Happy to answer the question guys. FX in general defaults to trying to give as many options as possible to the customer (colors, stock options, barrel lengths, with DonnyFL or with FX Mod, etc). Now while it's not a problem for us to offer all these options, it does create a significant headache at the retail level with the different amount of configurations (all of which each have a different order/item number).
Now each retailer is different. A smaller guy who's talking to customers, mainly taking orders one on one in person or over the phone, no biggy in theory. (Though the dealer needs to offer the flexibility of having the configuration you want which means carrying all the options which will be good for business, but involves some upfront cost, foresight and managing.) For the bigger retailers, especially with robust websites, this means creating listings that convey all the options, and carrying stock to fill them.
I could go on with the logistics side but essentially it comes down to the fact that FX does offer a ton of configurations to tailor for the shooter (more than any other manufacturer, impressive considering scale) but each new option exponentially increases the complexity for the dealers. Adding an option of tank size for each gun would double the amount of item numbers, then add which barrel liner (heavy or standard) and it doubles it again. If we were selling directly to the public we could handle that no problem. But we value our dealers who are on the front lines growing our sport, so we have a policy of not selling direct to the customer so we don't undercut the dealers (businessmen reading this are nodding in approval knowing how awesome this is but yet how few manufacturers do it!). That's a lot for a dealer to juggle on top of the fact that they aren't just selling FX, they also carry rifles other than FX for some reason

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So in the end savvy dealers can carry these barrel kits, bottles, liners and tailor to what you need. But they also have to make sure they aren't eating the cost of a liner or bottle. It's logistics on their side as well.
Long winded explanation, but bottom line this has absolutely nothing to do with trying to gouge the customer and get more money out of you. If we were wired that way there's so many easier ways to do that without burning calories: we could have made the Impact power plenum not backwards compatible, not offering swaping out an FX Mod for a DonnyFL Mod for much less than buying the moderator separately, not developed the STX liner system where you could swap liners and instead just make them full barrels, or even just design new barrel systems if we perfect things (as we did with the superior liners) which would make old rifles obsolete, etc. Seriously I could go on. I know that a majority of AGN users get it, but sometimes people still have the wrong idea of us. Hence the transparent explanation to help show how things work and who we are.
Take a look at our actions, it screams loudly who we are objectively as a company.
- Jonathan