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SureShot241
02-20-2011, 5:24 PM
When I first fired my home built AR-15, it performed well except 2 problems:
-Feeding Issues
-Bolt not being held open after last round

People told me it was probably due to the fact I had a really cheap mag. So I bought Pmags (which I Love!) and fired my rifle for the second time today. First time I fired I put a little over 100 rounds through it, and this time I put about 130 rounds through it.

The problem with feeing has gone away, so I think the mags helped with that, but the bolt problem still remains.

Any ideas on why my bolt wont stay open after last round has been fired?

Here is a link to what my rifle is composed of:
http://www.calguns.net/calgunforum/showthread.php?t=398896

bender152
02-20-2011, 5:29 PM
If you manually hold the bolt catch and rack the bolt, does the bolt stay open?

SureShot241
02-20-2011, 6:11 PM
If I hold the bolt catch down the bolt does not stay open, If I just cock the bolt without touching the bolt catch it holds it open.

G-forceJunkie
02-20-2011, 6:42 PM
What ammo? What weight buffer in it?

SureShot241
02-20-2011, 6:59 PM
I have used 2 different kinds of ammo, Remington and Federal, both ram fine in other rifles and seem to run fine in mine, and I cant find the specs on my biffer but its a DPMS buffer.

Sky_DiveR
02-20-2011, 7:10 PM
If I hold the bolt catch down the bolt does not stay open, If I just cock the bolt without touching the bolt catch it holds it open.

Could you clear this up abit? :confused:

If you put in an empty mag and pull the charging handle, does the bolt stay open?

SureShot241
02-20-2011, 7:24 PM
Could you clear this up abit? :confused:

If you put in an empty mag and pull the charging handle, does the bolt stay open?

Yes it stays open. The ONLY time it fails to stay open is after last round is fired. I have no idea why.

Hump0311
02-20-2011, 7:29 PM
Do you have the lot numbers and grain weights of the ammo you fired?

We can start narrowing down your problem one step at a time.

Your have a malfunction with your feeding, chambering, locking.

Let's starting eliminating.

Twoodland
02-20-2011, 7:34 PM
Sounds like a short stroke. If the bolt is being held open when he racks the gun with an empty mag in, then that means the follower is pushing up the bolt catch properly. However, if it fails to catch after the last round, that means the bolt is not going back far enough on the last round. This malfunction seems to be common on fresh ARs

SureShot241
02-20-2011, 7:36 PM
55gr Ammo. And I dont have the lot number. But the ammo was fired with 2 other guns than mine today at the range and no problems with theirs. Its Remington UMC ammo though.

Jaxpire
02-20-2011, 7:51 PM
Sounds like mag problems to me, try with some other brand of mags?

SureShot241
02-20-2011, 7:55 PM
Pmags shouldnt have any problems, the people I shot wit used the SAME mags as me, bought at same time, and they had no problems

Jaxpire
02-20-2011, 7:57 PM
Yeah shouldn't, but did you try anyway?

SureShot241
02-20-2011, 8:01 PM
well I used a dfferent mag last time and had same problem.

Twoodland
02-20-2011, 8:02 PM
I think a mag problem after replacing the mag with a brand new P-mag is very unlikely. Especially when he said if fixed his feeding problem and he put 230 rounds through it without feeding failures. Also he said that when he pulls the charging handle back with an empty mag, the bolt catch holds the bolt back correctly. sounds like the mag is fine. Like i said in post #9 it sounds like the bolt is not coming back far enough.

captbilly
02-20-2011, 8:03 PM
Sounds like a short stroke. If the bolt is being held open when he racks the gun with an empty mag in, then that means the follower is pushing up the bolt catch properly. However, if it fails to catch after the last round, that means the bolt is not going back far enough on the last round. This malfunction seems to be common on fresh ARs

I had a very similar issue (short stroking) on a new LR.308. In my case it was short stroking so badly that it would not feed properly about 1 shot in 3. My solution was to polish everything in the Bolt Carrier Group (BCG) that could cause friction while stroking. I used extremely fine sand paper, 2000 grit, and carefully sanded the BCG, bolt, inside upper receiver, etc. The whole process took about 15 minutes, and from then on the rifle has not has a malfunction of any sort. There are other possibilities, listed below, but since polishing and lubing are easy, and can't hurt anything, I would recommend trying that first.

You can also try careful cleaning and lubrication until the parts wear in. It is also possible that you have the wrong buffer or buffer spring, a partially plugged gas block or gas tube, or that the gas block is not perfectly aligned with the gas port in the barrel. I have heard of gas blocks that were partially blocked with metal filings from the original machining.

