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A new company, an old concept: if you've been at it for more than 30 years, you may recall this mild and useful wildcat, popular in the 1970s. Now it's back: does it still offer anything?

Alternate calibers for the AR-15 like the 6.5 Grendel or 6.8x43 SPC have gotten lots of attention in the past few years. But the search for a harder-hitting AR goes back more than 30 years.


There is a cartridge that offers some of the advantages of the 6.5/6.8 without sharing their disadvantages, the 6x45mm. It has been around for decades as a wildcat round. It was only recently legitimized as a commercial offering by Cor-Bon. While there was little fanfare when Cor-Bon introduced commercial 6x45mm ammunition, there was a big splash at the 2010 SHOT Show regarding this caliber.


Both Les Baer and Spirit Gun Manufacturing introduced 6x45mm ARs and Black Hills Ammunition announced it would be producing ammunition. So the question is what does this "new" 6mm have to offer? To find out, I had Spirit Gun Manufacturing send me one of their economical 6x45mm carbines to test.


The 6x45mm actually dates all the way back to 1965. Shortly after Remington introduced the .223 Rem. on the commercial market, a number of handloaders began to base wildcats on it for use in bench-rest competition. The 6x45mm was created by simply necking the cartridge up to accept .243" projectiles.


It should be remembered that at the time, handloaders couldn't choose from the wide variety of .224" projectiles available today, especially the heavy ones.


So necking the case up to 6mm allowed handloaders to take advantage of heavier and more efficient projectiles. The new 6mm wildcat proved to be extremely accurate and offered reduced wind drift over its parent cartridge. It also offered improved terminal performance.

Regarding accuracy, Jim Stekl, manager of Remington's custom shop at the time, used it to post a .3069"aggregate record in IBS 200 yard Sporter in 1973. It also found some followers among NRA National Match competitors. However it eventually fell by the wayside among competition shooters.

It was replaced in bench-rest competition by superior designs, like the .22 PPC (Palmisano & Pindel Cartridge) introduced in 1974 and the hugely successful 6mm PPC introduced in 1975. In National Match competition, the 6x45mm couldn't run with the .308 Win. in the wind past 300 yards.

Although the 6x45mm fell out of favor with competition shooters, it remained quite popular with varmint hunters for decades. There's good reason for this, as it is well suited to this application.

The small case dimensions meant it could be easily chambered in a very light and handy bolt-action rifle, like the small Zastava Mausers. It's interesting to note that it became quite popular in South Africa. It proved to be useful on game animals such as impala and blesbok.

Here in the USA, many AR enthusiasts took a shine to it as a simple way to increase performance. By switching to a .243 projectile, a varmint hunter could choose a heavier projectile with a higher ballistic coefficient and increased sectional density. The .243 projectiles were also intended for taking heavier game and there was a wider variety available.

One of the attractions of the caliber was the simplicity in the conversion. To convert an AR from 5.56x45mm to 6x45mm only required a barrel swap. Both the original bolt and magazine could be retained. Due to this it was both economical and easy to do for your average shooter.


Another huge advantage of this wildcat was the wide availability of cartridge cases. Up until the recent panic buying, .223 Rem. commercial cases and fired military 5.56x45mm cases have been readily available in huge quantities at very attractive prices.


Just as importantly the conversion from .223 Rem. to 6x45mm was very simple. You merely bumped the neck diameter up to accept a .243" projectile and loaded normally. Performance on game such as pigs and coyotes is quite good. In addition, while some states do not allow hunters to take deer with a .223 Rem., the 6x45mm was good to go. With proper bullet selection and careful shot placement, it was well up to this task.


I can remember one of my shooting buddies, Don Graver, took an interest in the 6x45mm back in the 1980s. While he liked the AR-15, he felt the .223 Rem. cartridge with the bullets available at the time was a bit anemic for big Maine whitetail.

I never got sucked in by the cartridge but was impressed when I used it on a pig hunt a decade later. As good a cartridge as it is though, the 6x45mm slowly began to fade away. Why? Well over the years the .223 Rem/5.56x45mm has continually evolved. Projectiles intended for this cartridge have continually grown in weight from the original 55 grains up to 90 and even 100 grains.

More importantly projectile designs have improved greatly compared to 30-40 years ago. Today a reloader can choose from a bewildering array of .224 cal. projectiles designed for competition, varmints or even medium game. Many of these are also readily available in loaded ammunition for shooters who have yet to take up the black art of handloading.

While the 6x45mm faded away, it was not forgotten and remained a favorite of many hunters and shooters. Now Spirit Gun Manufacturing is offering a wide variety of rifles and one economical carbine upper receiver in this caliber. The one many will find the most attractive is their inexpensive A55 carbine upper. So that is what I selected to review.

