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5mm Centerfire.

A simple, innovative conversion kit can turn your obsolete rifle into a delightful varmint plinker.

Much to the pleasure of riflemen everywhere, Remington has been a refreshing free spirit when it comes to introducing new cartridges or adding its mark to well proven wildcats like the .22/250 and .25-06. Remington's innovations in rifles, too, have been interesting with models like the compact 600 or the 591 and 592 series.

Never heard of a Remington Model 591 or 592? Few have, but these guns surely raised a few eyebrows in their day. These rifles were chambered for one of the most intriguing and short-lived rimfire cartridges ever fielded -- the 5mm Remington Rimfire Magnum.

For almost 20 years, the 5mm rimfire has been dead as a dodo. There's simply no ammunition available to feed the roughly 52,000 Remington rifles out there.

But now there's some good news. Bulletsmith Steve Schroeder of San Diego, Calif., has designed a complete kit that converts the Model 591/592 series 5mm rimfire rifles into 5mm centerfire rifles, and Schroeder is supplying the 5mm centerfire cases and 5mm bullets to make them shoot.

Origins Of The 5mm

Introduced in 1970 -- a good 11 years after Winchester had released the popular .22 WMR -- the modern-looking, bottlenecked 5mm RRM came loaded with potential. Here was a hot, fast, small game number capable of propelling a 38 gr., 0.2045" diameter, hollow-point bullet to a velocity of 2,100 fps.

It was 150 fps faster than the fastest .22 WMR loading at the time. Compared to the .22 WMR, Remington's 5mm provided 50 ft/lbs. more muzzle energy, and at 100 yards, 62 ft./lbs. of energy on target. With the improved sectional density offered by a 5mm bullet, it added another 50 yards to the practical hunting range of the .22 WMR. The 5mm Rem, was effective out to about 150 yards or so on small game.

Between 1970 and 1974, Remington produced approximately 27,000 Model 591 magazine-fed and 25,000 tubular magazine Model 592s for their new 5mm cartridge.

The 5mm rifle was based on Remington's successful Model 581 .22 rimfire rifle. Externally, one would be hard pressed to see any differences between the .22 rimfire and the 5mm versions. They shared the same Monte Carlo stocks, grooved receivers, 24" barrels, an overall length of 42 3/8", and a weight of about 5 lbs. They were lightweight little sporters with fairly heavy triggers -- plinkers really -- a fact that didn't help the long-term popularity of the new 5mm.

The bolt of the Model 591/592 was made in two pieces joined together by a cross-pin. The front section, or head of the bolt, carried the firing pin and, in the 5mm version, a strange looking external claw extractor. The bolt assembly on all models was released from the receiver by pushing all the way forward on the safety lever and withdrawing the bolt to the rear.

Giving The 5mm A Second Chance

The 5mm RRM was accurate and performed very well on game, if somewhat destructively Thompson/Center even climbed on the 5mm bandwagon and chambered approximately 30,000 T/C Contender barrels for the new cartridge. Yet, four years after they had introduced their 5mm, Remington abruptly discontinued the Model 591/592, and shortly thereafter discontinued the manufacture of 5mm RRM ammunition.

Did the 5mm really ever have a chance to succeed? I don't think so. First, there was the matter of cost. In 1974, 50 rounds of 5mm cost $4.20 while .22 WMR was selling for $2.95, and a box of high-speed .22 LRs for $1.20.

Secondly, Remington issued only one loading for the 5mm -- a 38 gr. Power-Lokt HP. It was a very explosive bullet at 5mm velocities -- excellent for varmints, but too destructive on edible small game. In contrast, the .22 WMR was available with a choice of two bullets -- a JHP and a FMJ.

Finally, the Remington Model 591s and 592s were just inexpensive, .22 rimfire models converted to 5mm with the addition of new barrels, magazines and bolt heads. They were too light to be serious varmint rifles. Their triggers were heavy, gritty and not adjustable. In short, the quality of the rifles did not match the performance and expense of the ammunition.

So with roughly 52,000 Remingtons and another 30,000 T/C Contender barrels out there sitting idle, along came Steve Schroeder with a brilliant idea. Why not convert the 5mm RRM into a 5mm centerfire in the form of a kit any 5mm owner could install themselves?

