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More Likley to get Pressure
7.62x39
Member Posts: 1,994 ✭✭✭✭✭
Are you more likly to get pressure if you seat a bullet too deep or seat one on the threads?
Im using a .308 bolt
Im using a .308 bolt
Comments
how deep would you have to seat a bullet?
No answer to all bullets.
It would vary do to weight and construction.
Example: A Barnes copper bullet will be longer than a cup and lead core bullet of the same weight and would generally take up more case space than a conventional bullet if loaded to the same length.
It would also vary due to different burn rates on different types of powder.
The best way to find your perfect seating depth is by measuring your depth from the head of the case to the ogive of whatever bullet you are using. You will need a special tool attached to your calipers to do this. Stoney Point Bullet Comparator with the proper insert for the caliber. If you do this, once you find out what the seating depth needs to be for the rifle you are loading for, it won't matter what bullet type you use because the ogive will always be the same distance from the head of the case. To do this, creat a dummy cartridge and barely seat the bullet into the neck of the case. Coat the exposed bullet with a black eraseable magic marker. Insert the cartridge into your rifle's chamber carefully. It will be sticking out. Close the bolt and force the cartridge into the chamber. Open the bolt carefully to extract the cartridge. You should see where the bullet has contacted the lands of the rifling of your barrel in the marker and the bullet should be seated a bit more into the case from being pushed in with the bolt. Clean off the marker. Measure your cartridge's oal from the ogive of the bullet and write it down. Insert the cartridge into your seating die and seat the bullet another thousandth in. Remark the bullet with the marker and repeat. Repeat these steps untill the instant you stop seeing the marks on the bullet from the lands of the rifling. The bolt should be easy to close. Now you have found your perfect bullet seating depth from the ogive of the bullet and no matter which brand or type of bullet you use for that rifle, it will always be seated in the right place. You can purchase Stony Point's Bullet Comparator sets from Lock,Stock, And Barrel and many other reloading supplies suppliers. HA! Say that ten times fast!! LOL!!
Ironsight - I do not believe this is true information. The info would be....IF....the hole in the bullet comparator is the same size as lands of the barrel.
OR...if the shape of the ogive of each bullet were the same.
I have multipe hours in multiple bullets for my 223 barrel....they are not the same. Yes, I measured bullets to make sure they were the same - everything from 40 BT's to 69 gr HPBT's. Ogive is different.
Also -- one 1/1000 off of the lands isn't always the best/perfect distance from the lands for every type of bullet or powder charge.
Somtimes accuracy will be better at closer or farther distances. I guess you could say it will always be off the lands though.
And some bullets like a barnes copper bullet will build very high pressures seated that close. It's sometimes best to start farther away and work your way in watching for signs of pressure.
Ok.. I may be misunderstanding what the ogive of a bullet actually is. I was under the impression that the ogive is the exact point at which the bullet or any bullet was at it's stated caliber. In otherwords, the excact point a .224 cal. bullet is at .224" in diameter. If this is true and you are using the same .224 comparator for each type of bullet (I do beleive the inside diameter of each comparator is 1/1000" smaller then the actual stated caliber), in theory, no matter what type of bullet you use, it will always set the ogive the same distance from the lands..... right....
Hmmmm...
Ok.. I may be misunderstanding what the ogive of a bullet actually is. I was under the impression that the ogive is the exact point at which the bullet or any bullet was at it's stated caliber. In otherwords, the excact point a .224 cal. bullet is at .224" in diameter. If this is true and you are using the same .224 comparator for each type of bullet (I do beleive the inside diameter of each comparator is 1/1000" smaller then the actual stated caliber), in theory, no matter what type of bullet you use, it will always set the ogive the same distance from the lands..... right....
Ironsight, the ogive is the curved forward portion of the bullet from the top of the bearing suface (that is actual bullet diameter) forward to the tip.
Not all bullets have the exact same shape or lengths due to construction, so to answer your question -- No they will not always be the exact same distance from the lands, and the same distance is not always the perfect bullet seating depth for all bullets.
Spitzers or "tangential ogive" bullets are a special case of secant ogives where the angle joining the nose and the shank is zero. That is, all bullet noses that utilize a section or arc from a circle as the major shape of the ogive are secants, but we reserve the tangent or spitzer name for the one special case of zero angle of junction.
