anyone else running a 7.5" upper?

slothlacrosse

slothlacrosse

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Oct 19, 2010
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#1
if so, what advice do you have to keep the gun running cleaner/longer?

and don't tell me to get a gas piston for the gun. i made this gun the way it is because i think it looks cool and i wanted to shoot 3 ft flames out of the barrel.

after about 200 rounds, the gun stopped cycling.

i took the gun apart and it looked like the BCG and firing pin were phosphate coated (i've NEVER seen a pitch black firing pin). everything had a rough, matte black coating on it.

i cleaned everything, lubed it with M-Pro, and put it back together and it's working fine again.

if having to clean my rifle every +/- 150 rounds, i will gladly do it as long as the giant orange flames keep coming!

bigflash.jpg
 
#2
Re: anyone else running a 7.5" upper?

I just built one last night for my M16, but it's piston driven. If you like fireballs you should shoot a HK51k. A couple mag dumps and your whole body os shaking.

With any luck, I'll get to try the 7.5 setup Sunday.

Jeff
 
#3
Re: anyone else running a 7.5" upper?

I'm running the Noveske Diplomat/KX3 Flaming Pig setup and am very happy with it. Getting your AR dirty is unavoidable, but you can mitigate it by using cleaner ammunition. Some ammo like PMC Bronze and Winchester USA Q3131, as well as the Russian ammo, are very dirty. Some are cleaner. Part of it is just the fact that the pistol gas system is pushing so much carbon back into the BCG. Such is life with a gun that short.

I have tips for making it more reliable, but not really for keeping it cleaner aside from trying different ammo.
 
#4
Re: anyone else running a 7.5" upper?

After market powder, your pic, I recommend XBR or 4198. It will burn MUCH cleaner than any off the shelf ammo out there. By far. but it takes more prep time to hand load your rounds. Worth it though.
 
#5
Re: anyone else running a 7.5" upper?

I ran a 7.3" DI complete upper from CMMG with a DeGroat Flame enhancer on a M16 registered lower....I NEVER EVER EVER had one single issue...I could run 2,000 rounds at a time and not have to clean it in the middle of it with Beta mag dumps or 30 rounders...it was PHENOMENAL...and then cleaning it was a piece of cake. It was one of the most reliable short barrel uppers I have ever seen...maybe I just got lucky??
 
#6
Re: anyone else running a 7.5" upper?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USACS</div><div class="ubbcode-body">

I have tips for making it more reliable, but not really for keeping it cleaner aside from trying different ammo. </div></div>

like what? you can't leave me hanging like that!
 
#7
Re: anyone else running a 7.5" upper?

hard to tell in the picture, but it looks like you have some sort of muzzle device on there. which one is it? I ask, because some can add back pressure, IE the pig, krinkov style brake, which can make it run dirtier. I am thinking the gas port may have been done larger then it may really need to.....I have seen quite a few of the Shorties that have had issues, and some companies/gunsmiths have a philosophy of "give it a bit more gas and it will run".

What weight buffer are you running?
 
#8
Re: anyone else running a 7.5" upper?

It's a Noveske KX3. I'm running a heavy buffer.

It was running fine but I've run into a problem with the bolt carrier. Let's call the 7.5 inch rifle gun A and my 10.5 inch rifle Gun B.

Gun A was working fine but suddenly stopped cycling. I put the whole BCG from gun B in Gun A and it worked fine.

I put the BCG from Gun A in Gun B and it wouldn't cycle.

I put the bolt from Gun A in the carrier from Gun B in Gun A and it worked fine.

So i cleaned the BCG from Gun A in boiling lemon juice and it's cleaner than it was when UPS delivered it to my house.

I lubed it up and put it back in Gun A. I took it out to the range and it still won't cycle. The BCG moves back a fraction of an inch when the gun is fired.

I put a standard carbine buffer in and it still won't cycle.

I don't get it. It worked fine one day but not the next.
 
#10
Re: anyone else running a 7.5" upper?

there's definitely a blockage in the gas key.

i've been running AR's for a long time and i've never had a gas key blockage.

i tried pipe cleaners, dental picks, and a paper clip and i can't get anything out of it.

if anyone has advice, i'd appreciate it.

if not, i'll be ordering a new gas key monday.
 
#13
Re: anyone else running a 7.5" upper?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: slothlacrosse</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: USACS</div><div class="ubbcode-body">

I have tips for making it more reliable, but not really for keeping it cleaner aside from trying different ammo. </div></div>

like what? you can't leave me hanging like that!</div></div>
Tactical Springs LLC Extra Power chrome silicon recoil spring, upgraded 5-coil extractor spring with the O-ring, and an H3 buffer. H is too light, and H2 is decent but you will still have case rim damage. The 6.1oz or 6.8oz VLTOR A5 setup is the best yet. It is a great way to counter the over-pressure and slow town the timing.
 
#15
Re: anyone else running a 7.5" upper?

dropped the carrier in boiling lemon juice and left it in there for a while. there was some flow through the carrier but it was still restricted. used a small drill bit and cleaned it out. it's GTG.

like i said, not practical but is a lot of fun.
 
#16
Re: anyone else running a 7.5" upper?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: slothlacrosse</div><div class="ubbcode-body">dropped the carrier in boiling lemon juice and left it in there for a while. </div></div>

now your problem is going to be a strong desire for lemonade everytime you go shooting.
 
#17
Re: anyone else running a 7.5" upper?

I have a kitty kat upper and haven't had the issues that you have described. I shoot some crappy cheap ammo out if it and it has a tendency to get really gummed up, but nothing that keeps it from firing.

Good point on the gas key, might be something to check. Also make sure that the gas tube is fully inserted into the gas key. I had a friend that built one, but had a damaged gas tube that he cut off and tried to use. It would make contact with the key but was too short to make full contact with the key. It would run while the gun was spotless, but once it started getting a bit dirty, it would start choking.

He changed out the tube and all was golden.
 
#18
Re: anyone else running a 7.5" upper?

We make our 7.5" uppers with the "pig" break and don't have any problems. When we go to the range with departments, it is not uncommon for us to shoot 1000rnds or more form each rifle without cleaning (other than dumping oil in the action). One thing I may suggest is to have the bolt and carrier group chrome plated. It takes a lot more to get it dirty and is a lot easier to clean. Another person suggested a nickle boron coating which is great but a lot more expensive than just having your bolt and group chromed. Also check your alignment with the gas block. I have seen a lot of misaligned gas blocks on rifles which created problems...
 
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