AR Sponsor
Posted: 1/2/2014 7:28:14 AM EDT
| Hello pros! I recently built my own AR. I have a Spikes lower with Stag trigger group, and Spikes T2 buffer. Not sure of the brand on my upper (given as a gift w/no package) Spikes BCG and Wilson barrel, Kies adj. gas block. When I fired the rifle, I adjusted the GB according to the man. spec and got it ejecting properly, but no matter how much I open it up it won't feed. All I get is on the round being fed gets scratched along the whole length. I finally traded upper and lower with a friend. His lower feeds my upper perfectly and my lower feeds his upper perfectly. Put mine back together and same feed issue. Any ideas? Oh and both feed off my Troy mags and one round will lock the bolt open. |
|
Would dare to guess, but buffer too heavy, and maybe even a touch of hammer wedging with your upper on your lower if the problem is a short stroke one.
The buffer is easy to solve, and just swap out the heavy buffer to a standard weight buffer. If you are both running telescoping stocks, then try swapping buffers since he may have a standard buffer in his rig. As for hammer wedging, take a look at the top/back of the trigger and disco tails for signs of hard hammer tail impact to them. If you find dents or white lines across either from the hammer tail, then removing .040 from the hammer tail solves the problem most of the time. I say most, since the problem could be that that tail may be contracting the end of round section of the disco instead, and in cases like this with something way out of spec. In cases like this, first try to swap the FCG to see if that solves the problem and if not, then the lower receiver pin channels are out of spec, and my have to replace the entire stripped lower receiver. And FYI, there is such a thing as over function, where the gas system gets too much pressure. Here the bolt tries to unlock too fast while the spent case in the chamber is still under too much pressure to be pulled cleanly, and the rifle acts like just like it does not have enough gas to short stroke as well. As for the first test before doing anything else, load a single round into a mag, insert the mag into the well, charge and fire the round, and confirm that the bolt is locking back on the catch. If the stroke is correct and the bolt locks back on the catch (face of the bolt, and not just on the bottom of the carrier), then figuring out the feed problems becomes a snap. If you know that the rifle is stroking correctly to lock the bolt back, then it just comes down to checking small thing like making sure that the mag catch threaded section is flush to the face of the mag release button, that your bolt catch is seating all the way down to not catch carrier as it moves forward, and in the case of a non shrouded carrier with L cut hammer, the firing pin stop collar is not catching on the hammer as the carrier moves forward (FP retaining pin will be bent to hell if it is). Lastly, would help to know if the upper has M-4 ramping, and if it does, are the ramps between the upper and barrel extension flush, or is the barrel extension ramps proud of the lower receiver extended ramps. I ask since have been seeing the problem from time to time, and here the bullet tip ends tagging the protruding lip to stop mass of the B/C before it can get a full lock up. Simply, without more information, the above is all I can suggest for now. |
| Ok so I looked at the hammer, there is only slight wear mark on the face. We do both have telescoping stocks. His bolt locked open on my lower 5/5 times I tried. Mine will lock open, I've only had it not lock open once or twice, that is how I set the GB. Firing one round adjusting up just until it locked open. It does have M4 feed ramps and they are flush with the lower, the barrel ramps may be a hair behind the lower but not proud. Would the heavy buffer really act so differently between two uppers? I also pulled my BCG to make sure there was nothing there dragging. I hope its as simple as swapping buffers. Thanks for all your ideas Dano! |
|
If the bolt is locking back then stroke is fine.
Show in a photo of how the rifle would not feed. Was the bolt on top of the middle of the case with the tip in the chamber, from a mag that did not recover in time/ being retained too low in the lower receiver? Was the tip in the round in the chamber, the bolt behind the rim of the round, with the B/C locked up that even the FA would not move the bolt forward, hence the FP caught on the hammer? Was the problem that the bolt could not climb over the rim to allow the bolt to be driven home into the barrel extension to lock up, a mix index of the key to carrier causing the bind, or maybe even the carrier key too wide for the upper receiver/ recoil spring having a end of wind bur that is scrapping down the inside of the receiver extension with either of these bind causing problems? Detail please, or just show me a photo of the action/ammo relationship on how it was when you had the failure to feed. |
|
Ok, the next round never leaves the mag. Sorry I don't have pics, this was all from yesterday. The next round in the mag has a scratch the whole length of it, including the shoulder at the primer. I thought it could be mags but they cycled fine in my friends AR and when I swapped our upper and lowers. Both sides of the mags had the same scratches.
*EDIT* I went through my bag and found an example! Take a look https://lh4.googleusercontent.com/Y93aIqFb5TrM8LfgdpBpPGhn7ZRrSyONbtGMjCXHtw=w288-h162-p-no https://lh4.googleusercontent.com/2rdhrJrIalP-DaZCll52mQOyKdWtOh7MV7E6F8xreQ=w288-h162-p-no |
|
Mag not retained high enough in the upper receiver, or the mag not recovering fast enough as the bolt starts to move back forward.
To note here, the buffer off the back of the receiver extension jolt does help a mag recover faster. So it could be that your friends rifle has more buffer to tube jolting, and the reason that the mags might be recovering faster in his rig. As for suggestions, Pull the mags down and CLP clean them. I could be as simple as the follower binding in the body, and CLP cleaning (and maybe a little follower molding line clean up) will solve the slow recover time of the follower binding in the mag body. Next, make sure that the mag catch threaded section is flush with face of the button. If the mag catch is under weaker spring tension, it can allow the mags to dance from to back more. Also, make sure that you are not using the mag as a tripod, or a hand hold, since both of these can cause the mag to be top, back edge tilted down in the well to cause the bolt over problem as well. P.S, You don't have a failue to feed problem, you have a mag stripping problem by the bolt instead. When you tested the single shot hold open, was the problem with the mags them, or later on, with say the rifle starting to foul out, and maybe the rifle not full stroking then? |
| That does make sense. These were the first shot fired from rifle and mag. Very first shots from GB tuning then full mag repeat test. After assembly I did fully clean and lube the rifle, but not the new mags I'll try that. The mag release lever is flush on the button and I don't use the mag well as a handle or anything. Thanks for your help on this I'll clean and lube the mags and let you know. So you are also saying maybe my buffer spring is more stiff maybe than his? |
|
Quoted:
So you are also saying maybe my buffer spring is more stiff maybe than his? Probably not the spring, but the T2 buffer you have in play causing more of a softer end of stroke impact (less jarring effect to assist the mag on recovering quicker) instead. Trust is, unless you are running Mk262 ammo, the standard weight buffer is all that is needed. The use of the H buffer in the M4 is due to the rifle needing to be able to cycle MK-262 ammo. With this ammo, it uses a slower burning powder, which cause higher working gas system pressure, and the weight of the buffer is used to slow the cycle back down to allow the residual bore pressure of spent case to the chamber to drop back down to normal pressure before the spent case is pulled (to prevent over function). In the military M-4, the heaver buffer works since M-193 and M-855 are hot as hell as well, but when drop down to standard 223 rem factory loads, just way to much mass of the buffer for the extreme difference in gas system working pressure from 223 rem back up to Mk-262. Simply, if you are shooting 223 rem load ammo, or ammo based on those gas system working pressures, then the standard weight buffer is all that is needed. So on that note, try a standard weight Carbine buffer, which may solve all your problems. |
Great clear explanation! Thank you! The only reason I put the heavy buffer in was for my wife. She loves shooting, but only weighs like 90lbs and isn't very strong so I was trying to work her in easy. Guess she'll just have to suck it up and work at it  not like they have much kick anyway
|
AR Sponsor