AR_15 Question


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RoboDuck
February 25, 2009, 10:17 PM
A friend purchased a used Bushmaster AR-15 at a gunshow recently. The gun was very dirty and needed a lot of cleaning. After all this it will only cycle 4 to 5 rounds and then fails to fully chamber the next round.You have to use the forward assist. We think there may be a problem with the bolt asembly. He has asked me to bring him the bolt out of my rifle to try in his gun. Will this damage my bolt? When I was in the service they always told us never to exchange bolts in our guns or they wouldn't function? Are they bolts interchangeable or will this cause damage?

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franconialocal
February 25, 2009, 10:29 PM
Hmmmm......good post. One of those questions I don't know the answer to and never thought to ask the question. I'll be curious to see the responses!

It would seem to me that (esp. a USED) bolt/rifle setup would be mated very purposefully and not intended to be interchanged. Or is it more like a "one size fits all" at least within brand (bushmaster in busmaster ONLY for example)?

latisimusd
February 25, 2009, 10:32 PM
How clean is the chamber - currently
Any strange markings on the brass that wouldn't chamber, if so on the neck or base of case. Any idea of the round count before he owned it?
Might be something as simple as weak buffer spring.

Interceptor_Knight
February 25, 2009, 10:36 PM
It is likely not the bolt. The gas tube may be clogged. Does he know how to detail clean and lube an AR??? What ammo is he using?

f4t9r
February 25, 2009, 10:36 PM
I know when you buy an upper you also buy the bolt seperately so I am going to say you could exchange them (not sure on this).
Could the gas tube need cleaning ?

kuntreeboy80
February 25, 2009, 10:39 PM
Pull the bolt out and look at the gas rings on it there should be three and the gaps in them should NOT line up. If they do simply turn them so they are misalligned. This actually happened during qualification firing on me a few days ago. It started like you described then after one of the rings broke off. It fired and even on burst (most of the time) But I wouldn't recommend it!

hadmanysons
February 25, 2009, 10:58 PM
You are not supposed to interchange the USED bolts on AR-15. Every AR develops different wear on the bolt faces and chamber. A new bolt in an old gun is fine but a used bolt in a used upper is not. Now a used bolt in a new upper I don't know :)

RoboDuck
February 25, 2009, 11:09 PM
Someone has put on a knockoff six-position collapsible stock. He also got a couple of hundred rounds of metal case ammo :eek:. We used my magazine and some good ammo that functions in my gun .

I will give it a good cleaning and see if that helps.

possum
February 25, 2009, 11:15 PM
there should be three and the gaps in them should NOT line up.
this is not true, it is a common misconception.

helz_mcfugly
February 25, 2009, 11:17 PM
I would have gave it a good chamber scrub, checked the recoil spring and gas port. if the brass is getting stuck chambering i would think it was just really dirty or the spring. not sure Ide try the bolt replacement yet. but yea, scrub the buh jesus out of the chamber.

gga357
February 25, 2009, 11:27 PM
Possum is the misconseption that if they line up it's bad? So they should? Shouldn't? Or it does not matter?

husker
February 25, 2009, 11:32 PM
if its steal wolf ammo thats your prob. my colt ar15 sportier wont cycle wolf no matter what the grain is. it will spit it out. but it wont cycle a new round. my buddy joe has a brand new bushmaster h bar 1/9 twist and his wont cycle it either. he has had some really bad jams that required running a steal rod through the bore to get the spent round out. iv been told that wolf doesnt have the gas pressure that American powder has. i think theirs some type of graphite in wolf powder. i was told this by the owner of AAA ammo in omahaN.E. he sells to the U.S. gov. try some cheap PMC bronze 55 grain. i have yet to have a prob with it 1500 fired so far. cabelas has it for $8 a box. if you do try wolf. make sure its 62gr. or more. i use wolf in my mini 14 but thats the only gun i put that crap in. and once its all shot up the only wolf i hope to ever see again. is one in my sites

briansmithwins
February 25, 2009, 11:42 PM
According to the TM, you need to check headspace when exchanging bolts between rifles.