Jaxpire
02-20-2011, 8:13 PM
I think a mag problem after replacing the mag with a brand new P-mag is very unlikely. Especially when he said if fixed his feeding problem and he put 230 rounds through it without feeding failures. Also he said that when he pulls the charging handle back with an empty mag, the bolt catch holds the bolt back correctly. sounds like the mag is fine. Like i said in post #9 it sounds like the bolt is not coming back far enough.

Yes, my reading comprehensionis bad tonight. Didn't even catch the part where he said he replaced it. :)

Sky_DiveR
02-20-2011, 8:21 PM
Sounds like another case of lubrication and a new build. Dragging just enough to keep it from locking open and but enough to load the next round. Clean, relube, and shoot some more.

Take a look at this (excuse the cussing)...

http://www.youtube.com/watch?v=OXIsKEHo-4g

dieselpower
02-20-2011, 8:42 PM
Smith & Wesson Lower Receiver - Good
- DPMS Lower Parts Kit - Ok, out of spec Bolt arm may add to problem
- Hogue Pistol Grip- Good
- DPMS Buffer Tube Assembly(Commercial) - Bad possibly part of the problem
- Magpul MOE Stock(Commercial)- Good
- 2 10/20 Magpul Pmags With Bullet Button Tool- Good
- Prince 50 Bullet Button- Good
- DPMS Sportical Upper Receiver Assembly w/ A1 Flash Hider - Good, possibly a problem
- Osprey International Quad Rail System (Carbine)- Good
- Tapco Forward Grip-Good
- DPMS Front Screw On Sight - Good
- Bushnell Trophy T Retical Red Dot Sight- Good.

I see two or three possible tolerance stacking issues that could cause this.
1) The DPMS LPK Bolt catch arm could be limited in travel. Remove the upper, load an empty mag and watch it trip the Bolt catch arm. If pushing up on the mag activates it more or there is a very loose push up, there is some of your problem. Replace the Bolt catch arm and the spring.

2) Ditch that commercial tube. Sorry sell the Magpul MOE with the commercial tube and buy a Mil-spec system...buffer spring and tube. Shake your current commercial buffer...does it sound like a babies rattle? If so...its junk. There should be two solid weights in there...not copper BBs. The spring could be bad too.

3) The Gas block could be slightly off and you are losing gas pressure. Look for carbon buildup around the gas block. Check your BCG Gas key bolts and see if they are tight, look close around the gas key for what looks like a spray pattern jetting out between the gas key and BCG. All this mixed with #2 and #1 could all = short stroking.

If you deal with #1 and #2 and check your gas key Bolts and all is well...if it still happens...its the gas block/Gas port. Its mis-aligned just enough to restrict the gas flow causing a short stroke.

SureShot241
02-20-2011, 9:19 PM
I did the mag trick and it didnt move so I think that thats fine, and I checked the gas block and there is no carbon build up. gas key rings seem to be in there, and I see no jetting pattern. The buffer sounds like 2 solid things moving as one, not a bunch of BB's. I think it might be my spring, whenever I cock the gun, it makes a really bad metal on metal sound and it has a different pull feel than other guns, but I could be wrong on that. I am gonna have the gas block looked at by a local gunsmith here. Hopefully all my gun needs is a $4 buffer spring. If you would like I could post pictures of all my internals. Gun was recently cleaned though.

Hump0311
02-20-2011, 9:22 PM
Malfunctions are caused by procedural or mechanical failures of the rifle, magazine, or ammunition. Pre-firing checks and serviceability inspections identify potential problems before they become malfunctions. This paragraph describes the primary categories of malfunctions.

1. Failure to Feed, Chamber, or Lock. A malfunction can occur when loading the rifle or during the cycle of operation. Once the magazine has been loaded into the rifle, the forward movement of the bolt carrier group could lack enough force (generated by the expansion of the action spring) to feed, chamber, or lock the bolt

1. Probable Causes. The cause could be the result of one or more of the following:

* Excess accumulation of dirt or fouling in and around the bolt and bolt carrier.

* Defective magazine (dented, bulged, or a weak magazine spring).

* Improperly loaded magazine.

* Defective round (projectile forced back into the cartridge case, which could result in a stubbed round or the base of the previous cartridge could be separated, leaving the remainder in the chamber).

* Damaged or broken action spring.

* Exterior accumulation of dirt in the lower receiver extension.

* Fouled gas tube resulting in short recoil.

* A magazine resting on the ground or pushed forward could cause an improper lock.

