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The Centurion 5mm Remington Rimfire Magnum

"Do you know this cartridge?"

Such was the question that came up during a congenial dinner during the 2004 SHOT Show with our friends at Aguila Ammunition and Centurion Ordnance. Efrain Peralta, the Chief Engineer for Aguila Ammunition, then held out a note book to writer Tim Mancillas and I, depicting a perfectly hand drawn blueprint of the long discontinued 5mm Remington Rimfire Magnum cartridge. Tim and I both looked at each other and grinned. “Yes, we know this cartridge” I said. “We’re both 5mm shooters.” And so it began…

The rest of the evening was spent discussing manufacturing techniques and pressures, as well as the potential for the revival of this obsolete rimfire. By the time we called it a night the table was littered with cocktail napkins covered with drawings, performance figures and rough R&D investments. Carlos F. Romero, the CEO of Centurion Ordnance and Mike Realme, of Centurion’s Logistics Department went from intrigued by this round but some what skeptical of consumer demand. By the end of the evening, however, they were amazed that there were so many rifles out there that had no readily available supply of ammunition. Mr. Peralta thought it feasible from a design and production perspective so Tim and I were understandably enthusiastic. The prospect of reproducing the 5mm again was intriguing but no one was ready to make any promises just yet…

Chief Engineer, Centurion Ordnance, Efrain Peralta
(June 2007 prototype ammunition testing)

Originally produced for the Remington 591M and 592M rifles in 1970, the 5mm Remington Rimfire Magnum was a Remington Arms attempt to market a high velocity, high pressure rimfire hunting cartridge. This bottle-necked case was capped with a .2045” diameter 38 grain Core Lokt™ bullet that attained 2100 feet per second from the ultra strong 590 series rifles. The 22 Magnum of the day fired a 40 grain bullet at 1910 feet per second and the then-new 5mm round out stripped it for power and accuracy. To do this, however, the cartridge generated pressures nearly twice as high as the 22 Magnum and 22LR cartridges. It was a revolutionary rimfire cartridge but when Remington’s interests turned elsewhere in 1973 the production of rifles ceased with the ammo being dropped from their line-up eleven years later. This left an estimated 50,000 rifles (and nearly as many devout 5mm shooters) without ammunition. Five millimeter shooters have been searching out and hording this ammunition ever since.

Vintage Remington Model 591 with Centurion 5mmRRM
Initial field test of production ammunition, Swift 3-9x40mm scope

During subsequent meetings with our friends from Aguila and Centurion Ordnance, the 5mm topic was raised at regular intervals. It was while attending the 2005 SHOT Show that Carlos F. Romero, the CEO of Centurion Ordnance told us that they were seriously considering producing the 5mm cartridge on a trial run basis. He pointed out that Centurion Ordnance was getting more requests for the 5mm weekly and they seemed to be going up as the remaining supply of original 5mm ammunition dwindled. Centurion was not the only outfit that recognized the demand for this cartridge. It is interesting to note that while we were attending the PMC sponsored shooting event for the SHOT Show that year, a major distributor approached Carlos, and confronted him with rumors of the 5mm work. “Hey Carlos, I hear you guys are thinking about producing the Five mm.” The gentleman said. Carlos responded “Well, we have been considering it, but we have no plans right now.” The gentleman replied, “Carlos, if you do, we’ll take the first 2 million rounds. And I’m serious.” This was a major distributor that many readers are familiar with, so it left no doubt in Tim’s and my mind that he was dead serious. Carlos said that he would keep that in mind if anything ever came of it, and the gentleman left to attend other business matters at hand. The look Carlos gave us was priceless! One raised eyebrow, and a smile at the corner of his mouth. For Tim and I this was encouraging but there was still no concrete plan or time frame for production. We were filled with anticipation but again, we had to be patient. And so we were…

The 2006 SHOT Show rolled around, involving more discussion but again, no hard assurances. Tooling for a new cartridge was costly and time consuming. It would require careful consideration and the willingness to commit a portion of the production line to the research and development needed to produce a marketable cartridge. We were optimistic but, again, we needed to be patient…

Production Centurion 5mm RRM ammunition
Note: Expanded 30gr JSP rounds retrieved from sand dune at 155yd distance

Tim was abroad on business last year and missed our annual meeting at the SHOT show. The 2007 Show was held in Orlando, FL. and on the opening day I met with our friends from Helotes, TX and Cuernavaca, MX. As I got into the car in front of my hotel, Efrain leaned over and dropped a small bag into my hand. Inside was a single drawn brass casing and a pair of copper jacketed bullets. I just smiled, wishing Tim was here with me to see these offerings of hope for the 5mm fanatics that have been desperately holding on since production of 5mm Remington ammo ceased twenty three years earlier. I called Tim the first chance I got and told him the news. I remember Tim finishing the conversation by stating in his normal Marine bluntness, that the longest wait would be “from now until we see some finished cartridges in our hands…” As always, he was right.

