Top Menu

How I Converted My Glock 27 To Fire 9mm During a Bar-Sto Precision Barrel Evaluation

I converted my .40 S&W chambered Glock 27 to shoot 9mm with nothing more than a magazine and barrel switch. We'll get to that in a few minutes, but first, let's talk about the company who made this possible.

When it comes to the art of making aftermarket barrels for firearms, there are a few reputable companies producing quality products.  One company, however, has an extremely impressive resume.  Bar-Sto Precision Machine has been making barrels for the U.S. Marine Corps Marksmanship Unit since 1977. The AMU, National Guard, and Air force teams also use BAR-STO Barrels and have been used to win every major pistol tournament worldwide, including Camp Perry, the U.S.P.S.A. Nationals, Steel Challenge, the Masters, and much more.  

Each high quality barrel is machined in house, and I figured they'd be the perfect candidate do this unique evaluation. I wanted to go a company who has been in the game for a long time, and customer service is just as important as a quality product in my book.  So I was impressed by the company's customer service pledge:

‘We WILL provide the best service HUMANLY possible! We are committed to you the customer. We will always look for a better way to provide you the best product and service.'  

I said above that this is a unique evaluation for a couple reasons. I not only wanted to see if there were benefits of using an aftermarket precision barrel, but also find out if it could be used to convert my Glock 27 handgun from .40 S&W to 9mm.  

When I explained to the people at Bar-Sto that I wanted to try this, they were all for it.  Because they do all custom work, they had to custom machine a ‘semi-fit' loaner barrel for me to run through this evaluation.  After about 2 weeks, I had it and was ready to evaluate how it functioned not only as a precision pistol barrel but also as a .40 to 9mm conversion barrel!

Bar Sto Precision Barrels

Absolute precision

The Scoop on Aftermarket Barrels:

Without getting extremely complicated, there are a few types of aftermarket gun barrels.  There are ‘true drop ins,' which, just as the name implies, are machined to be removed from the package and dropped right into the firearm without any fitting.  They have tight tolerances, but because every firearm may have very small variations, there is a slightly ‘loose' fit.

Next we have match grade barrels that are designed for more precision shooting.  Bar-Sto makes a ‘semi-fit' and a ‘match target' barrel.  These are designed to have a precise, custom fit to the individual gun.  The semi-fit should drop into most firearms but may require some fitting (mine did, and I will cover this later on).  The match target gun barrel is truly custom fitted and has to be precisely installed by a gunsmith.

Most aftermarket pistol barrels are produced with 1:16″ rifling, Bar-Sto included.  Factory Glock rifling is 1:9.84″.  I mention this not because it'll make a noticeable difference for the average shooter, but ballistics is a pretty neat science and a little knowledge can't hurt.

The effects of the rifling are dependent on the type of ammunition being used.  In general, a higher velocity bullet will probably perform better in a barrel with 1:16″ rifling, while a lower velocity round will perform better with the 1:9.84″ rifling.  Glock and other companies usually go with a higher rifling because they generally perform a little better across various loads.  Again, even though there is a difference in the rifling, the impact on grouping is likely to only be seen outside of 25 yards and even then may not be very evident at all.

The Bar-Sto barrel is also machined with tighter chamber tolerances, which brings up another consideration.  Some cheaper bulk produced ammunition does not have tolerances as strict as some of the higher grade ammunition.  This could potentially result in some feeding issues with certain types of ammunition.  For this test, I ran 400 rounds of ammunition of various types and grades through the barrel and I will let you know how it performed later in the article.

I was able to fit the barrel myself by removing a slight amount of material.


I mentioned that Bar-Sto provided me a semi-fit barrel for evaluation.  I had my fingers crossed that it would drop right into my Glock without an issue. Alas, it did not.  Bar-Sto will custom fit your barrel, and many gunsmiths will also perform this service.  But if you are like me, you like to do things on your own.

The fitting process was extremely simple, and anyone with a basic mechanical understanding should be able to handle it.  I used a flat metal file and a digital caliper.  I measured and compared the factory and Bar-Sto barrel and found that just like the Bar-Sto web page stated, there may be some extra material on the front of the hood.

All other tolerances were right on; so I took my file across the front of the hood of the barrel, only making one or two passes.  I then tested the fit and repeated this process several times until the barrel slid into place.  The barrel locked in with such perfect clearance it felt like it was always meant to be there.  I cycled a few snap caps through the gun several times to see how it performed before being satisfied it was safe to take to the range.


I ran 400 rounds through the gun, consisting of 115 grain Perfecta FMJ, 115 grain Freedom Munitions FMJ, 115 grain Federal aluminum case FMJ, and 147 grain Freedom Munitions JHP.  I first ran the ammunition through the gun with a 9mm Glock factory magazine, but I did not change out the recoil spring, guide rod or extractor from my .40 Glock 27 set up.

I ran the gun at various rates of fire and various distances from 5 yards back to 30 yards.  My goal was to try and see if I could create a situation where the gun would malfunction.

The gun functioned flawlessly, without a single malfunction while running all of the brass cased ammunition.  When it came to the Federal aluminum case ammo, I ran into some issues with several failures to eject the aluminum casing.  I can only surmise that the aluminum cased ammunition doesn't quite jive with the tighter chamber tolerances of the Bar-Sto barrel.