Teaching Old Guns New Tricks

For many years, Schroeder Bullets has been my constant source of supply for obsolete caliber bullets and cases. Need bullets for the Savage Hi-Power, 7mm or 8mm Nambu, .351 Winchester Self-Loader or the .242 Vickers? Schroeder makes them as well as cases for the .310 Martini, 6mm Lee Navy, .280 Ross, .50 Alaskan and others too numerous to list.

Schroeder's 5mm conversion kit for the Model 591/592 consists of a new bolt head and a set of petite Go and No-Go gauges. The new bolt head is beautifully machined, fully hardened, and is superior to the original. The centerfire firing pin is retained by a spring and is therefore safer than the original free-floating design. The new claw extractor is made from a tough stainless alloy and is not brittle and subject to breakage as was the original.

Making The Transition

To switch from rimfire to centerfire takes only a minute or so and requires just a hammer and punch. You punch out the cross-pin that secures the bolt head to the bolt body, remove the old bolt head, insert the new and drive home the cross-pin. You're done, except for checking the headspace with the gauges furnished. The complete kit sells for $125 and is worth every penny.

Reloading the 5mm Remington Centerfire Magnum is the fun part. Schroeder sells pre-formed 5mm centerfire cases and three different bullets for the 5mm -- a 40 gr. spitzer, round nose, and FMJ. The 5mm centerfire components are little jewels, and in providing three different bullets, Schroeder has solved one of the problems that plagued the success of the original 5mm RRM.

Cases are made from .22 Hornet brass. Schroeder swages down and lathe-turns the base of the Hornet case, thins and reduces the diameter of the rim and then trims, forms and anneals the case bringing it to its final and proper dimensions. At $25 per 50, they're a bargain. They also last through a number of reloadings.

The reloading dies I used were from C-H and RCBS will soon be carrying the caliber as well.

Loading The 5mm

Schroeder recommended 4.5 to 5.5 grs. of Win. 296 ball powder and small rifle primers. Selecting the 40 gr. spitzer. I loaded a series of cases with 4,5, 5.0, and 5.5 grs. of a new lot of Win. 296. One could probably pour a few more lOths into the case, but I was having fun at 5.5 grains.

Reloading the little cartridge was a cinch, although handling the tiny 5mm bullets can make you feel rather hamfisted.

As I fired the test lots, one obvious trend became apparent. As the charge weights increased, extreme spreads decreased and so did the size of the groups. Shooting initially at 50 yards, I found that 4.5 gra. of 296 produced 1,622 fps over the PACT Professional chronograph with an extreme spread of 91 fps and a three-shot group of 1".

The heaviest charge, 5.5 grs. of 296, produced an average 1,921 fps with an extreme spread of 37 fps and a three-shot group measuring 14". At 5.5 grs., extraction was still easy -- no stickiness -- the primers were slightly flattened but the edges of the primers were still quite rounded.

Loading more of the 5.5 gr. charge and backing up to 100 yards, I shot groups measuring from 1 1/4" to 1 1/2". That's good enough for most larger varmints out to 150 yards, although I think by testing various brands of primers and playing with the charge in increments of 1/10th gr., I could tweak out some smaller groups.

The petite 5mm centerfire features economy, efficiency and suitability for small game hunting in the suburban fringe areas. Imagine getting 1,272 reloads from a single pound of powder. It's a pleasant caliber to shoot as well.

It's quiet and produces no recoil. Why the factories haven't given us a true suburban centerfire like Schroeder's 5mm puzzles me to no end.

Did I hunt with it? Yes -- one flower-eating rabbit in the backyard and seven ground squirrels succumbed to the 5mm. It did not prove to be an excessively explosive varmint caliber as loaded -- it simply got the job done in a very workmanlike and sporting manner.

So if you're looking for some fun and a new caliber to play with, take a long, hard look at Schroeder's petite 5mm Remington Centerfire Magnum. It's a dilly.
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Author:Bodinson, Holt
Publication:Guns Magazine
Date:Feb 1, 2000
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