The A55 is a no frills 16 inch flattop upper receiver. The barrel is manufactured by Green Mountain and is not chrome lined. Profile is similar to an HBAR and twist is 1:9. The receiver has an M4-type barrel extension and it's equipped with a standard front sight and M4-type handguards. Retail price of the upper is $469.

If you are looking for something a little fancier, Spirit Gun Manufacturing will also be offering a host of high-end rifles. These will be available with either chrome-lined or stainless steel match barrels, Vltor VIS upper receivers, BCM Gun Fighter charging handles and a host of goodies. Prices on complete rifles start at $2,000 and go up depending upon the model.

A question I'm sure many of you have at this point is, "Who is Spirit Gun Manufacturing?" Well, I didn't know either. Actually they are a division of Abrams Airborne which is an international aerospace manufacturer. Established in April 1965, it is a precision sheet metal and CNC manufacturer and fabricator of aerospace, military and commercial assemblies.

Some of their products orbit the Earth on communication satellites, International Space Station Alpha and the space shuttle. They also produce products for military and civilian aircraft, armored vehicles and naval ships. They even supplied parts for the Voyager 1 and 2 projects. As to be expected the company is ISO 9001:2000 and AS 9100:2004 Revision B certified.

What does an aerospace company have to do with firearms? Well, a while back Abrams Airborne acquired Vltor. Vltor, well know for their AR components, accessories and stocks, is actually the manufacturer of Spirit Gun Manufacturing's rifles and upper receivers. They are produced by Vltor, a sister division to SGM, in a state of the art aerospace facility.

SGM sent me out one of the A55 uppers mounted onto one of its own lowers. Out of the box the piece looked good. I noted the upper is marked '6X45 AMMUNITION ONLY' just above the ejection port. I also noticed it was fitted with an A1, rather than A2, flash suppressor.

The upper operated smoothly and everything was in order, so I got to work. Ammunition was at the top of my list. While Black Hills Ammunition has announced they will be introducing two 6x45mm loads, they were not available yet. However, they plan on loading Sierra's 100-grain GameKing along with an 85-grain HPBT

These will be available not only in their standard 50-round boxes but also in military packaging. This will consist of 870 rounds loaded onto stripper clips and packed into a .50 cal. ammo can. I was told that Black Hills' two loads will be priced about the same as its 77-grain .223 Rem. match loads.

As Black Hills Ammunition's loads were not yet available, Spirit Gun Manufacturing provided me with a few hundred rounds of handloads. Test ammunition consisted of three different loads running in weight from 62 to 100 grains.

The lightest was loaded with Barnes' 62-grain Varmint Grenade on top of a charge of TAC. The middle weight load consisted of Barnes' 80-grain TTSX loaded onto a charge of H335. The heavy load consisted of Sierra's 100-grain GameKing loaded onto a charge of H335. These three loads were merely to allow me to test the upper and get a feel for it.

During testing I was interested in checking six points. These were:

1. Intrinsic accuracy

2. Practical accuracy

3. Handling

4. Controllability

5. Flash signature

6. Reliability

To check the A55's intrinsic accuracy, I shot it off a bench rest. Test conditions were 39[degrees] F with a 5 mph wind coming from 7 o'clock. Four consecutive five-shot groups were fired at a distance of 100 yards with each load. Velocity readings were taken 12 feet from the muzzle with an Oehler 35P chronograph. To facilitate testing, I mounted a Carl Zeiss 6.5-20x50mm Conquest scope onto the A55 using an ADM Manufacturing QD mount. I then proceeded to fire groups with the magnification set at 20X.


Off the bench, the short 6x45mm carbine acquitted itself quite well. The 62-grain Barnes Varmint Grenade averaged a respectable 1.2 inches. Best five-shot group with this load was .9". Velocity averaged a rather sedate 2582 fps. Switching to the Barnes 80-grain TTSX upped velocity to an average of 2639 fps. This load averaged 1.3 inches.


Sierra's 100-grain GameKing averaged 1.2 inches, but group size was inconsistent. Two five-shot groups were very tight, while two were in the 1.6-inch range. Velocity of this load was also sedate at 2270 fps. The rifle proved very comfortable to shoot from the bench with very mild recoil. I did have one old Colt 20-round magazine that caused malfunctions, so I pulled it from use. After that, the carbine ran without issue. Ejection was sure and positive.


Moving from the bench, I proceeded to check the rifle's practical accuracy, handling, reliability and controllability during rapid fire. This was accomplished by running it through some drills engaging cardboard and steel silhouettes set at unknown distances from 25 to 500 yards.


For this portion of testing I popped the Carl Zeiss off and replaced it with an EOTech Extreme XPS 3-0. This new EOTech model is significantly more compact than their previous holographic sights. Gone is the dual battery compartment. This has been replaced by a single transverse mounted 123 battery with a simple O-ring sealed tethered cap.

The shorter optic also takes up less rail space than previous models and the battery compartment now can hover over an AR's delta ring. The tried and true circle reticle (65 moa in diameter with a 1 moa aiming dot in the center) remains.

