Kiss the lands vs Freebore

[longwinters]

Seems strange that both can be so accurate.  How does that work?  Some guys are so adament that freebore cannot shoot, but my Sako's easily shoot MOA with a variety of bullets loaded to SAAMI.  Of course most rifles out there are not Freebore so people have a lot more experience with measuring OAL off the lands.  For me, I just have to measure off of the magazine to make sure my loads fit there and everything else just falls into place.

Long

[beemanbeme]

I think it shows that some of the looooong debates we have in here are really "full of sound and fury, signifying nothing".  Or, I like the way they put it in the Hornady Reloading book: "each rifle is a law unto itself and generalizations should be made with circumspection..."  
Thus, when someone sez "you MUST free float your barrel before it'll shoot", or "you MUST have xxx bullet jump", etc, etc, it often means they haven't as much experience as they profess.   :grin:

[Swamp Fox]

For most folks it doesn't matter. If you can hit a 9" paper plate at 100 yds the deer dies.

Comp shooters play with numerious variables to tweak one more 1/100 off of their group size.

[Iowegan]

longwinters, For openers, your SAKO has a unique throat not found in American made rifles. They use a forcing cone much like a revolver. This helps center the bullet without deforming it no matter if the bullet is seated deeper or not. This is great new technology and will probably start showing up in American made guns. The "forcing cone" technique requires a very hard barrel because it is more prone to throat erosion.

As for the standard chamber, you'll find free bore is a tad larger in diameter than the diameter of a case mouth. That means it's roughly .025" larger than bullet diameter. In standard chambers, free bore is large enough to allow the bullet to be pushed off center with the bore when several tons of pressure are applied from the powder burn. If a bullet trys to enter the bore off center, it will cause damage and make the bullet slightly out of round. Once launched, the bullet will act somewhat like a wiffle ball and open up the groups.

Add to this, most rifle manufacturers ream the free bore much deeper than SAAMI specs. This is to insure ammo from virtually all sources will chamber and shoot. Remember, foreign ammo makers don't always comply with SAAMI specs.

Let's add one more condition to the formula. All guns will suffer some throat erosion after being fired a considerable amount. The case design and power level dictate how fast the throat will erode. As erosion increases, the bullet will have even more opportunity to get pushed off center with the bore, thus more damage and worse accuracy.

One thing that really helps in a rifle with excessive free bore or throat erosion is to seat the bullet out where it almost touches the rifling (.010"). This minimizes bullet jump and causes way less damage to the bullet. A bullet that is seated deeper will get a "running start" and will have developed quite a bit of speed. This can cause even more damage to the bullet.

A bullet misalingned by a fracton of a degree will suffer quite a bit of damage. Another thing that really helps is annealing your brass. This makes the case mouth softer and tends to release the bullet a bit sooner, before it gets moving too fast. This helps minimize bullet deformation.

[longwinters]

So a forcing cone is not freebore?  Just trying to get my facts straight :-)  Very helpful info.

Long

[Iowegan]

longwinters, Maybe this would help a little. Example: A 308 Win standard chamber's throat accommodates the neck of the case and measures about .344" in diameter. The transition from the throat to the bore is a fairly abrupt step where it diameters down to .308" (bore size). This short step has a mere 3 degree angle (almost straight). The distance from where the case mouth stops and the bore starts is called free bore but it a misnomer and is really just an extension of the throat. This extended throat or free bore distance varies quite a bit from gun to gun and that's why some guns are bullet depth sensitive.

A true free bore would be bore diameter without rifling. The extended throat in the above example is actually .036" larger in diameter than a true free bore. This extra space is plenty to allow a bullet to be pushed off center.

OK now for your SAKOs chamber. The area in front of where the case mouth stops forms a gentle taper instead of an abrupt step and is way longer than in a conventional chamber. The angle is about 13 degrees, depending on caliber. It acts just like a forcing cone on a revolver and funnels the bullet into the bore. The down side to a tapered free bore is some propelling gasses escape around the bullet. This lowers velocity a little and is more subject to flame cutting (erosion). In a SAKO with the same barrel length as a conventional gun, the SAKO will loose about 50 fps. A token price to pay for superb accuracy and it's not fussy about bullet seating depth. SAKO puts some real hard steel in their barrels so life expectancy is about the same as a conventional barrel. Hope this helps.

[longwinters]

Iowegan,

It certainly does.  It also answers my questions about why my Sako rifles seem a little slower than other rifles of same caliber and barrel length . . although Sako rifles (280, 270,308, 30-06 etc...) are a little longer than the standard 22".  They always add a 7/16s or something on there for some reason.

