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Jesse's Hunting > Gun Room Articles > Gun Room Archives > Making a Dream Come True - the 5mm Centerfire Conversion
Making a Dream Come True - the 5mm Centerfire Conversion
Andy Moe - JHO ProStaff
- Southern CA
August 28, 2004
The Old and the New
The author's dreams of having his own 5mm stretch back to the days of his childhood. |
At $73 a copy they were pretty pricey but I figured I could make enough doing odd jobs to pay for it. My Dad felt otherwise. He didn't see any benefit to owning a rimfire other than a 22LR and let me know that even if I had money-in-hand he wouldn't sign for it. I was in misery.
Making matters worse was the fact that a neighbor, Billy Cutter, managed to get one that very summer. I went out with Billy on a few outings, all of which ended up being an afternoon spent watching him shoot from ranges far too great for my 22LR. About the time I was setting up my crawl to get within range, he was shooting. The very first chuck I saw taken with the 5mm was at about 135 yards. I couldn't believe he was going to risk a shot that far on such a fat old chuck but he obviously knew the new 5mm round better than I did. At the shot the chuck rolled -belly up and dead. I was agog. I excused myself to go home for conjured-up chores, wanting to wrap my old Winchester M68 single-shot around a big hickory tree.
I was miserable for a goodly part of that summer but discovered girls at the beginning of the next school year and found new objects of attention. The 5mm ache returned every so often but became less and less as time went on. Soon afterwards those fine Remington rifles were gone and somehow my father's reluctance to allow me my own 5mm Magnum seemed justified. The pang to own one never quite left, though. I was even a little sad in 1984 when I learned that 5mm ammo production had quietly ceased.
Three decades later, the Summer of Billy Cutter had become dull memory. At least it was until the morning I found myself browsing a gun shop website and their listings of used firearms. There, amongst the usual gun shop flotsam and jetsam was a listing for a Model 592M in "5mm Craig", with the description "rimfire converted to centerfire". The price tag was $165 complete with a Weaver 3x9 scope. Oh man! That old 5mm pang suddenly began to throb like a bad tooth! I called the shop without a minute's hesitation. They had no dies or brass to go with the rifle (rats!) but they confirmed that the rifle was simply the original 5mm Remington Rimfire Magnum converted to centerfire. They also had the address of Certech International, the company who did the conversion and assured me that they sold dies and brass -and would even supply reloading data. I'm sure that for a brief instant, Dad was frowning down from that Great Trout Stream above as I made all the financial arrangements. Or maybe he smiled? I finally had my 5MM Remington.
Distinctive 5mm Mag Grip Cap
Persistence pays. The author's 5mm Mag is finally in hand. |
I got in touch with Mike Craig from Certech International while waiting for the 5mm's paperwork to settle. Mike is generally credited with the development of the conversion of these rifles to centerfire, and has generated most of the loading data available for this little wildcat cartridge. Mike was amiable and willing to talk about his product to the uninformed-but-enthusiastic (me, on both counts) and we exchanged many e-mails… one of which included my order for a set of RCBS "5mm Craig" dies, 100 pieces of brass, and a few bags of Certech 5mm bullets in both 36 and 30 grains. His website had loading data and I was really looking forward to getting started with my own 5mm. Mike’s data showed that the centerfire conversion of this cartridge equaled the performance of the original rimfire round. I couldn't ask for much more than that.
For those of you too young to be familiar with this cartridge I'd like to give a brief overview of its capabilities. This 5mm was a radical rimfire round in 1970. Where the current darling of the rimfire market, the 17HMR, develops a mere 26,000psi of chamber pressure, the 5mm Remington developed a whopping 37,000psi with "maximum allowable individual pressure" of 42,900psi. SAAMI maximum proof pressure recommendations were for an action that would contain a pressure of 62,000psi… not the fodder for your average 22LR or 22 Magnum sized action!
