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Although first thought of by Colt way back in the 1930s, the .22 Conversion Unit usually consisted of a slide, barrel, lightweight recoil spring and magazine that allows one to convert a .45 (or .38 Super or 9mm) Government Model pistol (and all or most of its variations) into a rimfire arm,  and didn’t really come into its own until the early 1970s when Jonathan Arthur Ciener began marketing his very successful series of conversion units.

Since that time, others like Wilson Com-bat, Kimber, Jarvis, Advantage Arms, and Marvel Precis-ion have re-leased their own vari-ations on this theme. Through the products offered by these companies we are now able to convert such pistols as the Glock, Brown-ing Hi-Power, Beretta 92/96, Taurus PT 92/99 series and most 1911 models from their original chamberings to .22 rimfire (and back again) in a matter of seconds.

I’ve been fortunate enough to be able to test several of the available 1911 units over the last few years and have found them all to be reliable and relatively accurate. Each different unit, regardless of manufacture, seems to offer something just a little different from the other so one has a choice of steel or aluminum slides, fixed or adjustable sights, with either polymer or steel magazines.

I have found most of these conversion units to be capable of accuracy in the 1.5- to 2.5-inch range at 25 yards with ammo they favor. This is perfectly acceptable accuracy for practice and plinking and for the hunting of small game, provided it’s not too small, but there are times I crave more accuracy. I want a pistol or revolver that can consistently shoot better than I can. Enter my latest acquisition.

dscf2343Marvel Precision Unit 1
Back in the late 1990s, Bob Marvel and Lamonte Drees, both employees of Marvel Products at the time, developed a new and somewhat different .22 Conversion Unit that eventually became known as the Unit 1. What Marvel and Drees set out to do was develop a conversion unit that was not only convenient and reliable but extremely accurate as well. In this they succeeded.

The Marvel design differs from most other units in that it utilizes a barrel locking system that solidly locks its match-grade barrel to the frame via its adjustable recoil-rod tightening system. The barrel in this system neither moves nor pivots, nor does it depend on support at the muzzle from a moving slide and bushing. A removable sight rib is attached directly to the barrel so no play or movement between barrel and sights exists. The slide and top rib are machined out of aircraft-grade billet aluminum, while the barrel, slide lock and other required parts are fashioned from high-carbon steel.

One of these other parts is a hardened breech insert fit into the aluminum slide to facilitate steel-to-steel contact between breech and barrel to avoid any possible aluminum battering problems. All machining is done by CNC for a precise fit.

Marvel Products changed hands in 2002, was renamed Marvel Precision, and continues to offer not only the Unit 1 but a more conventional full aluminum-slide version called the Unit 2, as well. I first learned of the Marvel unit from Eddie Janis, single-action gunsmith and owner/ proprietor of Peacemaker Specialists.

Knowing Eddie’s penchant for accuracy, having shot with him and against him with the cowboy guns he’s famous for, when he recommended the Marvel unit for its accuracy I knew someday I’d have to have one. Well, someday finally arrived, as I recently contacted Marvel Precision and had them send me a Unit 1 complete with sights and an auxiliary rib for scope or red-dot sight mounting. I also requested that they send one of their new polymer magazines along with the metal magazine normally supplied.

It wasn’t long before UPS delivered a box to my door inside of which I found a neat, padded, zippered case designed to contain the Marvel Unit itself, a single magazine, a couple of wrenches and a pair of extra rib-mounting screws. Also inside this case was a test target showing that this particular unit had fired a five-shot group at 50 yards from a machine rest measuring a tidy 0.68 of an inch using CCI Standard Velocity ammo. Now, that’s what I’m talking about!

dscf2346A close look at the unit before mounting it up on a frame revealed it to be a handsome, well-finished package. Its aluminum slide has cocking serrations both front and rear and is finished in a pleasant-appearing matte black. It came wearing its sight-equipped rib, which held a fully adjustable BoMar-type rear assembly paired to a 0.125 of an inch wide front blade. A 0.270 of an inch wide raised, serrated rib runs the length of the slide between front and rear sights, and provides not only a pleasing profile but some relief from glare, as well. Its auxiliary rib is a Picatinny affair that allows several mounting positions using Picatinny- or Weaver-type rings.

