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Discussion in 'Long Range Hunting & Shooting' started by ovastafford, Dec 29, 2009.
Can someone explain to me why weatherbys have a free bore. And why they still use it?
It is dome on the Weatherby Mag rounds to keep pressure down. The overbore cartridges like most Weatherbys have it and so does Remington Ulta Mags. A Weatherby rifle in a non-weatherby round like my 22-250 SVM does not have it.
So all overbore cartridges have it? Like 7mm stw, .338 edge, etc...
No, it is mostly used for factory rifles Like Weatherby's and Rem Ultra's. In custom rifles it would be up to the smith building the rifle wether he chose to set his reamer up with it or not and how much.
Okay I get it. Thanks for the help.
Freeboring is a way to get higher muzzle velocity with the same chamber pressure. It slams the bullet harder into the rifling and typically ain't as accurate as standard throats which are shorter. Bullets are less deformed when more gently pushed into the rifling
Roy Weatherby knew this but it didn't matter. At the ranges his cartridges were used at, a slight degradation in accuracy was an acceptable compromise to get the higher muzzle velocity he wanted.
Not to be argumentative, but:
I'm not sure that you get higher velocity with the same chamber pressure?? Isn't it more being able to increase the powder charge because of the increased volume thereby increasing velocity?
Weatherby freebore rifles shoot very well. I have taken elk and deer out to 1340 yards with weatherby freebore rifles. Those are the ranges wby cartridges are used at if that is far enough to satisfy your long range hunting. I have standard off the shelf MK5 rifles in wby calibers that will shoot 1" groups at 400 yards.
What other size groups do they shoot?
I ask because it's rare that any Weatherby rifle shoots 1/4th MOA groups (all the time?) at 100 yards. To say nothing of the fact that few if any bullets typically shot in them (save match bullets made correct for their groove diameters) that well at 100 yards. To shoot 1/4th MOA at 400 yards, they'll have to shoot near 1/8th MOA at 100 yards; groups don't open up uniformly every hundred yards downrange past 100.
It's not an increased volumn in the case. Freebore is extra length of the throat for normal OAL rounds. With the rifling not engaging the bullet until its move a quarter to half an inch further, there's less pressure during this time. There will be less peak pressure with a freebored throat than a standard one where the rifling starts a couple hundredths of an inch from the ogive of standard bulleted cartridges. With freebore, one can put the same amount of a bit faster powder or, if case volumn permits, a few more grains of the same powder a normal chamber would get max pressure with.
It's the opposite as chambering a round with the bullet jammed into the lands. That will create higher pressure than if the bullet had a couple hundredths of an inch jump. That same load in a freebored chamber will have less peak pressure so one can add more horsepower inside the case.
I guess I didn't do a very good job but I think that's what I was trying to say
Freebore is still used as it allows a given case a little more room for the bullet to move out of the case before peak pressure hits. This allows larger charges safely. Freebore is not some uncontrolled free jump to the rifling where it is so loose it can get all crossed up before it smashes into the bore and forces the bullet to conform and grind down the bore all crooked. Freebore in the case of a Weatherby throat is a snug fit to the bullet that accuratly guides the bullet into the rifling where it engraves the bullet and starts the rotation of the bullet in a controlled manner. I think it also gives the rifling a slight relief from the hottest part of the combustion process and helps extend the life of the lead edge of the rifling. I have had great luck with Weatherby rifles with free bored chambers. Much more likly to be a shooter than most any other non custom production rifle. I ended up putting 25 power scopes on all mine as being so accurate I find myself shooting them at much smaller targets that require large magnification to see. Once I get tuned into shooting squirrels and birds at 400 yards, deer and elk seem so much easier to hit.
The highest regarded gunsmiths on this board frequently build rifles to seat very long custom made VLD type bullets way out of the case to optimise case capacity, frequently report their long throated rifles still shoot very well with much shorter production bullets.
I do not fear freebore.
WELL STATED...The point I was trying to make earlier was that free boring allows more powder to be loaded in the same case to reach equal pressure,essentially creating a larger chamber volume which allows higher velocity. No different than reaming a chamber from a std. '06 to an A.I. improved '06. If you loaded the A.I chamber with the same load as you did with the std. chamber, you would get "less" velocity (pressure) than with the std. '06........Rich
Not necessarily... I sometimes see MOA group size shrink with distance. Fairly often I will see groups the same size in inches and sometimes smaller at 200 yds vs 100 yds. In good conditions, with a good load I usually dont see much difference between MOA group size from 200-400 yds.
Same here, this is why I never draw a conclusion about a load anymore till I shoot it at 300 yards.