Hello, I built two pistol type ar's, a 10.5 inch kit and a 7.5 inch kit from model 1 sales useing oly arms receivers. I built tham just like I have built the others that function flawlessly. I used the same mags that I used for the other rifles so I know it is not the mags. This is what happens when I try to fire! I lubed them all up and checked to make sure they are allright. 1st problem is when I pull the charging handle the bolt dors not go in all the way,(I used the forward assist more yesterday than I have in all my years of experimenting with the AR)! I would then fire but it wont eject 1st spent round! It would only pull the round out about half way, the 10.5 inch kit's 1st two test rounds ejected the shells but after that it did the same thing the 7.5 kit did. The mags work good in other guns just not in these! So I dont know what the hell the problem is? Can someone please help me PLEASE! Any info would do!

THanks

Anyone?

Sounds like gas tube problems. Not enough gas is getting to the bolt carrier to drive it back and cause proper function.

What should i do?

Quoted: What should i do?

This may sound funny, but try it.  Clean it.  

Clean the gas tube w/ a gas tube cleaner and w/ some Gun Scrub.  Scrub down the chamber w/ a chamber brush.  Lube and reassemble..... test again.  If it still doesn't work, try different ammo; possibly something "hot".  If that doestn' work, a possible misalighment in the gas hole and front sight maybe???  Just suggestions.....

I had a 20" used upper that acted up and after cleaning gas tube and chamber, it was fine.

Quoted: Sounds like gas tube problems. Not enough gas is getting to the bolt carrier to drive it back and cause proper function.

+1

I have a buddy that built one and he is also having problems.  He is using a DPMS lower with a DPMS Kitty Kat upper with the Model-1 Buffer.  I would tend to agree with the logic that the gas system may not be giving you enough blast to rive the carrier.  The fix may be to open the gas port but not something you want to do until you exaust other possibilities.

In my buddy's case, was having problems feeding and he thought the new bolt/carrier was not real smooth so he swapped it with the B/C from his Bushmaster M4.  That seemed to work better for him but he said he had a couple rounds (out of 45) where the hammer followed the carrier home.  He is still looking at it and we were going to try his upper on my pistol lower when we got the chance...

I expect we will see quite a few questions about making AR-15 pistols run well in the days and weeks ahead.  I wonder if we could get a new section for AR-Pistols added to the boards?

Quoted: 1st problem is when I pull the charging handle the bolt dors not go in all the way,

I assume you are releasing the bolt under full spring pressure to chamber a round out of a loaded magazine, and not "riding the bolt home". Even full-size rifle springs can fail to fully lock the bolt if you close the action slowly with the charging handle to watch the chambering in "Slow-Mo."

I have a 7.5 pistol with the Model 1 buffer system for about a year now and had the same problem -- it was a real pain to fix in a fixed-mag lower with no F/A as well.

Look to see if the bolt is actually closing fully but bouncing back open and then sticking in the part-open/part closed position; I think you noticed that, using the bolt catch from a locked-open position the pistol recoil spring snaps the action shut with authority -- if not, you may need a new spring. My first one was visibly shortened after only a few rounds.  The spring seemed to actually shut the action so hard that the bolt carrier would bounce off of the breachface and then the drag pressure from the magazine was enough to overcome the spring pressure trying to close it again.

I have not solved the bolt bounce question in my own upper yet, although I have replaced the Les Baer upper to an A3 with a forward assist to help deal with it.

Second thing to check for: take the upper apart and take the bolt out of the carrier. Then re-insert the carrier only into the upper to see if  the gas tube and carrier key have anything other than smooth contact. Any binding and it can slow/prevent the bolt from closing AND opening.

I think the Model 1 pistol gas tubes are cut-down and reformed from longer tubes and they may be either oddly formed and/or undersized as they mesh with and try to form a gas seal with the carrier key. Check the end of the gas tube for a full diameter opening, no kinks, etc. I don't expect a new gas tube to be dirty, but you never know... I have 2 and they even look slight different, as if custom made.
The 10.5 should have a standard CAR tube, but check for seal and binding none the less.

I would then fire but it wont eject 1st spent round! It would only pull the round out about half way

Does it pull the empty out half way and stop there?
As with any short-stroking problem, first check your gas rings (new bolts may still have the gaps all lined up), and carrier to gas tube fit, above.
Then fire the upper with a loaded round over an empty magazine to see if it 1. ejects and 2. locks back on the bolt catch.

If it does both of those consistantly (ejects and locks back), then I have no idea why it wouldn't eject with a mag in place, unless the drag on the bottom of the bolt carrier from a loaded magazine is enough to overcome the pistol recoil spring strength and/ or gas pressure, and bog-down the system.

