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Joined:
Mar 2022
Posts:
535
EE: 98% (45)
VT, USA
Posted: 10/30/2025 8:01:09 PM EDT
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I call myself and idiot because I must be to not be able to figure out the problem here. Working with a DD DDM4 PDW .300blk pistol. Probably 1500+ trouble-free rounds on the unit. In the middle of a range session, I am suddenly getting a FTF every single round, cannot even feed manually. Nothing to do with the gas or spring, because even cycling it one step at a time manually, or locking the bolt back and inserting a fresh magazine. It seems like the BOLT WON'T GO BACK FAR ENOUGH, even manually, to strip the next round from the magazine, except by friction, causing a misfeed. When I lock the bolt back and insert a fresh magazine, I can literally see the bolt lug pushing the topmost round DOWN into the magazine. It won't go far enough back to catch ... but it IS all the way back because the bolt catch grabs it fine! Never seen anything like this. Magpul .300BLK specific magazines (tried 5.56 magazines too). Tried several varieties of subs and supers from different brands ... same issue every time. Any help appreciated! |
Joined:
Mar 2022
Posts:
536
EE: 98% (45)
VT, USA
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Some images. Yes, it's SOPPING with lube because I gave everything a spray with Ballistol out of frustration about 3 mins before these images. I've seen this sort of feeding issue many times with undergassed rifles ... but this happens even with MANUAL CYCLING and I can see the bolt pushing the round down in the magazine. So weird.   
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Joined:
Mar 2022
Posts:
537
EE: 98% (45)
VT, USA
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A few things might have happened especially if it was working before. I would check for popped primers anywhere inside the upper or lower. I would check the gas rings as sometimes they snap off and bind inside the carrier. Sometimes it is hard to spot. I would check the cam pin as well and the fire pin to verify nothing cracked or deformed. I would check the gas key on the carrier and make sure it’s not wiggling. I would check the bolt lugs to make sure they’re all there and not snapped or deformed. I would make sure the bolt catch didn’t snapped or deformed. I had a dd lower last year where the arm would raise slightly during firing and would cause a partial ejection. I would check for stuck casings or half broken case. It is sometimes hard to catch because it’s stuck way deep in the chamber. Plus any new magazine you may have. |
Joined:
Mar 2022
Posts:
538
EE: 98% (45)
VT, USA
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UPDATE - SOLVED!! For the few folks who actually read the post and suggested sensible courses of action - THANK YOU. Well, I said I was an idiot, and I was right. This lower came to me on a trade, with all the Gucci and faux-Gucci appointments, and, as I mentioned before, it worked perfectly, so I never found any need to change anything. One of these add-ons was a LAW FOLDER, which I actually found pretty useful for a shortly like this, as it could literally be stuffed in a small backpack. These units have a metal spacer that inserts into the rear of the carrier to bring the impact surface back thru the extra space created by the folder housing. These have a large rubber washer that prevents metal-on-metal contact between the spacer and an articulating retaining claw, which keeps the spacer in place when folded. I had not noticed at first that this rubber washer was missing. Somehow, this washer had broken, and, almost inexplicably, made its way all the way to the back of the buffer tube, and had been mashed up into a semisolid mass there. Just enough mass to prevent the bolt from cycling completely to the rear. How the hell it got past the buffer I will never understand, but there it was, and required the intervention of a repurposed coat hanger to remove. Luckily, I'm OCD about spare parts and had a bag of these washers from LAW to replace the trashed unit. Definitely a very weird malfunction. Weird enough for me to advise LAW about it. |
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