Parts is Parts… but that wasn’t always the case!

Have you ever heard the phrase, “parts is parts?”

Made somewhat famous by the old Wendy’s chicken nuggets commercial, it is normally used to indicate that one part is as good as another. And, that if you need to fix something, you will probably need replacement parts and those parts will fit.

Much like how our Double Diamond Conversion Barrels simply drop into your compatible Glock and just work.
Basically, it’s a part and “parts is parts.” But it wasn’t always that way. Back in the day, parts that fit on one product did not necessarily fit another product… even if it was the same product from the same place! Back then, everything was made from scratch… including the parts.
Indeed, in the beginning of the firearms business, and I mean the beginning — like in hundreds of years ago — all firearms were, by necessity, custom made. Each and every part was individually made and fitted to that particular firearm. And again, just because it was the same type of firearm, from the same gunsmith, it did not mean that a part from one gun would even fit into another gun, much less function.

Just because these two matchlocks look identical, does not mean the parts are interchangeable. Look at the trigger placement in the frame.
Parts swapping just wasn’t a option when these beauties were made.

And it wasn’t just with guns, it was manufacturing in general. Virtually EVERYTHING was custom made.

Then the industrialization age started and everything changed. Manufactured items became a commodity instead of a luxury, and the standardization of parts stopped being a mere concept and became an engineering mantra.

And firearms, the new technology that all the kings and such had to have in their armies, was an early impetus in the transitioning to standardized parts.

Almost as soon as the early firearms started breaking from the rigors of combat, military leaders started demanding that firearm parts be interchangeable. The goal was that firearms that broke in the field could actually be repaired and put back into service. They started voicing these demands from the battlefields of the 1700s.

Thomas Jefferson was introduced to the concept of standardized gun parts while he was the Ambassador to France in 1785. When he returned, he pitched this still radical idea to George Washington.

President Washington, impressed by the presentation, issued a contract to Eli Whitney in 1797. He was to produce 12,000 muskets under the new concept of using standardized, interchangeable parts.


For the first few years, weapons using interchangeable parts were actually MORE EXPENSIVE to produce than the custom made versions. That was mainly due to the need to develop more precise machine tools, and more efficient manufacturing processes, to make the actual parts.


This was state-of-the-art stuff back in the turn of the century… the 19th century!

Eventually, however, as the manufacturing techniques and machine tools got more sophisticated, true interchangeability of gun parts became not just a concept, or an anomaly, but a given.

And, of course, as standardization paved the way to mass production, guns produced with interchangeable parts became significantly cheaper to make than custom firearms and, thus, much more plentiful.


In today’s modern firearm arena, it can easily be argued that Gaston Glock has taken the concept of gun part’s interchangeability to a whole new level, and standard of excellence.

Within the various Glock models, most of the non caliber specific parts will fit any of the handguns within that model family. And even across the models, a number of parts will fit in ANY Glock, regardless of model or caliber.

Some will even fit across Glock GENERATIONS!


Glock 17, Gen4 Parts Breakdown

 Which brings us to our own little salute to precise engineering and parts interchangeability… our Double Diamond Conversion Barrels.

These conversion barrels basically replace the only part that is TRULY necessary for you to shoot 9mm ammo in your Glock, whether the original caliber was .40 S&W or .357 SIG… that part being the barrel.

Note, I did put the caveat, TRULY, in the above sentence because most people, GlockStore employees included, will recommend that you also use 9mm magazines.

It’s not because the mags don’t fit into the handgun, because they most certainly do.

30roundEven the Big Stick will fit just fine.
Parts interchangeability is a beautiful thing!

We recommend buying Glock 9mm Magazines because the lips that hold the bullets in place in the .40 and .357 Glock magazines are ever so slightly wider than those for 9mm.

Too wide for it to work with 9mm? Not by a long shot… as Lenny will show you in this video.


We should point out that this is a one-way conversion. Since the .40 S&W and .357 SIG have fatter barrels than the 9mm versions, the hole in the front of the slide is bigger as well.

And while it is perfectly acceptable to chamber a barrel for 9mm, when said barrel is thick enough to handle .40 S&W pressures, the opposite action would result in a barrel that is too thin to be safe.




As to the “WHY” you’d like to start shooting 9mm in your Glock handgun, here are a couple of reasonable justifications.

1. Less recoil – 9mm has a significantly lighter recoil than .40 S&W or .357 SIG.

2. Less cost – In our retail store a 50 round box of 9mm range ammo runs $13.95 while the same brand and type of ammo for .40 S&W costs $21.95.

Then, of course, for those of us who consider such things… the sheer ubiquitous nature of 9mm ammo means it will almost always be easier to find than any other centerfire pistol caliber, regardless of why pistol ammo may be in short supply.

That, in and of itself, might be the best reason to dedicate a little space in your gun safe to a Double Diamond Conversion Barrel.