HK21 Extractors and Springs
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    Default HK21 Extractors and Springs

    Problem: HK21 works fine when using the mag adapter and upgraded the recoil spring to E version. The problem is the belt feed mechanism. I have never got it to work correctly. It appears to function properly when using snap caps in the DM-1 belts and cycling by hand but when firing live ammo it will have a fail to eject right off and a loaded round trying to chamber. The spent round is mangled and also has a crease on the side. Most of the the rounds fired with the magazine also have a mild crease on the side. Normal? I have never got it to work with the belt feed mechanism using belts yet.

    I have tried everything including changing locking pieces-no effect, using a HK21E spring-no effect, the bolt gap is right-no effect and also cleaned the bolt and checked the ejector. I'm now wondering if it is the feed mechanism?

    Follow up: after hours on HK pro I replaced the extractor spring and wala it works! It still has ejection problems with a suppressor but without a suppressor, no issues. I did the same on my HK93 host which was very unreliable by changing out the spring. Works perfect now.

    Question is, I saw on a couple post that if I change out the extractor to the newer style, it would be much more reliable and also if I ever get a FTE to replace the spring and also check the wear pattern on the ejector. Comments? I am new to this

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    Quote Originally Posted by djohns11 View Post

    Question is, I saw on a couple post that if I change out the extractor to the newer style, it would be much more reliable and also if I ever get a FTE to replace the spring and also check the wear pattern on the ejector. Comments? I am new to this
    If a 21 ever jams/FTFeed you need to replace the spring IMO, its the weakest link on the gun.

    AFA the "newer style" extractor like a hk21e/23e bolts you cannot put that in a 21 gun unless you have the barrels cut for it. The extractor extends past the bolt head. You would also have to mill down the back of the bolt to fit the 21 profile.

    If you run the suppressor, you need to change locking pieces, don't know what you have but maybe try a 17 (36 degree). I dont think there is a more shallow one.

    there is also a "21e" ejector spring its stronger/longer than a g3/h3 ejector spring. RTG perts has them and I run them on my beltfeds.
    Last edited by TaylorWSO; 03-18-2019 at 12:12 AM.
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    Thanks! The newer extractor is the one for the HK91 or similar. I ordered one and if fits right in but have not tried it out. It looks smaller. I'll try the 17 piece or as Ralph at RDTS told me to try a 9 first and go from there. My impression is that these are very finicky guns and don't see how they were ever used in military service with any reliability. I have an M-60 and never had any issues. It eats everything.

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    Quote Originally Posted by djohns11 View Post
    My impression is that these are very finicky guns and don't see how they were ever used in military service with any reliability.
    They are very reliable if set up correctly. running a can on a beltfed is not normal, and it does require a different different setup.

    yes the 21 has the same extractor and spring as the 91/g3. I would get a few springs as you will go through some.
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    Thanks! I changed the recoil spring, the extractor, and extractor spring, and things seem to be working ok for now but not 100%. The ejection seems to be inconsistent (new ejector) and every once in awhile I get a FTE and after clearing it works fine for another 50-100 rounds then malfunction. Same for all ammo types. My question is if the extractor spring is the weak link how did the military deal with this. Because of reliability issues I would not go into battle with something as simple as an extractor spring causing a malfunction. I keep changing the extractor spring and everything works fine for awhile and goes downhill from there. I read the same complaints from others on the web going back 15 years.

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    Default HK21 Extractors and Springs

    Maybe I missed it...but did you also install the 21E ejector spring TaylorWSO mentioned above? For HK’s belt fed guns, the stronger ejector spring can make a big difference, particularly with ejection issues regardless of ammo.

    Link to that spring on RTG’s site is:

    https://www.robertrtg.com/store/pc/H...AN-12p5688.htm
    Last edited by HKPhil; 04-22-2019 at 02:29 AM.

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    HKPhil

    Yes I did. Ejector spring works well. One thing I noticed is that when swapping out the belt mech with the mag converter, I have no issues at all with the mags. I'm wondering now if the belt mech is causing all the issues. I just put in a #9 locking piece so back to the range to see how that goes. Right now I'm not using a can either.
    Last edited by djohns11; 04-22-2019 at 01:45 PM.

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    Quote Originally Posted by djohns11 View Post
    HKPhil

    Yes I did. Ejector spring works well. One thing I noticed is that when swapping out the belt mech with the mag converter, I have no issues at all with the mags. I'm wondering now if the belt mech is causing all the issues. I just put in a #9 locking piece so back to the range to see how that goes. Right now I'm not using a can either.
    the feed mech can take a lot of energy to cycle, if you put a 21e recoil spring in there with a stiff feed mech it could be too much for the gun to clycle.

    I would try the #9, and if that doesn't work put a 21 not 21e spring in it.

    are you running the can with this?


    eta look for any scratches/wear marks on the feed mech. it might be hitting the bolt carrier and taking some energy away

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    TaylorWSO

    Went to the range today. It's exactly as you said 21E spring is too stiff. Went to the 21 spring with a #9 and things went perfect. about 80-90 rounds no issues. Put the can on with 21E spring and things went well too. Can't believe it. Take the can off with the 21E spring and have intermittent FTE. In summary it seems if I stick with 21 spring, no can, the belt mech works fine. I took it out and cleaned it well and lubed it. Wow! after all this I got it to work with the help of folks like yourself. Many many thanks! With the 21E recoil spring on using mags the gun is a pleasure to shoot for a .308. I changed out the extractor spring as well after the last shoot just to make sure. I have a #17 locking piece but not messed around with that yet. I'll wait until the novelty wears off some. Thanks!

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    Update since April. Hk21 setup. #9 locking piece, new stronger ejector spring, new extractor, new extractor spring, new ejector, new HK21 recoil spring. Today used with the mag adapter and out of 120 rounds fired had 5 FTE with double feed. Not impressed. Used several different kinds of ammo. Same thing. Put in the belt feed mech and did not work correctly. It is a RDTS 21EUG. Reliability is very inconsistent. I will be sending the rifle to Ralph at RDTS in a couple of months to figure out what is wrong. The weird thing today is the gun would not work correctly and jammed on every round. When I put the suppressor on it, I went through through another 120 rounds with no issue both on semi and full auto. What???? I give up.
    Last edited by djohns11; 11-10-2019 at 12:21 AM.

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