Accuracy wise was more difficult to quantify.  I am not using this barrel for competition shooting, and I did not test it in a vice.  But I did find that the higher grade Freedom Munitions seemed to have slightly tighter groupings at 30 yards than the cheaper perfecta (which was not surprising).  Accuracy on everything inside of 15 yards was indistinguishable between the different manufacturers.

I found myself holding extremely tight shot groups during rapid fire.  This could be due to several factors, one of which being my years of shooting .40, and now using 9mm had me feeling like I was shooting a .22LR.  On a side note, I did test the ability to use a factory Glock .40 magazine, with 9mm ammunition.  The magazines are identical in size and both lock into the gun, however, the feed lips on the 9mm are slightly narrower.

This test resulted in rather poor results if you were hoping to use your .40 mag to shoot 9mm.  I experienced several double-feed malfunctions due to the fact that the 9mm round could more easily slip between the wider feed lips of the .40 magazine.

The superior fit and finish of Bar-Sto barrels is evident


I learned a lot while performing this evaluation.  First and unrelated to the barrel's actual performance, I was pleasantly surprised that there were no malfunctions due to the Glock 27's recoil spring, guide rod or extractor being used.

If I were to carry this configuration as an everyday carry handgun, I would possibly change the extractor, guide rod and recoil spring to a 9mm version, just to err on the cautious side.  Using a 9mm Glock magazine is going to be a must if you want any reliability.

During this 400 round sample size, the gun functioned flawlessly and I was extremely satisfied with the barrel.  As far as using the Bar-Sto barrel for everyday carry, I have to say absolutely; it is a reliable piece of equipment.  Using higher grade JHP ammunition, you are not likely to run into any of the issues caused by the cheap aluminum cased ammunition.  The barrel's fit and finish were also amazing.

If you are looking for a truly superior aftermarket barrel, why not go with a company who has been doing it for over 40 years?  If you want to get it ported, threaded, or match fit or a conversion barrel, they have you covered.  Each one is custom made, and Bar-Sto barrels are in high demand, which means you most likely won't be able to buy one and have it to you the next day.

If you are impatient, you may find the 6-8 week production time difficult to withstand.  But good things come to those who wait, and you will feel the quality just by holding the barrel in your hand.  Also, some may be scared off by the possibility of having to fit the barrel to their firearm, buy it really is not difficult and definitely will end up providing you a barrel with exceptional fit.

The price for a Bar-Sto barrel is not cheap, and after handling this one I can see why.  I know there are many aftermarket barrel makers out there, making the same old drop ins, but Bar-Sto Precision isn't one of them.

Have you used aftermarket barrels or conversion barrels in your firearm?  Let's hear how they performed.

, , , , , , , ,

5 Responses to How I Converted My Glock 27 To Fire 9mm During a Bar-Sto Precision Barrel Evaluation

  1. we2travlin May 6, 2017 at 12:27 pm #

    On my Glock 27 I installed a Storm Lake drop-in barrel conversion. Results have been most satisfactory. I have fired over 400 rounds…both factory new and reloads, which I personally reload. Oddly enough, the only problem I have had was with the Sellier & Bellot 115g FMJ, having three “failure to eject” occurrences out of over 100 rounds. Absolutely no failures with Federal 115g FMJ or my reloads (115g Xtreme copper plated bullets) after over 300 rounds. Still undergoing tests to make sure that the Glock 27/9mm conversion is totally reliable as it is my go to concealed gun during the warm weather months.. I ordered a 9mm magazine and use it at random with the original 40S&W magazine with no malfunctions that I could attribute to the 40S&W magazine. I do, however, recommend that using all 9mm magazines would not be a bad idea, removing any doubt of possible malfunctions due to the magazine.

    • Matthew Maruster May 15, 2017 at 1:46 pm #

      Thanks for the feedback. That is great that you have not experienced any malfunctions using 9mm with your .40 mags. I wasn’t so lucky at all. I would get a few rounds, but every mag I had an issue, and could only run my gun with 9mm while using the 9mm mags. Were you using Glock factory mags, and what generation gun and mags were you using. I was using a gen 3 gun with gen 4 mags. Have no idea if this would have any influence on the difference in our reliability using .40 mags with 9mm or not, but it may be an interesting experiment. Another possibility could be the age of the magazine. My magazines are rather worn and the feed lips may be worn down more than a new mag. Was your mag relatively new? Either way, that is great, and thanks for your reading the article and for your feedback! stay safe!!

  2. Kent Schmitz August 10, 2017 at 2:30 pm #

    I did a Bar-Sto barrel swap out from the factory 40 to a SIG 357 barrel. After a little fitting it worked well. No need to change the Mag. Fun to fire something hotter now and them. My Glock handled it fine.

    • Matthew Maruster August 10, 2017 at 2:53 pm #

      Kent, Thanks so much for the feedback. Awesome to hear you had a great experience with your Bar-Sto barrel! Stay safe out there and God bless.

  3. Chris L April 13, 2019 at 6:40 pm #

    As I turned 70, I decided the .40 was expensive and not fun in a G27. I got a 9mm conversion barrel from GlockStore and life is good.

Leave a Reply

All comments are moderated to ensure compliance with our community guidelines