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ISSI's Prototype Special Purpose Carbine / Rifle Concept
By Sgt. Steve Baughman

Whatever definition comes to mind when referring to the Special Purpose Rifle (SPR) and Special Purpose Carbine (SPC) concepts for AR-15/M16 platforms, rest assured variations of both will be forthcoming as the market seems to dictate “more is better.” Innovation is a good thing. It keeps our industry healthy. The variations and adaptability of the platform continue to evolve. An innovative SPC concept grew out of the varmint hunting product line from Insight Shooting Systems, Inc. (ISSI). ISSI has gained quite a following in the target and varmint shooting community by producing rifles capable of long-term repeatable accuracy and excellent reliability. Depending upon your definition of “varmint,” ISSI is now progressing into the mode of providing platforms that might fall under the defined role/need of the SPR and SPC.

ISSI is owned and operated by Lee Mosher and his son Damion. Both are Marines, and they understand and appreciate the wide variety of applications and needs of the hunting, police, and military community with regards to accurate small arms. Their rifles are tailored with various options depending upon customer request and are quite capable of better than, or equal to, consistent 5-shot 1/2 MOA at 100 yards. Several of their models are guaranteed to perform at that level. They are also keenly aware that distance always separates barrels when it comes to accuracy, so they usually suggest a stainless Lawrence, Douglas, or Hart barrel as the core of their SPC systems. Consistent accuracy over the long term is their goal as a gun manufacturer, with built-in attention to detail and quality.

In a previous test of one of ISSI’s uppers in caliber .20 Tactical, it was found to be exceptionally accurate. During that test, Mr. Mosher communicated his ideas for applying his designs to the SPR/SPC concept, and its potential adaptability for various uses. The first SPC model was put together from parts lying around the shop. Initially, Lee did not want to send his prototype model for testing as he did not consider the unit capable of meeting his minimum accuracy requirements. The unit was averaging around 1.25-inch groups at 100 yards during initial break-in. He relented with the assurance that a variety of Black Hills ammunition would be used to see if the gun would find a load that it liked. In reality though, any rifle defined as “mediocre” by his standards would probably equate to a thoroughly “acceptable” unit as defined by most people.

An Unconventional Design

The ISSI Model SPC concept comes forth based on the need for a rifle/carbine that provides accurate delivery of 5.56 at its core with a more effective range than an M4 Carbine, but in a shorter compact package than a standard issue M16. Its foundation is a free-floating 18-inch Douglas, Lawrence, or Hart barrel that can be optimized with button-rifled or cut rifling for adapting to a variety of loads. If requested, the muzzle is threaded with a standard 1/2-28 TPI cut, which adapts to a suppressor or any standard brake system. The handguards are a unique design, but currently have no rail system for accessories. The unit is primarily built around the use of quality optics. Basic rifle simplicity is apparent, yet it is of a different design from the norm.

The ISSI SPC upper uses a massive sized barrel nut that pulls the barrel, receiver, and scope mount rail all together before being bolted at five locations - essentially becoming one solid unit. According to Lee, the beefy components help dampen the bolt when it goes into battery while also supporting the barrel a full 1 inch in front of the base of the nut. The scope rail connects to both the receiver and to the barrel nut at the forward end of the receiver. It also connects via bolt at the rear of the upper to make for a very solid and stable platform.

One would assume it holds the assembly significantly more rigid than a conventional design. When one thinks about the high stress and wear points on the AR-15/M16 system, most would agree that the chamber area where the barrel and upper receiver mate are taking a significant amount of the pounding during firing. Over many rounds fired, heat-up and cool-down cycles, and general wear and tear from shooting, the gun basically does its own stress relieving of the structure. The theory behind ISSI’s concept is that this pounding eventually affects accuracy and changes point of impact over time. Typically, that is no big deal, as most of us know some routine maintenance is needed to keep things consistant with most rifles. ISSI’s theory is to provide a rifle system that maintains its accuracy and point of impact over the long haul, and be ready to deliver said accuracy at a moments notice, year in and year out. ISSI has an established customer base that provides feedback in these areas, and the feedback to date is running in the positive direction.


ISSI manufactures five of their proprietary AR rifle component parts in-house. As mentioned above, their handguards are different and utilize a polyurethane coated outer-liner fitting over a stainless steel tube allowing the shooter to get a good grip on the rifle. Barrel selections can include either cut or button-rifling options. ISSI can recommend which barrel would be appropriate for any particular application and bullet selection. Distance always shows the distinction between a good barrel and a great barrel, and ISSI’s test range is on the premises and can help them differentiate their criteria between good and bad. The unit sent for testing sported a standard Douglas barrel with a 1x9 twist with a gas block made in-house. After barrel fitting to the upper receiver, feed ramps are polished and opened up slightly to improve feeding reliability. The inside of the barrel lugs are deburred on the backside to help keep the brass from being nicked during extraction. According to ISSI, this helps keep the feeding and extraction cycle working smoothly, and keeps the brass from getting scratches/cuts during the firing process for those who might be inclined to reload.