The barrel of the Marvel Unit is of match-grade quality, has been carefully hand chambered with a .22 match reamer, and its front end wears a match-quality, recessed crown. Barrel length measures 5.5 inches as it extends half an inch in front of the end of its slide. I’m assuming that the barrel was left long to facilitate attachment of a compensator that Marvel also offers for this assembly. A special slide stop pin is included that works in conjunction with the adjustable recoil spring guide rod to lock the Marvel’s barrel to whatever frame it is mounted on. I could find no fault with the fit or finish of the Marvel Unit.

1911 Frame
To get the best results from the Marvel Unit, I decided to weigh the triggers from my best .45s and mount it on the frame from the one exhibiting the lightest, crispest pull. I have three custom Swenson .45s built in the 1970s and they all have nice, clean triggers measuring from 3 to 3.5 pounds. I also have a Colt Government Model that’s been dressed up, but its trigger didn’t break until the scale measured 4 pounds. The frame I eventually settled on was a stainless one made by Caspian that usually is paired up with a stainless slide from the same maker, forming what is one of my favorite 45s. It sports front strap checkering, a high-ride beavertail grip safety, and high-quality internals that mate to create a super-slick 2.25-pound trigger release. I guess it really didn’t matter what frame I selected because the Marvel Unit was designed to fit any and all of them.

dscf2314Although I would test the Marvel Unit using my Caspian frame, my plan was to eventually install it on the Colt frame, as it was the least used of my 45s. A better trigger job would be performed on the Colt frame before the Marvel Unit would ride there.

Installation
Following the directions in the Marvel brochure, I first removed the top end from the Caspian frame (after ensuring, of course, that it was unloaded) and then slid the Marvel Unit in place. It went right on without hesitation. I next installed the Marvel-supplied slide stop, being careful to make sure it captured the barrel. I then moved the slide out of battery about half an inch to the rear to give clear access to the specially configured end of the recoil spring guide rod and, using the special takedown tool, screwed the recoil rod firmly up against the slide-stop pin, thus drawing the Unit’s barrel down tightly onto the frame. A quick operation of the slide showed everything was in order. Also, as recommended, I applied a drop of gun oil to each rail before mounting the slide.

Since I was most interested in the accuracy of the Marvel Unit, I decided to go ahead and change from the adjustable sight rib to the optional scope-mount rib. Using the supplied hex-headed wrench, I removed the two screws holding on the open-sighted rib and installed the auxiliary rib in its place. The scope-mount rib uses three hex-headed screws to hold it on (the third located under where the front sight rides on the rib with the sights) and, following the recommendation in the Marvel brochure, I put a small amount of blue LocTite (#242) onto each screw before starting them in their respective holes.

The only unencumbered, long, eye-relief scope I had on hand was an older Burris 3x and, even though it was a tad longer glass than I’d like for this setup, I figured its power and clarity would help to get the most accuracy out of this combo. The scope-mount top rib is designed to accept Weaver-type rings, so I secured the Burris in place using a set of Millet Angle-Loc rings designed for this purpose. The Burris was long enough to cause some interference with access to the Caspian’s hammer, but the out-front grasping grooves on the Marvel Unit made operation of the slide relatively easy.

The Marvel Unit with the Burris atop took on a sort of celluloid assassin’s look, resembling armament that might have been seen in the movie Blade Runner or in an episode of Walker, Texas Ranger. Actually, the combination proved quite workable and the eye relief provided by the Burris scope was perfect for a two-handed Weaver hold. Neat. With the scope ring screws snugged up, I was ready for a trip to the range.

dscf2325Range Time
On my first trip to the range I put 275 rounds through the scoped Marvel Unit. Offerings from six different manufacturers in 14 different configurations were tried looking for the utmost in accuracy and reliability. All shooting was done off a sandbagged rest with my target, consisting of blaze orange 0.75 of an inch diameter dots affixed to the hostage side of an IPSC Silhouette target set 25 yards downrange.

The types of rimfire rounds tried ran the gamut from high-dollar, standard-velocity target stuff from Eley to some hyper-velocity screamers from Mexico’s Aguila line. Velocities ran from a sedate average of 922 feet per second (fps) to a speedy 1439 fps. Reliability was not 100 percent, but was ammo-specific in that it just didn’t like some of the rounds tried and worked with utter dependability with others put through it. Such is the nature of rimfire guns; they are sometimes finicky with what they like and what they will function with.

