This is a bit dated, but I'll throw it into this thread since it already exists...
I bought 7" JP Rifle/Viking Tactical kit (with 4 barrel lengths) from airsoftparts.ca (highly recommend) on a whim. Got bored...he was having a sale...I was bored...now Jugglez has all my money...
The fit and finish of this kit is excellent. Consistent anodizing, no blemishes, precise alignment. Beautiful, crisp trades. I have fitted the 7" kit to 3 different bodies so far (a Dboys, a CA and a G&P). The only minor, minor thing was that the gas tube was 0.5mm too high going through the "delta" ring setup and so it indexed slightly off of the gas tube hole in the body (12 oclock high). No biggie, i just filed the end of the gas tube a bit and it slid right in.
With the gas tube inserted into the body, the front end is essentially pinned/staked positively in place. On all three fittings, the top rail aligned perfectly with all of the flat top AR bodies. Very solid kit, no movement or twisting at all.
From delta ring to flashhider.
1. The "delta" ring assembly goes on like a dream and is very solid. Locks down tight and clamps the outer barrel firmly into the upper receiver. Aligning the inner locking ring and the outer ring to get the gas tube to line up might take one or two tries, but otherwise problem free.
2. The main barrel is solid. A bit lightweight but "beefy" looking.
3. The gas block screws on and has 1 cross pin. Nice tight lockup but just enough play to allow you to get everything lined up just right. A set screw locks it in place.
4. The different barrel lengths screw into the front of the gas block. There is a little o-ring that goes into the gas block before the end barrel. A set screw pins it in place.
5. The flashhider is very nicely made. There isn't a cap and spring, so I just screwed the flashhider down flush on the end barrel. Another set screw pins it in place. I then rotated the end barrel a bit to line things up perfectly (the o-ring takes up any slack and can compress a bit as needed).
6. Install the rails before screwing the handguard onto the "delta" ring. There are little floating female blocks that go inside the handguard and beefy screws are used to screw the outer rails onto the inner blocks. This setup allows you to near-infinitely position the rails (one long top, one mid-length and one short) fore and aft, or any of the slots on the handguard. Accessories fit like a charm on the rails, so no issues there.
7. The handguard tube attaches to the "delta" ring with 7 little screws. I did notice some torquing of the tube if you screw down some tight before others (i.e. better off to screw them all in lightly, then sequentially tighten them down). Very sturdy and the barrel is completely free floating.
8. I noticed that on both of my kits that the sling/bi-pod stud that comes with it, when fully/securely screwed down the stud is over rotated. I used a little rubber washer to take up the space and to give it some cushioning.
Overall...beautiful kit (in my opinion) and very well made.
I liked the 7" kit so much that I bought the 12" kit (w/ 4 barrels). The 12" kit is huge...especially with the 24" barrel and flashhider. But I'm more used to CQB guns so even a carbine seems long. Goes together just as sweet as the 7" kit.
Don't know if the 6 extra lengths of outer barrel that I have now are necessary...but it's nice to have the options....
As a note to other Madbull stuff...I installed a Madbull 1 piece M4 barrel into a build recently. The fit and finish was excellent. Same goes with a couple of their springs that I've used in recent past. So maybe just my experiences, but they've been good so far.