Writer/Gunsmith and ammunition consultant Andrew Moe, June 2007 prototype ammunition site-in and testing

Writer/Editor and ammunition consultant, Tim Mancillas, June 2007 prototype site-in and testing

It was a June meeting in Montana that saw the first field testing of the prototype version of the Centurion 5mm Remington cartridge. Tim and I met with engineer Efrain Peralta and Mike Realme of Centurion Ordnance in the sweltering June heat amidst young prairiedogs and away from prying eyes. After our sight in session Tim & I headed out to the fields with Efrain and Mike in tow, watching as we killed 35 prairiedogs with a pair of vintage 592M Remington rifles in the space of just a couple of hours. With each kill, careful examinations of the entrance and exit wounds were made and photographs were taken. No matter what the distance and no matter what the shot angle, an animal hit with Centurion’s 5mm Remington Magnum never required a second shot. The farthest shot taken was 160 yards at an overly curious prairie dog who thought he was safe up on a hillside half hidden by his mound. When he stood up to get a better look at us the 30 grain, twenty-caliber bullet flipped him cleanly off of his hole and landed him a foot back into the surrounding sage. The shooting was great but it was especially pleasing because we were shooting the first produced 5mm Remington ammunition seen in nearly two and a half decades. And so we had to be patient again waiting for the production ammunition to be made. And we were…


Prairie dog results with prototype ammunition at 100yds in Montana, June 2007

Finally! Two weeks prior to the SHOT Show, I received a phone call from Carlos. He stated simply, “A package is on the way”. Imagine my excitement! Unfortunately, up in here in Montana we were heading into a severe winter storm. The temperatures and conditions were not what one would call “ideal” (to say the least!), with negative degree temperatures and blowing snow, I was a bit frustrated but decided to at least attempt some cursory testing in the field. Meanwhile, I took half of the ammunition and overnight’ed it to Tim. He still lives in southern California, and would have an easier time testing (at least that was what I thought!).

Montana test conditions (-9 degrees and snow), January 2008

As I headed out the door with the new ammunition, even the wind and snow could not dampen my excitement and anticipation. Though methodical and controlled tests were virtually out of the question, I wanted to see if perhaps a few uneducated rabbits were about (too ignorant to get out of the weather and impending storm), and so a few shots were taken, ranging from 50 to75 yards. The terminal performance was impressive, and an added benefit of a similar zero to that of the prototype ammunition aided in quickly producing results. At fairly close range, the 5mm was…well, as expected…explosive to say the least!

A few days later, (and in much warmer conditions I might add!) Tim was able to head out to an undisclosed location in the desert for some testing. We both had thought that he’d be able to conduct a more thorough test, but alas, he had a full week’s worth of rain and wind rolling in! Despite this, Tim attempted to conduct some velocity testing as well as accuracy testing (if the wind gods were willing). Tim had a Model 591M (magazine fed version) and confirmed that the cartridge does function well with the magazine. He also ran 25 rounds of the precious little production ammunition we had, across a chronograph. Surprisingly, in the mild temperatures of the southern California desert, he received an average velocity right around 2400fps! (2393fps to be exact) This was 100fps faster than touted in the press release that Carlos had been gracious enough to share with us in advance. Tim told me that he’d had a hard time conducting accuracy tests due to the gusting winds and a rickety table but managed some decent grouping in spite of that. He offered that testing at a formal range with solid benches would have been more a better way to document the accuracy. Also, he wondered how a current production firearm would perform, as the rifles we were using –though like new- were fairly dated with regards to manufacturing techniques. He stated that with a standard deviation of 18.49fps and extreme spread of 52.88fps the cartridge showed every sign of outstanding accuracy that a precision built rifle could take advantage of. We had both consciously chosen to leave our rifles unchanged or modified. No bedding, no free floating the barrels, no re-crowning or trigger jobs. We wanted an accurate comparison to the older (discontinued) ammunition and as such, did not modify the rifles in any way. Despite this, the new ammunition still performed every bit as well (accuracy-wise) and at lower pressures to boot. We both feel there is definitely room for increased performance in this cartridge despite it already being a marked improvement over the older ammunition. The production ammunition exceeded our expectations, and we feel that shooters will be very pleased by its performance. This initial run of ammunition started out as a way to fill a need for the existing rifles and shooters, but now, is heading down the path of really bringing something new and improved onto the market.

100yd group with Centurion 5mm RRM ammunition
Model 591, Swift 3-9x40mm AO
65 degrees, cloudy, 9-3 wind at 10-15mph, elev. at sea level (SoCal desert)

For those who held onto their Remington 5mm Rimfire rifles in hopes that someone, someday, would revive this fine cartridge, their prayers have been answered in the Centurion made 5mm Remington. For those of you who wished for a new generation of 5mm rifles and handguns, your day is at hand. There can be little doubt that the reintroduction of this cartridge will produce a new line of firearms to augment the original Remington rifles that might be in a shooter’s rack. And with current powder technology, better bullets and a better understanding of internal ballistics, there is yet, more to come! Future development of newer, higher performance Centurion 5mm Remington ammunition is already underway! The future indeed looks bright for this old veteran cartridge…

In closing, it is gratifying to think that a generation of shooters who did not get to enjoy the ballistic benefits of the original 20 caliber rimfire will now get the chance to see it in action first-hand. No doubt a new wave of 5mm enthusiasts will be cropping up soon to carry on the passion and love of what truly is an amazing cartridge. It is said that in Egyptian mythology there lives a great bird known as the Phoenix. The Phoenix would live 500 years and then would burst into flames, arising, reborn from the ashes. And so, like the Phoenix, the Five Millimeter Remington Rimfire Magnum –gone from production for nearly a quarter of a century- has been reborn from the ashes: Refreshed, revamped, and better than ever! Only time can tell what is store for shooters and future releases of the 5mm, but I for one, am confident that it will usher in from the past a new era of rimfire shooting!!!

Tim Mancillas is a Technical/Guns Writer/Editor and an ammunition consultant.
Andrew Moe is a Technical/Guns Writer and an ammunition consultant.

Editor's Note: Both Tim and Andy are dedicated shooters who work far beyond the standards set by most gun writers and we welcome their insite and expertise regarding this exciting new offering by Centurion Ordnance - EM

More Stories on the history and versatility of the 5mm Remington Rimfire Magnum:

Classic Calibers - Actual articles from the past, available for you to read in their original format!

Bring Back the 5mm Rimfire Magnum - Originally published in August - 2005 - The New 5mm Forums - Home of the 5mm Rimfire Magnum



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