AR-15 teething problems?


September 19, 2004, 04:04 AM
So I'm now the proud owner of my very first AR-15.

LMT M-4 16" upper (cb, 1/7), Bushmaster lower, KAC RAS-II, LMT BUIS, ACE ARFX stock.

The stock was purchased from Model 1 Sales and came with the receiver extension, buffer spring, and buffer - which I suspect might be part of my problem.

Q3131A ammo. I know, I'll get better groups with heavier stuff in my 1/7 barrel.

I picked up an older GI 30-round mag and 3 "in the bag" SA-80 mags at the gunshow today.

Went home, gave the Beren Sunset Rifle a cleaning, made sure it was oiled as per the book, and hit the range.

Right away, I started to have problems with the mags. The first round simply was not feeding - the bolt wasn't stripping the round from the magazine. After fiddling with the magazine and reinserting it, I did get it to feed.

I only experience this malfunction after inserting a magazine, and it doesn't happen regularly. In every case, the magazine appears to be properly inserted and locked in place.

When the rifle cycles upon firing, it functions flawlessly.

The frequency of the "initial round feeding problem" declined as time went on.

Q1: How "snappy" should the bolt return to battery? Mine seems to return a little "soft", which might be due to a cheapo M1S buffer spring.

Q2: Is there something I should be doing to break in the magazines themselves? (As far as breaking in the rifle, the general consensus I received was "clean it, oil it, and shoot the darn thing for a couple hundred rounds. Then take it home, clean it, and do the same tomorrow.")

Q3: Inserting a mag with the bolt closed is difficult. I'm strong enough to force it in easily enough, but is that going to damage my AR? Or do I just slap it home?


Around round 80, I either had a light primer strike or a hard primer. In either case, the round didn't fire. Which brings me to another question:

From the book I was reading, it states that if you experience a misfire you have ten seconds to clear the round before you're in danger of a cook-off. However, general firearms safety states you must always wait at least 30 seconds in case of a hangfire.

Q4: Which rule takes precedence? Do I worry more about a cook-off or a hangfire?

Today, I followed the 10 second rule and made sure the ejected round went someplace safe for a few minutes. I finished the rest of that magazine without incident. After a few minutes passed, I inspected the "misfire" round. It looked like it had a proper primer strike, but the round hadn't fired. I put it back in a mag, charged, aimed, and squeezed the trigger. This time it fired.


General observations:

- My eyesight sucks. I need new glasses.

- I need to get back in shape!

- At first I was getting, ah, embarrassing groups at 50 yards, but I improved with time. Once I can achieve acceptable groups (4cm?), I'll worry about setting a proper zero. I'm reasonably sure it's me and not the rifle. :)

- That barrel gets hot!

- Aluminum mags are noticably lighter than steel. I bet that adds up if you're carrying 20 of them.

- I need to wear plugs under my muffs. At least, until I purchase that suppressor. :)

- I want a collapsing buttstock. It'd make transport that much more convenient. In a couple weeks I'll probably put down the cash for an LMT Crane or a Vltor.

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September 19, 2004, 05:02 AM
Q1: If you try letting the bolt close on an empty chamber, it should be similar with a round. There will be a noticeable difference, but it shouldn't be great. Hard to explain, but it's similar to a slide closing on a pistol with and without a cartidge.

Q2: Magazines should work right from the start. Do you have the same problem if you load the magazine with one round less than full capacity? It could be the first round is under too much spring tension. That would make it hard to strip off. Possibly that would improve with use, but it shouldn't be like that to begin with.
Another possibility is burrs on the underside of the feed lips, causing the 1st round to drag too much. The 1st round is under the most spring tension, and will be the 1st to show a problem like that.

Q3: The top round has to be able to move down into the magazine when pressed against the bottom of the closed bolt carrier.
When you insert a full, or partially full magazine, you will feel spring tension if the bolt is closed. It will take more force than an empty magazine, but it should not feel like you have to force it.

Try inserting a magazine with one less round than full with the bolt closed. A full mag should take only slightly more force.

If the bolt is locked back, it should take no force to seat the magazine. If you have to force the magazine in with the bolt locked back, then something is wrong. Receiver or magazine is out of spec.

September 19, 2004, 05:21 AM
- I need to wear plugs under my muffs. At least, until I purchase that suppressor What db rating are they? And almost more important, does your eye protection lift the ear seals away from your head? The seals need to make good contact all around or they don't work.

Steve Smith
September 19, 2004, 05:42 AM
Beren, please try what RJ suggested. Also, try chambering a round from a fully loaded 30 roung mag, with the bolt having been locked to the rear. If this is doesn't work well, I would guess a weak buffer spring is a possible culprit. The bolt should close smartly, like a vault. If it is "slow" then you don't have enough pressure from the spring. check the bottom of the bolt for drag marks (from mag lips).

