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Posted: 12/2/2004 6:42:47 PM EDT
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Hello all. First post here so forgive me is this isn't the right forum. I've been involved with AR15's and M16's since 1968 and know the in's and outs's of 5.56mm pretty well. However, I just got a 9mm upper for my Colt AR15A2 RR and it's got me a bit stumped. Here's the setup: Lower is as stated above (Runs flawlessly with both A2 HBAR and 14.5" M4 uppers) Current upper is a new Colt 9mm with a 10.5" barrel Colt M4 collapsible stock Hahn magwell block Colt 9mm buffer and 32 rnd mags KNS anti-rotation hammer & trigger pins Total round count in 9mm is 150 It's properly lubed 99.5% of the time it runs great on full auto but every so often, it throws a stovepipe jam on me. 5.56 has never done this. Current ammo is Remington 115gr FMJ ($60/500 at Bass Pro Shops). I haven't tried my 124gr NATO ammo yet. Any ideas on why the jams? Upper needs breaking in? Ammo? Something else? Thanks for any ideas. |
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Make sure your ejector is emerging from the bolt face (as you hand-cycle the bolt) as tight to the center of the casing as possible. It should be just shy of rubbing the side of the channel it rides in. If it's too far out, it will occasionally miss the rim of the casing and not eject properly. Bend as needed. Also check the extractor. Sometimes the slot for the rim is a bit undersized or has a burr and then the rim of the casing isn't solidly grabbed. Remove the extractor once in a while and clean it well, as it tends to accumulate gunk. Number your mags and note when the stoppages occur. If it's just happening with a specific mag or two, then look at them for problems. Good luck |
Break your problem down to the variables and then try and reduce that variation. Ammo: The Hahn block is designed to use the widest variety of ammo. Try 124gr, the bullet shape and lenght may improve reliability. I have had the worst luck in terms of reliability with Remington UMC 115 gr 9mm and will not use it, your mileage may vary. Block: Make sure the block, when installed is flush with the top of the lower receiver. Mag: When the mag is installed, the front top edge should be contacting the bottom underside of the feedramp. Does this failure happen with all magazines? Contact me directly if you need any other help. Steve |
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