New AR Build Issue

[.Scarecrow.]

I just built a new AR and I have an issue with chambering. It WILL chamber but seemingly only with the full force of the BCG from the rearward most position. It also is not easy to pull the BCG rearward when a round is chambered, it seems to be a little stuck unless you pull on it with both hands, then it will come free and eject the cartridge.

Is this normal "Break-in" behavior for a new build?

Parts

Sionics Barrel
Rainier Upper
Griffin Armament Enhanced BCG

 

[kwg020]

Are you shooting reloads? It sounds like the brass/rounds are not sized right. Also confirm you are using the correct ammo for the rifle chamber.

 

[MachIVshooter]

Is this normal "Break-in" behavior for a new build?

Sometimes.

If it runs alright, don't worry about it. And don't condemn it if it hiccups during the first couple mags

 

[MistWolf]

If using reloads, it could be your ammo. From your description, it sounds like it takes too much effort to extract the unfired round. You may need to scrub the chamber with a brass brush if there is any preservative in there.

In any case, contact Sionics. They're good folks and will take care of you

 

[.Scarecrow.]

I have not shot the weapon, but after chambering and ejecting a few snap caps, it seems to have loosened up. However, in the process, some of the melonite finish has worn off the front of a few locking lugs. Is this anything to be concerned about?

 

[MachIVshooter]

No.

You have to remember when assembling with components from multiple manufacturers that tolerances and tolerance stacking can just as easily render a rather loose or very tight final product as one that is just right. Bolt lugs that are at the max and barrel extension at minimum gives the condition you describe.

It will wear in.

And FYI, the bolt itself is probably just parkerized, maybe nitrided. I've never seen a melonited bolt.

 

[Tirod]

There are now completely melonited bolt assemblies. I bought one about three years ago, and they are getting common.

Two things, lube the upper pin channel, the TM states heavily, which means drippy wet. The cam pin has to flip up and turn the corner in the upper to unlock, there are square edges which may need some room to accomplish it.

As for loading it, yes, anything less than a complete travel from the rear will cause misfeeds. The action cycle requires it, anything less isn't correct. When loading, pull back on the charging handle and lock the bolt to the rear. Insert mag, punch the button and let the BCG slam forward. That is exactly what the action would do if fired - so it's not going to damage or break anything.

Self loading actions are designed for this sort of slam bam thankyou activity. Again, anything less is what causes issues.

Don't ride the charging handle, lock the bolt back.

 

[carbine85]

Does your bolt slide into battery easily with out a round in the chamber?
You should also be able to push it in with a very small amount of pressure from your thumb.
Do this with the upper opened.

 

[LiveLife]

If you assembled the barrel to the upper receiver, you should check the headspacing.

I use go/no go gauges to check.

If bolt won't close with "go gauge" the chamber is too short.

If bolt will close with "no go gauge" chamber is too long.

I use Clymer gauges and they are about $30.

 

[HOOfan_1]

And FYI, the bolt itself is probably just parkerized, maybe nitrided. I've never seen a melonited bolt.

Melonite is just a brand name for nitriding

 

[.Scarecrow.]

The action is very smooth when there is no round in the chamber, feels better than other guns I've felt because I used a chrome silicon buffer spring. But anyway, now it hangs up just a little bit when I try to eject the round. I also noticed that when I was chambering the round, it left a very small dent in the primer. Is this of any concern?

 

[HOOfan_1]

ARs have a floating firing pin. There is no spring to stop its inertia when you let the bolt carrier go forward so it will hit the primer and leave a dimple.

I use standard CCI small rifle primers and have never had a problem, but some people suggest harder rifle primers.

 

[.Scarecrow.]

That's kinda what I was thinking about after i posted that.

 

[Tirod]

There is a difference in hand cycling the action and having 55,000 pounds of gas pressure doing the job. So far the gun has only been cycled by hand.

Nothing wrong with hand cycling to help smooth the rough edges but shooting it will do it a lot quicker. The only significant symptom so far is having to pull the charging handle back with two hands - that is an excessive amount of pressure needed. Something isn't right if it takes that much effort.

