Diagnose AR Malfunction

[Coronach]

I think I know what it is, but I'm not able to test the hypothesis until after the first of the year...

OK. I assembled an AR a few weeks ago, and finally got to test fire it today. Here are the particulars of the rifle:

Used M16A1 upper from Ohio Ordnance Works (outside looks like heck, but the innards look good)

Bravo Company complete BCG

RRA stripped lower

Armalite LRPK

RRA receiver extension/buffer tube

Cav Arms C1 stock

RRA A2 buttplate

Milspec rifle buffer and buffer spring from Bravo Company

OK. So, I went out and sighted the rifle in, using an old 20-round magazine for shooting off the bench. I loaded 3-5 rounds for each shot string, and I had it sighted in PDQ. Looks like the previous user had it dead nuts on for windage, and only slightly off for elevation. The gun was accurate and reliable throughout sight-in.

After getting it sighted in, I loaded up a 30-round magazine with 30 rounds, slapped the bolt release, and prepared to have some fun. I pulled the trigger and...

no workie.

Hrm. I flip the rifle on its side and note that the bolt has not gone into battery. It has stopped about 3/4" short of lockup. I clear the rifle, reload the magazine, and try it again. Same deal.

I try a few more times, with that mag and different mags (all known good), and each time the bolt would not go home. I back off the rounds in the magazine, and it turns out that the gun will function fine with a magazine under one-third load (less than 10 rounds).

What's the diagnosis?

Here's my guess:

I ordered rifle and carbine buffer springs from Bravo Company. They came unmarked. I think I may have goofed up and fitted a rifle buffer with a carbine spring. Alas, I JUST headed away on vacation, so I can't just swap out the spring easily to see, unless I can find a known-good rifle buffer spring somewhere nearby (or, unless I order another one, which just seems silly).

Questions:

1. Would that mistake cause the malfunction?

2. How do you tell the two springs apart? I thought the longer spring would be the rifle spring, but I may have been wrong.

Thanks,

Mike

 

[mr.trooper]

Sounds like the magazine spring is overpowering the buffer spring. Replace.

 

[Coronach]

You think the buffer spring was mixed up (car for rifle), or just bad?

Mike

 

[taliv]

coronach, i haven't thought it through yet, but for the record, I believe teh action spring lengths are as follows:

rifle: 12.5" 44 coils
carbine: 10.7" 36 coils

go figure out which you've got and we'll ponder this a bit more

 

[longdayjake]

Put more lube on the bolt carrier! This is a common problem that people get when they don't have enough lube on their bolt carriers. Also, most fellas only load 28 in their 30 round mags for that same problem. That and they are easier to lock in with just 28 rounds in. Try the lube thing first but have a new buffer spring on hand if it doesn't work. My money is on the lube. I speak from personal experience on this one.

 

[wally]

Assuming the mags work in other ARs (you said "known good") its not that the mag spring is too strong so its logical to assume the buffer spring is too weak.

Make sure the bolt carrier is not binding in the buffer tube, or elsewhere. Other than that, good chance you got the wrong spring in there. Sorry I can't tell you which would be which.

--wally.

 

[W.E.G.]

buffer and spring info

http://m4carbine.net/showthread.php?t=6827

 

[Coronach]

Put more lube on the bolt carrier! This is a common problem that people get when they don't have enough lube on their bolt carriers.

Maybe. I tend to be sparing with the lube. OTOH, I tend to be sparing with the lube on my other rifles, and they run fine. Perhaps the interior of the A1 upper was a little tight...it looks like they did some quick and dirty refinish on it.

Also, most fellas only load 28 in their 30 round mags for that same problem.

Yeah, but this one was doing it with only 11 rounds in the magazine, so I'm going to guess that this is not the problem

Mike

 

[Coronach]

Taliv-

Hrm. I'm 99% sure I put the longer spring in there, but I'll pull it and check.

Mike

 

[Coronach]

huh.

12" even, 42 coils.

That doesn't match either carbine or rifle buffer spring specs. Thanks, Bravo Company!

Mike

 

[taliv]

well, by some coincidence, i also bought 3 carbine and 1 rifle spring from bravo last month. until you mentioned it, i hadn't bothered to measure them, but I just did and much to my amazement, all 4 are the same length! (12" exactly)

one is noticeably different color than the other three (sort of a silvery) so I assumed i'd received one rifle and 3 carbine like i'd ordered.

reckon i'll be calling them in the morning

 

[Coronach]

Direct them to this thread. And yeah, mine look like yours. Close to the same length, two silvery, two more golden or yellowish. IIRC, the two silvery ones are slightly shorter than the other two.

This doesn't bode well for either of us, I'm afraid. My rifle spring doesn't seem to work right, and your Carbine springs are a different length than mine.

Nice.

Mike

 

[taliv]

fyi, coronach, after about 15k rounds on my old spring, i experienced exactly the symptoms you described about halfway through the last stage of the creekside tactical rifle match
results: http://www.ar15.com/forums/topic.html?b=8&f=35&t=332712
pics: http://www.ar15.com/forums/topic.html?b=8&f=35&t=332528

the carrier/spring just didn't have enough uummph to go into battery, despite being well-lubricated (and covered in blue sand and red mud).

that's what led me to place the bravoco order and i swapped that spring (and buffer) out with new bravo parts and shot two more 3gun/rifle matches last month with no issues. so i assumed problem was solved. now i'm not sure

 

[taliv]

and your Carbine springs are a different length than mine.

bizarre

 

[Coronach]

It could just be a break-in issue, too, but I'm really displeased that the springs I ordered from BravoCo, supposedly the place to go to get in-spec parts, do not match up to spec. Of course, the specs listed on m4carbine could be wrong, but I bet they aren't.