Mags should be clean and DRY.

Aluminum USGI mags should be most reliable. SA80 mags might be ok, but don't take anything else.

September 19, 2004, 08:11 AM
Same thing happened the very first time I tried to chamber a round in my Bushie.

Be sure not to ride the charging handle at all. It only takes a very small amount of "riding" to cause a problem. Or, as Steve said, pull the charging handle and bolt carrier back, lock it there by pushing the bottom of the bolt release, and then release the bolt.

Also try some new USGI mags - the EE forum has some good deals.

September 19, 2004, 09:21 AM
I'm not really familiar with the ACE stock and how it attaches, but your problem sounds very much like the one I had when I replaced my A2 stock with an A1 and didnt swap out the A2 stock screw for the A1 screw, which is shorter. The gun would function OK when you pulled the charging handle to the rear and released it, but the bolt would over ride the round when you released the bolt using the bolt release after a mag change and would either jam or close the bolt on an empty chamber. I believe the bolt carrier was catching on the bolt stop and not the bolt head itself, leaving the bolt on top of the round. The problem can be intermittent too and can drive you nuts in diagnosing the problem. Dont know if this is the case here, but it may be worth looking at if nothing else seems to be it.

September 19, 2004, 10:44 AM
What db rating are they? And almost more important, does your eye protection lift the ear seals away from your head? The seals need to make good contact all around or they don't work.

The muffs aren't staying sealed. I'm cross-eye dominant, and 6'7" with a big head. :) So when I get a good sight picture, it often disturbs my muffs - if not immediately, then upon firing.

September 19, 2004, 10:50 AM
To clarify - I have no trouble seating a mag with the bolt locked open. Only when it's closed. Also, I generally have had no more than five rounds in a mag at a time - range rule.

The colt closes "smartly" with no mag, but it's somewhat sluggish with a mag. I do see some copper/bronze marks on the bottom of the bolt, but I thought that was from dragging over the next round in the mag.

I think I'm going to do three things:

1. Wear plugs under my muffs today.

2. Make sure I am not interfering with the charging handle whatsoever when I release it.

3. Order a new buffer spring. They're like $4.

Once I have free cash again (a week or two), I'll order some new GI mags.

And, I found a dealer who has a Gemtech demo unit he's moving for $450, with bi-lock. I think I'm going to put an offer on it, so long as it works and is still under warranty. :)

September 20, 2004, 08:38 AM
Second day at the range yesterday.

No malfs on cycling, but experiences more malfs when stripping the first round. If the rifle was canted at all upwards, I had to use the forward assist to finish stripping and seating the first round.

Going to replace the buffer spring and test again.

Bartholomew Roberts
September 20, 2004, 09:47 AM
Beren, are you having the problem with both the USGI mag and the SA80 mags? If so I would be more inclined to look at the gun. If not, try marking the mags that are in the rifle when the malfunction occurs. I am betting it is mag-related and that one or more of the SA80 mags is the culprit.

I believe Model 1 Sales is the old Nesard parts company. If so, then they are certainly not above slipping in whatever batch of low-cost parts they managed to dig up from whatever source. 90% of the time, those parts will work just fine; but occasionally, they will need some tweaking out of the box.

Q2: I ususally just shoot them and mark the ones that malfunctions occur on. I take the marked mags and compare the dimensions on those to a known good mag to make sure the mag body is in spec (distance to mag catch and feed lips being the dimensions I look at close). If those are good, I will try first replacing the spring, then the follower, and then finally I'll bin the mag if it still doesn't work.

With new USGI mags being $12 from TAPCO, you may not even want to do that now that the ban is over.

Q3: In my experience it hasn't ever damaged an AR; but it can be hard on the feedlips of the aluminium mags. It is pretty common for a full 30-round mag to be difficult to seat with the bolt forward though. Downloading to 28 rounds per mag will make this a non-issue.

September 20, 2004, 10:13 AM

I can cause the malf fairly regularly by canting the barrel at a slight upward angle with any of the four mags I have. It's possible all my mags are junk, but I hope not. Thanks for the pointer to TAPCO; I hope to pick up 10-20 more mags once funds are available.

I'm only inserting five rounds per mag currently, as per my range's rules.

Is it possible my Bushie lower doesn't like my LMT upper?

I have a Stag lower I plan to build up in a few weeks. If a new buffer spring or mags doesn't clean up the problem, I'd be curious as to whether I'd see the same issue with a different lower.

September 20, 2004, 10:38 AM
SA80 mags are okay. I always load 28 in a 30 mag so there is no feeding problems or bolt-riding problems.

Pull T handle all the way back, let go. Then push the handle back into it's locked position.

