Freebore in a hunting rifle.

[Apache]

Here is a very good article on freebore that is from a TC site but the principles will be the same:

http://www.bellmtcs.com/FAQ/ChamberThroats101.htm

According to his acticle, if I read correctly, freebore length isn't nearly as important as freebore diameter He builds some of the most accurate TC barrels around. Check it out.

 

[velocity-is-key]

Freebore concept is simple, volume vs expanding gas has a direct relationship to pressure. Pressure = velocity. The pressure curve is lengthened NOT reduced and is also effected by bore diameter (volume).....
No freebore = less bullet STOP from 3 stops to 2..
Get it?
For those whom actually knows what happends during the ignition process they should understand..
1. primer ignites, bullet moves, hits lands.
2.powder ignites bullet moves again.
3. pressure builds exponentially bullet moves once again all in a billionth of a second...
Less bullet stops = less variables..
For the average shooter not in search of the "one ragged hole group" which is what the production rifle cannot expect to accomplish, it does the job fine and with safe higher pressure...

I once had a Accumark 30-378 and did extensive load development when only 378 brass was availiable and not the loaded round ...
It , with its 3/4" freebore chamber (mark V) was the strongest action I ever loaded for..
Typically with H50 BMG powder of 126 grains and a noslar 180gr Ballistic tip yielded 3675 FPS when the pressure signs became a question, powder started igniting out of the barrel with hugh muzzle blasts and barrel harmonics caused the rounds to deflect off of the muzzle brake...

I would of loved to see what a 32 inch would have revealed but either way I can be pretty confident that those velocities could never have been reached without "freebore"
Good luck to all....

 

[Trickymissfit]

The 300 Weatherby set up in a match chamber without all the freebore will deliver one ragged hole accuracy with any other 30 cal. In fact the 300 weatherby held most of the records and is the base cartridge for most of the successful 30 cal wildcats in 1k BR.

BH

used to have a buddy in PA that built 1000 yard benchrest guns for folks all over the place, plus a lot of tacticle rifles for that folks that had a need for them. He told me once that the best cartridge to start with was always a .300 Weatherby, or one of the sharp shouldered clones. He told me about a 16 year old kid that literally tore up the 1000 yard shooting circut on the east coast with a MK.V. in .300 WBY mag!

Virtually every rifle built has some free bore in it, but the amounts will vary (most bench guns don't have very much). Weatherby only uses a large free bore in their WBY. Mag cartridges, and everybody else does as well (hunting rifles). They do this to reduce chamber pressure spikes.
gary

 

[load]

correct me if i'm wrong but i beleave the .300 winchester is also built around a long freebore of about .25"

 

[backwoods83]

Ok I'll correct you, depending on the manufacturer a typical 300wm has .060-.100" freebore. And most of the post are bs, gary has it rigth the .361" freebore in weatherby mags is to prevent an enormous pressure spike when using factory weatherby ammo loaded upwards of 75k psi. When ole man weatherby started these (drag car) rifles surplus Imr 4350 was about the slowest powder available so they were loaded hot as hell and given extra freebore to prevent injury. Its fact that if you use the same bullet, case, primer, and powder charge, seat 1 .005" in the lands and another .005 off the lands the one in the lands will be faster. Since some one was on the subject of cars, look at it this way, 2 cars both identical except one is a powerglide (automatic) with a trans break and a 2 step, the other is a straight gear, when there staged up beside each other the auto car is sitting there at 5k rpm holding pressure against the drivetrain with the transbrake, the straight is sitting there free revving at 5k with all the slack in the drivetrain, when the light turns green who do you think will be faster and more consistent? I can get 3070 from a 300wby/210berger/imr4350 and my match chamber has .060" freebore, hell I bet I could add a 10grn higher charge of retumbo and break 3200 but I doubt the accuracy would be the same.

 

[Trickymissfit]

correct me if i'm wrong but i beleave the .300 winchester is also built around a long freebore of about .25"

I have not looked at a .300 Win. reamer print in several years, and you may well be right
gary

 

[Trickymissfit]

Ok I'll correct you, depending on the manufacturer a typical 300wm has .060-.100" freebore. And most of the post are bs, gary has it rigth the .361" freebore in weatherby mags is to prevent an enormous pressure spike when using factory weatherby ammo loaded upwards of 75k psi. When ole man weatherby started these (drag car) rifles surplus Imr 4350 was about the slowest powder available so they were loaded hot as hell and given extra freebore to prevent injury. Its fact that if you use the same bullet, case, primer, and powder charge, seat 1 .005" in the lands and another .005 off the lands the one in the lands will be faster. Since some one was on the subject of cars, look at it this way, 2 cars both identical except one is a powerglide (automatic) with a trans break and a 2 step, the other is a straight gear, when there staged up beside each other the auto car is sitting there at 5k rpm holding pressure against the drivetrain with the transbrake, the straight is sitting there free revving at 5k with all the slack in the drivetrain, when the light turns green who do you think will be faster and more consistent? I can get 3070 from a 300wby/210berger/imr4350 and my match chamber has .060" freebore, hell I bet I could add a 10grn higher charge of retumbo and break 3200 but I doubt the accuracy would be the same.

