Alright...
I missed this thread til now!
Here's the info I got for you:
Charging Handles:
PRI Gas Buster is basically worthless on a non-suppressed rifle. The charging handle and latch aren't any stronger than the standard mil-spec one. If you really want a bigger latch, get the BCM Gunfighter charging handle from bravocompanyusa.com. It's the strongest, most ergonomic latch out there right now.
Pistons:
I would definitely recommend not getting a piston. I own one and it really isn't a big deal. If you think you need to clean your AR15 all the time... You really REALLY don't. Do it if you want to but Pat Rogers (of EAG Tactical) ran a Bravo Company Manufacturing (BCM) carbine for 50,000 rounds with only a single cleaning. It was "dripping sludge everywhere" according to the article he wrote called "Filthy 14" (google it if you want, great article). He replaced some wearable parts and just kept the thing lubricated with Slip 2000 EWL lubricant.
AR15s like to be run wet. No matter what anyone tells you, there's no such thing as too much lube on an AR15. If you put "too much" it will throw it off on the first couple shots. Use a good lubricant like Slip 2000 EWL or Break-free LP (not CLP, LP does not have the cleaner in it and is much thicker, doesn't dry out and stays in place much better than CLP).
The other issue with pistons is a lot of the systems on the market introduce problems with carrier tilt, the cam pin digging deep into the upper receiver, and the forced unlocking of the bolt causing more wear to the bolt. A lot of them run well, as does mine, but the AR system was not originally designed for that operation and that can cause some headaches if the piston system isn't perfect.
Barrel Twist Rate:
1:7 will let you shoot a wider variety of bullets and all of the claims about 55gr and lighter ammo "spinning apart" in the barrel is a bunch of BS. Someone posted it on the internet or someone said it in a gun store and it got accepted as fact. Many people on AR15, specifically Molon, has proven many times that 55gr ammo shoots just fine in a 1:7 twist barrel and it was actually MORE accurate than his 1:9 twist barrel. They were both chrome-lined barrels.
That said, 1:9 is fine as well. The only advantage 1:9 really has is that it will have slightly more velocity due to less rifling. This amount is very small though and is not noticeable to basically anyone without chronographing it.
Magazines:
I'm a big fan of PMAGs. I have had some issues with the bolt not locking back on an empty chamber when putting weight on the magazine and I had to modify them because my Spike's lower's magwell is slightly out of spec. What I would do is buy a few of each type and test them after you build the rifle. Function test them. Make sure you don't have feeding problems. Test that they lock the bolt back on an empty chamber. PUT WEIGHT ON THE MAGAZINE (I use it as a monopod) and make sure it still functions properly. Despite what a lot of people say, this DOES NOT cause malfunctions if things are working properly.
Muzzle Devices:
I don't really see the point of a flash hider unless you're going into combat or intend to do a lot of night shooting. Even then, an A2 and even some compensators are just fine at night and don't blind the shooter nearly as much as a lot of people claim. I personally use battle comps on both of my AR15s and I think they're a great balance between flash hiding, muzzle rise reduction, and recoil reduction. The sound is about the same as an A2 equipped rifle. Please do remember that shorter-barreled rifles are louder than longer barreled rifles. A lot of people comment on how loud my AR15 is at the range. It's likely because it's a 14.5" barrel with a battle comp. It's still quieter than a registered SBR or a longer barrel with a true compensator. ARs are just loud guns.
Barrel Profile:
I would highly recommend against the heavy barrel profile unless you don't ever intend to do anything except high power or bench shooting. If you intend to use the rifle as a home defense weapon, a hunting rifle, or for tactical training classes that heavy barrel is going to be a beast to lug around. The only time you really benefit from the heavy barrel is if you do lots of mag dumps in a row or if you intend to shoot groups very quickly or after a mag dump. Even a "pencil" profile barrel doesn't bend or flex much at all if you're only shooting 10 rounds a minute or less.
Of course, the benefits of reduced recoil (greater weight = less recoil) and a greater stability (more inertia) from the bench and from the competition "slinged" position would be provided by the heavy barrel profile.
It's all about what you want to do with the rifle.
Hope this has been helpful.
