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At times, I've wondered which is truly best for accuracy: PDI's 6.01mm barrel, or FF's 6.03. This review compares one to the other, in the same pistol and with the same barrel length. With a sample size of one, it shouldn't be considered a be all and end all guide to barrel accuracy, but it does allow one to draw some reasonable conclusions.

First, let's look closely at the two barrels. They're both stainless steel, and as such won't tarnish like a stock brass barrel. Additionally, they are both cut to fit a Tokyo Marui Hi-Capa 5.1 or M1911A1, 112mm in length with a hop-up cutout for a VSR type bucking.




The most noticeable distinguishing feature between the two is that while the First Factory barrel lacks any markings, the PDI barrel is conveniently engraved with ".01 PDI Japan". Certainly helpful for keeping your upgrade parts bin in order.



With a very close look, however, we start to see more differences. Notice that the FF barrel is cut for the same hop-up type as the PDI, but the retaining cut for the bucking has beveled edges, while the PDI uses straight ones. This is nice for removing the hop-up bucking without tearing it, but could mean a less secure seal.



Moving to the back of the barrel, another difference is readily apparent. The top portion of the barrel is cut away to allow the nub of the hop up to protrude into the barrel and contact the BB. This cut is slightly different on the PDI - in addition to the main portion milled away, there is a surface perpendicular to the bore axis, perhaps to garner a little extra room for the hop up with a smaller main cut. Additionally, the rim of the barrel along the bottom and sides is beveled on both the PDI and FF products, but noticeably more so on the First Factory barrel.



Additionally, a few machining marks can be seen on the flat area on the top of the PDI barrel, not as completely polished out as on the FF tightbore.



Flipping both barrels around, a significant difference is clear on the front rims of the barrels. Both are crowned with a beveled area sunk partway into the bore, however the FF uses a more steep crown which extends deeper into the barrel.



The exterior finish of the tightbores is virtually identical to the eye with the First Factory barrel slightly shinier in bright sunlight.



Enough on the physical differences - time for the tests. My testing platform is a Tokyo Marui Glock 17 with the following upgrades that could potentially affect accuracy:
BoomArms Shuey Custom G34 Slide and Outer Barrel
FireFly Recoil guide w/ bearings
FireFly Aluminum Floating Valve for G26
Firefly soft V-hop bucking
SD Hammer spring
SD 150% recoil spring
PDI Piston head

It was very important to avoid variances in assembly of the barrel unit that could throw off the tests. As such each barrel was cleaned with seven cotton patches and hop-up unit parts were dusted with computer duster to keep tiny debris from affecting the consistency of reassembly. Both barrels were to be tested with the hop-up turned all the way down to ensure the setting would be the same. First up is the PDI 6.01mm barrel:

When conducting an accuracy test with a pistol, it's important to be sure of what you're testing. For example, clamping the frame or grip of the pistol in place and firing away at a target tests how accurate the pistol will be for someone who uses the frame or grip to aim (which is useful for certain pistols using red dot sights anchored to the frame). The outer barrel, slide, recoil rod, and inner barrel will be moving in relation to the frame with each shot; as such you are testing the variation between inner barrel and frame in addition to the variation in the barrel itself. Most people use a slide mounted sight - that is, iron sights or an Optima 2000 type red dot, so in this test I will be using the sights on the pistol to align it for each shot (testing with variation between inner barrel and slide in play).

For this purpose I spent a few minutes constructing a crude adaptor for an old camera tripod. The adaptor consists of a piece of polycarbonate sheet which mounts to the camera tripod with a nut, then to the bottom half of a scope ring via two Allen screws. This allows the tripod to be used for anything with a Weaver or Picatinny accessory rail in a suitable location, including the Glock pistol to be tested.

I loaded the pistol's magazine with 10 KSC Perfect .25g BBs, a common brand and weight. Then I filled the magazine with unlubricated propane until excess gas spurted from around the fill valve. For general use, propane should be lubricated to maintain the O-rings of the magazine valves and piston head, but to ensure consistency of the tests unlubricated propane is best. After allowing the magazine to sit for 10 minutes for its temperature to return to normal, I locked the slide of the pistol back, inserted the magazine, and hit the slide stop lever to chamber the first BB.



My target was taped to a cardboard box, so that every BB would make a hole in the target, but not ricochet back through and distort the grouping. The tripod was positioned so that the pistol's barrel measured 20 feet away from the target. I aimed carefully at the center of the target, ignoring the three dots of the sights and instead focusing on the dark outlines of front and rear sights for the most precise sight picture. When satisfied, I locked the tripod's mounting bracket in place and fired. For the subsequent shots, I allowed 10 seconds for the magazine to warm, carefully checked the alignment of the sights, adjusted if completely necessary, and fired again.

When the test was complete, I removed the upper assembly from the pistol, leaving its frame locked into the tripod, and replaced the barrel with the First Factory unit. I then taped a new target in place and repeated the process exactly.

The results? Surprising. The PDI 6.01mm barrel grouped thusly (1" grid):


Whereas the First Factory 6.03mm barrel actually performed a little better:


On measuring the size of the groups, from center to center of the holes farthest apart, it turns out that the FF barrel produced a grouping of 28mm, while the PDI barrel came in at 39mm. About a centimeter of difference in group size at 20'.

I felt that another test was required to cement the groups. This time, I used the same testing procedures, but fired at 35' and with 15 shots. My hope was that the greater distance and number of rounds fired would lessen the possibility of error. Additionally, I considered the possibility of variance in assembly, and uninstalled and reinstalled the 6.03 barrel before performing more tests. For obvious reasons the 6.01 barrel would also be reinstalled.