Stolen from the arfcom AR15 troubleshooting checklist:

---EXTERIOR EXAMINATION
-Unload the rifle and verify clear.
-Check the rifle for any damage from being dropped. Check the muzzle, front and rear sights, hand guards, barrel, buttstock, and sight alignment.
-Ensure that the drain hole in the upper buttstock is clear.
-Check steel parts for rust and porosity.
-Check for any parts that may be loose on the rifle. Check the pistol grip, buttstock, front sight assembly, barrel, and the flash suppressor.
-Pull charging handle back to check carrier for any binding or roughness.
-Check the bolt catch tension and range of motion; depress bottom of bolt catch and retract carrier, check for binding of carrier on the bolt catch.
-Check the magazine catch tension and range of motion. The magazine catch latch should sit flush in its slot and its threaded end should be flush with the surface of the magazine catch button.
-Check that the ejection port cover functions in the open and closed positions. Make sure that the “C” clip is on the ejection port cover hinge pin and that the ejection port cover spring is properly installed.
-Operate safety and check for proper function, tension, and range of motion.
-Check the trigger pull and disconnector engagement; perform the “function check”.
-Check that charging handle locks into upper receiver easily.
-Check that the “paddle” of the bolt catch is not hitting the outside of the upper receiver.
-Ensure that the gas tube roll pin is present.
-With the bolt slightly out of battery, ensure that the forward assist fully closes the bolt.

---INSPECTION OF UPPER
-Pivot upper open/ “shotgun”, you should feel the buffer pushing against the carrier when you do this, check the takedown pin for ease of movement and fit.
-Check that the bolt carrier moves easily from the locked position to the recoil position by moving it with your finger, not with the charging handle.
-Check to make sure that the rear of the carrier is flush with the end of the upper receiver when the carrier is fully forward.
-Separate the upper and lower receivers. Make sure the pivot pin moves easily and is secure.
-Remove the bolt carrier and the charging handle.
-Ensure that the auto sear clearance cut is present.
-On A2, sights make sure that the drain hole under the elevation wheel lock screw is clear.
-Ensure that the takedown pin lug has the proper bevels and facets and that the pinhole is chamfered and oblong.
-Check the charging handle for damage and straightness, check for damage to the upper where the charging handle locks in place.
-Clean and inspect the bore, look for excessive wear, rings, scratches, or other damage. Look for evidence of chrome plating around the muzzle and chamber.
-Check the crown of the barrel for burrs and wear.
-Check the end of the gas tube for excessive wear or damage.
-Inspect the inside of the upper for damage, such as cracks or wear around the cam pin clearance cut.
-Check the gap between the receiver and the barrel extension; it should be no more than 0.012”.
-Inspect the feed ramps for smoothness and completeness.
-On A2, sights make sure that the rear sight base hits the receiver on the last whole click of the elevation wheel. Check the alignment of the 3/8 or 3/6 with the index mark on the receiver.
-On A2 sights, run the rear sight base to its highest elevation, ensure that it does not rock back, or twist more that it does in its lowest position.

---INSPECTION OF BOLT CARRIER
-Check the carrier key. Make sure that the key is tight, the screws are tight and staked in, and thee is no damage to the front of the key. Use a wrench to make sure the carrier key screws are not broken.
-Operate the bolt to make sure it moves smoothly in the carrier.
-Remove the firing pin retaining pin, the firing pin, and the cam pin, with the bolt in the unlocked position stand the bolt carrier on end. The bolt should not slip into the bolt carrier.
-Remove and inspect the bolt, inspect the locking lugs for damage or excessive wear, ensure that there is a swage on the cam pin hole.
-Check the firing pin retaining pin for damage and straightness. If the firing pin retaining pin is bent, then the hammer may be dragging on the firing pin.
-Check the cam pin, firing pin, and the gas rings for damage and wear.
-Check the firing pin protrusion. Use a gauge or calibrated eyeball.
-Depress the ejector to check its tension and to make sure the ejector goes flush with or below the bolt face.
-Check the extractor’s tension and range of motion using a cartridge case. Check it in both the locked and unlocked positions in the bolt carrier.
-Remove the extractor. Check the pin and hook for damage, and check the spring and bumper.
-Check to make sure that the gas tube does not bind in the carrier key and for proper gas tube alignment.
-Clean and inspect the chamber, look for scratches, rings or other damage.
-Reassemble the bolt carrier; make sure that the head of the firing pin retaining pin is flush or below the surface of the bolt carrier.
-Slide the carrier and charging handle back into the upper receiver, lock the charging handle in place, and hold the bolt carrier to the rear.
-With the upper at a 40 angle to the ground release the bolt carrier and check that it locks fully into the barrel extension under its own weight.
-Check the headspace. The barrel must take a civilian or military GO gage; most military barrels will also accept the civilian NOGO gage.