Bartholomew Roberts
September 20, 2004, 01:53 PM

It seems plain that the bolt carrier doesn't have enough oomph to strip the next round from the magazine and feed it. Here would be the things I would look at:

1) Are the mags using "heavy-duty" or "extra-strength" mag springs? These are frequently sold as "reliability" upgrades; but can sometimes work against reliability by putting too much tension on the ammo.

2) Buffer spring - it isn't unheard of to get some springs with a bad set in a parts kit. Replacing the buffer spring should be a cheap patch.

3) Out of spec parts are causing the bolt carrier group to impact with something it should not be striking and this is slowing it down and leaving it unable to strip the rounds out of the mag.

Places to look:
3a) Buffer retaining pin in the lip of the buffer tube - if this comes loose, it can do this quite nicely
3b) Mag catch location too high / bolt stop out of spec - causes BCG to catch here
3c) Out of spec mag bodies - feedlips stick into path of BCG - probably not an issue since your GI mag has the same problems.
3d) Improper dimensions of the bolt carrier or bolt itself

The easiest way to check these issues is to get someone with an AR that is a known performer and start swapping parts to diagnose the problem. One of the things with an AR is that a lot of different issues can display similar symptoms. Once you know what part is causing the problem, it becomes a lot easier to diagnose what is going on and correct it or replace the part if necessary.

Edited to add:
4. Tolerance stacking - Parts kits can often have parts that are just a little outside of the normal specs. In most cases it doesn't affect functioning but if two or more parts that are a bit too fat start working against each other, the gun may not be reliable until the parts wear each other down some. You should see obvious wear marks in the upper if this is the case.

September 20, 2004, 03:36 PM
I had a similar problem with my BM not stripping the first round properly, but that was with fully loaded mags and using the bolt release. After about 300-500 rounds (not too sure of the number) it was broken in and I haven't had any issues. Give it some time and a good cleaning and it should break in just fine.

September 20, 2004, 08:14 PM
The SA80 mags have the mag catch notch positioned a hair lower than conventional AR mags. You may need to raise the notch a bit with your particular lower/mag catch.

Bartholomew Roberts
September 20, 2004, 10:35 PM
Also, here is the acceptable range of lengths for the carbine buffer spring

CARBINE: 10 1/16 inches (25.56 cm)
minimum to 11 1/4 inches (28.58 cm)

I'd check to make sure your buffer spring is within that range.

Steve Smith
September 21, 2004, 01:21 AM
Bart gave a good list. The rifle should load and feed no matter what angle it is at.

If you see brass marks on the bottom of the carrier that is normal, but if you see scratches in the grooves of the carrier, that is mag feed lips and a bad thing. High bolt stops do happen, as to mags sitting too high, but that is pretty rare. Buffer and mag springs are the most likely culprits, I think.

Oh, btw, you know I shoot an AR a LOT. I don't wear muffs because of the same thing you ran into . I suggest the custom made injection molded plugs.

September 21, 2004, 08:03 AM
Thanks for the tips on plugs and spring length. What's the acceptable range for a rifle length buffer spring? I believe that's what my ARFX stock uses, not the carbine length.

I have a better solution in the works than plugs. :) I found a local C3 dealer who stocks Gem-Tech M4-96D suppressors, and the paperwork starts in a few weeks once I have pics and money in hand. That said, I'll still need to use the plugs in the meantime. I'll double up with plugs under the muffs.

I'll check the bolt carrier grooves for scratches. I don't recall seeing any, but I may not have recognized what I was seeing the first time either.

Bartholomew Roberts
September 21, 2004, 09:03 AM
A Gemtech! Color me green... I've been looking at one of those for months now; but no relief in sight on the financial front.

Here are the Rifle specs:

RIFLE: 11 3/4 Inches (29 85 cm)
minimum to 13 1./2 inches (34 29 cm)

Check the buffer spring for kinks or any other obvious weak spots as well.

September 21, 2004, 07:12 PM
I had the same symptoms on a build. I played with the parts a little bit, and found that the bolt carrier was a slightly too snug fit in the upper. I think YammyMonkey was on the right track on just shooting it 'til it loosened up a bit, but I swapped in a used bolt carrier. That fixed it for me.

Try just sliding the bolt carrier back and forth in the open upper and see if it feels snug. A stronger buffer spring will overcome that, sure, but also try a different bolt carrier for kicks.

Oh, and I wear plugs and muffs, too.

September 26, 2004, 03:41 PM
A new buffer and buffer spring from a Bushmaster buttstock kit appears to have resolved my feeding issues. It looks like Model 1 Sales had bundled a cheapo crap spring with my Ace buttstock bundle I'd purchased from them.

September 26, 2004, 04:14 PM
BTW, there was a guy with a chrono at the range this morning. He was nice enough to let me put some shots through it with my AR. Q3131A was averaging in the high 2800's from a 16" barrel, about 10 feet from the muzzle.

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