Q&A for HK 51000384 UPPER RECEIVER KIT MR556A4 16.5"

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Heckler & Koch + Gun Parts Heckler & Koch Gun Parts HK 51000384 UPPER RECEIVER KIT MR556A4 16.5" HK 51000384 UPPER RECEIVER KIT MR556A4 16.5" Q&A Heckler & Koch + Gun Parts Heckler & Koch Gun Parts + AR 15 Parts Heckler & Koch AR15 Parts + AR15 Upper Parts Heckler & Koch AR15 Upper Parts HK 51000384 UPPER RECEIVER KIT MR556A4 16.5" HK 51000384 UPPER RECEIVER KIT MR556A4 16.5" Q&A Heckler & Koch + Gun Parts Heckler & Koch Gun Parts + Rifle Parts Heckler & Koch Rifle Parts + AR 15 Parts Heckler & Koch AR15 Parts + AR15 Upper Parts Heckler & Koch AR15 Upper Parts HK 51000384 UPPER RECEIVER KIT MR556A4 16.5" HK 51000384 UPPER RECEIVER KIT MR556A4 16.5" Q&A Heckler & Koch + Gun Parts Heckler & Koch Gun Parts + AR 15 Parts Heckler & Koch AR15 Parts HK 51000384 UPPER RECEIVER KIT MR556A4 16.5" HK 51000384 UPPER RECEIVER KIT MR556A4 16.5" Q&A Heckler & Koch + Gun Parts Heckler & Koch Gun Parts + Rifle Parts Heckler & Koch Rifle Parts + AR 15 Parts Heckler & Koch AR15 Parts HK 51000384 UPPER RECEIVER KIT MR556A4 16.5" HK 51000384 UPPER RECEIVER KIT MR556A4 16.5" Q&A Heckler & Koch + Gun Parts Heckler & Koch Gun Parts + Rifle Parts Heckler & Koch Rifle Parts HK 51000384 UPPER RECEIVER KIT MR556A4 16.5" HK 51000384 UPPER RECEIVER KIT MR556A4 16.5" Q&A

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HK 51000384 UPPER RECEIVER KIT MR556A4 16.5"

$2,499.00 $2,179.00 Save 13%

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Adrian Sprott, member, from TX, United States, asked on November 07, 2025

Don you have to use the Geissele mr556 trigger for the new A4 variant or can you use other Geissele triggers like the SD-E?

Answered by Sonofmk12, member, from NV, United States, on January 24, 2026

No it takes a specialized trigger with a slightly longer hammer . i googled that and learned in less than 5 seconds.

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Q&A for HK 51000384 UPPER RECEIVER KIT MR556A4 16.5" — 1 Questions & 1 Answers

Don you have to use the Geissele mr556 trigger for the new A4 variant or can you use other Geissele triggers like the SD-E?

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Q&A for HK 51000384 UPPER RECEIVER KIT MR556A4 16.5" — 1 Questions & 1 Answers

Don you have to use the Geissele mr556 trigger for the new A4 variant or can you use other Geissele triggers like the SD-E?