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Thread: 7.62x39 in style of M4

  1. #1
    Join Date
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    7.62x39 in style of M4

    14.5" KAK barrel (was 16" when purchased), perm attach LANTAC brake, AIM nitride BCG, Aero upper & lower, the upper has the T-marks. Geissele SSP trigger w/ KNS Gen G pins, Aimpoint Comp M4 M68 CCO (or Trij MRO). KAC RAS with UK/SAS lower panel. KAC 98474 rear BUIS. Troy QD mount under the buffer tube castle nut. Lapped the receiver front face, also polished the barrel feed ramps, and smoothed out the sharp edges on the barrel feed ramps. Melonite gas tube, CTR stock for now, until I get a B5 Bravo. GG&G QD mount on top rail. Yeah I know it doesn't have the A2 FH, pistol grip, or the M203 cuts, chalk it up to "artistic license". I did think about having the barrel gunsmith profile the front part of the barrel with faux M203 cuts, but didn't want to introduce an ornamental "weak point" on the barrel, so that was a conscious decision. and I do like the "tacti-cool" and performance of the LANTAC. Tango Down QD stubby vert grip. I like the YHM EZ Pull take-down pins, use them on all my lowers. Ejection port dust cover is laser engraved inside & out. Standard M4 chrome-silicone carbine buffer spring with Spikes T3 buffer. I round off & polish the cut ends of the buffer spring so it doesn't dig into aluminum. Ergo grip, usually have to put a dab of contact cement to keep the rubber plug from flying out. BCM A44 ambi charging handle. not visible, Norgon mag release latch. I don't like the shiny nitride finish on the castle nut, might replace that with a parkerized one sometime down the road.
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    Last edited by rpoL98; 04-20-18 at 19:52.

  2. #2
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    Nice build! Stock up on good magazines and try various bulk ammo to find out what she likes for feed.

    Made one similar, less I stayed w/ 16” barrel, Spikes hardware and went the Ace skeleton stock ... and no verticle fore grip, despise them, haha! I did add a JP Ent adj gas port.

    Scoped it w/ a Trijicon 1-4X for pig hunting and nasty weather deer hunting when the mod70 Win Featherweight wants to stay indoors nice & dry & warm.

    With ammo she likes, it is amazing the accuracy one can get out of the -39mm cartridge!
    Given that 10-shots are a group and 5-shots may be a favorable trend ... know that just one good 3-shot group can make you an instant internet superstar!

  3. #3
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    Looks awesome!

    I use C-Products mags primarily. Work wonders with the 30 rounders.

    Really like your A2 sight base.

    Screw the cuts, you made the right decision. Really took advantage of the price on KAK barrels to get something awesome custom built from a smith.

    How's the gas system after pulling length off the barrel? Did you need to open the port? Or was it ported well enough to start that the length reduction was positive for the system?

  4. #4
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    Quote Originally Posted by HeruMew View Post
    Looks awesome!
    How's the gas system after pulling length off the barrel? Did you need to open the port? Or was it ported well enough to start that the length reduction was positive for the system?
    even with the barrel shortened about 1.75", since it's carbine, not mid-length, there's still sufficient dwell time.

    probably too much gas, in fact. Started off with the 5.4oz buffer, and had last round bolt hold open, so then i put in my "test only" 6.5oz buffer, and still had LRBHO (I would've preferred if it hadn't). Wolf steel case 123gr ammo. Next test would be to put in the Wolff extra power buffer spring, which I unfortunately didn't have with me this range session. I also have an 8.5oz carbine buffer floating around somewhere for test purposes, just gotta find it.

    ETA: using numbered drill bits as hole gage, the gas port is about .096". I think IMHO should be around .080 to .090. I see that BCA uses .093", even on their 14.5" 7.62x39 carbine barrel.

    ETA2: the .096" (#41 drill bit) gas port on the KAK barrel is a little big, even for 14.5" DI carbine. To restrict the gas flow, I partially tapped the vertical gas channel of the A2 FSB just a couple of threads with 10-24, so I could put a really short SS set screw in there, ended up with a drilled restrictor hole of .070" (#50 drill bit) in the set screw, for operation with a 4.1oz buffer. Sort of like a carburetor jet. I started off with a 3/16"-long SS 10-24 set screw, ground down the hex end to a minimal hex recess, just enough for the hex bit to engage to screw, unscrew. Then drilled the #50 hole in the set screw, then trimmed the cup-point end of the set screw down to about .15" OAL so that it wouldn't protrude into the gas tube hole. not tapping the hole in the FSB all the way helps with limiting how far the set screw goes in. I had to get a long-reach tap to tap the 10-24 threads since the tap has to reach through the bottom of the A2 FSB sling swivel fixture.
    Last edited by rpoL98; 07-10-18 at 17:16.

  5. #5
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    My PSA midlength shooting this week I had a 3.0 buffer shooting Tula. Swapped to a 5.5oz. It softened it up to .223 feel. Went to Wolf HP Mil-Spec. More thump! Then went to a 6.1oz. Still working good.

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