Bolt not locking back on new build, gas block alignment?

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Is there a rule of thumb for this? I built a rifle in Dec and just got it out today and it will not lock the bolt back. I have a White Oak SPR barrel with rifle gas and a SLR Sentry 7. I started at 3 clicks open and the bolt didn't even move. Went another 3 and bolt moved but no ejection. Kept opening the gas block until fully open and it ejects no problem but will not lock the bolt back. I tried 2 different mags. If I pull the charging handle on an empty mag it locks back. If I use the bolt catch it will lock back fine. All this is leading me to think the gas block isn't properly aligned but I assumed with a dimpled barrel it was basically self aligning. Is there a way to check my current alignment without something like a bore scope? Also, of the few youtube vids I've looked at people just slide the gas blocks right up against the shoulder. Mine was an absolute fight to seat it against the shoulder by hand. Probably just super tight tolerances from quality manufacturers but figured it was worth mentioning.
 
Sounds like it isn’t perfectly aligned to me
 
Sounds like it isn’t perfectly aligned to me

That's what I'm thinking. Just not sure on how to go about perfectly aligning it. Saw on youtube people drawing a long line through the center of the gas port down the barrel and a line in the center of the gas block but with how tight mine fits I'm pretty sure the pencil wont survive the gas block being pushed over it.
 
Also, I forgot to mention that it is ejecting with enough force to turn the case mouths into D shapes but still not locking back.
 
Also, I forgot to mention that it is ejecting with enough force to turn the case mouths into D shapes but still not locking back.
If it’s throwing then hard enough to dent the case mouths but still not locking back something else could be the issue. Luckily I haven’t ran across this issue yet.
 
As I mentioned in the other thread, how heavy of a buffer are you using? If the buffer is too heavy, it can cause (or contribute to) short stroking.
 
Mine had the same problem. It was the bolt catch. Replaced spring and took a little off both sides of bolt catch (hit both sides with a file about 3 times) and it worked fine. I also replaced the gas block twice which had no effect as it was not the problem with mine.
 
If it’s throwing then hard enough to dent the case mouths but still not locking back something else could be the issue. Luckily I haven’t ran across this issue yet.

I thought the same thing which is why I started looking at the bolt catch but it seems to be working properly.
 
Mine had the same problem. It was the bolt catch. Replaced spring and took a little off both sides of bolt catch (hit both sides with a file about 3 times) and it worked fine. I also replaced the gas block twice which had no effect as it was not the problem with mine.

How did you go about troubleshooting the bolt catch?
 
That's what I'm thinking. Just not sure on how to go about perfectly aligning it. Saw on youtube people drawing a long line through the center of the gas port down the barrel and a line in the center of the gas block but with how tight mine fits I'm pretty sure the pencil wont survive the gas block being pushed over it.

Use a fine sharpie to mark the location of the gas port at the rear of the barrel shoulder, and do the same on the rear face of the gas block. That should get you close enough to insure that you'll get good alignment. (Good) Gas blocks are designed to have a little forgiveness for inexact alignment, you have to be fairly unaligned to suffer gas loss.
 
I bought a new Ruger a while ago that would frequently not lock back on the last shot. I found that the spring in the bolt catch was a little too strong. I put in a different spring and have had no problems since. If you have another AR, try swapping springs to see if that helps.
 
I had a bolt catch bind up because the roll pin was locking it in place. Double check to make sure it moves freely.
 
When you insert a empty magazine and pull back on the charging handle does it lock open?
 
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Couple of questions

What ammo? (you didn't state)
When you seated the gas block, is it touching the shoulder? Gas port should be at 12 o'clock, seat the GB to the shoulder (tap if it didn't go)
You stated SPR rifle, I'm assuming rifle stock, rifle receiver extension, rifle spring and rifle buffer?

CD
 
I had the same problem on 2 different rifle. I know this is gonna sound dumb, but also check your buffer tube and compare the length to a different one. I ordered 3 and 2 of the 3 where shorter than the other one. They were also shorter than the ones on my other side rifles.

Swapped out tubes and golden.
 
Bolt catch moves freely, bolt locks back if I pull charging handle on an empty mag, already compared measurements of rifle tube with another member, rifle tube/buffer/spring with a luth AR stock, ammo was 62 gr PMC 556.

I think my next plan of action is going to be to swap the upper onto a known good lower and try to at least rule out gas.
 
Where is the brass landing after ejection? Any damage to the back of the follower on the magazine?
 
Brass is all ejecting at 3-4. No damage to follower. I'm using brand new 20 rnd pmags and tried 2 different mags to try and rule that out.
 
Tilt the upper and insert an empty magazine into the mag well. Push the bolt catch as you would to release the bolt and see if the mag follower pushes it up completely and quickly when you release the bolt catch. It would not do it on my new Ruger until I installed a different spring. If it does, the spring is not your problem. It is worth a try.
 
Tilt the upper and insert an empty magazine into the mag well. Push the bolt catch as you would to release the bolt and see if the mag follower pushes it up completely and quickly when you release the bolt catch. It would not do it on my new Ruger until I installed a different spring. If it does, the spring is not your problem. It is worth a try.

I kinda did this last night. Pulled the upper off this upper and another and studied how the mag follower interacted with the bolt catch and I didn't see any oddities from one to the other.
 
Any pictures of the brass that was damaged during ejection? If they are being damaged as described I do not believe it to be a gas problem. By chance does the upper and lower fit really tight or is there a tension screw in the lower to make them fit tighter? I have seen a rifle with a tension screw fail to lock back due to having to much tension and putting to much friction on the BCG. It would lock back when manually pulling back on a empty magazine or by pushing the bolt release by hand. But not when fired.


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Any pictures of the brass that was damaged during ejection? If they are being damaged as described I do not believe it to be a gas problem. By chance does the upper and lower fit really tight or is there a tension screw in the lower to make them fit tighter? I have seen a rifle with a tension screw fail to lock back due to having to much tension and putting to much friction on the BCG. It would lock back when manually pulling back on a empty magazine or by pushing the bolt release by hand. But not when fired.


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I can take some pics when I get home. It does have a tension screw but I haven't messed with it. The upper and lower for nicely with no rattle and the takedown pins are easily pushed out by hand. My other noveske lower also has a tension screw and I have to use a tool of some sort to push the pins out and that one has had zero failures in around 2k rounds.

I saw on YouTube a guy had an issue with a Magpul bad lever limiting the range of motion of his bolt catch so I pulled mine off just to rule it out but again, I have a bad lever on my other rifle as well with no issues.
 
Finally got some time to mess with this thing again and the BAD lever was the issue. It was hitting the receiver and limiting the travel of the bolt catch.

Figured I'd post up in case someone stumbles on this thread in the future.
 
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