Once again, the First Factory barrel outperformed the PDI barrel in accuracy. This time, the group produced by the PDI 6.01 measured 59mm, while the First Factory grouped a tad tighter at 50mm. So, the difference is not as great in this test, especially considering the increased distance, however the PDI still didn't beat out the FF.



Comparing products using a sample size of one is unlikely to produce exact numbers that can be applied over an entire range of products. However, I would cautiously conclude that, at least in a Tokyo Marui Glock with a barrel length of 112mm, a First Factory 6.03mm barrel is slightly preferable from an accuracy standpoint. The 6.01mm barrel can be expected to produce a bit more power in a gas gun, though I do not have a chronograph and so will have to wait until a skirmish to confirm this.

Of course, I am left to wonder why a 6.03mm barrel would have better accuracy than a 6.01mm barrel. The immediate answer which comes to mind is the quality of the barrel in matters other than interior diameter, and this test offers one possible explanation. The pictures and a very rudimentary knowledge of German make it clear that a precise measuring machine was taken to a number of barrels, measuring their roundness. Scrolling down, one can see that PDI and Prometheus both were very close to a perfect microscopic circle, but Prometheus (AKA First Factory) was a little better. Notably, the PDI barrel beat out both DB Customs 6.01 barrels.

In conclusion, inner barrel quality is more than mere diameter - accuracy tests may bear this out. Both PDI and Prometheus/FF make great choices for inner barrels, but based on what I have observed in my testing and experience, out of the two PDI is the choice for power, Prometheus/First Factory for top accuracy. If you have a different testing procedure to suggest I would be happy to read it and if it is not too time consuming or expensive, try it out.

Very nice RSP, very nice. It also backs up some off hand "testing" others have put forth which is that KM 6.04mm and PDI 6.05mm tight bores are more accurate than the PDI 6.01mms. Very happy to see a well constructed test that backs this up. I choose power myself.....

Thanks. With the TM G17 I am selecting accuracy over power whenever I can, take advantage of the gun's natural strengths and don't push it to break its natural limitations. Although one could also argue that I should be trying to 'find' all the power I can and leave the accuracy alone... hmm. I might use the 6.01 in a skirmish to see if the slight decrease in accuracy is something that actually affects my effective range. At the moment I just need to apply elevation at long range.

I think one of the key differences in the barrel designs can also account for the accuracy of the larger bore barrel. That deeply recessed barrel crown probably improves barrel harmonics, controlling vibration and increasing accuracy. My 6.02 Mulberry Field barrel in my g18c shot outstanding groupings and gave great range too. It too had the deeply recessed muzzle crown of the FF and KM barrels.

Interesting. My own uneducated guess upon looking at the difference between the crowns was that the deeper one would mean a more gradual widening of the barrel, so any effect on the BB's flight from an imperfection at this point in the barrel would be softened. I didn't think of it as responsible for the difference in group size, but since you mention the KM barrels with their excellent reputation for accuracy and your G18C barrel also shared this feature, it's definitely worth considering.

Great work on the review! This kind of work is probably the most time- and patience-consuming things you can do with an airsoft gun. I've thought about barrel comparisons for a long time, but just can't get myself to start the work. My motivation is further reduced by the fact that in the end the differences are small.

Again I must point out that the 6.01 mm inner barrels are made for power, but are less accurate than looser 6.04 and 6.05 mm inner barrels. I don't see a reason why PDI - the manufacturer of 6.01, 6.04, 6.05 and 6.08 mm inner barrels - would lie about the qualities of barrels when they make all sizes. I would like to see the Nine Ball 6.03 mm inner barrel against the PDI 6.05 mm barrel, and maybe even the PDI 6.08 barrel.

PDI and Prometheus got near-perfect figures in that German test. Prometheus got higher marks mainly because it stuck to the nominal 6.03 mm value better, while PDI 6.01 was actually 6.02 mm. I don't think the difference in groupings that you shot comes from the manufacturing quality - these are both incredible pieces of engineering.

We know for a fact that there has to be a clearance between the inner barrel and BB. A too tight inner barrel would interfere with the hop-up spin. How small can you make the gap? Looks like 6.01 leaves too little clearance with KSC BBs. It would be interesting to see how Excels would group with these barrels, since they are smaller than other BBs.

When I shoot groupings, I shoot five shots in one string, and several strings to various targets. I've shot 30 mm groupings with five shots from 10 meters (33') off-hand with an airsoft pistol, so I'm quite confident about my findings even without a shooting rest. This is the best accuracy I've seen from a self-loading airsoft pistol, and it was mainly the result of a "compensator" mounted on an extended frame, with an O-ring inside to hold the inner barrel tightly supported. Freedom Art makes those.

-Sale

Sale, good to read your comments. Posters on ASB and Arnies also wanted to know about the PDI 6.05mm barrel - this of course does make me curious as to how it compares to the FF barrel, and throwing a KM 6.04 in for comparison would be great as well. While I might acquire one of those in the future and expand the test, it's unlikely - too many other things to try out.

Your comment regarding the offhand 10m group bears out the importance of consistent postion of inner barrel and hop-up unit in relation to the sighting device after each shot. I've been looking carefully at anything I can do to improve fit in the relevant parts. Currently with this G34 the slide to outer barrel fit is secure and the strong recoil spring pushes the outer barrel axis down slightly into the bottom of the slide, wedging it in place. From there it's a matter of inner barrel to outer barrel fit, and I think I might play around with O-rings and see what I get. On the other hand the slide to frame fit has a little rattle so I wouldn't be surprised if I had a noticeable loss in accuracy with a frame-mounted red dot.