Thanks

Long

[Iowegan]

longwinters, I manufactur and sell chamber tools for rifles. One tool measures throat depth so you can trim your cases to optimum length. The other is a bullet seating depth tool where you insert the bullet you plan to use in the mouth of the tool, then insert the tool in the chamber. You then push the handle in until the bullet contacts the lands. Aftewards, you use the same bullet to measure for best OAL (subtract .010"). These work great in conventional chambers. See: http://www.cactustactical.com/reloading.html

I sold a set to a customer with a SAKO chambered in 308 Win. He was not satisfied with the results of the bullet seater tool and called me to discuss the situation. I thought he had a defective chamber but promised to look into it. I called Beretta and got no where. All they would say was the chambers on SAKOs and Tikkas were a proprietary design. I do not own a SAKO so I borrowed a few from friends and made chamber castings. That's when I learned about the forcing cone concept.

Armed with this information, I called SAKO in Finland and talked to a very nice gentelman that confirmed my findings. He told me all SAKOs chambered in conventional cartridges had the same throats and also Tikka T-3s.

I now tell customers that my bullet seating depth tool won't work in a SAKO or Tikka. By the time the bullet touches the lands, it's almost falling out of the case.

[PaulS]

This does not apply to any but conventional chambers and reflects my experiences ordering and designing chamber reamers.
Chambers reflect the case dimensions with a bit added for clearances depending on the intended use. Chambers have a body, shoulder, and neck at which point they are reduced to the diameter of the bullet or freebore area of the chamber. Ideally the freebore is the same diameter as the bullet but in practice are a bit larger (.001 inch). This area is followed by the lead (pronounced leed) that is conical that goes from the bullet diameter to the groove diameter cutting a cone into the rifling as it moves forward at between one and three degrees (typically).

Target rifles have a very short lead, allowing just enough room for the bullet to be seated in the case and moved forward a bit to within .010 inches of the rifling. Modern hunting arms typically have a lead that is long enough to allow room for the longest bullet to be seated to the bottom of the neck and not hit the rifling - plus some room for insurance. Military "service" rifles have a longer lead to allow for dirty chambers and long bullets. They will accept nearly any ammo and keep pressures in acceptable limits under extreme temperatures. Then there are the Weatherby magnums. Weatherby has arguably the longest leads that I have ever seen in production rifles. They use the long lead to get the extremely high velocities, and to control the pressures under temperature extremes from the arctic to the deserts of Africa.

Lead length only affects accuracy if it is of a diameter that is larger than the bullet and allows the bullet to enter the rifling out of line. With age and wear (including erosion) all long lead guns will eventually lose accuracy. Whether the barrel will last that long or not is just one point of contention in the ongoing discussion of chamber design. The best design for accuracy seems to be the target chambers but they might fail to be usable under the extremes of hunting. That is why we have hunting chambers. If you are building a custome gun you can modify the design to coorespond to the desires that you have for accuracy so long as you are willing to trade off the flexabilities that are built into the hunting chamber. Using a short lead will limit your bullet selection and might cause higher pressures when using in extreme temperatures. It will also require you to keep your gun  and ammo meticulously clean. You can compromise the design to fit whatever you are willing to do in your circumstanses. My 6mm-30 uses a modified chamber in that I knew that I would only be using one bullet in it. The lead is designed to be just long enough to accomodate THAT bullet. The neck area is close tollerance. (I am willing to turn the necks to fit the chamber) and the angle of the lead is 1.5 degrees - comon in target guns but unusual in hunting rifles. The gun is a tack driving hunting rifle that requires special considerations to load for. Most people would not want to limit themselves to one bullet choice, turning necks and keeping the cartridge neck length within the tollerances of my chamber and loading for the temperature that I find when hunting. (There are no extremesand are typically between 20 and 85 degrees F at an altitude of between 3000 and 5000 feet.

[Questor]

I just load to standard lengths unless there's a complelling reason to do otherwise. Fooling around with OAL has only made a difference for me with some older barrels that aren't made as well as today's barrels.