2. Corrective Action. Applying immediate action usually corrects the malfunction. To avoid the risk of further jamming, the firer should watch for ejection of a cartridge and ensure that the upper receiver is free of any loose rounds. If immediate action fails to clear the malfunction, remedial action must be taken. The carrier should not be forced. If resistance is encountered, which can occur with an unserviceable round, the bolt should be locked to the rear, the magazine removed, and the malfunction cleared. For example, a bolt override is when a cartridge has wedged itself between the bolt and charging handle. The best way to correct this problem is by

* Ensuring the charging handle is pushed forward and locked in place.

* Securing the rifle and pulling the bolt to the rear until the bolt seats completely into the buffer well.

* Turning the rifle upright and allowing the overridden cartridge to fall out.

I got the malfunction info from here.

Malfunctions (http://www.armystudyguide.com/content/army_board_study_guide_topics/m16a2/malfunctions-probable-cau.shtml)

Thinking it's short stroke also. But read through the above list and start checking off the ones you already tried.


I looked at a picture of your rifle and I have two quick questions.

1.) What is the length of your barrel?

2.) Do you know that your FSB is on backwards?

http://www.calguns.net/calgunforum/attachment.php?attachmentid=86663&d=1298149964

SureShot241
02-20-2011, 9:28 PM
Malfunctions are caused by procedural or mechanical failures of the rifle, magazine, or ammunition. Pre-firing checks and serviceability inspections identify potential problems before they become malfunctions. This paragraph describes the primary categories of malfunctions.

1. Failure to Feed, Chamber, or Lock. A malfunction can occur when loading the rifle or during the cycle of operation. Once the magazine has been loaded into the rifle, the forward movement of the bolt carrier group could lack enough force (generated by the expansion of the action spring) to feed, chamber, or lock the bolt

1. Probable Causes. The cause could be the result of one or more of the following:

* Excess accumulation of dirt or fouling in and around the bolt and bolt carrier.

* Defective magazine (dented, bulged, or a weak magazine spring).

* Improperly loaded magazine.

* Defective round (projectile forced back into the cartridge case, which could result in a stubbed round or the base of the previous cartridge could be separated, leaving the remainder in the chamber).

* Damaged or broken action spring.

* Exterior accumulation of dirt in the lower receiver extension.

* Fouled gas tube resulting in short recoil.

* A magazine resting on the ground or pushed forward could cause an improper lock.

2. Corrective Action. Applying immediate action usually corrects the malfunction. To avoid the risk of further jamming, the firer should watch for ejection of a cartridge and ensure that the upper receiver is free of any loose rounds. If immediate action fails to clear the malfunction, remedial action must be taken. The carrier should not be forced. If resistance is encountered, which can occur with an unserviceable round, the bolt should be locked to the rear, the magazine removed, and the malfunction cleared. For example, a bolt override is when a cartridge has wedged itself between the bolt and charging handle. The best way to correct this problem is by

* Ensuring the charging handle is pushed forward and locked in place.

* Securing the rifle and pulling the bolt to the rear until the bolt seats completely into the buffer well.

* Turning the rifle upright and allowing the overridden cartridge to fall out.

I got the malfunction info from here.

Malfunctions (http://www.armystudyguide.com/content/army_board_study_guide_topics/m16a2/malfunctions-probable-cau.shtml)

Thinking it's short stroke also. But read through the above list and start checking off the ones you already tried.


I looked at a picture of your rifle and I have two quick questions.

1.) What is the length of your barrel?

2.) Do you know that your FSB is on backwards?

http://www.calguns.net/calgunforum/attachment.php?attachmentid=86663&d=1298149964

It is a cabine length 16" and it looks funky with that going the other way. I dont think its backwards but I could be wrong.

Hump0311
02-20-2011, 9:38 PM
LoL i like how you sprinkled the rounds around in the case. Does some of that brass have dents in it thought or is that just the lighting?

dieselpower
02-20-2011, 10:22 PM
I did the mag trick and it didnt move so I think that thats fine, and I checked the gas block and there is no carbon build up. gas key rings seem to be in there, and I see no jetting pattern. The buffer sounds like 2 solid things moving as one, not a bunch of BB's. I think it might be my spring, whenever I cock the gun, it makes a really bad metal on metal sound and it has a different pull feel than other guns, but I could be wrong on that. I am gonna have the gas block looked at by a local gunsmith here. Hopefully all my gun needs is a $4 buffer spring. If you would like I could post pictures of all my internals. Gun was recently cleaned though.



Your not wrong...trust the force Luke... I bet you just found your issue.

