Ok here comes my own personal opinion, gathered and constructed from the ground up by mixing powerful elements when it comes to learning:
- Listening to suggestions, guidelines and insight information from experienced users
- Asking questions rather than doing guess work
- Being careful and respectful towards the rifle and DIY stuff
- Spending quality time testing, shooting, gathering data and analyzing it
I own three gas rifles/platforms:
Primary: G&P WOC SR-15 URX SBR (GBB)
Secondary: KSC P226 PTP NS2 (GBB)
Special Purpose: Tanaka M40A1 PCS (NBB)
The only "project rifle" in the list is the Tanaka M40A1 PCS, which is heavily upgraded. The other two platforms are left at their stock stage or 95% near-stock.
I don't know if your question relates to gas guns in general or specifically in the sniper world of airsoft..so I will try and give you an answer that is a jack-of-all-trades
To me airsoft replica guns are just gas..I would never go for a spring or electric gun. I try and keep the experience with the gun as close as possible to the real thing and I think gas guns relatively deliver the most realistic experience from the outside and the inside.
As with every airsoft gun type, gas has its cons too, and I'll focus on these rather than saying all the good stuff, which you probably already know.
Consistency in gas rifles depends on the gas rifle itself and its magazine design..in my opinion you cannot say "gas rifles are inconsistent to a point in which they become unplayable".
From a mathematical point of view, they might have more FPS inconsistency compared to spring and electric counterparts, but measuring performance is not just about reading the chrono..You'll have to scout not only for good brands, but also models made by a good brand, whose design and construction schematics have been more successful.
If the magazine design has enough gas efficiency when releasing it and a good redundancy of gas in relation to how many BBs the mag holds, you will be good for most times of the year. If you need more protection against cold weather, you can make sure the rifle you buy (at least your primary) allows for CO2 magazines (e.g. GHK makes CO2 magazines for the G&P WOC) so you can get those and use those in winter conditions.
The other thing you have to look for is good efficiency in the rifle design, because even if you use good magazines, you might have inconsistent valve hits from a faulty rifle design and this will translate into inconsistent gas volumes getting out of the magazine itself.
Now, when you head towards sniper rifles AND gas, things get even more hairy because the precision factor in a "precision rifle" amplifies what I wrote above.
When looking at your shots through a scope and trying to send them far away at the extreme range of your platform capabilities..and in a predictable manner, you will be pushing the limits of the gun itself.
Most sniper rifles do not come near close to the expectations, in stock form. This is also true for gas sniper rifles. In sniper rifles you have to consider investing a whole lot of time for upgrading and testing. This translates into a lot of money for gas, bbs, parts, and collateral expenses.
If you are thinking to buy a sniper rifle and keep it near stock, you'll probably be disappointed regardless, because it won't behave, role-wise, as a valuable asset in the field. Anyway, if you want to follow that route, I would advise you to NOT buy gas rifles, because in stock form you might be better off with a TM VSR BAR-10 of some sort.
If you are looking to go down the rabbit hole and invest around $1000 total in rifle and parts, I would advise you BUY a gas rifle and upgrade it.
To get into the details, a Tanaka M40A1 is an example of a great platform for a project gun (expensive, too) and a poor performer out of the box. Its stock magazine (10 rounds) is the epitome of consistency fail because it does not load well, it is super exposed to outside temperature changes and holds exactly the amount of gas to expel 10 BBs, with close to NO redundancy. This will translates into shots visibly decreasing in FPS.
I am telling you that if you get the idea of gas rifles by shooting a stock Tanaka sniper or similar gas rifle from other brands..you'll think gas rifles are pure garbage.
If you start upgrading the rifle, you'll realize how much it can sit, piece by piece, in its "precision" role. There goes a list of viable examples:
- Getting a 29-round extended magazine looks like having a whole new rifle: the redundancy works great and your shots are now very usable
- Getting a VSR hop and barrel conversion allows you to fit a better hop design (the proven VSR style) and inner barrel (Prometheus/Laylax 6.03 is the winner).
Even with the above two, your rifle is starting to shine with little to no investment, compared to what follows:
- Replace all parts with steel counterparts and reinforce the striker spring, this allows for a more consistent hit on the mag valve and gets rid of faulty shots in case of extreme hot weather..most important though, it makes sure the valve opens, every time..because:
- You want to get an HPA rig. One with dual regulators will allow you, if properly built and with quality material (consider $300 or close to that, just for the rig and build experience) fluctuations of 2-3 FPS.
- Make sure you level your sights and put enough time adding DIY stuff, which every gun needs, depending on the model..e.g. barrel spacers
- You can go even further and add high quality custom hop ups. If you want the extreme level of accuracy possible, you have to leave the commercial hop ups and go for a custom R-Hop installation (not the clones, the HunterSeeker Armories R-hop). It requires time and some tinkering skills (some gun techs can do it for you), but it's worth the final extra step.
The above works for ANY FPS range.
If you want a great semi automatic sniper rifle and you want blowback (I personally would not live without, but I'll make exceptions for bolt action sniper rifles), you might want to check out the KC-02 RATech version. Semi auto, blowback, gas beauty (works with HPA rigs, too).
I might edit this post in case I find typos or stuff that I want added, but hopefully this answer will stay here as a milestone for my personal point of view on the matter. It is such a common question and hardly answered properly in ANY forum, and I know sometimes I wish I had the full version of the explanation instead of hoping for the rifle to shine before pulling the trigger on a $600 purchase.