Of the 14 different configurations tried, the Marvel Unit balked with four of them. Three of them were low-velocity target rounds where slide impulse was low, and the fourth was a round with a heavy lube or coating on its bullet that inhibited reliable function. I found that if I fed the Marvel Unit rounds it liked, it not only functioned with exceptional reliability but produced nice, tight, little groupings as well.

How tight? Well, after everything was measured and averaged, groups out of the Marvel/Caspian combo ran from a small of 0.64 of an inch (averages now, remember) attained with CCI standard-velocity fodder to a large of 1.22 inches when utilizing the hyper-velocity stuff from Aguila. These Aguila rounds were traveling an average of 1439 fps from the 5.5-inch tube of the Marvel Unit and, although they produced the largest average groupings, still shot tight enough to make this an effective small game combo. I actually think this setup is much more accurate than what I’m reporting, as centering that pistol scope’s reticle on that small orange dot at 25 yards proved a challenge, so much so that I repeated this exercise with 2-inch dots just to see if overall accuracy improved. It did to a small degree.

Out of the 14 different .22 rimfire rounds I tried, 12 of them consistently produced groups under the 1-inch mark at 25 yards. I’m sure a machine rest would shrink these averages considerably, but I certainly couldn’t complain about the results I obtained from my sandbagged rest.

dscf2330Since it did some of its best work with CCI Pistol Match and Winchester’s Super X Solids, I decided to take these rounds, plus my favorite squirrel bullet, the Win-chester PowerPoint, out to 50 yards to see what we could do from this distance. For this exercise I switched to some “easier to aim at” 5.5-inch bull’s-eye targets.

Although I couldn’t replicate the magic under 1-inch five-shot group claimed by Marvel on demand, I did manage to produce an occasional target that bested this mark. With the CCI Pistol Match, groups average an awesome 0.96 of an inch. The Winchester Super X Solids managed groups averaging 1.19 inches, while my squirrel-busting PowerPoint routinely stayed under 1.25 inches. That, pardner, is exceptional accuracy from a handheld rimfire pistol. It’s a definite keeper.

Final Notes
Because this combo is so darn accurate it’s hard to find fault with it, but there were a couple of things, albeit minor, that I found to grouse about. All of the Conversion Units I’ve tested in the past fit every piece of leather I have for a Government-sized pistol. The Marvel Unit, with its adjustable sight rib installed, was just a tad oversized to fit any of my holsters without forcing it. They all could be made to fit with some re-forming, but didn’t from the get-go. Ditto with its half-inch longer barrel. I know it’s there to hang a compensator on but, frankly, I’d like my barrel to end at the end of its slide. That’s it.

The Unit 1 currently sells for $418, plus shipping with either the adjustable-sighted rib or the Picatinny Rail Scope Mount rib installed. A second rib in either configuration will cost you an extra $67, if purchased at the same time (slightly more if purchased later).

Get both ribs, trust me. Maybe better still, Marvel now offers a Picatinny Rail/Adjustable Sight Combo Rib incorporating both features. Either way, you’ll get an adjustable-sighted pistol to mirror your carry/competition piece and the ability to configure a scope-sighted handgun capable of taking the smallest of game at the greatest of distance. It’s definitely a combo more accurate than I am, and I like that!

Load Velocity ES 25 Yards 50 Yards
Aguila Super Maximum Hyper Velocity 1439 132.1 1.22 ——
CCI Pistol Match 922 42.7 0.70 0.96
CCI Standard Velocity 985 54.2 0.64 ——
CCI Velocitor 1151 207.4 1.07 ——
Eley Tenex 985 34.0 0.80 ——
Federal Gold Medal Match 944 48.4 0.88 ——
Federal Gold Medal Target 1041 49.0 0.80 ——
Federal Gold Medal UltraMatch 939 53.1 0.80 ——
Remington Target 1028 84.5 0.84 ——
Remington Thunderbolt 1040 43.7 0.90 ——
Remington Yellow Jacket 1270 102.7 0.93 ——
Winchester PowerPoints 1092 67.0 0.88 1.21
Winchester Super X Solids 1092 54.4 0.75 1.19
Winchester T22 Target 1006 41.8 0.91 ——

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