This sort of thing just chafes my nether regions.

Mike

 

[taliv]

well, i wouldn't freak out yet til we make sure we didn't just receive the wrong parts, or mix up the rifle/carbine springs. that's entirely possible given that i placed my order right at the peak of the obama craziness

 

[Coronach]

Me, too. But, here's the thing. We just examined our springs (well, the ones we could...3 of mine are 300 miles away), and they don't match either spec, rifle or carbine. If it was just a mixup, what did they mix them up with?

Not the end of the world, but still. Annoying.

Mike

 

[taliv]

well, their carbine spring ad does say " Made to M4A1 Mil-Spec specifications. "

while their rifle spring ad says "Action spring for M16, M16A1, M16A2, M16A3, M16A4.
For use with a full size M16 Rifle buffer and full size rifle M16 receiver extention. " (and has a pic captioned "carbine action spring")

perhaps the latter is NOT made to spec?

 

[longdayjake]

Maybe. I tend to be sparing with the lube.

Before I got into the ar15 platform I used just enough oil to coat metal to metal parts on my rifles as well. Not until I got an AR did I realize that new ar15's need to be heavily oiled (wet to the touch) just to function correctly. However, though I believe that oiling it well will help, I agree that there may be some other problem. Good luck to you.

 

[Coronach]

perhaps the latter is NOT made to spec?

Perhaps. You have two carbine and a rifle spring, per BravoCo, there, correct? Do any of them match the milspecs for either carbine or rifle springs?

Thanks,

Mike

 

[longdayjake]

A couple of questions. Did you use the bolt release to load the rounds or did you pull back on the charging handle? This problem often occurs if you let the bolt drop too slowly. Also, are you familiar with the ar15 or is this your first one? If its your first one take comfort in knowing that many people experience trouble with their first AR if they haven't much experience with them. I was one. One thing that you might try to see how bad the spring is is to put one bullet in the chamber by hand and then drop the bolt. After you drop the bolt put a loaded mag in (I suggest 28 rounds). Fire the first round and let us know how far the bolt pushes in the next round. I have always found it fun to try a bunch of experiments to try and diagnose the problem and then get it to finally work. I hope you end up getting a working rifle and enjoy the effort it took to get it to be "your" rifle.

 

[mljdeckard]

Crap. I just assembled a lower, I didn't have a stock, so I borrowed a cheap 3-pos from a friend to hold in the buffer pin and rear TD pin detent, I think both springs were in the box, now I don't know which one I used. I planned on using a different stock anyway, but....crap.

 

[taliv]

well, there seems to be some disagreement about what the spec really is. (imagine that)

my numbers came from a reference CD I got in Caputo's AR Operator Diagnostics class (which appears in turn to have come from a post about colt's on biggerhammer). http://www.biggerhammer.net/ar15/pins.html

rifle: 12.5" 44 coils
carbine: 10.7" 36 coils

the post on m4c WEG linked to has conflicting info. one spreadsheet (copyright "slash's heavy buffers" wth? doesn't sound spec to me) says

rifle: 12.75
carbine: 11.25

and another

Carbine 10 1/16" to 11 1/4"
Rifle 11 3/4" to 13 1/2"


so who knows? i'm afraid to go look at arfcom for fear I'll find 8 more versions of "mil-spec".

like I said earlier, all 3 of my new springs are 12" even.

 

[SHvar]

A good friends colt Hbar still does the same thing on a rare occasion. It was a used rifle, but the original owner had more money than sense, the lack of sense to reseach and take proper care of the expensive rifle he bought new.
The thing was sticking, it was so tight, so stiff. I told him to put a bit more oil than just a thin coat on the bolt and carrier group the first few times he oiled it. After a bit extra oil, and around 100 rds it was no longer so tight, and since then did not go completely into battery 2 times, this took a very light tap to finish the movement forward.
After another 50-100 rds it seems to have loosened up and stopped sticking.
By the way his full size rifle spring is the same length as my 16 inch carbine rifles spring, but the colts spring is thinner.
I think you have a lack of enough oil for a new tight setup, like working on cars, firearms can have difficult problems that the real issue can be very simple, and not require over thinking it. Always start with the simplest remedies, and work your way to the most difficult expensive remedies.

 

[Coronach]

like I said earlier, all 3 of my new springs are 12" even.

How many coils?

A couple of questions. Did you use the bolt release to load the rounds or did you pull back on the charging handle? This problem often occurs if you let the bolt drop too slowly.

Dropped it from the bolt release.

Also, are you familiar with the ar15 or is this your first one? If its your first one take comfort in knowing that many people experience trouble with their first AR if they haven't much experience with them. I was one.

I don't consider myself an expert, but it's not my first AR. My other ones run like tops.

One thing that you might try to see how bad the spring is is to put one bullet in the chamber by hand and then drop the bolt. After you drop the bolt put a loaded mag in (I suggest 28 rounds). Fire the first round and let us know how far the bolt pushes in the next round. I have always found it fun to try a bunch of experiments to try and diagnose the problem and then get it to finally work. I hope you end up getting a working rifle and enjoy the effort it took to get it to be "your" rifle.

I'll try that the next time I'm out. I'm pretty sure, though, that it won't feed with anything over about 10 rounds. I'm not sure that it is a buffer spring issue (though that seems likely) or a lube/break-in issue (also possible). One way or the other, there is insufficient forward force to overcome the resistance of a loaded magazine. I'm sure I can get it running with either more lube, more break-in, or a stronger buffer spring.

Mike