AR pistol issues

[kanewtervalve]

Built an AR pistol awhile back as many of you know, have been having problems with FTF, round going all the way in but 1/8 inch, I can push on the groove of the bolt carrier with my thumb to go the rest of the way but makes the AR basically a bolt action AR. I have tried a heavier spring and even some washers on the buffer guide to try and get it to function correctly. I have an extra spring(they have to be cut down) but didn't want to destroy it unless I tried everything else.
Anyway, that's the background, my question is when I studied the lower I found I had installed the hammer spring backwards, I corrected the problem but I am wondering if it was part of my problem from the beginning. I'm thinking the bolt carrier may have been "dragging" on the hammer more so than usual with the hammer spring installed backward but did not see much of a difference in the height of the cocked hammer compared to my other ARs. Any thoughts guys? TIA for any help.
Mark.

 

[Brian Ski]

I sure ain't much of an AR pro... How does the bolt slide with the upper off the lower?? To me it should slide really easy. It seems like it is dragging on something.

When it hangs up on the last 1/8 inch... Is it pushing a round in or an empty chamber?? Gas tube isn't bent...Dragging???

 

[kanewtervalve]

Tried different carrier, hard to tell if it's dragging anymore than usual because they all have contact to some extent. Carrier is free moving off the lower. Failed to mention that with 5 rounds in a 20 round mag it will fire every one without FTF.

 

[az_gun_nut]

Take the upper off, strip the bolt off the carrier and see if the carrier key drags on the gas tube that way. You should be able to slide the carrier back and forth by hand with no drag. If it does drag then you need to tweek the gas tube and try again. You should be able to see where it's making contact inside the carrier key tube. Just bend the gas tube with a large flat blade screw driver in the opposite direction.

What weight 1911 spring did you use by the way. You may need to use a heavier spring. I've been reading where some guys are using 18 and 20 pound springs as replacements. You may not have enough spring tension to strip the rounds from a full or partially full mag since those rounds are under a good deal of tension.

 

[kanewtervalve]

This is the link to the spring I used: http://www.gunsprings.com/SemiAuto/ColtNF.html#Longslide
I bought 2 of the #1 and thought I cut it to length but may have been too short, thats why I used the washers. I didn't want to mess with the other spring unless I was sure all other issues were addressed. I'll try the bolt removal thing you mentioned.

 

[amphibian]

Failed to mention that with 5 rounds in a 20 round mag it will fire every one without FTF.

Sounds like it may not be getting enough gas.
Have you checked your gas rings?
Have you made sure the gas key is not loose?
Have you tried loading 1 round in the mag and firing then does the bolt stay open?
If the bolt does not stay open after the last round and all the above is done then maybe the gas port needs to be enlarged.
I am assuming this is 5.56mm?
What kind of buffer are you using?

 

[az_gun_nut]

That's a good point as well. Make sure your gas rings are spaced out properly. The gaps in the rings need to be spaced out just like the piston rings on a car engine or you'll get blow by and short strokes.

I'd try using the other spring but uncut first. See if you can cycle the gun with it like that. Then if it won't cycle, or cycle completely you can start to cut a coil at a time until you get it right were you want it. Do the one round at a time deal until you can get the bolt to lock back on an empty mag. Have you check the gas port opening as well like Amphibian said? It should be .078 to .081 max opening for a 7 1/2 inch pistol length barrel.

A buddy of mine just put a Model One Sales AR together and it was running great for about 200rds. Then all of a sudden it started short stroking and FTE's. After swapping parts between my gun and his it still wouldn't run. We got it home, pull the front site base off and checked the gas port hole. It must have had a burr in it when they drilled it out because it was partially closed when we checked it. We just stuck the proper size drill bit in the hole and twisted it by hand to clean up the burr, put it all back together and it ran like a champ after that.

 

[kanewtervalve]

I've tried another complete carrier from one of my other ARs, does the same thing. It cycles fine stripping another round just that last 1/8th inch it won't go. I polished the feed ramp and checked the gas tube, sticks a little but no more than my other 2 ARs. I'm still wondering if the hammer spring being installed backward had anything to do with this, I have not gone shooting since I found this out. I got the kit from Model 1 sales, it's a 7 1/2 kit on a bushy lower registered pistol receiver.
Here's a link to the type of buffer I'm using:http://www.model1sales.com/item-det...878&CFTOKEN=49648314&jsessionid=84307515176cq$FA$D6$

 

[az_gun_nut]

Have you tried hand cycling the rounds through it since you fixed the hammer spring? If you can hand cycle them, then at least you know it's not a drag issue and is more likely either a gas or spring issue.

 

[cookie]

Is the bolt carrier hanging up (or rubbing severely) inside the receiver extension (buffer tube)? That's a common problem.

 

[kanewtervalve]

Have you tried hand cycling the rounds through it since you fixed the hammer spring? If you can hand cycle them, then at least you know it's not a drag issue and is more likely either a gas or spring issue.

Have not tried that yet, I'll do that next.

 

[kanewtervalve]

Is the bolt carrier hanging up (or rubbing severely) inside the receiver extension (buffer tube)? That's a common problem.

Just the normal wear enough to make the parkerize a little shiny but not silver lines for severe wear.
P.S. Guys, your help is very much appreciated, I'm sure we'll get this little .223 working soon.

 

[JWH 223]

Bolt bounce is also very typical. The people that I know that fixed it was by using a longer buffer tube...like a M4 tube...sounds crappy, but that is the experience they were having....back before the ban I played with one myself using a Pistol buffer assembly and was getting the same thing.

My $0.02

 

[az_gun_nut]

Bolt bounce is also very typical. The people that I know that fixed it was by using a longer buffer tube...like a M4 tube...sounds crappy, but that is the experience they were having....back before the ban I played with one myself using a Pistol buffer assembly and was getting the same thing.

My $0.02

I'm still guessing that it's a weak spring.

Failed to mention that with 5 rounds in a 20 round mag it will fire every one without FTF.

 

[cookie]

I agree with az_gun_nut about the spring. Why not try the extra longslide spring as is (without trimming it)?

 

[kanewtervalve]

I agree with az_gun_nut about the spring. Why not try the extra longslide spring as is (without trimming it)?

The spring I have is way too long to fit, going to try the extra after the other suggestions, I may have cut the existing one as much as 2 inches too short.

 

[az_gun_nut]

Did you ever get it to run?

 

[kanewtervalve]

Weather is not cooperating, temp is around 20 degrees high during the day, I'll go when it gets above freezing.

 

[Mad Mike]

It sounds,to me as well, as if you aren't getting enough gas to the bolt. You may want to look into a product called a "Pig-tail" gas tube, they replace the short tube and actually wrap around the barrel. It's designed to give more gas to a short barreled M-16 type weapon. I think you can order them from Brownell's and I've seen them advertized the Small Arms Review as well. Good luck.
Mike

 

[Vegas SMG]

A pig tail won't increase the ammount of gas to your bolt. It increases the dwell time. You can only increase the flow of gas by drilling and enlarging the gas port itself. I'd do this as a last resort. Pig tails are good for curing bolt bounce and that doesn't appear to be your problem.

Try loading one round in your mag and see if the bolt locks rearward after firing. If it does, you're gas supply should be OK. Based on your comments that the gun runs fine with only five rounds in the mag, then I agree with the others that you may need a stronger recoil spring at least until you get the new bolt/carrier combo broken in.

You stated that you'd swapped carriers out with the same results. You may consider swapping out both the carrier and bolt from another gun and see if the wear on the bolt lugs allows the pistol to function properly. I know many would advise against swapping bolts between guns but I've never had a problem doing so. YMMV