---INSPECTION OF LOWER
-Trigger guard should not protrude into the magazine well.
-Insert a magazine into the magazine well and ensure that it drops free.
-Check the pivot pin, and takedown pin for wear and fit, they should be snug but slide easily.
-Check disconnector engagement: with the trigger forward, rotate the hammer to just short of the cocked position; the tip of the disconnector should almost touch the middle hammer hook. Holding the trigger to the rear, cock the hammer and release the trigger, the trigger should catch the hammer, and the hammer should smoothly slide out from under the disconnector hook.
-Do not allow the hammer to strike the lower receiver or the bolt catch.
-Remove the hammer and check the hammer spring for proper placement and tension. Inspect the middle hammer hook, lower hammer hook, and the “J” spring for damage. Ensure that stake retaining the “J” spring is present.
-Remove the trigger and disconnector. Check for proper installation of the trigger spring and that the disconnector spring is present.
-Check the hook of the disconnector for damage.
-Inspect the trigger, check the tension of the trigger and disconnector spring, and look for wear or damage on the sear face of trigger.
-Ensure that the disconnector slides easily in the trigger slot.
-Check the inside of the lower for foreign matter, such as a primer in the pistol grip hole.
-Remove the buffer and spring and inspect them for damage; such as small indents in the face of the buffer caused by the buffer retaining pin. Check the buffer spring for proper length; 11 ”-13 ” for rifles 10 1/16”-11 ” for carbines.
-Check the buffer retaining pin for function and range of motion.
-Check the buttstock screws and lower receiver extension for tightness.
-Reinstall the buffer and spring.
-Reinstall the trigger, disconnector, and hammer.
-When installing the hammer the hammer spring legs must be on top of the trigger pin and in the outside annular groove on the trigger pin. Failure to do so will allow the trigger pin to move. The wide end of the disconnector spring goes into the hole in the trigger.

-Reassemble the upper and lower receivers.
-Check to make sure that the charging handle does not drag on the “bridge” of the lower receiver.
-Look into the magazine well to ensure that the upper receiver does not overhang the magazine well.
-Insert an empty magazine and check for fit and function of magazine catch and bolt stop. The magazine should release smoothly and insert without undue force. Pull the bolt to the rear with the charging handle. The bolt should lock to the rear.

---THE RIFLE IS READY TO BE TEST FIRED---

---TEST FIRING PROCEDURE---
-Unload the rifle and verify that it is clear.
-Check the bore for obstructions.
-Load the rifle with one round from the magazine. Use quality ammunition and a proven magazine for this.
-Aim downrange and fire, the bolt should catch on the bolt stop. Hold the rifle as loose as possible.
-Reload and repeat the process if the rifle does not lock open Depress the bottom of the bolt stop before firing this time. This allows for weak magazine springs, sticky followers, or an overly strong bolt catch spring.
-If the bolt does not lock open then there is a gas system problem. Investigate and repair the problem.
-If it only locks open with the bolt stop depressed, repeat the process with a different magazine. If the rifle still fails to function then look at the bolt stop as a probable culprit.
-If it does lock open then continue to the grouping phase.
-At your favorite zero distance, fire a group. Three, six, ten rounds it doesn’t matter. Look for center wind and mechanical zero on the front sight. The rifle should shoot somewhere near those settings. Adjust the windage if it is excessive, from the front sight, with a rawhide mallet. If the elevation or windage is greater than can be adjusted for at close range, there could be serious problems with the rifle. The barrel may be bent or the sights may be crooked or mounted too high.
-Your windage zero should be within five clicks of center wind/mechanical zero at 100 yards/91.4 metres. I prefer my rear sight to be a centered as possible as it allows me to get on the sights faster.

butters
February 26, 2009, 12:19 AM
there should be three and the gaps in them should NOT line up.

this is not true, it is a common misconception.
__________________

I just was reading my Bushmaster manual and it states that the gaps in the three rigs should be 120 degrees apart for proper operation. i.e. should not line up. Whether this will have an adverse effect or not I don't know, but the BM manual seems to state otherwise.

