One thing that a lot of people don't realize is that barrel length and a TBB don't mean everything. They help but if the initial base platform is crap there's only so much you can do.
You can still have a TM Mk.23 or a Hi-Capa that's tuned properly be more accurate and out range a long barrelled rifle.
In addition if anything breaks, you have a plethora of aftermarket parts support (and they're cheaper to boot) since it's more common more companies will make stuff and they need to undercut other companies for those same parts. Whereas, if you have a less common rifle and not as many people make parts for it then good luck getting cheap parts, they'll probably price gouge you because they don't sell as many parts and have to somehow recover the costs of making parts for that specific rifle. It's like making a million of ___ part for a Honda Civic (smartish idea) vs. making a million of ___ part for a Ferrari or something (just a stupid idea cause I don't think that many people will ever have that part break on them and have to replace it, instead they'll probably make 10,000 of that part and because not many other shops make the same part they can price gouge you because there aren't many of that part available and it costs more to make a smaller run of products than it does to make a million of the same product).
Anyways, you don't/won't need to "upgrade" the M16 to an SPR if you don't want to, it's just externals that make up what you call it. Internals are what matter, you could have an SPR with just external upgrades shooting stock or the same M16 with internals upgraded and shooting more accurately and be more durable than the M16 converted to the SPR.
Anyways, I'll leave you to whatever you choose and just keep in mind that if you want a reliable and durable gun then start off with a good base. After that it's a matter of hop up chamber, rubber, and TBB to get consistency/accuracy. After that all you need to do is just upgrade the player.
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READY TO >> RACE