The new EXPS 3-0 is only 3.75x2.4x2.4 inches and weighs in at 8.8 ounces. It's submersible to 33 feet and built to operate in conditions ranging from -40 to 150[degrees] F. One big change for this model is the relocation of the controls to the left side of the unit. This allows the controls to be reached even with a magnifier or night vision device mounted.

Ballistic adjustments are made on the right side with .5 moa clicks. Battery life is approximately 500-600 hours at brightness level 12. This model is also compatible with Gen I-III night vision with the push of a button. Mounting is by a well designed side-lever on the left side of the base. This is easily adjustable and features a lock-out to prevent accidental rotation of the locking lever.

Putting the 6x45mm to work revealed it to be fairly quick-handling but a mite muzzle heavy thanks to the barrel profile. This meant engaging multiple targets up-close was a snap. I had no problem hitting silhouettes out to 300 yards from a low sitting position with it. All it takes is proper trigger control. Knocking them flat was relatively easy from the prone resting on the magazine.

Stretching out to 500 yards was quite a bit more difficult, just seeing a LaRue at 500 yards is getting tough, but with a bit of hold-off for drop and wind, I was able to make quite a few hits even with just the EOTech mounted. Now, to be frank, a carbine of this type in the hands of LE and lawfully armed citizens is not likely to be used past 100 yards. Inside 25 yards is probably more realistic. At this distance you can write your name with it, so practical accuracy is more than acceptable.

The 6x45mm's controllability in rapid fire was also quite good. My benchmark of comparison here is a 5.45x39mm AK-74 that kicks sand in the face of just about everything. While, as to be expected, the 6x45mm SGM jumped around more, control was still quite good. Recoil, even with 100-grain loads, is much closer to a 5.56x45mm than a 6.5mm Grendel or 6.8x43mm SPC from a similar weight AR.

Lastly, testing was performed in almost complete dark ness to check flash signature. Visible flash was checked from behind the carbine, 90[degrees] to the muzzle and 10 O'clock from the muzzle (using a remote camcorder). The old school Al performed fairly well during this portion of testing. While there are better designs available, the Al is still capable of getting the job done.

All in all Spirit Gun Manufacturing's 6x45mm AR performed well. It's attractive, well made and accurate. With a retail price of just $469 for the upper receiver, it's also priced right. Anyone with a 5.56x45mm AR can buy one of these uppers and easily swap it onto their existing lower. No new magazines are required; you simply have to feed it the correct ammunition. It's a very easy way to step up in performance.

EOTech's EXPS 3-0 also offers a step up in performance over its previous holographic sights. It's substantially smaller, yet still offers excellent performance. I really like the looks of this new sight. I also really like the new side-lever. It's a very streamlined design which is simple to use. Plus this new model only requires one, rather than two batteries. The downside is that it weighs in at more than half a pound, and battery life still cannot compete with Aimpoint. All in all, though, this is a good combat sight. Suggested retail is $609.

Does the 6x45mm offer enough of a step up in performance? That is a question only you can answer. It's not in the same class as the 6.5mm Grendel or 6.8x43mm SPC, both of which offer a significant step up in performance over anything the 5.56x45mm or 6x45mm can do.

Preproduction specs for Black Hills' two loads, though, do look good. As I write this the manufacturer is claiming to run an 85-grain HPBT at 2850 fps and a 100-grain GameKing at 2700 fps. Velocity figures for both loads are from a 20-inch barrel. So things might get interesting if they can actually pull that off.

Is the 6x45mm right for you? Maybe, maybe not. Keep in mind that while factory ammunition will be available, it will not be cheap. Or at least not yet. How ever, it's an easy round to handload. It just depends on how much of an increase in performance you are looking for. It will be interesting to see what Spirit Gun Manu facturing comes up with next, and how factory 6x45mm ammunition evolves.
Accuracy and Velocity:

Spirit Gun Manufacturing 6x45mm A55

Load                                      Velocity (fps)  100 yards

Handload 62-grain Barnes Varmint Grenade       2582          1.2

Handload 80-grain Barnes TTSX                  2639          1.3

Handload 100-grain Sierra GameKing             2270          1.2

Groups are an average of four 5-shot groups fired from the bench at 100
yards. Velocity readings were recorded 12 feet from the muzzle at an
ambient temperature of 39[degrees] F1,030 feet above Sea Level with an
Oehler 35P chronograph.


Spirit Gun Manufacturing

561-623-5980 |

Barnes Bullets

435-856-1000 |

Black Hills Ammunition

805-348-5150 |

Carl Zeiss

800-441-3005 |


800-626-7266 |


734-741-8868 |

Sierra Bullets

800-223-8799 |
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Title Annotation:The 6x45mm AR
Author:Fortier, David M.
Publication:Shotgun News
Geographic Code:1USA
Date:Apr 20, 2010
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