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Detailed Information on SMc™ Cartridges

Encompassing an entire series, SMc™ cartridges are designed to provide superior ignition and a more efficient propellant burn. Compared to conventional cartridges generating similar performance, the patented SMc design provides many advantages, chiefly:

Increased velocity potential (superior ballistics) – significantly so in relatively larger versions

Reduced barrel vibration (increased accuracy potential)

Less barrel heating (extends shooting strings before heating disrupts accuracy)

Reduced bore damage (increased barrel life)

However, owing to unique design characteristics, parameters of SMc cartridges and chambers are more critical than those are in conventional cartridge designs; hence, specific loading precautions are important. For example, in SMc cartridges, base of seated bullet should never be located significantly deeper that flush with interior juncture of case shoulder and case neck. Seating bullets so that base extends more than about 0.015-inch below base of neck progressively reduces SMc cartridge effectiveness.

Bullet-specific throating might be beneficial for those requiring maximum accuracy. With conventional bullets and guns, ample evidence suggests that near optimum accuracy results when bullet-to-rifling jump is about 0.020 inch. However, we believe that the combination of proper throat diameter (perhaps no more than about 0.0005-inch greater than bullet diameter) and sufficient bullet pull (neck tension, see below) eliminates most accuracy problems that have traditionally been attributed to "excessive freebore." Generally, excepting benchrest applications, we have demonstrated that cutting a proper diameter throat that is deep enough to accommodate the longest bullet that might be used will not significantly harm accuracy potential with properly prepared SMc loads that happen to use a shorter bullet.

We have adopted a useful cartridge designation system; SMc designation accounts for caliber and usable case capacity. For example, our 5/35 SMc is a 20-caliber (5mm) cartridge holding about 35 grains of water (to base of neck). One important patented design characteristic of all SMc cartridges is a powder column that is between about 2 times and about 2.1 times bullet diameter:

Caliber	17 (4.3mm)	20 (5mm)	22 (5.56mm)	24 (6mm)	25 (6.43mm)	26 (6.5mm)	28 (7mm)	30 (7.62mm)
Optimum Case Base Diameter	0.400"	0.470"	0.510"	0.550"	0.590"	0.595"	0.635"	0690"
Potentially Usable Cases	None	6mm BR	284 Win.	WSM	None WSM is close	416 Rigby	505 Gibbs	None
Potentially Usable Cases	None	444 Marlin	45-70	348 Win.	None WSM is close	470 NE	505 Gibbs	None
Anticipated Introduction of Factory Cases and Dies	?	2005	2006	2007	?	?	2007	?

No readily available cases properly accommodateSMc cartridges in bore sizes larger than 28-caliber.

Consider the 22/40SMc: Usable capacity is similar to the 22-250 but ballistics far exceeds feasible 220 Swift performance. The original reamer was designed to properly accommodate Sierra's 69-grain MatchKing. This 22/40 chambering safely launches that bullet at >3600 fps, it also safely launches the 40-grain Nosler BT at >4600 fps, both with benchrest accuracy! When necessary, we can design optimized chambers for use with longer or shorter bullets. However, only authorized SMc reamer manufacturers can legally make SMc reamers.

As a safety consideration, we strongly urge SMc cartridge handloaders NEVER to concoct any combination where correct powder charge (amount needed to generate normal pressures) fills less than about 95% of available powder space. Secondary explosions have been observed with reduced charges in some cartridges and theSMc design might exacerbate this potential.

As noted, significant interference fit between case neck and bullet is often helpful. For the following calibers, expander ball diameter should be approximately: 22 » 0.2215", 24 » 0.2403", 25 » 0.2541", 26 » 0.2611", 28 » 0.2808". High neck tension is important to prevent bullet movement during handling, or from recoil, or in response to primer blast; this aspect is particularly critical when using "friction-proofed" bullets.

Basic SMc™ Cartridge Principles

SMc™ Cartridge designation specifies caliber and usable capacity; for example, 6.5/60 SMc indicates a 26-caliber (6.5mm) cartridge holding 60 grains of water (to base of case neck) – similar in usable capacity to 6.5-284 Norma but with superior performance, 7/75 SMc indicates a 28-caliber (7mm) cartridge with a usable capacity of 75 grains of water, etc.

Choose propellants so that correct charge fills available powder space or is somewhat compressed

To date, we have demonstrated highest velocities using ball-type propellants

Use relatively high neck tension, as necessary to create good bullet pull

Primer choice may significantly alter velocity, pressure, and accuracy potential

Because SMc cartridges work best when bullet base and base of case neck are approximately aligned, optimum reamer (chamber throat length) design may depend upon bullet length:

Generally, use of shorter bullets results in minimal loss of accuracy or ballistic potential
Conversely, the necessary deeper seating of heavier (longer) bullets in a chamber designed for lighter (shorter) bullets can significantly compromise performance

Suggested Primer Types

Charge

Powder Type

(grains)

Extruded

Ball

<30

RWS/CCI-BR

CCI-BR

30-45

CCI-BR

Fed Match

45-60

Fed Match

Fed Magnum

60-90

Fed Magnum

Win WLRM

>90

Win WLRM

We Hope you enjoy your SMc cartridge experience,

Byrom Smalley & Mic McPherson

Suggested Primer Types
Charge	Powder Type
(grains)	Extruded	Ball
<30	RWS/CCI-BR	CCI-BR
30-45	CCI-BR	Fed Match
45-60	Fed Match	Fed Magnum
60-90	Fed Magnum	Win WLRM
>90	Win WLRM	Win WLRM