Hello to all! I'm new here, but from what I've read in some of the threads, there is a lot of AR knowledge on this forum... I have been putting AR's together since the first aftermarket lowers were available... in that time, I've had a lot of good, and a lot of bad, parts that have gone thru my hands... early on, I didn't know the difference on what made a part good or bad.. A lot of the time I just kept switching parts till the unit worked! In the last few years, it seems as if there is a multitude of excellent parts, and assemblies, compared to 20 years ago.. But, I still run into an all to common problem once and awhile..  and that is a minor problem with short recoil. The parts all go together perfectly, everything seems to be, or measures up, to spec. Here is what I'm experiencing, if you load a round in the mag, and shoot the rifle from the shoulder, it will work perfectly, if you load the same type round in the mag, and hold the rifle loosely, it will fail to lock open? If you hold it firmly with one hand, it will lock open, but if you just cradle it loosely it will not... I recently started using Win.Q3131A ammo for my test, I had been using PMC (once a rifle functioned correctly, it would run forever on PMC, no problems!)... should the weapon function 100% with no resistance, what is a finite test for function?? I certainly would appreciate some insight... Thanks in advance! Till...later...GT

You may have a weak recoil cycle.

This could be caused by several problem, with the most importation would be the rifle is still new/tight, with the bearing surfaces still new/rough. Anther problems could be a rough chamber.  Since the Q3131a is hotter than PMC, I would suspect that the chamber is a little rough/tight, and the higher-pressure ammo case is sticking to the chamber walls a little more than the weaker round, causing the weaker cycle on hotter ammo.

My attack plan would be to polish out the chamber to smooth it out, and keep all the bearing upper parts lubed with CLP until they mate.

Also, if you can give us a little more detail on the rifle, including the receiver type, configuration and whom the kit came from, this would help narrow down the problem even more.

And, to answer your question, As for the cycling of the rifle, shooter input should not have any effect to the rifle cleanly cycling.

Hi Dano, Thanks for the reply, right now, I am having the problem with two rifles, one has an FN upper, with a used colt 20" A1 barrel...  the second rifle, has a DPMS upper, with an origonal car type barrel (16" with full length handguards) I can understand the shorter barrel having some issues, as just about everyone I've talked to has had issues with these... but the 20" A1 colt barrel really has me perplexed?? The bolt/carrier assemblies I have tried include complete Bushmaster and complete DPMS, along with a used SGW assembly... none of them made any difference....  I even tried swapping out hammers, switching lowers, etc... no difference... That is why the question about correct function... if I have the correct ammo in the win.Q3131a, and the correct test criteria, (unsupported rifle should cycle) then at least I have some hard and fast parameters to test with......I certainly appreciate your input as to this info.! Perhaps I just need to fire a few hundred rounds thru them untill the wear in... but it has been my experience that a good one works right out of the bucket! First shot... can't hardly make the damn thing malfunction! Could the chamber still be the problem with a chrome bore rifle? These are used barrels, what should I look for? I appreciate the input... tha for all, till...later...GT

On used barrels, the first step is to soak the gas tube/barrel gas ports with CLP, then let them sit.  The CLP will dissolve any tube/barrel/gas port fouling, and the fouling blows out on the first shot. Also, it helps to soak the chamber in CLP, then spin (drill with a few cleaning rods) a CLP soaked 30 cal cleaning mop to get out all the fouling that builds up at the last chamber cut before the throat.  A lot of people miss this area, which causes the standard round to act as if it was loaded too hot and cause the case to stick.

On the chambers, a used chrome lined chamber should be smooth as a baby's ass.  If there are any scratches or grooves, you have problems.

One other area that you have not mentioned was the uppers.  If the uppers or carrier keys are brand new, then they will need to mate.  You can help them out by checking all the corners on the key to make sure that there are no sharp edges that are catching on the upper key slot (just below the cocking handle slot).  This slot is what keeps the carrier from twisting, and if the two are tight or the key has a sharp edge, it slows the hell out of the carrier on the way back.  Hint, lubed parts are less likely to bind, and helps the worn anodizing powder to clear the areas as they break in.


As for right out of the box, only if all the parts are in spec, which there is no such thing on a AR-15. If your referring to a factory gun, then yes, it has been test fired for function before it ever left the factory.