The BCG should be able to lock and unlock with heavy pressure by thumb on the recessed area exposed in the ejection port. If it won't - then something isn't right. Snap caps are not a valid means to checking function as they are polymer and may not be uniform or the correct size.

Empty brass cases would be a better choice in checking function. Does the action require the two handed pull retracting the bolt on an empty chamber?

The answer is in the details, each one is significant when the gun cannot be held and manipulated in real time. This is why a 30 second check by an experienced user/builder takes a week on the internet.

 

[.Scarecrow.]

Well when I had my Daniel Defense, I wasn't even able to close the bolt with my thumb of that one, so that's just me being a wuss. In terms of needing two hands for the ejection, that was only with a snap cap. With a loaded shell it only hangs up a little so far, and by a little I mean just enough to notice if you do it slow. But it's definitely not hard to extract. I will try an empty shell today.

 

[Blade First]

Please note that Melonite [Tenifer, Nitron, etc.] is more than a "finish" and you are not losing the benefits of the nitro-carburizing if you see the black oxide wearing off.

 

[maxxhavoc]

Split the rifle, remove the bolt, and push one of the rounds in the chamber with your thumb.

Turn the muzzle up, and the round should drop free. If it doesn't, post back here.

 

[.Scarecrow.]

Round drops free, casing alone does not. Just being clear.

 

[.Scarecrow.]

I'd also like to go back to the wear on the bolt lugs. It has only worn really on the bottom ones. 2 or 3 on the bottom are now down to bare shiny metal, while the top ones are untouched. Is this wear pattern a problem?

 

[MachIVshooter]

I'd also like to go back to the wear on the bolt lugs. It has only worn really on the bottom ones. 2 or 3 on the bottom are now down to bare shiny metal, while the top ones are untouched. Is this wear pattern a problem?

Probably not, but rather than beat your head against a wall, just go see if the thing runs. You can check headspace if you want, but if it fires, extracts, ejects and chambers the next round without a problem, don't worry about it. Go run a mag, then pull the BCG and make sure you don't have a cracked or broken lug. Run a couple more mags, check it again. After that, just shoot the snot out of it.

Machine parts just need to wear together a little for everything to smooth out. Ever build an engine? No matter who did the machine work, no matter how good they are, no matter how high quality the components you use, there will be metallic debris in the oil on the first oil change, which is why we do it after a short break-in.

 

[AR-15Nutt]

.223 Rem./5.56mm NATO chambers vary with makers, i have been reloading this caliber for many years with RCBS SB resizing die, the ammo functioned fine in all my AR's, Bravo Co. had a sale on "Blem Uppers", i bought one, when i tried to shoot my reloads in this upper they would not chamber, so i tried new ammo and had no problems chambering, when i visited my local ACE Hardware, there was a set of new RCBS SB dies, i bought them, reloaded 100 rnds. of ammo and they functioned just fine in all my AR's, RCBS told me to send the resizing die back as it is obviously out of specs for a SB die.

conclusion: all .223 Rem./5.56mm NATO chambers vary with makers, maybe just a few thousands/ten thousands of an inch.

are you using new factory ammo ?

 

[.Scarecrow.]

Yes, some XM193 and PPU.

 

[.Scarecrow.]

Put a magazine through it, ran like a champ, and it feels significantly smoother.

 

[ac6916170]

Lower lugs showing wear and not the top ones is probably caused by the receiver not being squared prior to the barrel being installed. "MAY" wear out the bolt sooner to where a lug breaks, more than likely not. You really can't tell whats going on with it until you shoot it.

 

[MachIVshooter]

Lower lugs showing wear and not the top ones is probably caused by the receiver not being squared prior to the barrel being installed. "MAY" wear out the bolt sooner to where a lug breaks, more than likely not. You really can't tell whats going on with it until you shoot it.

How exactly do you "square" the receiver before installing a barrel on an AR?

(Before you answer this question off the cuff, remember that some of us are very experienced with building ARs, including machining parts from raw stock)