A friend is having cycling problems with his 11.5" frankengun (here in Paraguay where they are legal), apparently too little gas to cycle the action…
We’ll check the chamber to make sure if it is 223 o 5.56
what are the recommended specs for:
Thanks in advance 
http://noveskerifleworks.com/cgi-bin/imcart/display.cgi?item_id=kx3556p&cat=141&page=1&search=&since=&status=
He should try one of these out. They are designed to sling a little more gas through the system. Try a lighter buffer maybe?
Noveske and PWS both make a muzzle device like that.
My gas port on a 11.5" Wilson barrel is .071. I use a H2 buffer, carbine spring and FA BCG.
It’s run everything I put through it, including Wolf.
Thanks to all. The KX3 seems like a good try, but we are located in south america, price would be high for something that may work or not and importation is very complicated. Probably we could machine a similar device to enhance back thrust, but the best alternative would be to have everything in spec to allow for proper functioning without add-ons.
If possible, I’m looking for information or experience like the posted by shadow65
My recommendation to you is to provide us more information so we can make an informed decision.
What make and model is the weapon? What components were used to build it?
What ammo were you shooting?
What exactly is the weapon doing or not doing?
The only way to reliably check the chamber is to get a 5.56 chamber gage (from Ned Christiansen) and test it.
1- as stated, frankengun. I don’t kow the origin of all components
2- various brands of 223 and 5.56, 55 and 62 gr
3- the gun cycles weakly, sometimes too short so it picks round from mag but fails to feed properly
4- we were thinking about doing a chamber cast, if that is inconclusive we’ll have to ream the chamber to 5.56.
Edited to add: my friend has already opened up the gas port to 2.0 mm (0.079"), he will try several buffers, upgrade extractor springs, etc., we’ll see…
Good luck, Frankenguns can be a bitch to diagnose especially without knowing what components were used.
Start with the simple things.
Try a known quality magazine (PMAG) with known quality ammo (Winchester, Lake City, etc.).
Check to make sure the gas key is tight and properly staked.
Use a liberal amount of grease on the bearing surfaces of the bolt carrier and the bolt, when in doubt add more grease. I use red lithium wheel bearing grease from any auto parts store.
Next, make sure the buffer spring is within specs and that the buffer tube hasn’t been bent.
Make sure you have a H or H2 buffer.
Make sure the gas rings are in good shape.
The extractor should have a spring, a insert and a O-ring.
Checking the above items usually fixes 90% of the malfunctioning SBR’s in my experience.
After checking and repairing all of the above, do the following checks and let us know the results.
Put 1 round in a known quality magazine. Fire the round. Does the bolt lock to the rear on empty?
Put 2 rounds in the magazine. Fire the first round. Does it properly feed the second round? Fire the 2nd round, does it lock the bolt back?
Put 5 rounds in the magazine. Fire one round, does it feed properly?
Put 20 in the mag, fire one, does it feed. Fire five rounds, did they all feed? Finish the magazine off 2 shots per second, did they all feed and the bolt lock back on empty?
30 rounds in the mag and repeat the previous. How’d it work?
Iraqgunz, yes a frankengun is not what anybody would recommend… a mix of a bunch of parts of mostly unknown origin and quality, perhaps mismatched for this barrel lenght, etc.
JodyH, sounds like a plan, thanks
Runs like a sewing machine now, various types of 223 and 55 and 62 gr 5.56
the barrel was really 10.5", not 11.5"
port opened to 2.0 mm
H buffer
carbine spring
used semi BCG, without upgraded extractor springs (it was finicky with a brand new FA BCG), we’ll see if the springs need upgrading down the road…
what difference does the BCG makes?
A lot if the gas key wasn’t tight.
FA BCG has more mass which will increase the dwell time.
Thanks to all,
I thought the BCG weight difference was very minor (don’t have the numbers of FA vs semi) and would not make a difference, but apparently these short barrels are very finicky and you have to balance everything just right.
BCG weight is completely negligible. I wouldn’t want a gun where that slight of a difference would choke it up.
If he’s already checked that the port is open, I’d be looking at the gas key. I had a broken bolt that appeared tight… but it actually allowed the key to lift up a very slight amount. That caused bad short stroking.
The main points of the gas system are the gas rings, gas tube, carrier key and the gas port. I would start with the obvious.
Check the carrier key and if necessary remove the key from the carrier and check it. Then reinstall and stake the screws. Make sure that there is nothing inside the key itself.
Check the gas rings and perform a ring test. You can read about it in the inspection stuff that I posted and stickied.
Make sure that the FSB is straight. If you absolutely have to remove the FSB and check the port size. Though this shouldn’t be ncessary. (Can you identify the barrel at all? Any markings?)
Remove the gas tube and soak it in something that will break up and disolve carbon. Then blow it out using an air hose.