Gearing up

The Leupold Mark 4 Mid-Range/Tactical (MR/T) 3-9x36mm scope was chosen for this platform. It came with an illuminated duplex reticle, and seemed to fit this rifle very well. The MR/T series scopes are built on a 30mm tube milled from 6061-T6 aluminum. These scopes come with what the manufacturer labels M1 or M3 adjustment turrets. Our unit had M1s and are target/competition style with 1/4 MOA adjustments. The M3 version is designed primarily for LE or military users, is shorter than their M1 counterparts, and feature 1/2 MOA adjustments on windage and 1 MOA on elevation. The M3 turrets are also marked with numbers and can be used to adjust for bullet drop compensation for long range shooting. The illuminated duplex reticle worked well for our use and provides 12 positions of varying brightness of the cross hairs. The illuminated MR/T models use the same battery as the Aimpoint red-dot sight. Its compact size and low weight made the ISSI SPC feel a bit more compact in height than most scoped ARs. As is typical with Leupold, their optics quality is excellent and the MR/T worked well out to the 300 yard distances engaged.

Black Hills .223/5.56 ammunition was used due to their continued ability and reputation to produce highly accurate ammunition that works well across a wide spectrum of firearms. Jeff and Kristi Hoffman stake their reputation on every round the company produces, and they continue to make some of the best factory ammo available. It is obviously a challenge for them (or any manufacturer) to produce ammunition that shoot great in every firearm, so 14 different Black Hills loads were used to be tested with the SPC. These started out on the light end at 40gr, and included 50, 52, 55, 60, 68, 69, 73, and topped out at 75gr bullets. This strategy for testing has been used for many years and generally, one or two loads shoot extremely well in any particular firearm. This turned out to be true with the SPC as we found two loads that helped extract better accuracy out of the gun than ISSI anticipated. A few rounds of the new Winchester Q3283 with its 62gr Partition bullet were also used. The Q3283 was recently selected as the standard .223 duty round for all Federal Law Enforcement and the Dept. of Homeland Security.

Using five 5-shot groups at a minimum to report averages, all the rounds fired through the ISSI SPC were shot using the Harris bipod attached to the rifle. That particular configuration helps to produce realistic accuracy reporting when listing 5-shot group averages. The ISSI SPC produced entirely acceptable, and more importantly, repeatable accuracy with 60gr VMAX and 73gr HP Match loads. The 73gr. load is the same one the USMC Rifle Team uses and they tend to shoot very well across a wide spectrum of firearms.

Shots Fired

The SPC went through a fair amount of “wring out” at the square range, and we included some full-auto shooting from prone and during CQB drills. During that time, approximately 3,000 rounds were used. The SPC was mounted on a PWA lower. When engaging in the full-auto mode, the SPC unit was mounted to an NFA registered Bushmaster lower. No jams or misfires of any kind were noted during testing. The Triple-X suppressor made by American Manufacturing was used to cut down on noise levels and to see if it would affect barrel harmonics or perhaps improve (or decrease) accuracy. It added a fair amount of weight to the unit, but the added weight helped dampen any recoil or muzzle jump. Bullet impacts on the targets were easy to keep within scope view thanks to the extra weight. With the scope set to 3x power, several hundred rounds were fired in full-auto bursts from the prone position at targets 100 yards away with surprising controllability.

The plan was to feed the rifle copious amounts of a variety of ammunition to assist in determining/evaluating the basics of reliability, accuracy, and repeatability. The shooting volume and pace also provided the opportunity to evaluate how the unit dealt with temperature cycles. Although the barrel got quite hot, the handguards stayed relatively cool. As the smoke cleared, it became easier to see that a couple of loads generally produced a running average that was repeatable across the spectrum of conditions. A complete performance chart is included in this article.

Overall performance continued to be good and shooting impressions are as follows:
  • The SPC maintained good base-line accuracy very well after 3,000 rounds even when it got hot from rapid firing during long shooting sessions.
  • The general trend was that the unit delivered consistent groups, even with a dirty and fouled barrel.
  • The recoil impulse of the SPC is smooth, and makes it easier to shoot more rounds without fatigue. It also makes it easier for the operator to see the bullet strike the target through the scope.
  • Those experienced riflemen needing to “reach out there” to maximum effective ranges should be pleased with accuracy within the confines of the 5.56 cartridge limitations.
  • The innovative scope rail system helps mount scope to gun without need for risers, and provides comfortable shooter positioning for proper eye relief.

Improvements? It is suggested that the following be offered as options or otherwise as noted:
  • Offer scope-mount platform option for MIL-STD 1913 rail system to complement “as-delivered” weaver-style mount system.
  • Offer additional rail system/attach points on handguards for use with widely accepted array of accessories, optics, etc.


There is much to like about this rifle concept. It is definitely unique, and this vision of one man’s definition of the SPC gets back to the basics of what a rifle is - that being well built, simple, rugged, accurate, and dependable. In weapon manufacturing, new and different concepts come and go all the time. It is an evolving process. New approaches either are accepted and take hold, or fade away over time. The varmint hunting community appreciates what ISSI is doing and time will tell if their concepts take hold in other arenas of Law Enforcement and the Military. This SPC configuration was not a disappointment in any category considered important.

Reference & Contact Information:

Insight Shooting Systems, Inc.
Mr. Lee Mosher
P.O. Box 3523
Pueblo, Co 81005

Leupold & Stevens, Inc.
P.O. Box 688
Beaverton, OR 97075-0688

Black Hills Ammunition
PO Box 3090
Rapid City, SD 57709-3090

Winchester LE Ammunition
East Alton, IL 62024

American Manufacturing
Wentzville, Missouri


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