The original ballistics had a .2045" diameter, 38 grain hollow point bullet at 2100 feet per second. That might seem anemic by today's standards but it's still a giant (though perhaps posthumously) in the realm of rimfire cartridges. With that 38-grain bullet the 5mm delivered 371 ft/lbs of muzzle energy. Compare this to the 30-grain Federal 22 WMR at 2230 feet per second generating 330 ft/lbs ME; and the 17 HMR, which puts out 254 ft/lbs of energy with its 17-grain bullet at 2600 ft/sec. In a side-by-side comparison it would still rate as rimfire's top, heavy hitter.
It also shot flat: When sighted in at 100 yards the 5mm's 38-grain "Core-Lokt" HP dropped only 4.3" at 150 yards and arrived with 165 ft/lbs of retained energy. That explains Billy's 150-yard chucks! He simply held a couple inches over a sunning chuck and squeezed off, letting trajectory and ballistic coefficient drop that bullet into the chuck's brisket! So much for Billy’s self proclaimed shooting ability.
Ok. So now I'm presented with the prospect of duplicating that fine performance I envied so greenly in my youth. The loading data for the 5mm Craig was limited to a few powders. Alliant 2400, IMR 4227, and Accurate #9. In all the loading data it was recommended that the loader work up in 1/10-grain increments. With a cartridge that only measures a quarter inch across and just a little over an inch long, the advice is well taken. I stocked up on CCI 450 small rifle magnum primers but held off on the powders. I had other plans. For some time I'd been hearing about the fine performance of Hodgdon's "Lil Gun" powder in sub caliber miniature cases. I thought perhaps I could work up loads for this powder and make use of its well-documented reputation for delivering high velocity with low pressures. As it turned out, Lil Gun worked so well that I never used another powder.
On the very day the brass and dies arrived from Certech, there came a package from a fellow 5mm Craig fanatic in PA with 25 cases that had been made from 22 Hornet brass by Schroeder Bullets in San Diego, CA. The gentleman enclosed a note that suggested I try this brass as it had a greater case capacity than the lathe-turned Certech brass and, being reformed drawn cartridge brass, would tolerate resizing better than the half-hard brass Certech used in production of their cartridge. I opted to try these donated casings instead of the Certech casings for my initial loads and I sized and trimmed that brass in preparation for the arrival of the rifle.
It took a while but my decades-awaited 592M arrived finally. The 592M is the tube feed model of the 5mm Remington series. The 591M is fed from a detachable magazine. The rifle was in excellent condition and was topped with an early 70's vintage Weaver V-9 with an adjustable objective and a fine reticule. Retailing for $74 in 1971 this scope not only cost more than the rifle it was mounted on, but it could well have been on the rifle since it was purchased. I was pleased!
Bolt Head Conversions
The ingenious conversion from rimfire to centerfire is visible in the boltheads. |
The bore was like new, as was the throat. Using both the 36 grain SP and the 30 grain HP I was able to determine that I would be able to seat the bullets just off the rifling while still maintaining an OAL short enough to feed through the tubular magazine. These bullets were designed for the 5mm Craig, that's for sure. A box of 5mm, Hornady 33 grain V-Max - the only commonly available .2045" diameter bullets on the market - somehow found it's way to my house while I was waiting for the rifle to arrive. The allowable OAL for the V-Max round showed that it would be a single-feed proposition.
I had nothing to go on when it came to finding a starting load for the 5mm Craig using "Lil Gun", but by comparing case capacities of the 22 Hornet and the 5mm Craig, and extrapolating the data for Lil Gun Hornet loads to the 5mm Craig, I came up with a starting load of 5.1 grains of Lil Gun that should work for all bullet weights. (You always have to do a lot of head scratching when you start out loading a powder for which there is no data. I wore a bald spot pondering case capacities and burning rates. It isn't something that I'd recommend to anyone without a wee-bit of reloading experience.)
