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Can someone please provide a brief history on the HK21A1 and its 5.56/.223 variant such as how many were made and whats the actual numbering for the 5.56/.223, is it a HK23A1? ive got a barrel that came the 5.56-.223 feedmech and it has the HR21 small handle and is 17.7 inch,are these interchangeable with 23E or strictly 21a1 usage,im debating weather to build one or just sell the parts,also can a HK21bolt carrier group be modified to fit the HK21a1?This unit has such little info on it.
 

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...are these interchangeable with 23E or strictly 21a1 usage...
Not sure what you are asking? Are you asking if a 21A1 barrel (.308) is interchangable with a 23E (.223)? It might help to post some pics of these components.
 

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HKTIM

Was looking thru some of my HK literature last night and came across an article from "Machinegun News" that was in the March 1990 issue on the HK 21 and its upgrades. It is a very old issue of a magazine that was replaced by "Smallarms Review" many years ago. Email me your address and I will send you a copy as it may help you understand the differences in the various models.

In general, I have always heard that 21A1 parts and 21E parts are interchangeable same for the 23A1 and 23E. For instance, the A1 barrels have a small handle and the E barrels have a large handle other than that there is no difference and one can be used in place of the other. The beltfeed units are interchangeable,too; however, the E mechanism advances the belt half-way on the reward motion the bolt and the other halfway on its forward motion thus making the operation of the mechism smoother than the A1 which does not function that way.
 

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Another interesting midstream change is that the 21A3 does have the same feed mechanism push/pull as the E version. The limited # of real HK21A1 guns I have seen in person the top splines were marked 21A1. They are short shrouded without the later version safety catch and without the E style scope tabs and no forward assist. I havent seen an A1 belt feed unit in about 3 years... I did post a pic of the A3 and E feedmechs on here a few years ago to confirm the push/pull. Easy look to confirm - see if the rear of sprocket has 1 or 2 cams on the part of shaft that is outside of the feedbox.

I wouldnt bother to modify a 21 group as the feed actuator path is completely different - get an E bolt group as it is same path. On the bolt it is just the top tube that isnt cut for F/Assist.
 

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Discussion Starter #5
Chuck, sent off email as requested,being new here to the HK family and the belt-fed system as well,im very thankful for your insight and feedback.
 
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