Hello everyone,

I've read for awhile on this site and finally picked my self up a like new delton middy. It was like new with little to no wear patterns on the bolt carrier.  


600 bucks came with 4 mags and 100rds of brown bear. Face to face Deal

I think I did OK on the deal.

After picking up a few different brands of ammo (tula brown bear silver bear pmc brown and black hill 69 grain HP."

I seem to be short stroking. I say this because the bolt very very rarely locks to the rear after the last round has been fired.
never has a issue feeding round after of all brands. Just when it comes to locking to rear after the last round.


Will do some. Investigating and see what i can find.

Thanks everyone for this site along with all
the great info.



Edit: the problem occurs with all the mags and each brand of ammo. I've checked the common cause but everything appears tight
Locks back fine when charging handle is pulled to the rear after last round.

probably the mags (use a P mag if you are no using them) or ammo (try some higher grain count 5.56)
the extreme things are the bolt catch is off spec or the buffer is the wrong weight causing it not to lock back fully

welcome to the site

What kind of mags?

How many mags did you try/ Did you only try the mags that came with the rifle in the purchase? Maybe he stored ammo in them for to long and caused weak springs?

3 are the original ones that came with the ar15. One is a little different is a dark black plastic one and says for government or law enforcement use only? "Probably go to jail after saying that last part.

At first I thought it was the weak ammo, but black hills and pmc should be hot enough to full cycle it right?

The last thing I noticed was it seems  to recoil harder than the ar I used in the military. I figured it was due to a shorter barrel, maybe it means to stiff of a buffer spring?


Thanks in advance I didn't expect such quick help

Probably just the mags or possibly the bolt catch. what gas length system are you running? Govt uses rifle length mostly so if you used to shoot that and went to a smaller length then it will seem to be more recoil

I'm honestly so new I can't tell you for sure. I'm guessing mid because the gas tube goes to the front sight post?

I may look into getting some praised p mags to see if that's it.

Its actually not that big of deal because its just a plinker but I'm a huge fan of things working the way they are suppose to.


Edit: 16 inch barrel-1&9 twist

Storing loaded mags does not weaken mag springs

And OP you will not go to jail for using the leo only mag. It sounds like a thermold if it is it might not hold the bolt open.

Correct says thermold on magazine.



Hopefully its something simple like the magazines or buffer spring. I would be disappointed in myself if i didn't catch a flaw in the bcg or something along those lines.

did u check that buffer?

I'm feeling dumb. What is there to check?

it could be that u are using a heavier buffer and not a carbine buffer this causes the BCG to travel back but not far enough if you are stuck shooting 55gr rounds etc.. and another thing is the bolt catch might be out of spec not stopping the bolt when the follower reaches the top

or of course could be you need to try a 5.56 rounds or higher grain count ammo xm 193f 55gr (ex.)

or magazines like P mags or lancers if you can afford them.

Is there a way to tell if you don't have a factory buffer?

Visually is there a way to tell if out of spec?

I can get a set of gauges Monday but I wouldn't even know where to begin with measuring for tolerances.
I question it being out of tolerance not only becauase that's bad news but also it locks back perfectly Evey time when charging  handle is pulled and released quickly.

I think it should have a H on the flat part of the buffer. some 14.5 rifle have them put in to balance the rifle.

but my guess dude is ammo or the magazines check that first less headache and money.

Don't see an H but it seems really light weight.

As for ammo "I'm probably wrong" but isn't black hills plenty hot enough to fully cycle the weapon?


I should of bought some 5.56 but talked myself out of it BC I'm just punching paper/home made targets.

try magazines otherwise check the bolt catch

Lets see if I understand the problem.

Weapon cycles, loading a new round after each successive round in the magazine when fired, last round out fails to engage bolt catch, weapon returns to battery on empty chamber with empty magazine.

Possible causes: Follower fails to engage bolt catch. Bolt catch too tight to engage (not very likely but possible) missing "tail" to bolt catch that normally makes contact with follower (possible but not too likely - easily checked). Weak magazine springs. Faulty followers.

Likelihood of buffer spring failure <99%. Exclusion, deductive reasoning -  Weapon is cycling.

Diagnostics:

Use other magazines, USGI or PMAGS. Observe performance. Try original magazines in different weapon if possible.

Solutions: Observe bottom of bolt catch, MANUALLY ENGAGE bolt catch from left side of weapon on empty chamber w/o magazine. If no failure, remove and replace followers, Remove and replace magazine springs. Cycle on empty chamber. Bolt should lock open.

Report findings.

I have photos of the "tail" of the bolt catch AND proper magazine followers. I think the biggest suspect in the loop at the magazine follower springs, next the follower, next the bolt catch. If the problem persist, you may IM me. Chase these down first, sadly, you're not just down the street, I could figure this out in <1m.

Many have H on the buffer, but not all. in my NG unit, many of the buffers do not have an H on the face. Also, extremely unlikely that this is a buffer issue.

Caveat, I am not a "small arms repair technician" or Armorer. I am just a long time AR15 hobbyist.

Guys I really appreciate the help.

You have the problem correct.

Next I manually watched as I slid the empty magazine in and the follower pushed the bolt stop all the way up with no hesitation.

Is the part of the bolt that comes in contact with the bolt stop suppose to be cut at about angle?

Hopefully that makes sense ^^


Edit: as per ur test,  bolt locked as it should when bolt stop is manually operated on left side of gun.

Yes, it should be angled, sounds right.

The empty mag that you used, this was a DIFFERENT mag, correct?

No all 4 magazines engaged the bolt lock.

I don't have any other magazines laying around such as pmags to test.
Ill order some tomorrow.

Thank goodness for the angle being expected.

I'm more bothered now by this problem then I was at the beginning of my hello and here's my problem post.

Noooooooo need to be perplexed. This weapon system is so easy to work on, you're going to give yourself a benny hill slap later. So, don't get twitterpated, your rifle works, your mags just need some tlc. Go lick your rifle and make it yours.

Refurb those mags and go to the range again. Stuff 'em full and shoot. Dollars to pesos that does the trick. Essentially, you simply order springs and followers, remove floor plate, remove and replace guts, place floor plate back, and DONE. Springs and followers are cheap.

Well, get those mags and shoot the heck out of that rifle! Can't ya feel the itch?