your post is dead right about "Old Roy's" cartridges and chamber designs. But I'll dissagree with you about the cars, and why. The real reason is that the art of clutchless power shifting has been gone for twenty years.
gary

 

[backwoods83]

Nah gary I was just trying to simplify things, actually I still run a 5 speed liberty in a 66 deuce with with a fogger and delay when I get a wild hair up my ***!

 

[velocity-is-key]

Ok I'll correct you, depending on the manufacturer a typical 300wm has .060-.100" freebore. And most of the post are bs, gary has it rigth the .361" freebore in weatherby mags is to prevent an enormous pressure spike when using factory weatherby ammo loaded upwards of 75k psi. When ole man weatherby started these (drag car) rifles surplus Imr 4350 was about the slowest powder available so they were loaded hot as hell and given extra freebore to prevent injury. Its fact that if you use the same bullet, case, primer, and powder charge, seat 1 .005" in the lands and another .005 off the lands the one in the lands will be faster. Since some one was on the subject of cars, look at it this way, 2 cars both identical except one is a powerglide (automatic) with a trans break and a 2 step, the other is a straight gear, when there staged up beside each other the auto car is sitting there at 5k rpm holding pressure against the drivetrain with the transbrake, the straight is sitting there free revving at 5k with all the slack in the drivetrain, when the light turns green who do you think will be faster and more consistent? I can get 3070 from a 300wby/210berger/imr4350 and my match chamber has .060" freebore, hell I bet I could add a 10grn higher charge of retumbo and break 3200 but I doubt the accuracy would be the same.

I still have my chamber cast from one of the first "Weatherby .30-378 Accumarks" ever delivered and in fact it has a freebore of .750"..Loaded ammo was not availiable and .378 brass had to be necked down and turned..After reaching the plateau of its velocity of 3675 fps with a 180 grain Nosler and 126grs. of H50BMG in addition to my several unfortunate experiences with that rifle pertaining to bullet contact to muzzle brake it was visually clear the bore was not concentric with the OD of the barrel..
Explaining this to Weatherby and after their ridiculous attempts to remedy it, ( 2 muzzle brakes replaced /sent as a FAILED remedy for bullet contact ) Weatherby sent me a new rifle..Since a factory $1,295 CNC rifle did this I took the new one in its unfired condition and traded it for 2 new Smith & wessons; a 29 and 57 with 8-3/8 barrels...
My point is this particular factory rifle ,proto type or what ever you may feel appropriate to call it did indeed have .750" freebore (NO bs) and you could not seat bullets to touch the lands. That is what I call freebore and not throat length (no disrespect to anyone here)..
I have sold all the 200 plus pieces of brass since then and the Wison custom made hand dies (which is what the chamber cast was made for) that I used to take to the range for loading, but I still have all the load data logged down in the books accrued during my research using the H50 BMG powder...I'm talking detailed research with all targets,chrony results, and even a few photos some of the guys at the range took of me catching the gigantic muzzle blasts that they got a kick out of...If anyone needs to know anything related here to my research feel free to ask...
Since I was a kid I wanted one (Weatherby) and when they started to manufacture them in the U.S. again I ordered one...
I lost all respect for the Weatherbys with my experience since the old man died and his son ran the bis, but before when they were Jap made I refused no matter what the quality was to buy a gun with "MADE IN JAPAN" on it when it was a American legacy Belgium made or not..I still loved that cartridge to death and disagreed with the old man saying it was not a practicle cartrdge to manufacture a gun in...I also don't need a corvette to get the groceries or to go to point A from B either when a Volkswagon Bug will do the same...
Just my 2 cents on my freebore facts gents...
velocity

 

[Dr. Vette]

I also don't need a corvette to get the groceries or to go to point A from B either when a Volkswagon Bug will do the same...

Me either, but I sold my VW Bug once I bought my first Corvette.

 

[J E Custom]

I just got off the phone with Weatherby. I was talking with a rifle technician about the 1.5 inch accuracy guarantee on the Accumark. While I was at it, I asked about seating depth and freebore. Apparantly all Weatherby rifles have a ton of freebore for various reasons. Just how much effect does freebore have on accuracy? Why on Earth would anyone put a bunch of freebore in a Krieger barrel? Am I creating demons where none exist?

