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Posted: 8/11/2017 8:37:09 AM EDT
[#1]
Maybe the lower isn't the issue. Have you tried different uppers?
Also I'm a bit confused, At first you say it shoots long 6-7 rd bursts, to me that's a bad sear or trigger not catching and letting it run long or a super high rate of fire making it hard to do short bursts. But the. You said it was not cycling and you had to cycle manually, that sounds like a bad gas block not letting enough gas in to push the BCG and eject the round. |
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Posted: 8/11/2017 9:58:43 AM EDT
[#2]
If nothing has been changed for years, I would look at replacing all the springs in the gun and maybe the FCG.
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Posted: 8/11/2017 10:05:56 AM EDT
[#3]
Check or just replace the hammer/trigger/disconnector/sear springs. If they are weak/broken the timing will go off. Make sure the selector is not worn and that the selector detent (and spring) is not worn (allowing the selector to wiggle when firing). If the hammer is worn where it catches the sear it could allow hammer to follow the bolt and cause the stoppage. Also check the disconnector "tail" for wear .... after all it has been "years"
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Posted: 8/11/2017 10:11:27 AM EDT
[#4]
Like changing your oil in your car X number of miles.
For an M16, need to change all the springs out in the lower about every 5k to 6k rounds. That includes hammer/trigger, disconnector, and the buffer spring. You shouldn't really need to change the sear spring, but you can if you want. |
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Posted: 8/11/2017 6:32:02 PM EDT
[#5]
Thank you for the replies. To clarify, the first problems were shorter and short bursts, but now its become a bolt action in full auto. Technically not full action because it does eject the spent round and chambers a new one, but longer fires and the trigger doesn't move, thus when I pull the charging handle a loaded round emerges.
I have tried swapping two other complete fullauto carriers/bolt/pin with no change. Have no tried swapping complete upper half. I'll give the area mentioned another inspection then proceed to investigate the springs. |
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Posted: 8/16/2017 2:12:39 AM EDT
[#6]
Couple more thoughts.
Does the fact that it functions perfectly in semi but not in full help diagnose this? Makes me look to the auto-sear. I have a couple lower parts kits (semi of course). I've built several semi lowers, but never touch a full. Any pitfalls I should watch out for? Any springs that will be different? Thanks. |
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Posted: 8/17/2017 1:08:12 PM EDT
[#7]
I would just pick up a new fcg and springs and see if that fixes the problem. They install just like every other AR fcg.
FA FCG |
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Posted: 11/20/2017 12:30:49 PM EDT
[#8]
Any updates on this?
My SP1 RR was approved last week..waiting on stamp |
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Posted: 11/20/2017 3:16:22 PM EDT
[#9]
I'm not the OP, and I don't have any more info to give than what was offered above:
Change the FCG springs, and if necessary, the FCG parts as well. After all, you don't know if the previous owner(s) never "changed a thing" on it for years
That's what I plan to do when my Olympic Arms/PAWS RR transfers to me. |
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Posted: 11/20/2017 3:56:50 PM EDT
[#10]
If it's functioning in semi, you know you have serviceable springs in the FCG, a functional disconnector, and good sear surfaces on your hammer and trigger.
FCG springs won't affect "timing".....the auto sear either catches the hammer and releases it when the carrier trips it, or it doesn't.... I'm guessing bolt bounce due to a weak recoil spring, or maybe something went wonky with your buffer...... With it empty, set to auto, pull the trigger, and slowly cycle to verify the auto sear is releasing the hammer when it should.....(check your timing).....if it's on, pull the recoil spring/buffer, and drop 3-4 quarters down the buffer tube....then return spring/buffer, and give it a try with ammo..... If that fixes it, get a new recoil spring and make sure you have a proper weight buffer... |
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Posted: 11/20/2017 5:10:03 PM EDT
[#11]
Quote HistoryQuoted:
For an M16, need to change all the springs out in the lower about every 5k to 6k rounds. . maybe every 20K |
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Posted: 11/20/2017 5:30:17 PM EDT
[#12]
Did you figure it out yet? Where is the hammer? When you shoot it on full-auto, and it fails, flip the upper open and see if the hammer is locked back, or if it followed the the carrier back. If it's extracting and chambering, it's unlikely it's in the upper.