The spitzer bullet is constructed on paper by drawing two arcs with a compass, the radius of each being identical, and being specified in "calibers". The two arcs are drawn so that they start at the shank and curve toward the center line of the bullet, crossing or at least touching the center line. The origin of the radius is located on a line perpindicular to the centerline and even with the end of the shank.
A spitzer is designated in calibers of radius, such as 2-S, 6-S, or 10-S. This means that the length of the radius of the ogive arc is 2 calibers, 6 calibers, or 10 calibers. Since the arc has to go from the shank to the centerline, it isn't possible to make a spitzer with less than 0.5 caliber radius (which is a round ball nose and is identical to a 1/2-E eliptical ogive).
Tangential ogives are the most popular and common shape, and they are mathmatically easy to describe and to create on paper. The one thing people often forget is the jacket thickness, which prevents the tip of the bullet from being closed to a sharp point. If the jacket has .035 inch thick walls, then the absolute minimum tip closure will be 0.070 inches across, and more likely it will be 0.091 to 0.105 inches because of the pressure that smaller closure would require and the strength of the ejection pin needed to push the bullet back out of the die.
Most rifle bullets use a 6-S ogive because it gives the best range of weight to length, until the caliber becomes large enough to make the weight excessive. Usually a 4-S or shorter radius is used for calibers of .375 and larger, until we get to the very large and heavy .512 (50 Browning Machine Gun) bullet, which is used in guns that can handle 600-900 grain bullets. This lets us use a longer ogive radius again, from 6-S to 10-S being typical.
The larger the ogive number for a spitzer, the more pointed the bullet becomes. It also becomes longer in a non-linear manner. The greatest changes in length take place in the low end, and become less and less as the same amount of change takes place in larger numbers. That is, a bullet that goes from 2-S to 4-S becomes significantly longer and more pointed. Going from 4-S to 6-S makes a noticable but smaller difference. From 6-S to 8-S is a moderate change, and from 8-S to 10-S is less so. But from 10-S to 12-S, you can barely tell the difference, and for longer ogives, the only noticable difference is at the very tip, and only if the meplat or end is very sharp.
Secant ogives are just like tangents except the junction of the ogive and shank makes an angle other than zero. Therefore, it is not enough to specify the secant ogive radius in calibers. You must also define either the angle of attachment, or the distance that the ogive would have to be moved sideways in order to make it meet tangent with the shank.
A secant ogive has a bit of a discontinuity or non-smooth change from ogive curve to shank. The idea is to join a long ogive radius to the shank so that the axial length (along the centerline) can be made shorter than if the entire arc from tip to shank were joined tangent to the shank. We "slide the ogive" over to one side and chop off a bit of the curve, in other words.
The reason for doing this is to try to fool Mother Nature into thinking that there is a smooth ogive, without any discontinuity, and get a more streamlined curve that isn't so long as it would be in a spitzer. That makes the bullet closer to a practical weight, because the over-all length is shorter. A 14-S secant with .014 offset can be as short as a 10-S tangent, depending on the relative size of the meplats. If the angle is increased enough, the secant starts to generate a secondary shock wave from the disrupted air flow, and the advantage of having a longer ogive curve is lost. There is a narrow practical range where a secant works well for supersonic bullets, and not much reason to use it at all for subsonic bullets. Pushing the design to the edge of practicality is a mistake in most cases, if you are not positive about the atmospheric pressure and humidity at the time of firing and design for it. A bullet that is optimized for low drag at normal air density may develop a secondary shock wave if the density increases slightly, spoiling any plans to get lower drag than a more normal bullet design. Worse, the conditions might be "on the edge" of switching back and forth, where a tiny change in pressure generates a shock wave from the ogive-shank junction over just part of the flight, depending on velocity as well as shifts in weather, and your groups go all over the target. Better to sacrifice a little "paper advantage" and work well within the area where such small changes in conditions would have no effect.
If you look at any of the Sierra bullets in the photo, you'll see an example of tangent ogives. If you look at the 140 gr. Berger or the 140 gr. JLK you'll see an example of the secant ogive.
This is a section of a form factor chart: