Ogive Bullet Measurements ?

[Wilbur]

I asked because

A typical closely fitting reamer pilot for a 6mm benchrest barrel is .236 in diameter. It would seem that the actual bearing surface (by definition) for such a barrel/bullet would be from the base of the bullet to the point on the ogive where the diameter is .236.

I suppose we need a descriptive term for that segment of a bullet and bearing surface is as good as any.

 

[Larry Willis]

John S .......

I've always heard this part of the bullet referred to as "the point of transition" to the ogive. Like Wilbur says ... we could probably use an actual descriptive name for this transition area. However, I don't think "shoulder" will work, because that implies another surface like a semi wad cutter has.

Wilbur .......

The surface of a reamer pilot bearing rides on the inner surface of the lands (not on the groove diameter).


- Innovative

 

[John S]

OK Larry

You can call it anything you want.

1-800-223-8799

 

[DR4NRA]

Exact definition of ogive, picture included.


Applied physical science and engineering

A secant ogive of sharpness E = 120 / 100 = 1.2In ballistics or aerodynamics, an ogive is a pointed, curved surface mainly used to form the approximately streamlined nose of a bullet or other projectile.

The traditional or secant ogive is a surface of revolution of the same curve that forms a Gothic arch; that is, a circular arc, of greater radius than the diameter of the cylindrical section ("shank"), is drawn from the edge of the shank until it intercepts the axis.

If this arc is drawn so that it meets the shank at zero angle (that is, the distance of the centre of the arc from the axis, plus the radius of the shank, equals the radius of the arc), then it is called a tangential or spitzer ogive. This is a very common ogive for high velocity (supersonic) rifle bullets.

The sharpness of this ogive is expressed by the ratio of its radius to the diameter of the cylinder; a value of one half being a hemispherical dome, and larger values being progressively more pointed. Values of 4 to 10 are commonly used in rifles, with 6 being the most common.

Another common ogive for bullets is the elliptical ogive. This is a curve very similar to the spitzer ogive, except that the circular arc is replaced by an ellipse defined in such a way that it meets the axis at exactly 90°. This gives a somewhat rounded nose regardless of the sharpness ratio. An elliptical ogive is normally described in terms of the ratio of the length of the ogive to the diameter of the shank. A ratio of one half would be, once again, a hemisphere. Values close to 1 are common in practice. Elliptical ogives are mainly used in pistol bullets.

Missiles and aircraft generally have much more complex ogives, such as the von Kármán ogive.

wikipedia

 

[Pete Wass]

What is needed to solve the problem

Are dies with larger O.D.' stems that could be machined to fit near the ogive-shoulder junction. These would go a long way toward solving the Heartburn this whole bullet thing brings along with it. I suppose one could order a die that was made to seat a larger caliber, say in the case of a 6 MM, use a 7 MM or perhaps even a .30 cal. Use a .32 cal or .35 cal for 30's, etc, etc.

People who jam the heck out of their bullets when they tune never encounter any problems in this area becaues their bullets are always fast into the lands but for those who use an exact seating depth; different story. I like to be able to open the bolt with a live round and have the loaded round come out without the bullet being pulled; terrible mess otherwise. To be able to do this, one can not go much beyond .012 with "Normal" neck tension.

There are a few other reasons to want to be able to exactly control seating depth but being able to get a live round out intact is a darn good one.

 

[DR4NRA]

John S .......

I've always heard this part of the bullet referred to as "the point of transition" to the ogive. Like Wilbur says ... we could probably use an actual descriptive name for this transition area. However, I don't think "shoulder" will work, because that implies another surface like a semi wad cutter has.

Wilbur .......

The surface of a reamer pilot bearing rides on the inner surface of the lands (not on the groove diameter).


- Innovative

John S

Point of transition will work I guess, but your semi wadcutter statement is a fact as far as " shoulder", because it just does not apply to the ogive.

The Ogive is an arc, no shoulder. But there is a shoulder in the base of a new boat-tail design. will post a link.

But for another poster, the "Anatomy of a Bullet" is below.


Form Corbin dies, the cats meow in bullet making.

Core Swage Die : This is the die which adjusts the lead weight, and turns a piece of cut lead wire or cast lead core into a precise cylinder of the correct diameter, with flat ends. The CSW die is seldom used by itself, but is followed by the CS or PF (or both).

CS-1- Core Seat Die : This die presses the lead core into the jacket and forms the precise bullet shank. The core seater can also produce a finished jacketed semi-wadcutter bullet or lead semi-wadcutter bullet, by using a nose punch having the desired cavity shape. However, the bullet will be about 0.0002-inches undersized compared to using a LSWC or PF die.