Jeff White
February 26, 2009, 12:45 AM
If it's a Bushmaster the problem might be that the carrier key is not properly staked to the bolt carrier and you are losing gas there. Bushmaster is notorious for letting rifles leave the factory with improperly staked or unstaked carrier keys. That is probably the cause of your shot recoil problems.

I'd check that as the first step in diagnosing the problem.

As for gas rings, I have seen rifles function with one. I broke a gas ring at some point in a Pat Rogers Carbine course a couple years ago and didn't even know it until I disassembled the rifle after the class to clean it. For all I know that rifle fired 1300 rounds without a malfunction with a broken gas ring.

Right now I'm at 35 years experience with the M16/AR15 system and I have never seen one malfunction because the gas rings were misaligned. The gas rings move while the bolt is moving in and out of the carrier. Carefully align them, assemble the rifle, shoot a magazine or two through it and take it apart. There is a good chance that the rings will be out of alignment.

nicholst55
February 26, 2009, 03:56 AM
The gas tube may be clogged.

Sorry, gas tubes DO NOT clog up. Well, maybe if you blow wet concrete down one with an air hose and let it dry... :barf: At least, I've yet to see one and I've been shooting, repairing, building and inspecting M16s and AR-15s for 35 years.

Gas tubes do break, usually right where the roll pin goes through them, but even that is very uncommon.

Gas port pressure on a 20" rifle firing M193 Ball ammo is 15,000 PSI. D'ya think much in the way of solid material stays in the gas tube?

Lloyd Smale
February 26, 2009, 08:46 AM
ive been swapping bolts around in ars for 25 years and never had a problem with any of them. I would guess that either its an ammo problem or possibly when he cleaned it he didnt go all the way and take the bolt apart and clean it too. Also dont be afraid to get a chamber brush and go to town.

husker
February 26, 2009, 09:57 AM
ammo, its ammo ,its ammo. you said you were shooting steal ammo. i assume you mean steal casings.

erict
February 26, 2009, 10:58 AM
I would suspect a gas or buffer spring problem. I've swapped numerous bolt combos with numerous rifles and never had an issue. I'm not saying that it's not a possibility but it's pretty unlikley.

beatcop
February 26, 2009, 11:15 AM
Some good advice & some bad so far...BRIANSMITHWINS....that covers it perfectly....I feel the urge to type though...

-Have someone who is familiar with AR's inspect it after it's cleaned again.

-Load one round in mag, charge it, and ensure bolt locks back every time you fire. This would lead me to believe that there's probably sufficient gas pressure to cycle the action. If you have failures at this point, it's likely that you have issues with the gas sytem. Check the rings and stagger them, (do what the manual says). Take the BCG out, extend the bolt and rest it on a table...it should not settle back into the bolt carrier...if so, you're rings are shot. There will be additional pressure on the bottom of the bolt with a full mag, so you may be able to isolate it down this way as well.

-Check that pesky roll pin at the gas tube, that can cause issues if missing.

-You can swap lower assy's to eliminate the buffer...usually not an issue.

-Get some different mags...try different ammo.

-The textbook answer on swapping bolts is to check the headspace. Cheap insurance....although I've done it without checking before.

Let us know how this turns out.

61chalk
February 26, 2009, 11:48 AM
I did some research on the buffer spring, they are usually good for 5000 rds. after they loose their strength you will get jams every so often, or constantly. Also, I have had some brands of ammo in the past that seemed to jam alot, try an new buffer spring, they run from a few $'s to 25.00 for ones that will stay strong up to 10,000 rds.

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