Now to preach,

Since we build our own rifles, then we become our own tester, and smiths.  If you just throw a rifle together using mixed parts, you need to do some hand fitting/checking to make sure that they all fit correctly; something overlooked by a lot of people that build kits.

Thanks Dano! I shall follow your directions and report back on the results! I appreciate your input! Thanks again,...til...lat...GT

OK Dano, Here's what we did.. on the 20" Colt A1 barrel, we removed the gas tube and soaked the front sight gas port area with breakfree... then we turned our attention to the chamber area, it appeared pretty dirty, we tried the soaked chamber mop, but soon moved to an AR chamber brush, followed by the mop again, the chamber is now spotless and smooth...  When reinstalling the gas tube, we noticed an uneven wear spot on the end that goes into the key, we replaced the gas tube, lubed up everything..and headed to the great outdoors! Our test ammo was Win. Q3131A and the new Fed. XM193 ball..  The gun functioned perfectly on the first shot! And, every shot after that, no matter how light you held it, or in any position...  In short, your advice was outstanding! You got this one right! BTW, The XM193 ball seems slightly snottier then the Win. loads, but they both worked flawlessly! Now, it's on to the carbine... also, we did not remove the front sight base, or make any alterations to the gas port... Thanks again Dano! till...later....GT

Good to hear that you got the rifle up and running.  

As for the XM-193, it hot and fun as hell, just a bit over the top (fireball) when pushed out of a 11.5" barrel.

P.S. Who is the "WE", got a mouse in your pocket?[:P]

Hi Dano! The "we" is whichever one of my buddies we are building the AR for! Actually I have a friend who helps me buck out some of the problems... it is a learning experience for both of us! I will let you know the developments on the carbine length barrel as we get deeper into the test procedure.. I'm having second thoughts on the origin of this barrel, I know they (factory) made them early in this length, but I fear this is not one of them...  still looking for spec's on early carbine type barrels with the full length handguards, overall length? Gas port size? Barrel markings?, etc...... Thanks again Dano! till...later...GT

On the car/shorty length barrel with mid/full length hand guards, normally there is a gas block under the hand guards (would be at the normal Car sight tower location, with the front sight placed at the muzzle section).  The front sight tower is not used as a gas block, just as a sight.

If your barrel is using full-length hand guards, with the tower being the gas block, then you have just opened a can of worms.  The problem that you will have is the same as if the barrel was a 10.5, due to lack of barrel after the gas port.  

If the barrel is a 20" commercial chromed lined barrel that has been cut down, Chrome lined being the key, forget about getting the barrel runningby openning the gas port.  The only way that you would be able to save this barrel is to have it sent off, re-profiled and gas block installed at the Car location on the barrel.

I will spell out what I think your game plan will be on the barrel.

First off, you plan on opening up the gas port to get the barrel to run.  The problem is that the port is going to be very large in order for the tube to fully pressurize the gas tube to unlock the bolt. The problem here is that the barrel is still under a lot of pressure (high spike), and the case is still pressure bound to the chamber.  

At some point you will get the bolt to unlock, and will have to reinforce the extractor to keep it from being torn off the rim. Once you re-enforce the extractor/spring (read D-fender), you will find that it now has a weak stroke, and you will have to open up the port even more to over come the new resisted spent case extracting stroke.  

Now that you have the case being extracted, and the bolt fully cycling, the carrier is moving way too fast, and you will need to slow it down so it does not knock the back of the receiver extension off.  So, your next plan of attack is to install a stronger buffer spring to slow the carrier down.  The problem is that strong spring applies more pressure to the carrier, so you have to open the gas port even more to get it to full cycle and extract the spent case.  

Now you open the port up again, and find yourself back at trying to slow the carrier back down.  This time you add more weight to the buffer, using tungsten powder and epoxy (it's a semi, so your not worried about bolt bounce).  Now when the buffer comes back, due to the added weight, you can really feel the buffer impacting the back of the receiver extension, and know for sure that the receiver extension will not last long.  About this time you figure that you have had enough fun, chuck the barrel into the spare parts box and install a factory barrel that you know will run.