[PaulS]

Yep! there are those who swear by loading "X" amount away from the rifling while others swear over the process until they find their rifle's "sweet spot". Like Questor I use the specs supplied in the data for seated length. That way the load is predictable and should be safe to load in any rifle in good condition. I did once try to seat a bullet, a 180 gr BTSP, out close to the rifling in my 03A3 30-06. I was beginning a workup of a new load so I used the minimum listed load of WW760 powder, the large rifle primer listed, a WLR primer, and because I had such a long free bore I allowed the bullet to find its depth by closing the bolt on the cartridge with the bullet barely seated in the case. This seating depth was less than 1/2 of one caliber deep. When I fired the first of three rounds, it sounded "funny" like a cap and ball rifle more than a modern cartridge gun. The second shot sounded like a flint-lock with a pufft followed almost immediately by a boom. If I ever get that kind of sound again I will stop and pull the remainder of the bullets apart to check all the components. The third round fired as a pop - from the primer and silence for about a full second and then the loudest boom I have ever heard from any rifle and a recoil that hurt like nothing I had felt from my '06 before. I knew that was so wrong on so many levels I just sat there stunned for a long time. I looked the gun over and it seemed fine and I had no cuts or scratches - other than the bruise to my shoulder I was fine. I opened the bolt - harder to do than ever before. I pulled what used to be a 3006 cartridge out of the bolt. The rim - yep! it now had a rim was over 9/16 inch in diameter, the primer pocket was so large that the primer had fallen out as I removed the case from the gun and it was badly deformed. The head of the case was over-expanded and bulged to a point just in front of the web where there was a split that was open and about a third of the way around the case.
I inspected the gun and it seemed to be in good shape but I packed everything up and took it all to the gunsmith.
He checked my gun over with gauges and micrometers and announced that it was in great condition. I asked him what happened - after telling him about my experience. He explained that I had experienced a situation that "can't happen". When I used the minimum load and combined that with the long seating of the bullet it reacted like a very light load of slow burning powder in a large case. The primer had gone off separating the bullet from the case and lodging it in the rifling while blowing the powder all over inside of the case without properly igniting it. He said that there were probably a few grains of powder burning in several different locations in the case and they gradually burned, igniting more of the powder as they burned. At some point the heat was high enough to pruduce an increase in burn rate as the pressure began to rise. The powder began to burn very fast - from several different places in the chamber and the pressure wave and burn rate all came together at once, known as detonation, which caused the pressure to go well beyond anything similar to normal pressure. Looking at the case he said the pressure was probably close to 100,000 psi and told me I was very lucky to be uninjured and it was a miracle that my gun was in shootable condition.
Since that experience I use the listed load data as listed. Period! I start new loads with minimum powder charges and bullets seated to the listed O/all length. I work my loads up in increments and when I find an accurate load that is close enough to maximum to know there won't be another accurate load closer to but not exceding the maximum listed load.
When I find my accurate load I load more of it and some on either side of the load in .2 (2/10 ) of a grain increments. I use this data to find the limits of the loads accuracy envelope. I can play with primers to see if they affect the accuracy. The most stable primer - the one that provides the widest range of accuracy is the one I choose. I then pick the accuracy load that is close to the center of these accurate loads. The most accurate load (usually) allows for the greatest range of error that will not affect the point of impact of these bullets.  I then load a box or two of this load. I fire it over a period of several weeks using a "first shot" target and a "cumulative aggregate" target system where I place a target on the board with another one over it. I fire five shot groups and replace the overlay target with a new one. I five five more shots. I continue this until I have fired no less than three separate times at the range and collected at least one three shot aggregate on the first shot target and three 20 round aggregate targets and their five shot individual targets. I compare the first shot point of impact with the aggregate and individual group target points of impact to determin whether the first shot from a cool dry barrel hits outside the "average point of impact" or that changes occur in the groups under the differences in conditions over the four or five week period of time that I have been firing. I measure all of the five shot groups for an average group size and compare this size to the aggregate group size and compare the group of first shots with the group size for the single five shot groups and the aggregates to make sure that my average group size represents a true representation of the accuracy of the load and rifle. I record all data at each session and at the final evaluation session.
I test the load over the chronograph with a minimum of 40 rounds to get a good sample of the velocity, mean average deviation, standard deviation, extreme spread and the high and low velocity produced. Then I calculate the trajectory and site in range (point blank range) for a target size of 2" diameter. After this I run tests through my fackler boxand at ranges to test the trajectory print outs. Clicks above to extend point blank hold to ranges beyond my PBR are calculated out to a maximum hunting distance. (my personal limit is 200 yards)

This is how I spend my time working up a new load for my rifles and pistols. Once a bullet is tested in the fackler box I dont have to test it again unless it's construction is changed. I can calculate the reaction up or down for velocity using the expansion index calculation in my software and compare it to other bullets that I have tested.