In comparison a few more alterations are needed and the pieces that connect the barrels are a bit more challenging, but other than that it wasn't overly complicated to build. I still urge you only to attempt this mod, should you be convinced that you are able to execute it. Otherwise you might damage your blaster.
Even if you are not planning on building an 18 shot version of the blaster and are just generally interested in modifying a Strongarm, I think this instructable is worth a read (especially the first step).
Take a look at the video:
Btw. I am completely aware of the irony of taking a blue-orange-white blaster apart in order to sand and prime it and afterwards painting it blue-orange-white again... but as some of you already noticed in the comments, I wanted it to look like something straight out of Borderlands.
Step 1: Common misconceptions + how to increase the speed
DON'T DO IT!!!!
Even though they might tell you that this improves the strength of you blaster, it doesn't! In fact, this actually damages your blaster, because it is not an air-restrictor, but an ingenious method to prevent dry firing. Since after building this 18 shot blaster I had some plungers left over I tried to do the mod and to compare the results by measuring the dart speed with a chronometer.
I also removed the barrel posts from one barrel, to measure the effect. Unless you are planning on using Stefans (If you don't know what I am talking about, here is an instructable) I wouldn't suggest you to do so either, because it also decreases the strength of the elite darts.
The only effective way to improve the dart speed that I found was to change the spring! The second picture shows the improvement after adding the Orange Mod Works (OMW) kit (from here).