Bottom line is to add a new gas block at the Car location.  If the barrel is not chromed lined, then you can open up the chamber sidewall dimensions (not head space).  This will aid in the spent case being able to be extracted, but causes the barrel to be less accurate for semi shooting, due to case blow by at ignition, plus shortens the life on the brass if you plan to reload (think M-249).

Either way, the only solution for this barrel on a semi rifle is to add a gas block, which leaves enough barrel after the port to allow the gas tube to slowly pressurizes threw a smaller port, and not have the high spike needed to make the current gas block location work.

The only problem is see on the current barrel would be is the barrel is profiled/lightened, which leaves no steel for a secondary cut back from the current sight tower location to add the new gas block/location.

P.S. If you want to know why I have figured this out, I can dig in one of my spare part boxes and send you a nice 17” round paperweight.

Hi Dano! Right now, the barrel works fine for plinking, and if fired from the shoulder, functions as it should...  it just won't pass the "lock open with no resistance test!" I have yet to try a new gas tube, as we last tested this unit, we had the suspect "bad" gas tube from the other rifle installed.. so we are not done testing yet... of course I had a new gas tube at home, right on the bench, no use to me yesterday! On the other hand, I am beginning to believe that this barrel is nothing more then a cut down 20" barrel. If this is the case, then I think it has been cut to short, and will never work...So, it most likely is a paperweight already! BUT, I know for a fact, that barrels in this configuration, (perhaps slightly longer past the port) Were made and I believe they functioned? I don't think the military would have released them to service had they not at least functioned under normal conditions...  Also, the early Bushmaster dissapator (sp?) barrel series was made this way, until they got smart, and ported the barrel as you suggest, like on a standard 16" barrel. I had one of the early Bushmaster dissapator barrels and it worked fine, although I wasn't testing it to the same criteria as I now know to be correct. I would still like to know the original manufactures specs on this barrel type? Barrel length? port size? etc? Imostlikely won't proceed any further without some specifications! Thanks Dano... till...later...GT

Funny you bring that up, seems that the XM-177 (model 610) was a disaster until they changed out the 10.5" barrel to the 11.5" barrel on the E1/E2 models.  The extra inch on the barrel resolved more that just a place to hang the old style M-203. Even with the added back pressure of the moderator to the 10.5" barrel, the rifle still had problems due to the high gas spike at unlock.

Use a Wolff REDUCED-POWER action spring.  I use these in all my AR's because I handload light loads.  I like them.

Thanks G35, I'll replace the gas tube first, and if no change, the reduced spring will be the next attempt! Thanks, till...later...GT

Hi G35! Well, it looks as if the reduced power recoil spring is the next attempt... We took it (the 16" std. handguard barrel AR) out last Sunday and ran some Q3131A thru it... if you imparted any resistance to recoil at all, it would lock open... if you just let it float, it would not...  for the most part, it is really, really, close to functioning correctly...  I may just put a 1000 rounds thru it, and see if it loosens up just a tad more... although it is not a tight unit to begin with...in the mean time, I will get the reduced power recoil spring as you suggested.... I will let you'all know what happen's! till...later....GT

Hey GLT,

It does sound like the reduced power spring will make it function.  Although this would be considered a band-aid approach, and not really fixing the true problem.

I have a new Busy 16" Shorty that failed to cycle (short stroking extremely bad).  I sent it back to Bushmaster.  They fixed it by applying red locktite around the gas tube in the front sight tower.  But, on the otherhand, this is what I can visiblily see.  Bushmaster MIGHT had polished the chamber, I don't truely know.  But, it has functioned perfectly after Bushmaster worked on it.

Again, the reason I use the reduced power springs is to allow me to make reduced-power handloads and still have guranteed cycling.

Hi G35! Thanks for the note...  Yup, I know the reduced spring is kinda like a band-aid fix.. but this AR is kind of a mutt anyway! I might try a different bolt carrier or two, I know this is not the correct way to go about troubleshooting, but sometimes I just throw parts at an AR problem and see if it disappears!
This thing is pretty close to working..  The front sight base appears to have never been removed, and the newly installed gas tube is a tight fit...  I'm going to give it one more soaking with CLP and install a new extractor spring, (left the empties laying in the port at the end of last weeks test!) and shoot a couple of hundred rd's thru it! I'll keep you informed! Thanks, till....later....GT