What Is A Cast Bullet Grease Groove Angle Option

Grease groove angles   There’s more than one way to measure the groove angle.   The picture shows how I measure it, just so we’re on the same page.   55° is about as steep as I care to go, any steeper and you’re inviting difficult release from the mold.   The steeper angle does hold a little more grease so it may get the nod for black powder bullets and original Keith bullets.   A 45° angle offers a slightly better release and is a good choice for most other applications.



Explanation of Cast Bullet Base Options

Plain Base, equal length the computer will determine the band layout that satisfies your specs.   All body bands will be the same length.

Plain Base, define length you set the bottom band length and the computer decides the length of all other body bands.   Use this if you want lots of small body bands but with a larger bottom band.

straight check shank

stepped check shank puts a slight step on the shank near the top of the check.   This gives the check something to grab hold of.

Bevel Base  Not recommended because it is harder to get a good seal with a bevel base bullet, and also messy to lube in a Lyman/RCBS lubrisizer.   A bevel base may be a good choice on paper patch bullets, where it serves to help keep the paper from tearing.


What Is A Cast Bullet Bearing Length

Bearing Length  Includes the “fat” part of the ogive on ogival flat points, to the point where the ogive diameter = the typical bore diameter.   It also includes the bore riding length on bore riding bullets.   It does not include the gas check.


What Are Cast Bullet Crimps

Depth of Crimp Grooves  all crimp grooves are the same depth as the lube grooves because that’s the simplest way to program it and it works well enough.

Why do you offer several crimp groove lengths ?  Because the depth of the crimp groove varies with caliber and bullet style, so you have to adjust the length of the groove to maintain sane crimp groove angles.   For example, a 0.045″ long crimp would be all screwed up on a 20 gauge Keith bullet.   Play with several crimp lengths and let your eye be the judge of which looks best on your particular bullet design.

0.045″ long crimp  a good choice for up to around 35 – 40 caliber.

0.055″ long crimp appropriate for 41 – 50 caliber bullets that have standard depth grooves.

0.070″ long crimp appropriate for big bore Keith bullets.

0.090″ long crimp mainly for 20 gage bullets.


Explanation of Cast Bullet Diameter Options

— TOLERANCES: yes, we have them.   Zero-tolerance may exist in the political world but the the world of machining and casting will always have tolerances.   The DIAMETER refers to the AVERAGE diameter, obtained by measuring several bands in several places.   Some measurements will be higher and some will be lower.


What Are Bullets Front Band / Bore Ride Lengths

What Is A Bullet Groove Diameter


Groove Diameter  is not an option.   On Keith bullets, the groove diameter is always 85% of the body diameter.   On other bullets, the groove diameter is standardized for each caliber, usually the same as the check shank diameter for that caliber.   Exceptions are made for calibers with odd shank diameters, like the 35, the 9.3mm, and the 41s.

Why isn’t it an option?  1) it is hard to lathe-bore deeper grooves because the cutting tool has to reach around the grooves and the chips have to squeeze pass the grooves and 2) I have not seen ANY data suggesting that deep grease grooves are helpful in modern firearms.


What Is Groove-to-Band Length Ratio

Groove-to-Band Length Ratio (GtoB)  is a way for the computer to decide how big to make the grease grooves.

If the groove is very long relative to the depth (say GtoB = 1.5), the lube may refuse to stick to the groove, creating problems at the reloading bench.

It is very desireable, from the mold maker’s point of view, to avoid grooves with a “V” shape, because the sharp corner on the “V” is prone to have burrs and does not facilitate fill or release. Instead, please select a design that has a flat at the bottom of the groove like “\_/”. It doesn’t need to be a big flat, as long as the flat is there.

Please do not attempt to imitate the Lee tumble lube design. The Lee bullets have shallow, rounded grooves which this program will not create. Furthermore, any grooved bullet can be tumble lubed.

When the paper patch mode is chosen, the program will draw a bullet with small grooves, but the mold will actually be cut smooth. This is due to program limitations. Please note that conventional grooved bullets can be paper patched and may shoot better anyway.

What is a Bullet Leade Length


Leade Length  Includes the “fat” part of the ogive on ogival flat points, to the point where the ogive diameter = the typical bore diameter.

If the diameter at the bottom of the ogive is   “
And if the ogive radius is   “
Then the ogive diameter is   “
at a point    ”   above the bottom of the ogive.

