reamers with identical freebore and different chamber lengths will affect the loaded case OAL where it touches, but freebore is identical.
Now back up to answer the first question, I adjust my freebore to a seated dummy round with the bullet I plan to shoot. I throat in a separate operation and make it what I want. I care less about the number.
Like I said before...freebore is misunderstood by many. This thread was way much more complicated than what it is, lol.
IF IS A HYPOTHETICAL …..
tom
Gold $$ Contributor
No. But if you get a new reamer with a chamber length of 1.590, your bullet/neck relationship will effectively be out another .020". But none the less the reamer will still have a freebore of .025".
Tom
you appear to be one of the many.
Exactly. And that increased amount to the lands is what I am calling "effective" freebore since the bullet has that much more to go before being in the lands. I think everyone here understands what I am saying but let the semantics of the word FREEBORE give them an excuse to argue. If the bullet must be seated out farther before engaging the lands then the effect is an additional freebore. The pissing contest on my part is over.
ridgeway
Silver $$ Contributor
James, nobody is looking for an excuse to argue with you. It's being explained plain as day, no semantics involved. You are simply twisting it around with your own terminology to make it complicated with adding freebore. By all means not looking to make this into a whizzing match.
25 cal bullets are .257 in diameter. The freebore diameter shown in the 25 Creedmoor drawing above is in fact only .0005 over bullet diameter.
Lucky Shooter
Gold $$ Contributor
No need to make this into something difficult.
Take a look at a SAAMI chamber drawing-----and you'll see exactly what the term, "freebore". means in reamer/chamber dimensions.
From these drawings its easily seen that longer free bores require the bullet seated out further to engage the lands.
Mr. Mock's definition of "effective freeborn" is not on any of the reamer/chamber drawings but is defined by him
and he's free to use it as he pleases-----although he's not the first person to think along these lines.
He understands that he's working with the "specified freebore" plus an additional amount. Call it what you wish---it still "effects"
how the bullet must be seated to engage the lands.
Hope I got this stuff right.
A. Weldy
Take a look at a SAAMI chamber drawing-----and you'll see exactly what the term, "freebore". means in reamer/chamber dimensions.
From these drawings its easily seen that longer free bores require the bullet seated out further to engage the lands.
Mr. Mock's definition of "effective freeborn" is not on any of the reamer/chamber drawings but is defined by him
and he's free to use it as he pleases-----although he's not the first person to think along these lines.
He understands that he's working with the "specified freebore" plus an additional amount. Call it what you wish---it still "effects"
how the bullet must be seated to engage the lands.
Hope I got this stuff right.
A. Weldy
OK thanks for that.
Never shot a .257. .0005" is more appropriate then.
(Why the heck don't they call 'em 260's? .257's closer to 260 than .264, ain't it?
Some things I just won't live long enough to truly get my head wrapped around....)
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