PRO-1-R Pro-Swage : The PRO-SWAGE is a special form of the CS die which is built for use on reloading presses only, and finishes the bullet in one stroke. It is used only with soft lead and may or may not use a jacket depending on the caliber. Only SWC-style noses can be made. These are all type -R prefix since they operate in a reloading press. Example: PRO-1-R (specify caliber, nose, base shape).

PF-1- Point Form Die : The Point Form Die or Point Former shapes the ogive curve on the bullet. If you want a bullet that does NOT have a step or shoulder between the shank and nose, you must use one of these dies to create it. Forming the nose in a punch cavity always leaves a shoulder (the edge of the punch), which we refer to as the Semi-Wadcutter shoulder. The point form die is always used with a matching CS die for jacketed bullets, and usually with a CSW die for lead bullets

LT-1- Lead Tip Die : The Lead Tip Forming die reshapes a lead tip bullet made in the point former to remove the distortion produced by ejecting the bullet from the point former die. It is never used without the PF die. The PF die comes first, then the LT die is an option if you want factory-finished lead tips, especially in sharper rifle nose shapes (many blunt or round nosed shapes look OK without using the LT die to clean them up).

RBT-2- Rebated Boattail Set : The dies to produce rebated boattails are the BT-1 and BT-2 dies. These are used as a set, INSTEAD of the usual CS die, to seat the lead core. The jacket and core are put into the BT-1 die and pressure is applied to the core with a punch, expanding the jacket and also forming a conventional angled boattail on the base. Then the assembly is ejected and put into the BT-2 die, where the angled base slides past a shoulder or rebate shape. Pressure is applied again, expanding the base section perfectly into the rebate shoulder and producing a gas sealing, muzzle blast deflecting shoulder that adds about 15% to the tightness of the group (compared to a conventional BT bullet). The RBT dies always come as a set of two, called the RBT-2.

A lot of good info from these folks
http://www.corbins.com/fjfb-3.htm

 

[amamnn]

Maybe I'm just excessively anal, but I've always culled bullets for base to ogive and base to tip variations. I set aside all the ones that have the same ogive and then measure the tip; any that can be trimmed at the meplat to get the same measure I keep, but any needing a trim over .002" do not seem to work well.


Lately I've been buying bullets from Don Lahr at Precision Bullets LLC, and he'll do all that for you as will some others, which can be worth the extra money, if you are the opposite of me: that is, you have more money than time.........

 

[Pete Wass]

I checked yesterday

I took a .30 cal stem and tried a 6 MM bullet in it just holding the two in my hand. It looked to me that the 6 MM bullet touched the stem roughly where the bullet would touch the lands. This might be a solution. I have heard that opening smaller stems wide enough to touch bullets down near the ogive/shoulder area the angle causes the bullets to stick to the stem. Perhaps a larger stem with a steeper angle would solve that problem.

 

[Joe S]

One thing I haven`t seen mentioned as a possible cause of the OPs COL variance is the type of tip on the bullet. I`ve found in 2 different caliber seaters, both RCBS that some plastic tipped bullets will bottom out in the seating cup. There is just enough variation in the ogive up by the tips that they don`t always hit everytime one is seated. I use a Stoney Point and normally find ~ 0.002" max variation with my loads usually much less depending on the bullet. The plastic tipped though were at times showing as much as 0.005" difference at the ogive. I cured mine by drilling a small dimple in the bottom of the cup for added clearance with a dremal tool.

 

[Pete Wass]

What I have found

One thing I haven`t seen mentioned as a possible cause of the OPs COL variance is the type of tip on the bullet. I`ve found in 2 different caliber seaters, both RCBS that some plastic tipped bullets will bottom out in the seating cup. There is just enough variation in the ogive up by the tips that they don`t always hit everytime one is seated. I use a Stoney Point and normally find ~ 0.002" max variation with my loads usually much less depending on the bullet. The plastic tipped though were at times showing as much as 0.005" difference at the ogive. I cured mine by drilling a small dimple in the bottom of the cup for added clearance with a dremal tool.

Is competition seating stems have a very deep clearance hole bored in them. There would be no way for a bullet tip to touch the inside of the stem.

An interesting situation I observed this winter as a man was showing me how he used his computer to work up his loads for long distance shooting, the program perscribed measuring the OAL of the loaded round from the tip to base of the case. That situation seems to fly in the face of what some of us are finding here.