I went out to shoot my new SBR this weekend and, well, it didn't go as planned. First things first, when dropping the bolt on a new mag the round would catch on the feedlip, then eventually insert.

The fun part happened when I pulled the trigger, I got a click and no bang. Ejected that round, another inserted, another no bang. Another pull of the charging handle and bang. Then another click. It fired 3 rounds and dropped the hammer but no firing maybe 10 times. Once the bolt visibly didn't go in to battery. I tried another new bolt I had with me and same story.

Any ideas? Wondering if there is an extension issue.

The barrel is a Ballistic Advantage 7.5"
The upper is an Aero
The BCG is the AIM V2 (both that were tried)
Upper was assembled by Adco

I tried the BCG on another new rifle with me and both were fine there. So this is isolated to something on that upper in my mind.

Thanks for your opinions.

Is bolt fully locking Into battery?

Check your FCG springs, the hammer and trigger spring legs in particular.
If you didn't get them right they will not work properly. I know from experience.

Hammer spring backwards?

I can confirm the hammer and trigger springs are in right, I checked a few times (my OCD kicked in).  

I'm wondering if it might be a matter of the bolt not going in to battery.  I know at least once it got hung up --- but when I cycle it at home, it goes right in.  So bizarre.  

I'm not sure Adco checked the headspace, so I'll do that (never hurts to double check, even if  they did) so I'll look at that as well.

New build? Not going into battery every single time? How dry is it?

You'll hear a lot of old timers saying you should "run it wet" all the time. While I disagree with that as an overall rule - it's definitely a good thing to do through the break-in.

I'd double check your headspacing. An issue you may be running into is tolerance stacking. While all your parts may be within spec, the barrel extension may be to one extreme of the spec range while your BCG may be to the extreme in the opposite direction, which could cause your headspace to come up just a bit tight. As for your feeding issue, have you verified that your barrel extension is compatible with your upper receiver? (ie- both M4 or rifle style feed ramps)

Post a pic of your feed ramps and also your fire control group inside the lower.

Here are a few pics

FCG: https://goo.gl/photos/1PYhZ8dbM1dNbSu39

Lips 1: https://goo.gl/photos/5Ny1oozi9vyvHmL88

Lips 2: https://goo.gl/photos/gSeg5iTApZd95Siz9

Hi, I would ask a mod to move this to the troubleshooting forum. Dano and Sully are AR troubleshooting gurus. First, Im not a gunsmith or an armorer. I've been around the block once or twice and I'm always happy to share what I've learned about AR-s with others. If I can. If not, I keep my mouth shut. A possible headspace issue did come to mind. Firing pin protrusion also came to mind. Please let me mention something about having your AR go "click" but no "bang". I've heard about and seen multiple stories and videos of AR's going ka-boom. Many times, it starts out with a click and no bang. Gun gets racked chambered new round same thing no bang, a third, a fourth time then the ka-boom. If you get a click no bang STOP! Check your chamber, barrel, upper, bolt, magazine and try to find the problem. That first click could leave an obstruction (bullet) in the chamber/bore. You have to check this each time. Watch some YouTube ka-booms. Click, click, click Ka-boom! It seems to be a common denominator. That said, move this over to TS and the big dogs over there will get you fixed up. Good luck, I'll read along over there too so I can avoid a similar problem. -CB

Not sure why, but I can't view your photos. I'd like to help you, but without seeing your pics I can't do much...

Mods will likely not see this. Too damn busy to scan threads.

Use your REPORT button, it'll get moved to the appropriate forum.

If you don't have another SBR/pistol lower you can't test that upper on a rifle lower, but you could throw a rifle upper on the lower and see if it works.
Swap out the fcg from a working weapon. Compare everything. What looks different?

The troubleshooting forum is very dead. Tried there first and got a single response. Since this was a build, thought I'd pull from the collective knowledge here.

What FCG are you using?

For your feeding issues, use a felt cone polishing bit on a dremel to massage the feed ramps to match the receiver and take off the sharp corners that are visibly catching bullet jacket.

As stated, for break-in, run the upper wet.  If your hands are clean enough after handling the BCG that you wouldn't think twice about eating finger food, add more lube.  Once things are worn in, you can lube to preference.  To save money on ammo, I hand-cycle the rifle (no ammo) in front of the TV until my fingers hurt on the charging handle, I get bored, tired, or my wife tells me to knock it off because "enough is enough".  Then clean and re-lube wet, it will be noticeably smoother.  

For the couch cycling, I usually lube with grease so I don't get oil on my clothes or couch.

If the bolt is visibly not going totally home into battery every time, it could be some drag that will correct in break-in, or could be rounds catching on the feed ramps (or corners), slowing down the bolt.  Either way, the hammer will be trying to finish closing the bolt rather than expending all that energy to the primer.

I would have just swapped the uppers onto each gun and tried again.

This way, you have known for sure if it was an upper issue....because if the questionable upper doesn't work on another lower....you would have your answer.



.

While I don't disagree... he did say SBR lower.

What did the primers look like?

Also, to be helpful here is the pictures he shared from his Google photos Account:

Thanks for the insight.  This is the first of my several rifles that has ever had a problem.  I was surely running it too dry, so I will clean up the chamber, lube it and continue to cycle it a bit.  To answer your question on the FCG, it is a Larue MBT.  

Thanks!

I'm lucky enough to have several SBR lowers, so next time I'm out I'll bring a known working back-up and swap the uppers on it.  Thanks for the idea!

Now that I've seen your pics, I can eliminate a possible FCG issue. In my opinion, you were getting a click and no bang because the bolt wasn't in battery. You mentioned in your first post that the rounds were catching on the feed lips, so that tells me you've got a hang-up somewhere. I would try different mags or even another buffer spring because your feed ramps look decent from the photo. There may be a slight lip there between the barrel and extension, but I think it's the angle of the photo. I say try another spring because it's possible yours, even if new, doesn't have enough energy to overcome the magazine spring and strip a round off and into the chamber. Also, its possible you had a problem with your mag that was causing the hang-up. Did you try more than one mag? Since you already said the rounds were hanging up and not chambering, it only seems logical to assume the bolt lugs weren't fully engaged with the barrel extension lugs, in other words, out of battery. If your bolt is just slightly out of battery and you pull the trigger, your rifle won't fire. It's a great safety feature and is because there is a very small amount of firing pin protrusion on these guns. The firing pin doesn't extend through the bolt face far enough to fire until you're fully seated in battery. I could be wrong, but I'd try different mags and if that doesn't work another spring.

I think your problem might be the feed ramps more than anything else...

On my first build, when chambering a round, the casing would get caught on the feed ramps. you could see that the casings had gouges in them. I fixed this problem by polishing the ramps with a Dremel and some wax. I got all the sharp edges and burrs off, and polished the area real nice. After that I didn't have any issues.


I hope this helps.

Have you measured firing pin protrusion? firing pin all the way forward, from bolt face to tip of firing pin. I forget the spec now, surely someone knows it. Just wondering if it's a hair to short causing light strikes.

Although I don't think this is his problem, for anyone interested, firing pin protrusion should be between. 028-.036". You can purchase a protrusion gauge to measure, but it's not necessary to get an accurate measurement.

I just used a caliper to measure it on my BCM.. which was to long and causing blown primers.