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VA, USA
Posted: 1/8/2026 12:28:20 AM EDT
[Last Edit: Lordwetrust][Edited]
hi folks i tried asking this on reddit but never got a responce there so im gonna try my luck here, Im looking to try and make a retro m16a1 build with the full sized heatshield using one of psa's H&R Retro M16A1 20 inch upper with LMT's m203, however I am unsure if the pencil barrel profile will work for it or if I need to use another H&R upper so that I can mount it to the barrel and not use the picatanny attachment, does anyone know if that upper works or will I need to buy the m16a2 upper instead with the a2 barrel type? |
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To build a period-correct M16A1 with an M203, you are facing a common "cloner" dilemma: the original M16A1 used a pencil barrel, but the M203 mounting hardware was traditionally designed for thicker profiles. The short answer is: Yes, the H&R M16A1 upper will work, but you need a specific adapter for the pencil barrel. You do not need to switch to an M16A2 upper unless you prefer the heavier barrel profile. Mounting an M203 to a Pencil Barrel The LMT M203 (and the original military versions) mounts at two points: the barrel nut (at the rear) and a mounting bracket (at the front). The Issue: Standard M203 mounting brackets are designed for a .750" diameter barrel (A2/Government profile). The H&R M16A1 uses a "pencil" profile barrel which is .625" at the mounting point. The Solution: You need a .625" M203 Barrel Bushing/Spacer. This is a small metal shim or sleeve that fits around your pencil barrel to increase its diameter at the mounting point so the M203 bracket can clamp down securely. LMT and other retro-parts suppliers (like Brownells or specialized retro shops) often sell these specifically for A1 builds. Why You Should Keep the A1 Upper If you are going for a "Vietnam to Cold War" retro look, the A1 upper is the correct choice for several reasons: The Carrying Handle: The A1 upper has the fixed, non-adjustable field sights which are iconic for that build. The Heatshield: The M203 "full-sized" heatshield (the one with the cooling holes) was designed to fit into a standard triangle handguard cap, which your A1 upper already has. Weight: One of the main benefits of the A1 is its light weight. Adding an M203 adds significant bulk, so keeping the lighter pencil barrel actually helps balance the rifle better than the heavy A2 barrel would. Summary Table: A1 vs. A2 for M203 Feature H&R M16A1 Upper (Pencil) H&R M16A2 Upper (Gov Profile) Barrel Diameter .625" (Requires Spacer) .750" (Direct Mount) Handguard Cap Triangle (Fits Heatshield) Round (Usually works, but A1 is "correct") I copied your question and put it on google gemini AI and this was the response. |
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They should be the same diameter where the mounting bracket goes TM-9-1010-221-23&P shows the same bushing is used for A1 and A2, no mention of spacers for the A1 It does mention that you may have to file a little off the length of the mounting bracket tab if it is too tight front to back on the A1  |
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Destiny has the kit for sale on GB. https://www.gunbroker.com/item/1143087348 |
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Originally Posted By backbencher: @HenryKnoxFineBooks You are looking for this: Attached File Gunbroker used to be the source for this kind of stuff before it sucked. Other issue will be the side sling attachment - there are three types (A) for the A1 only (B) for either A1 or A2/4 and M4/A1 (C) for the A2/4 and M4/A1 only. Pictured is (C) but (A) looks like this, just narrower: Attached File |
That's no way for guys like us to go out. We should go out in the midst of a desperate battle, doing great deeds. - COL Rick Rescorla
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Originally Posted By Dex223: That's a big difference in price, but it doesn't show or say anything about the insulating spacers. Maybe they could be made of a modern material or 3D printed if OP is not going for 100% accurate. Or he could buy them from Sarco: https://www.sarcoinc.com/m203-grenade-launcher-fiberglass-insulators/ |
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