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Posted: 8/9/2006 5:35:09 AM EDT
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I got a LMT/LCW lower that will not run on a CMT upper with BM 24" barrel. What its doing is, it will eject the fired case but it will not grab the next one in the mag. I have a Magpul PRS stock on it with a buffer tube from a old A1 stock. The Buffer and spring i believe is from a A2 stock. s there a difference between the A1 and A2 buffer tubes, springs, and buffers? I don't have a A2 tube anymore so i have not been able to switch it. Ive used the upper on a different lower and it worked flawless so i don't think its a gas problem with the upper. Ive tried 6 different mags witht the LMT lower and still no luck. The only other thing that is different with the LMT lower is that it has a RRA 2 stage trigger. Any ideas on whats going wrong |
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A-1 to A-2 receiver extension assembly is nothing more than a longer butt stock screw and spacer on the A-2 set. Sounds like either the spring has a end of wind that may be scrapping down the inside of the tube (slowing down the stroke), or hammer on the FCG is getting wedged, and this may be the problem (read pull the FCG and look for indenting lines from when the carrier is lowering the hammer, and the hammer running out of room to be lowered far enough down to clear the carrier and the carrier to freely glide past. |
Thats what i thought about the buffer tubes The inside of the tube is clean no wear marks at all. There are some rub marks on the carrier from the hammer but nothing that shows that its getting wedged. Ill try a normal FCG to see if the RRA 2 stage is out of spec. |
No the bolt does not lock back. I tried wolf in it but its not what I use normaly. I mostly use Hornady Tap or reloads I load myself. Ive also tried South african surplus. |
The screw is the right size i just tried a 2 other bufertubes all together. It dosen't catch on the last round becasue for some reason the mag catch is a bit stiff and pushes down on the mag follwer. Would that keep it from feeding with a full mag? I thought the mag catch didn't come into play until the mag was empty. I also used lowers with collapsible stocks on this and it ran. Could that be making a difference? |
When you build the lower in regards to the bolt catch, you need to dry fit the roll pin into the bolt catch hole outside of the receiver to make sure that the roll pin is smaller than the bolt catch hole (so it glides on the pin), and that the bolt catch will glide in the receiver channel to achieve a full stroke (up and down). It does sound like you need to pull the catch out of the receiver and check the fit of it to the pin and the channel, and confirm that the bolt catch will spring all the way back down (read if it's not going all the way down, it will catch the B/C and slow down the rearward stroke, which could be your problem). Also, with the bolt catch pulled, check the catch spring channel for build up in the spring/buffer hole that may be adding some additional tension that will not let the mag follower spring tension over ride the return tension to push the catch up on a empty mag. Note: If the catch is just a little sticky/bindy in the receiver, you can lube the catch and try to work it by hand to loosen it up. |
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OK the spring was damaged a little right at the end making it wider than the hole. I Just trimed about a half a turn of the sping and the bolt will now catch eveytime by hand. There was also a little rub line on the bottom of the carrier that I just though was normal wear from the hammer. It might of been draging on the catch. Im off to the range right now to see if that was the cause of the FTF. |
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