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Posted: 8/6/2025 7:44:35 PM EDT
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So here's the deal - I have a G3 type rifle built on a FMP receiver and a full auto pack, gun runs fine in 308 but won't run with my HK 91 22LR conversion kit. HK produced two kits - one for the semi 91 guns and the other for the G3 full auto rifles. The difference is the 91 kits have a short extension added to the rear of the carriers to reduce bolt travel when cocking the gun which prevents the hammer, in a semi-auto HK91, from getting jammed under the 22 bolt / carrier assembly. The full auto hammers sit lower when cocked than a semi hammer and don't require said extension. It seems that in my gun the FA pack appears to sit high enough that the hammer strikes this extension about the same time it hits the firing pin. The result is that it only fires 50% of the time and full auto function is basically zero. My FA pack runs fine in my buddies custom JLD/PTR G3K receiver with his G3 kit that lacks the extension. I have not tried my kit in an actual German HK 91 but we may do that in the near future. I've tried using the semi pack that belongs on the rifle along with another German semi pack out of my HK 93 and the hammers in all of them hit the extension. At this point I think tolerance stacking is too blame and I have a couple options to fix things. To be clear this receiver was imported over 20 years ago as a fully rolled and welded piece by the FMP plant before they shutdown and sold off their equipment. All HK furniture and other parts fit like they would in a German gun. #1 - grind a deeper chamfer in the tip of the hammer in my FA pack. Don't really want to go this route since its a retimed hammer in a transferable pack. #2 - cut off the extension on a somewhat rare HK91 22 kit carrier. The 91 & G3 conversion carriers are the same otherwise in that both have material added to trip the sear. #3 - trade my 91 kit for a G3 kit. Problem here is my kit is practically new and I don't want to end up with a kit thats been ridden hard and put away wet. I'm leaning towards fix #2 unless I can source a G3 kit that is equal to mine in condition and work out a trade or swap deal. So what would the hive do? |
| I’m not sure I can help you out. I have a 91 converted to a 51 for .22 fun. I have one magazine out of 4 that seems to work reliably. Have you checked different mags? I know they are hard to find. In fact I found a second 22 conversion kit that I bought specifically to get the extra 2 mags. |
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Yeah we tried 4 different mags the other day and its pretty much the hammer hitting the carrier extension causing the problem not the mags. Admittedly some mags seemed to function better than others in my buddies gun but my gun doesn't run well enough to bring mags into the equation. I did breakdown my two mags and clean them up even though they weren't bad. Sadly I'm leaning towards grinding on a beautiful 91 22 kit. 
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Originally Posted By DragonGuard: How about getting a different hammer and modifying it. I was always taught to modify the cheaper part. A friend of mine has a 22 kit for his semi that I always thought was cool I didn't realise there were different versions for the G3 and 91. A quick search turns up retimed hammers at HKParts.net listed for $170.00 so not really a cheap option but a spare hammer might be worth the expense. I don't want to grind on the original hammer in my LaFrance pack either since it functions fine in 7 host guns I own. Perhaps I can add a shim the shelf to lower my pack on this rifle and gain some clearance that way. I have a couple extra polymer SUO trigger housings that I could clip and try them too. |
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Originally Posted By JoshNC: Could the extension on the carrier not simply be removed to convert it to G3 22lr conversion spec? Yes it could and I'm leaning that way or at least milling a channel along the bottom of the extension to eliminate the area of contact. My problem is I don't have easy access to a milling machine any longer. I do have a vise & grinder tho.  II'd like to keep some of the extension since it prevents over travel of the bolt if you want to run the kit in a semi auto rifle. Most guys with the G3 kits place a section of plastic tubing over the recoil rod to do the same thing. |
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It's not cheap, but would save you from grinding on your somewhat rare HK91 .22LR semi auto carrier (I own one as well). Apex shows to have the G3 spec .22LR full auto carriers in stock. https://www.apexgunparts.com/g3-hk91-22lr-conversion-bolt-carrier-group-complete-very-good.html |
MateFrio - "Evil is not a mental disorder. We cannot treat a misguided moral compass with drugs and institutions." 08/26/15
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if I remember right....if you take apart a G3/91 22lr mag you will find a HK 270 20rd magazine inside , 270 20rd mags use to be pretty cheap(yikes, not anymore). the 270 mags are what all the HK 22 kits used, 91,93, mp5 to the OP, I would buy that G3 22lr carrier or sell your 91 kit and buy a G3 kit, the 91 kits sell for a good deal more than the G3. I would think you could find a minty G3 kit. i have 2 of the 91 kits, and quite a few spare mags as well as 20rd 270 mags, but no G3 kit or I would trade you. Originally Posted By LVJD: I’m not sure I can help you out. I have a 91 converted to a 51 for .22 fun. I have one magazine out of 4 that seems to work reliably. Have you checked different mags? I know they are hard to find. In fact I found a second 22 conversion kit that I bought specifically to get the extra 2 mags. |
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