That metal on metal sound is the spring and buffer scraping across the tube side wall...the tube is deformed slightly. When the buffer is on its rearward travel the contact it makes "brakes" it and slows it down, just enough to stop its motion and the spring then overpowers it and pushes it back too early.

Replace the tube and spring with Mil-spec. Go to the Post office and weigh the buffer...what does it weigh? 3.? OZ They are cheap so it doesn't even matter...get a whole new Mil-spec kit, tube, buffer, spring, castle nut and end plate. Stag sells them for $90ish. Or buy them piece meal used if you are strapped for cash...just make sure you get mil-spec.

SureShot241
02-20-2011, 11:07 PM
Your not wrong...trust the force Luke... I bet you just found your issue.

That metal on metal sound is the spring and buffer scraping across the tube side wall...the tube is deformed slightly. When the buffer is on its rearward travel the contact it makes "brakes" it and slows it down, just enough to stop its motion and the spring then overpowers it and pushes it back too early.

Replace the tube and spring with Mil-spec. Go to the Post office and weigh the buffer...what does it weigh? 3.? OZ They are cheap so it doesn't even matter...get a whole new Mil-spec kit, tube, buffer, spring, castle nut and end plate. Stag sells them for $90ish. Or buy them piece meal used if you are strapped for cash...just make sure you get mil-spec.

I jst happened to have an extra commercial tube laying around so just to see I changed the tubes, sure enough the scraping sound went away! If this is the cause of my problem then I will be very relieved. I dont currently have the cash for a new Mil Spec system, but will look into it when I upgrade my gun in the future. Thank you so much!

Capt. Speirs
02-21-2011, 7:02 AM
When I first fired my home built AR-15, it performed well except 2 problems:
-Feeding Issues
-Bolt not being held open after last round

People told me it was probably due to the fact I had a really cheap mag. So I bought Pmags (which I Love!) and fired my rifle for the second time today. First time I fired I put a little over 100 rounds through it, and this time I put about 130 rounds through it.

The problem with feeing has gone away, so I think the mags helped with that, but the bolt problem still remains.

Any ideas on why my bolt wont stay open after last round has been fired?

Here is a link to what my rifle is composed of:
http://www.calguns.net/calgunforum/showthread.php?t=398896

Put at least 500 rounds through it before you expect it to perform as designed. You don't build a brand new engine and expect it to run the Indy 500 right away, let it break in.

SureShot241
03-06-2011, 4:29 PM
Your not wrong...trust the force Luke... I bet you just found your issue.

That metal on metal sound is the spring and buffer scraping across the tube side wall...the tube is deformed slightly. When the buffer is on its rearward travel the contact it makes "brakes" it and slows it down, just enough to stop its motion and the spring then overpowers it and pushes it back too early.

Replace the tube and spring with Mil-spec. Go to the Post office and weigh the buffer...what does it weigh? 3.? OZ They are cheap so it doesn't even matter...get a whole new Mil-spec kit, tube, buffer, spring, castle nut and end plate. Stag sells them for $90ish. Or buy them piece meal used if you are strapped for cash...just make sure you get mil-spec.

Yup, that was the problem. Went to Angeles Shooting Range today with different buffer tube, ZERO problems! Worked flawlessly! Thanks for the help!

Etihtsarom
03-06-2011, 5:10 PM
Not to bring this back, but my newly assemble AR does this some times where it does not lock the BCG after the mag is empty. On a previous post, some one suggested sanding down the carrier, which is what I was thinking of doing. Has this ended poorly for some one with rust issues, etc..? After every round of cleaning, the carrier gets a little bit more exposed and worn down to the steel any ways doesn't it?

dieselpower
03-06-2011, 5:45 PM
Not to bring this back, but my newly assemble AR does this some times where it does not lock the BCG after the mag is empty. On a previous post, some one suggested sanding down the carrier, which is what I was thinking of doing. Has this ended poorly for some one with rust issues, etc..? After every round of cleaning, the carrier gets a little bit more exposed and worn down to the steel any ways doesn't it?

DO NOT SAND the carrier.

This is now the third person with this problem in a week.

Swap the tube...check it
Swap the BCG...check it

If it still does it, then the threads on the lower where the buffer tube screws in is threaded at an angle. Nothing you can do but replace the lower. Check the CH before replacing the lower.

More then likely if your BCG is scraping the inside of the tube, the tube is bent slightly.

On the back stroke, the BCG scrapes slowing it down, on the spring forward motion it again hits and slows it down just enough to stop it from going back far enough to lock back.

A bent CH does this as well. A Ch that is bent causes the gas key to scrape on the inside...does the same thing as a bent tube.