If it doesn't then the problem is gas and or spring related.  A strong spring (evidenced by suspected bolt bounce, above) with a weak link in the gas system is my guess.

Check bolt rings allignment, gas tube/carrier allignment and seal for each upper, and then check the gas port size.  (The 7.5 and the 10.5 have different gas port size requirements, and I don't know what they should be.  Only as a last resort, and with AR guru help, would I think of enlarging a gas port.)
Also get a new pistol recoil spring from Model 1 ($5) and check it against your current one. As I said, mine was visibly shorter after only a few rounds, so I don't think they are that durable.
BTW how hard is it to cock the hammer? This "cut down from a carbine" system may be tempermental partially due to banging back against a super-stiff hammer...

One final item, and I've only seen it referenced one place (not in relation to Model 1), is that the pistol buffer tube has so many threads for the end cap so that you can adjust the recoil spring tension.
BEWARE that backing off the end cap from fully tight may allow adjusting the rearward movement of the bolt carrier, backing off too many threads would allow the back of the gas key on the bolt carrier to strike the top of the reciever extension area of the lower receiver, and in doing so can hammer it.  Only one impact under fire can bust it off and ruin your lower - cast or forged, it doesn't matter -- a carrier key hitting the receiver extension under recoil will crack the aluminum.

You should be able to check maximum rearward movement of the carrier using the bolt carrier in the lower reciever and psitol receiver extension without the upper assembly in place and with or without the recoil spring between the 2. Experiment at your own risk -- I havn't tried it myself.

Long post, but I agree with Quarterbore -- there will be many asking these questions.

Cheers, and good luck (I'm anxious to shoot mine witha removable magazine now)
Otto

Thanks alot guys, I'll keep you posted!

Quoted: Hello, I built two pistol type ar's, a 10.5 inch kit and a 7.5 inch kit from model 1 sales useing oly arms receivers. I built tham just like I have built the others that function flawlessly. I used the same mags that I used for the other rifles so I know it is not the mags. This is what happens when I try to fire! I lubed them all up and checked to make sure they are allright. 1st problem is when I pull the charging handle the bolt dors not go in all the way,(I used the forward assist more yesterday than I have in all my years of experimenting with the AR)! I would then fire but it wont eject 1st spent round! It would only pull the round out about half way, the 10.5 inch kit's 1st two test rounds ejected the shells but after that it did the same thing the 7.5 kit did. The mags work good in other guns just not in these! So I dont know what the hell the problem is? Can someone please help me PLEASE! Any info would do!

If I understand it correctly, you are having problems with bolt carrier assembly going home...

That is likely the problem that needs to be solved and everything else will work.

Is the bolt carrier assembly hitting the magazine?  The bolt not going in is likely causing interference with the extraction/ejection also...

Check that out and let us know what you find.

mark
[email protected]

Make sure the bolt carrier is not dragging on the hammer.  On my .458 SOCOM with the RR NM trigger, I had to take off .003 inch from the height of the hammer as the bolt would drag on it.  Also, you might consider switching to carbine buffer, tube, and spring.  I have heard that those parts give better reliability in the pistols.

I just recently built a 11.5" Model 1 pistol kit myself.  Although I haven't had any ejection problems (brass lands about 12' at the 4:00 position) I have had the bolt fail to fully go into battery.  Usually it is close and a push with the FA is all it takes to seat it.

This problem seems to be going away the more I shoot it.  I had it at the range today and had to use the FA apx. 10 times during the first 30 rounds, but only about 5 times the next 30.  This pistol has only had 100 rounds through it so far and I'm beginning to think that the problem will solve itself as it breaks in.  If not, I will be installing a carbine buffer tube, buffer, and spring.

A couple good points in above notes.

Does the bolt notgo into battery when a magazine is NOT inserted into magwell, without a problem?

Also keep it well oiled - WET...  AR's like to run well oiled.

mark
[email protected]

Check the brass for scratches because the chamber may be a little rough and cause it to hang up. I had this problem on a carbine years ago.

Quoted: If not, I will be installing a carbine buffer tube, buffer, and spring.

Actually, that is the ONE way to insure the pistol upper will run reliably without mucking around with the springs and/or gas port.

On my 1993 pistol build I fabbed a receiver extension that was the same INTERNAL length(depth?) as a Colt CAR buffer tube, and used a carbine spring and buffer.  She ran 100% perfect, right off the bat, using a BM 10 inch upper.
BM will sell you a short buffer tube like they use on their tactical entry fixed stock.  NO, it will not be as short as a Model 1 buffer.  But it WILL work all the time, as reliably as any other Arf.  HTH.

