Custom Rifle Designs

Custom Rifle Designs

These illustrations are of typical custom designs requested by a cross-section of custom orders. We can incorporate a wide variety of bullet profiles and ogives, and almost any combination of driving bands and grease grooves.

Why lathe-bored moulds?

By lathe boring a mould no cherries are required. The same tools used to make a 30 caliber mould can also be used for any mould up to 50 caliber. Blocks are clamped together to machine them. Doing it this way, the blocks are held rigid and are perfectly round inside. Hoch lathe-bored moulds are made on a Hardinge second operation lathe specially tooled for making moulds.

Making moulds by lathe boring can produce several moulds of one design, but all having different diameters. If moulds of the same design are ordered at one time, then all can have the same diameter or different as one desires. This is a time consuming process, and moulds are made only on a custom basis. None are stocked.

Machining tolerances: 0 to + .001.

All moulds are tested before leaving the shop by casting several bullets using the alloy specified by customer and measured with a Mitutoyo electronic micrometer.

Greenhill Formula

BL = 150 ÷ (T ÷ D²) T = [150 ÷ (BL ÷ D)] x D
T = Rate of Twist BL = Bullet Length D = Diameter (Bullet) in Thousandths

Gyroscopic force from spin tends to keep the bullet pointed in the same direction. Atmospheric resistance produces forces which tend to tip the bullet sideways. As long as the spin produces more stabilizing force than the atmospheric resistance produces upsetting force, the bullet will fly straight, i.e.,stabilize.

For practical purposes, as long as we spin a bullet fast enough to be stable, a little exra spin doesn't seem to hurt. However, if you want the gun to shoot well at long ranges, you don't want the bullet 'over-stabilized' very much. As the trajectory arches over and starts down you want the bullet axis to follow the trajectory line. A bullet that does this is said to 'trail'. If the bullet is spinning too fast, it will continue to keep its spin axis pointed along the bore line and end up flying through the air partly sideways. That's not good.

The Greenhill Formula is an excellent formula and was developed from trial-and-error shooting tests. The factor of 150 in the formula isn't dependant upon bullet shape or specific initial velocity - this was established by experience in the shooting tests.
.30 CAL 185 GC
.30 Cal.
.30 Cal.
.32-40 Cal.
.32-40 Cal. Hudson
.30-40 Cal.
.338 Cal. GC
.375 Cal GC
.38 Cal. ML
.38 Cal. Hudson
.40 Cal. 420FN
.416 Cal. GC PB
.45-70 Cal. GC PB
.45-70 Cal. Hudson
.45 Cal.
.45-70 Cal. .45-90 Cal.
.475 Cal.
.50 Cal.
.50 Cal.
.54 Cal. ML 590GR

Give us a call anytime:  575-627-1933 or 575-627-6156