All modern high pressure rifles have some freebore not just the Weatherbys.

In order to reach higher velocities manufactures have added more freebore to
reduce pressure with greater powder volumes, and velocity sells.

This is an old debate and you are likely to hear all sorts of things about freebore length
and diameter.

There are many things can make a rifle shoot badly and freebore is not one of them if the
chamber is correctly done.

If you shorten the freebore you will lose velocity and gain pressure. This is the reason that
you should not shoot factory Weatherby ammo in a little or no freebore chamber. (IT
will be very hot and possibly blow the primers).

If you shorten the freebore you give up the velocity that led you to that cartridge in the first
place.

It is common for a well chambered (Factory SAMMI reamer)Weatherby cartridge in a custom
barrel to shoot less that 1/2 moa and in most cases 1/4 MOA.

I would recommend that you stay with the standard reamer and not create more problems
for your self.

Just my opinion.

J E CUSTOM

 

[velocity-is-key]

All modern high pressure rifles have some freebore not just the Weatherbys.

In order to reach higher velocities manufactures have added more freebore to
reduce pressure with greater powder volumes, and velocity sells.

This is an old debate and you are likely to hear all sorts of things about freebore length
and diameter.

There are many things can make a rifle shoot badly and freebore is not one of them if the
chamber is correctly done.

If you shorten the freebore you will lose velocity and gain pressure. This is the reason that
you should not shoot factory Weatherby ammo in a little or no freebore chamber. (IT
will be very hot and possibly blow the primers).

If you shorten the freebore you give up the velocity that led you to that cartridge in the first
place.

It is common for a well chambered (Factory SAMMI reamer)Weatherby cartridge in a custom
barrel to shoot less that 1/2 moa and in most cases 1/4 MOA.

I would recommend that you stay with the standard reamer and not create more problems
for your self.

Just my opinion.

J E CUSTOM

AMEN..
Maybe you can/or someone from this forum can comment on a idea I have thought about when dealing with the shorter barrel and velocity loss..
I recently chopped off 10 inches of my straight 1.350", 29 inch , 1:8 twist kreiger chambered in 6/284 with a tight neck on a single shot 40X for the practicality of a package that I can tolerate in the field at night with a 5 pound thermal scope and with the 13" long silencer attached.
In all reality velocity loss was only 200 fps leaving me with a 105 VLD Berger at 3150 fps which is outstanding considering the weight reduction AND oal of that combination afterwards and further more, accuracy was enhanced also all with a 18-5/8" barrel..
I am building another in that chambering due to the love and experience I have for this cartrIdge and components on hand using a 591 Surgeon..It too will also be suppressed but I will be limited to a detachable mag system determining cartrdge oal and limiting my bullet length also.. Therefore I decided to design the package with lighter more explosive bullets and velocities in mind using a 1:12 twist with one of Bettins carbon graphite bull "24" inch tubes and a modified carbon graphite suppressor to lighten the whole rig wthout sacraficing accuracy. Obvoiusly Im going for speed at moderate distances (5-600 yds)..
I know that overall longer barrel length will benefit a heavy bullet /powder combo more than a light bullet/powder combo so I think 24" can be a great short barrel length for this setup..
Lately I have been researching the "freebore" concept and I too believe that in the field and not at the competition bench it may be of a benefit to enhanced velocity with a shorter barrel length being able to load up to a more potent charge with a lengthened not reduced pressure curve to keep pressure tolerable while not sacraficing velocity with the correct powder to benefit this 30-06 cased capacity round...
I obviously know what I can do to take advantage of this case capacity in building a rig and know I could just shoot a more milder cartrdge like the 6mmAI or alter barrel length..However I'm determined to deal with this combo and get the max and wonder if using Freebore in a setup as this could help me get back the velocity lost in going with the short fat barrellightbulb...
If anyone out here has had these same demons and experimented, researched or even read about this subject please feel free to vent....It can't be too bad if most of the major firearm builders use this practice whether for the "idiot" proof solution or pressure/velocity solution...

I did the unthinkable once when loading at the range for this rig and while at my near max load I very stupidly but accidently bumped the SC4831 powder and scale up "1 grain" instead of ".1 grain" ..The results were a pierced primer and a case head that could no longer be read as it was mashed smooth, anyway me and the 40x survived but that chrongraph revealed that this 18-5/8 inch barrel yielded a wopping 3450 FPS with the 105 VLD Berger and I was astonished that that powder charge still continued to benefit velocity having thought a portion of it may have burned outside that short barrel...Of course the pressure curve must have been staggering but what if I could smooth it out to a more moderate curve in that short barrel?
Food for thought...Thank you for all and any response...There is a galactical amount of experience on this sight and I am thankfull for any insight into this understated concept......


velocity

 

[DKA]

Have a Weatherby 300 Win Mag & Weatherby 7mm Rem Mag & both are very accurate.

