The G18C mechbox

The internals of the stock G18C mechbox

PDI has come out with some amazing upgrade parts for the Glock 18. The parts we will be testing are the Piston Head, Hi-speed Cylinder, Spring guide, and 05 Inner Barrel. We will also be testing the Nine-ball spring from Laylax for power.

A commonly overlooked upgrade is the spring guide. The PDI spring guide is made of Delrin.

The stock spring guide (left) and the PDI version (right)

This material has a lot of good properties that are beneficial to airsoft upgrade parts. Delrin is stronger and more durable than most standard plastics used in airsoft guns and parts. It’s more durable than reinforced polycarbonates used in many other aftermarket parts too. Additionally Delrin can be made very smooth and is self lubricating. These are properties to look for on a piece that needs to withstand the stress of spring compression and not give any resistance to a spring which will compress over 10 times a second. The PDI spring guide is also constructed with a metal base to anchor it into the Glock mechbox. The spring guide comes with 4 thrust ring spacers. I’m not sure why there are 4 as only one is needed and adding extras will take up too much space and could cause mechbox damage. This ring is also made of Delrin and acts similarly to the ball-bearings found on many AEG spring guides, reducing wear and kinking on the spring as it compresses. It’s nice of PDI to give extras but to be honest I don’t see the ring wearing out any time soon.

Let’s look at the Piston Head. It is also constructed of Delrin for durability and the other previously mentioned properties. The PDI model has 6 ports where as the stock version has 3. The ports are also slightly larger than the stock ones.

The stock piston head

PDI piston head

What do these ports do? They have 2 functions. First of all they cause the head to act as a one way valve to let air into the cylinder on the back stroke when the o-ring shifts forward, then the o-ring seals the air as it goes to the non-ported rear of the piston head on the forward stroke (see illustration).

This gives shot to shot consistency, especially on full auto. Second, the ports cause air to push against the o-ring in the forward stroke, causing it to expand and give a better seal. Having the 6 ports over 3 allows the o-ring to stretch on all sides. The velocity gain from this piece alone is rather insignificant, giving only an increase of about 5fps, but the shot to shot consistency makes this upgrade well worth it.

The cylinder has 4 small holes rather than one large slit like the stock one.

Stock cylinder (top) and PDI cylinder (bottom)

The 4 holes will let air in and out of the cylinder more evenly than one large slit. The holes are also set farther back to give a higher total air volume per piston stroke. To be honest, the cylinder alone doesn’t give a huge performance gain by itself; however when you use it with the PDI piston head you get excellent shot consistency.

The nine-ball spring by Laylax gives a slight boost in power. The increase is not much, only about 30-40fps more than stock. While it doesn’t give the velocity boost one might expect for an upgraded spring what it does is add compression to help the PDI piston head seal even better. You also need to remember that the Glock is a small platform with a base line of only 210fps; 30fps might not seem like much but it is a 15% gain. Rate of fire went down a bit but full auto is still fast enough for gaming use. And with a 30rd magazine you don’t want blazing fast auto anyways.

Stock inner barrel (top) and PDI 05 inner barrel (bottom)

The most notable upgrade is the PDI 6.05 diameter barrel. This barrel is made of steel and has a high polish, much like the popular Prometheus barrels. I must admit when I first saw PDI was making 05 barrels I thought: “what company would spend money and time to make a barrel that’s not as tight as the competition?” Truth is PDI 05 barrels give the biggest boost in power when compared to 6.04 and 6.03 barrels from their competitors. Accuracy is equal to these tighter barrels. The barrel alone adds about 12-15 fps on this small pistol. What the barrel also does is give the Glock phenomenal accuracy and retarded range. What do I mean by retarded range? Well lets just say a Glock with the 6.05 barrel shoots farther than some upgraded M4s. The cut for the hop-up assembly is better on the PDI barrel than the stock barrel. This helps with the incredible range. The PDI barrel is also a bit longer, extending to the very edge of the outer barrel. When used with the other upgrade parts you get a phenomenal little pistol. The barrel is the most costly of the upgrade parts, but it is the most important.

Inner barrel and hop-up assembly

PDI also has a 6.01 barrel for those who insist tighter is better. The 6.01 actually doesn’t give as high velocity as the 6.05, but you get slightly better accuracy. If you use a 6.01 though, you need to use good slick bbs like biodegradable Excel or Tokyo Marui Tactical Grade, or I guess you could use Maruzen 0.29g Grandmasters. Forget about KSC, Viper and “ebay bbs”. Even regular Maruzen and Guarder have trouble in a 6.01. Maybe PDI went a little too tight in the tight bore competition. Now I see why 6.05 was the way to go. One other note; PDI is also making extended barrels with silencer attachments, similar to their Hi-Capa barrel and compensator kits.

After upgrades, the G18 turns in an impressive grouping at 8 meters using .20 gram BB's

So how does the Glock perform with all the parts installed? Well, when we started the gun shot at 210fps with excel 0.20g bbs and gave an effective range of 130 feet. After the upgrades this pistol shot 255fps. It’s a very consistent velocity, ranging up and down by only 2-3fps. This level of consistency is something no gas pistol will ever have. At this point most readers are thinking: “255? That’s it?! Why even bother with upgrades on this gun.” Well the reason you should bother is because the Glock 18 now has an effective range of 230 feet with recorded shots of 260 feet using 0.20g bbs. I don’t know of any other pistol that can shoot this far and this accurate. In fact, some rifles don’t even shoot this far. Maybe I’ll use this pistol to go against Tyler when he’s using his G-Spec.

Editorial Note:
Grant Woo has been modifying and repairing airsoft guns for over 8 years. In 2003, he opened his own store called Impact Games. You can visit his store at:
Impact Games
98-027 Hekaha Unit3-19
808.488.4120