So What Do You Do With It?  Use the leade length to figure out if a bullet will fit in your rifle.   You have measured your rifle’s throat length, haven’t you?   The leade length should be a little less than the throat length.   Bear in mind that the leade length number is approximate, because it assumes a “typical” bore diameter, and your bore may be different.   Bear in mind that your throat length measurement will be approximate, because, if you are lucky, your throat is gently tapered so it’s hard to say exactly where the rifling starts.   Bear in mind that your seating depth may vary, and that will effect the leade length.   The leade length assumes that the case mouth will be even with the top of the uppermost grease groove.   If we have to, we can seat the bullet a little deeper, but we probably don’t want to seat the bullet out farther and then have the grease groove exposed.   In general, use the leade length as a ballpark number, not as an exact number, and leave yourself a little wiggle room in case you need to seat the bullet deeper or further out.

How Do You Measure the Rifle’s Throat Length?  A chamber cast is best, a chamber slug is pretty good, too, or you can use a dummy round with a jacketed bullet seated butt-out.   Seat the backwards bullet progressively deeper until it just barely will chamber.   The length of bullet sticking out of the case is the approximate length of the throat.


What Is A  Bullets Meplat

Meplat  refers to the flat nose (and for now, flat noses are the only kind I make).   It is expressed as a percentage of bullet diameter.   For example, a 0.300″ meplat on a 0.432″ bullet would be 70%.   A 70% meplat is similar to what some call a “Long Flat Nose” except now you can make the nose as long or as short as you like.   An 80% meplat is similar to what some call a “Wide Flat Nose”.   Bigger meplats punch bigger holes in the target, but may not feed in some guns and may be more difficult to stabilize, just depending on the gun and the load and the range.   Smaller meplats are more likely to be accurate but are less effective on game.   A 70% meplat is a great compromise, usually accurate yet adequate on game.

What is a Bullets Nose Length

Nose length refers to the part of the bullet that sticks out of the case.   On crimples bullets, this is measured from the bottom of the front band.   On crimped bullets, nose length is measured where the crimp groove intersects the front band, which, because of the groove angle, is not the same as the bottom of the front band.


Why Won’t This Bullet Work in This Block?

long, unsupported ogive, means you have a long, unsupported ogive.   Either shorten the nose or lengthen the bore riding section.   This rules kick in when the ogive length is greater than 83% of the bullet diameter.

SBS,  the dreaded Shrunken Bullet Syndrome.   Causes certain places on the bullet, usually near the base, to be undersized.   Known to be a function of alloy, mold temperature, and bullet size.   To avoid SBS, either use a more resistant alloy or a bigger block.   Also, aluminum blocks are more resistant to SBS than iron.

SBS ratings of alloys from best to worst:

  • Best Pure Lead
  • Straight Wheelweight
  • 30:1 & 20:1
  • Linotype
  • Lyman #2
  • WW & 2% tin
  • Worst 50% lino / 50% WW or 91/3/6 (but these are good alloys for smaller bullets)


Bullet Too Long either the bullet is too long for the block or else the bullet is too long for the boring bars.

Won’t Fit caliber is too big for this block.

What Is A Bullets Sectional Density

Sectional Density (SD)  is a bullet’s weight, in pounds, divided by the square of its diameter, in inches.   A bullet with a high SD will usually penetrate better than a bullet with a low SD.   Al Marion has demonstrated that Terminal Sectional Density (TSD), based on the weight and diameter of bullets recovered from game, is a better predictor of penetration.

SD = (weight in grains / 7000 grains-per-pound) / ( diameter2)


Explanation of Weight Tolerance

The “+/-” number is the worst case variation between cavities, based on the 0.002″ diameter tolerance and also a 0.002″ length tolerance.   Most of the time, the actual variation will be less than this number, but in theory, the cavities could have that much weight variation and still meet the dimensional specifications.

Example: A commercial caster wants a matched set of eight 2-cavity blocks for a Magma casting machine.   The bullet is a 300 gr. 44 caliber, with a 2.3 gr. “+/-” weight tolerance.   The worst case variation between the lightest and the heaviest of the sixteen cavities would be 2 times 2.3 gr. or 4.6 gr.

The tolerance is what the math predicts.   Of course, we would all like to have tighter weight tolerances, but that would require tighter dimensional tolerances, and it’s not easy.

This tolerance does not include weight error caused by imperfectly estimated alloy density.

This tolerance does not include weight error caused by internal voids.   No one can predict or control internal voids.


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