 

[J E Custom]

AMEN..
Maybe you can/or someone from this forum can comment on a idea I have thought about when dealing with the shorter barrel and velocity loss..
I recently chopped off 10 inches of my straight 1.350", 29 inch , 1:8 twist kreiger chambered in 6/284 with a tight neck on a single shot 40X for the practicality of a package that I can tolerate in the field at night with a 5 pound thermal scope and with the 13" long silencer attached.
In all reality velocity loss was only 200 fps leaving me with a 105 VLD Berger at 3150 fps which is outstanding considering the weight reduction AND oal of that combination afterwards and further more, accuracy was enhanced also all with a 18-5/8" barrel..
I am building another in that chambering due to the love and experience I have for this cartrIdge and components on hand using a 591 Surgeon..It too will also be suppressed but I will be limited to a detachable mag system determining cartrdge oal and limiting my bullet length also.. Therefore I decided to design the package with lighter more explosive bullets and velocities in mind using a 1:12 twist with one of Bettins carbon graphite bull "24" inch tubes and a modified carbon graphite suppressor to lighten the whole rig wthout sacraficing accuracy. Obvoiusly Im going for speed at moderate distances (5-600 yds)..
I know that overall longer barrel length will benefit a heavy bullet /powder combo more than a light bullet/powder combo so I think 24" can be a great short barrel length for this setup..
Lately I have been researching the "freebore" concept and I too believe that in the field and not at the competition bench it may be of a benefit to enhanced velocity with a shorter barrel length being able to load up to a more potent charge with a lengthened not reduced pressure curve to keep pressure tolerable while not sacraficing velocity with the correct powder to benefit this 30-06 cased capacity round...
I obviously know what I can do to take advantage of this case capacity in building a rig and know I could just shoot a more milder cartrdge like the 6mmAI or alter barrel length..However I'm determined to deal with this combo and get the max and wonder if using Freebore in a setup as this could help me get back the velocity lost in going with the short fat barrellightbulb...
If anyone out here has had these same demons and experimented, researched or even read about this subject please feel free to vent....It can't be too bad if most of the major firearm builders use this practice whether for the "idiot" proof solution or pressure/velocity solution...

I did the unthinkable once when loading at the range for this rig and while at my near max load I very stupidly but accidently bumped the SC4831 powder and scale up "1 grain" instead of ".1 grain" ..The results were a pierced primer and a case head that could no longer be read as it was mashed smooth, anyway me and the 40x survived but that chrongraph revealed that this 18-5/8 inch barrel yielded a wopping 3450 FPS with the 105 VLD Berger and I was astonished that that powder charge still continued to benefit velocity having thought a portion of it may have burned outside that short barrel...Of course the pressure curve must have been staggering but what if I could smooth it out to a more moderate curve in that short barrel?
Food for thought...Thank you for all and any response...There is a galactical amount of experience on this sight and I am thankfull for any insight into this understated concept......


velocity

There are several things that I would recommend for you Application/Need.

I would set the chamber back just enough to clean it up with a new reamer with these dimensions.

3/16 to 1/4" freebore, the freebore should be bullet diameter(NO More),The big issue for accuracy
is head space in a chamber with Lot's of freebore (On belted cases I head space .0005 to .001 max,
And on shouldered cases .000 to .0005 max) On the shouldered cases the bolts camming action will
compress enough to close the bolt with no movement of the case during firing.

I do not recommend this to an inexperienced re loader or if factory ammo is to be used, because of
inconsistencies.

The other option is to fire form and neck size only 90% of the neck.

To also reduce the pressure have the reamer cut to allow the neck to expand .002 to .003
thousandths more than loaded rounds. Or turn the necks down for the same clearance.

The tight head space and 10% of the neck that was not re sized will align the cartridge perfectly
for greater accuracy and the freebore will allow for larger powder charges with no more pressure.

I have my 30/378 Weatherby setup this way and using 126 grs of 50 BMG and a 200 grain partition
velocity is off the charts, and case extraction is easy with no signs of pressure. The best 5 shot
group to date at 100 yards has been .092 (Less than 1/10 of an inch).

And all of this with a belted case, and lots of freebore And a Mark 5 Weatherby action.

J E CUSTOM