Conventional wisdom holds that if a handgun’s primary purpose is self-defense, “bigger is better”—bigger being .40 or .45 caliber, rather than .38, .380 or 9mm. And while there may be considerable debate as to the superior effectiveness of one caliber compared to another, there’s no question that when you take a box of ammo to the checkout counter, size does matter. With a few exceptions, the expense of ammunition increases with its size.

Availability of ammunition has recently become another concern. With ammo sales increasing almost as fast as certain politicians are burning through money, (which is only slightly slower than a speeding bullet) it’s not always possible to find cartridges of a specific caliber. Being able to fire multiple caliber cartridges from a single gun is especially advantageous when ammunition is in short supply.

Barrel Conversion

The solution to all these annoyances is a gun that can fire lower-cost ammunition during target practice, yet can be loaded with bigger and better cartridges for self-defense solutions. That’s precisely what you get with a conversion barrel, which allows a gun to be quickly and easily converted to shoot bullets of one caliber—even though it was originally designed for another. Since 9mm is the cheapest major caliber ammunition you can buy, that’s the caliber of choice for most pistol conversion barrels. On the other hand, the absolute cheapest ammunition on this or any other planet is .22 LR—a caliber that constitutes another popular conversion.

There’s no question that these conversions reduce ammunition costs, but I had some questions about their ability to perform as reliably as original equipment barrels and slides. That was “BBC”—Before Barrel Conversion. I can’t attest to the performance and quality of all brands of conversion barrels, (nor their performance on guns produced by different manufacturers) but the ones I tested functioned as advertised—or better.

My test pistol, a Glock 22, is dead reliable when loaded with the .40 S&W cartridges for which it was designed. Over 1,500 rounds have blasted down its barrel without a single malfunction. After switching to a 9mm Bar-Sto stainless steel barrel and firing about 750 rounds, not much has changed, except the cost of ammunition.

According to Bar-Sto’s Irv Stone, all of the barrels his company produces (conversions and standard replacements) are listed as “semi drop-in,” because some massaging may be required for installation. A common point of concern is barrel-to-slide fit; Bar-Sto literature states that all barrels are machined to the high side of tolerance to assure the tightest fit and lock-up. Depending on the side of the tolerance scale to which the original slide was machined, a barrel can either fit perfectly or require some massaging to provide necessary clearance.

Bar-Sto claims that approximately 70% of its barrels drop in without the need for any machining, and that was my experience. I installed the barrel in the slide, reinstalled the slide on the frame, pushed a loaded 9mm magazine in place, racked the slide and pulled the trigger. No fuss, no muss, no jams, no drama, and the bullets even hit the target.

Mechanical Limitations

Mechanical considerations limit the range of practical conversion barrel sizes. A minimum wall thickness is required to avoid unsightly barrel bulges and even more unsightly fractures, so with a few exceptions, conversion barrels are designed to handle cartridges that are smaller in diameter than those for which the host gun was originally designed.

The most common major caliber conversions for polymer frames are 9mm and .357 for .40 caliber guns, and .357 SIG and .40 S&W for 10mm guns. Choices for .45 caliber 1911-style frames are a bit wider and include .38 Super, 9mm, .357 Sig, .40 S&W and 10mm.

In addition to the conversion barrel, some guns may also require caliber-specific magazines and recoil springs. Doing a .40 S&W to 9mm caliber conversion on a Glock is particularly easy because the original recoil spring can be retained, and a 9mm clip for a G17 is externally identical to the .40 caliber clip supplied with a G22. The situation is the same with compact G23 and G19.

The only potential negative aspect of using a conversion barrel is the possibility of an unceremonious introduction of a bullet of one caliber to a barrel of another. Aside from a bit of embarrassment, the consequences of a bullet-to-barrel mismatch aren’t too serious. Within the range of common conversions, a mismatch will result in the incorrect bullet locking the slide partially open—or, the cartridge will plop out of the business end of the barrel when you release the slide—providing evidence that the spirit of Barney Fife is alive and well.

Aside from caliber-based cost reduction, an aftermarket conversion barrel may also bring shooting costs down by allowing the use of unjacketed bullets. Glock and a few other gun makers manufacture barrels that incorporate polygonal, as opposed to broach-cut rifling. Polygonal barrels are formed by hammer-forging, a process in which a barrel’s exterior is machine hammered, forcing the interior to conform to the shape of a mandrel that’s positioned in the bore. The resulting contour has smooth, rolling transitions between the rifling and bore surface. By comparison, in broached barrels, highly defined grooves are cut into a bore.

Polygonal barrels tend to be intolerant of lead build-up and Glock specifically recommends against the use of un-jacketed bullets. On the other hand, naked lead and broached barrels have gotten along famously for years, so the use of un-jacketed bullets in broached barrels is not a problem. Some proponents claim broached barrels also offer superior accuracy, but that’s another subject for another time.

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