As it turned out, that 5.1-grain load was fine. In fact, with the 36 grain Certech bullet I eclipsed original 5mm Remington Rimfire Magnum velocities, turning out velocities of 2340 ft/sec. over my old Tepeco Time Meter Chronograph. I was pleased as pleased could be. That equates to 451 ft/lbs of muzzle energy! When I put the load on paper I was in heaven. My fifty-yard groups were ragged holes. Oh! To be living in woodchuck country again! With no worthy game on the horizon I decided to see how far I could get, velocity-wise, and still maintain safe pressure signs. After nine loadings I wore out those free casings, increasing the load by one-tenth of a grain at each outing. I finally quit at 6.3 grains and a MV of around 2500 ft/second hauling 498 ft/lbs ME. The primers still had rounded edges and the bolt lift was smooth and easy.
The 30-grain Certech were loaded on fresh brass purchased from Mr. Schroeder in San Diego. Using the same careful loading techniques -weighing each individual powder charge- I worked up a load of 6.8 grains of "Lil Gun" for a velocity of 2588 ft/sec and 455 ft/lbs ME. This load was flat shooting and accurate. The smallest 100 yard group I've ever fired -for more than 5 shots- was fired with this load. I fired 8 shots fed from the magazine that went into a buttonhole. The smallest three shot group I've fired was with this bullet and load combo as well.
The 33-grain Hornady V-Max bullets proved to be extremely accurate as well. They are so accurate that I once took Second Place in a Postal BR match coming in behind a 17 Remington SAKO heavy Varmint in the Production Class. Loaded with 6.2 grains of Lil Gun my 592M gets 2490 ft/sec and averages .6 moa for 5 shots. While the 5mm Craig cases loaded with the Hornady V-Max bullets are too long to feed through the magazine it has never posed a problem. They are easily loaded single shot. Besides; a ground squirrel hit with the 5mm Remington / Craig would never require a quick follow-up shot.
The brass life has been good. I have kept accurate records of my loadings and the last batch of Schroeder brass lasted 10 loads before I noted a case mouth crack. Annealing might have lengthened the brass life. Trimming between loads is a must and requires you to find a trimmer pilot for your favorite trimmer. I made one but you could easily spin a 22-caliber pilot in a drill and stone or file it to the proper diameter. A funnel for a 17 caliber is a must for dispensing powder. The cartridge is tiny and requires care in sizing and seating bullets. Otherwise, it’s a straightforward reloading job; no different than any other bottle necked cartridge. Somehow though, the results make the process just a little more pleasurable. 
100 Yard Group
The proof is in the pudding, and with 100 yard groups like this one (three shots), the 5mm CF has nothing left to prove. |
So what has this trip down Memory Lane shown me? Not much about the original 5mm rimfire magnum. Sure, the rifle is the same, but the centerfire conversion’s performance is far beyond what 1970 technology could produce. Still, there was a little latent 14 year-old satisfaction derived from shooting this 5mm. I was happy to see that years of shooting hadn't made me so analytical as to prevent me from reliving some of the wonder that racy little bottlenecked 20-caliber generated in me 30-odd years ago. Nostalgia aside? The 5mm Craig can stand on its own two legs; especially where a 22 Magnum is too little gun and a 22 Hornet is too much. It's a great little close range varmint cartridge.
Certech sold its 5mm conversion operation to Eagleview Research Center in January of this year. They still provide the same fine service that Certech provided. Schroeder Bullets also offers a conversion in the form of a replacement bolt head and firing pin. Conversion, dies, 50 pieces of brass will run you in the neighborhood of $240 from either outfit. If you have a 591M or 592M gathering dust, think about having a center-fire conversion done. Reviving the cartridge in the form of the 5mm Craig is a great way to get a taste of what was certainly the “King of Rimfires”.
Suppliers of Conversions and Components:
Eagle View Research Center
130 SE Kodiak Ridge Drive
Shelton, Washington 98584
Telephone (360) 432-2339
Fax (360) 432-0094
Schroeder Bullets
1421 Thermal Ave.
San Diego, California 92154
Telephone (619)423-3523 / -8124
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