[JoshNC]

BPP’s E scope tabs are fully finished and are great. Personally I’d go with a welded rail.

 

[JoshNC]

this,

its gonna get freaky.

cant wait

I’m surprised it didn’t get real freaky when all the 11a1 kits arrived. 21E feed mechs were $3800 at that time from HKP. BPP and MM have barrels. I’m glad it didn’t get crazy, because I was able to get some feed mechs and barrels. But it’s odd the feeding frenzy over the 21 kits when there wasn’t one for the 11a1 kits.

 

[JoshNC]

make the 21 adapter plates and use better/after market stuff. the "drums" really do suck

Yep. An adapter to use mk48 nutsack. And maybe you need to start producing the Kydex belt box you’ve made.

 

[JoshNC]

2,500 is the total

interesting. An enterprising smith who bought a bunch at dealer cost could do a small production run and make some good money.

 

[JoshNC]

Good opportunity for a barrel manufacturer to do a run! I would think it would be hard pressed to find
that many barrels in the wild.

The bolt heads are likely at the end of their service life. Would be great to have a run of E type barrels and E type bolt heads to use in these kits. I bet RCM is doing just that.

 

[JoshNC]

Comparing the two bolts side by side, the 21 looks just like a G3 w/ a hole bored in it for the barrel pin safety and smaller feed lips. You could EDM the hole into a G3 and some time on a T&C grinder could make the feed lips match. Not easy but doable (whereas the E bolt you can't make from G3.) Would be nice if RCM did a run of bolt heads too.

It would be best to have new 21E boltheads and 21E barrels to use in these 21 kits. The E extractor design is so much better than the G3 extractor.

You could do both like MM does his, keeping the 21 barrel safety pin and corresponding recess in the bolthead. Or just forgo that and the E extractor and recess for the extractor in the barrel essentially perform the same function, but with the risk of damaging the extractor if you drop the bolt on a barrel that’s not fully locked in place.

 

[JoshNC]

Posted to arfcom….

 

[JoshNC]

Any source for new springs? If not I wonder if we can find the specs for weight and original length. Maybe Wolff or someone could make some replacements since there’s so many kits out there. I doubt HK makes them anymore.

As far as I know, Numrich was the last source for 21 springs. I bought a few about 2 years ago and can see no difference between them and the 23e/21e spring. The 21 spring is reportedly longer and stiffer than the 23e/21e spring, but I’ve not actually compared the two.

 

[JoshNC]

I was told by a few different people the hk21 came with minus sized rollers to allow for longer bolt life using roller changes (since you can't set the bolt gap by setting the barrel). I can't remember if they said -2s or -4s is what they came with. Anyone know the answer to this?

idk about the 21, but the 21E came with -4 rollers from HK to do just that.

 

[JoshNC]

I also found that the barrel shroud can fit standard Mlok

View attachment 430913
View attachment 430912

Be careful how firmly you tighten those, as they can deform the shroud.

 

[JoshNC]

Just found out I’m going to run into my first real challenge. When mocking up the 21, the PTR receiver seems to be just a couple thousandths taller than the shroud/cocking tube. When the front of the carrier enters the cocking tube it’s causing the middle of the carrier (where it steps up) to hang up on the top of the trunnion. Time to tinker. Thoughts?

ETA: Solved. Nothing a dead blow hammer couldn’t solve!

did you use a mandrel with a dead blow hammer? That area is a common issue it seems when building 21 and E guns on a flat. More than a few recent 21 builds post to the grams have some irregularities at the junction of the cocking tube and receiver.

 

[JoshNC]

In my rush to swap my 21 to an E recoil assembly i overlooked that the recoil rod guide rings are not the same. Im going to try and shave down the lips. If unsuccessful, i believe an 11 ring will work.

Don’t destroy those E rings. They will one day be rare. Just buy the correct rings.

How are you swapping to an E recoil assembly?