I am leaning towards something in the lower, as stated earlier, change all the springs. If that doesn't work, I would look at the sear, hammer, and trigger. If it works in semi, chances are it's either a worn sear or the sear catch on the hammer is worn. Jason |
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Posted: 11/20/2017 9:08:29 PM EDT
[#13]
Quote HistoryQuoted: your kidding right? maybe every 20K If you are running milspec configurations and calibers, the springs might make it to 20k rounds. I change them at 10k because I cannot afford to buy a replacement M16 if this one breaks. But if you are running 10" uppers or shorter, or calibers other than 5.56 (9mm and 7.62x39 are particularly hard on '16s), it is a really, really good idea to swap out springs much sooner than that. Again, Your Mileage May Vary. |
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Posted: 11/20/2017 9:22:39 PM EDT
[#14]
Quote HistoryQuoted:
Did you figure it out yet? Where is the hammer? When you shoot it on full-auto, and it fails, flip the upper open and see if the hammer is locked back, or if it followed the the carrier back. If it's extracting and chambering, it's unlikely it's in the upper. I am leaning towards something in the lower, as stated earlier, change all the springs. If that doesn't work, I would look at the sear, hammer, and trigger. If it works in semi, chances are it's either a worn sear or the sear catch on the hammer is worn. Jason |
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Posted: 11/20/2017 10:23:20 PM EDT
[#15]
“Beta dumps”, you say? I’m betting that the issue is with the upper, specifically the gas port in the barrel. It’s probably a bit toasted...
After thousands of rounds of use and (especially) abuse, the AR gas port becomes flame-cut, eroded, and in effect “larger”. This problem is more pronounced when the gas port is closer to the chamber, making “carbine” gas systems more susceptible to this issue than “rifle” gas systems. A larger than ideal gas port on an AR will manifest itself as good ol’ “bolt bounce”, which is almost certainly what the problem is with the OP’s rifle. An easy way to check this is to swap in a heavier buffer. An SP1 would’ve originally had a standard carbine buffer, which is marginal for full auto at best. Try swapping the carbine buffer with an “H” buffer or even an “H2” buffer, and I’ll bet the problem “goes away”, at least until the gas port erodes a lot more. Then you can keep putting in progressively heavier buffers, install an adjustable gas block, or fix the problem by replacing the barrel. |
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Posted: 11/21/2017 12:13:41 AM EDT
[#16]
Quoted:
I have a Colt SP1 RR, s/s/a. Been rock solid for years, beta mag dumps no problem. Never changed a thing since I've owned it. Recently it started to only fire long bursts (6,7,8etc) but perfectly in semi. Did a heavy cleaning, then tried again, a couple 3 or 4, then single, yet perfectly fine in semi. This time spent good time cleaning and inspection shows no obvious issues, breakage, or excess wear with any parts (auto-sear appears pristine to my novice eyes). Next took it out and tried swapping complete bolt carriers, same issue. Multiple full auto carriers, magazines, ammo, no change. Semi perfect, full only is bolt action. First round fires, then nothing. I pull the charging handle, and loaded cartridge ejects. Now fires once, and same issue. I'm at loss, maybe it's something obvious another pair of eyes would see, but hoping this sounds familiar to someone. Since this is a A1 fire control groups, means that we don't have to worry about a burs cam or burst disco in play. So first thing is to check the disco, being that with the selector in Full, when you pull the trigger back and hold it back, make sure that the selector is camming the back of it down and out of play. Hence you should be able to hold/tie the trigger back with the selector in full, cock the hammer to the auto sear, trip the auto sear, and the disco should not catch the hammer on release as you ride it by hand past the sear. Note, with the selector set to semi, the back of the disco is not cam'd down by the selector to take it out of play, and when you hold/tie the trigger back, when you release the hammer for the auto sear, the disco should catch the hammer. Note, disco spring gets installed large coil side down into the rear trigger tail that you may have to seat with a pair of plyers; not the small end down with the large coil side up against the tail of the disco isntead. Now lets check the auto sear timing. Again, tie or tape the trigger back, selector set to full, pull back on the charging handle and with both a #44 and #45 drill bit, where going to use the back end of them to check the auto sear release timing. We start with the #45 drill bit of .086", and as you are riding the charging handle back forward, put the back end of the drill be between the face of the carrier and the face of the bolt. With the drill bit between the two, the auto sear should not release the hammer. 
Next we do the same with the back end of the #44 drill bit that is .082, and since the correct gap for the auto sear to release the hammer is at a .084" gap, the auto sear should release the hammer just about when the carrier/barrel extension, and the back of the #44 drill bit all touch each other. Now at this point will bank that the auto sear dropped the hammer when the gap was .086, hence the #45 drill bit, so break out a 3/32" drill bit that is .0938 and test again to see if the auto sear release is this advanced. Get us this far on what the release timing is, and the conditions of your FCG and receiver channels as well. |
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Posted: 11/21/2017 7:03:18 AM EDT
[#17]
Quote HistoryQuoted:
I had a dd big hole upper that sat a little loose and it would tilt up enough that the sear would not trip and the hammer would be back with the sear holding the back of it. That problem went away with that upper, but it did not happen to where I noticed it when I first used that upper. |
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Posted: 11/21/2017 4:21:56 PM EDT
[#18]
I have a stripped big hole DD upper that I'll build out eventually...using small hole with adapters for now. I bought like 5 in case some work better than others...
Hope you get this sorted out! throw a SSF into it anyway |
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