Paladin

regarding the use of a carbine buffer tube, that does make sense, because then when "converting" to a rifle, all you would have to do is install the stock portion, having FIRST removed the short barrel and installed a rifle length(16 or longer) barrel.  I am uncertain what ATF's take on using part of a butt stock assy. for your pistol build would be though, which is why I fabbed my own in the first place.

Quoted: Quoted: If not, I will be installing a carbine buffer tube, buffer, and spring.

Actually, that is the ONE way to insure the pistol upper will run reliably without mucking around with the springs and/or gas port.
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That was my 1st guess. From experiance with previous AR's the actions functioned alot smoother with a standard buffer tube. It seems to me that the buffer spring on these pistol tubes get hung up on the guide rod and or other parts in there. My biggest problem is that the spent casing will not eject all the way(the casing is only pulled out half way) and the bolt stays holding on to the casing but it is also stuck in the half way position. I have not tried it with an empty mag. I will do that today!
Thanks alot fellas, You have been very helpfull.

Well I tried a regular buffer tube and still got the same results! Even on the last round of the mag the bolt still gets stuck half way open! Im AGGRIVATED

[quoteActually, that is the ONE way to insure the pistol upper will run reliably without mucking around with the springs and/or gas port.

On my 1993 pistol build I fabbed a receiver extension that was the same INTERNAL length(depth?) as a Colt CAR buffer tube, and used a carbine spring and buffer. She ran 100% perfect, right off the bat, using a BM 10 inch upper.
BM will sell you a short buffer tube like they use on their tactical entry fixed stock. NO, it will not be as short as a Model 1 buffer. But it WILL work all the time, as reliably as any other Arf. HTH.

Paladin

regarding the use of a carbine buffer tube, that does make sense, because then when "converting" to a rifle, all you would have to do is install the stock portion, having FIRST removed the short barrel and installed a rifle length(16 or longer) barrel. I am uncertain what ATF's take on using part of a butt stock assy. for your pistol build would be though, which is why I fabbed my own in the first place.
]

So where is the Bushmaster Buffer Tube you are talking about? I looked and looked for it? I am waiting on a Stripped lower as we speak along with my lower parts kit. However I haven't ordered a buffer yet as I wanted to be sure about which one to get. Frankly I was a little worried about these pistol buffers anyway? However everything else is the same, right?

Quoted: Well I tried a regular buffer tube and still got the same results! Even on the last round of the mag the bolt still gets stuck half way open! Im AGGRIVATED

Did you lok at the things that I and others asked you about?

mark
[email protected]

So where is the Bushmaster Buffer Tube you are talking about? I looked and looked for it? I am waiting on a Stripped lower as we speak along with my lower parts kit. However I haven't ordered a buffer yet as I wanted to be sure about which one to get. Frankly I was a little worried about these pistol buffers anyway? However everything else is the same, right?

You will have to get the short tube from them the "old fashioned way".  Call them on the phone, as it is not listed separately on their web site.  HTH.

Paladin

Quoted: Quoted: Well I tried a regular buffer tube and still got the same results! Even on the last round of the mag the bolt still gets stuck half way open! Im AGGRIVATED Did you lok at the things that I and others asked you about? mark [email protected]

Well I experimented with the mag in the gun and out of the gun. Still the same results. I'm aggrivated because I really wanted to see this work but I have to be patient! Does anyone know how far the hammer is supposed to stick out past the top of the lower receiver when it is in the cocked back position? The gas port hole is my last resort!

Thanks!

Does anyone know how far the hammer is supposed to stick out past the top of the lower receiver when it is in the cocked back position?

No, but you may want to swap a hammer/trigger/safety part set from a working AR and try that next.  

Your comment reminded me of the only problem I have ever had with a Model 1 kit -- the hammer and trigger engagement seemed out of spec. and the hammer didn't "cock" exactly right and other assundry problems.  (note: I didn't try to send it back, although I'm sure they would have replaced them, for I had spares and wanted to monkey with them myself.)

Cheers, Otto

I think there has to be something you aren't telling us. Are you useing handloads? Don't do that! It sounds to me like the cartridge is to tight in the chamber. Use new ammo, I recommend U.M.C. Also I would check to see if the bolt will close without a round, leting it down slowly so as to check for binding. I hope you weren't useing that coated russian ammo, that stuff'l gum up your chamber like crazy! After you see if the bolt closes without a round, take a live round and drop it in the chamber and see if it is tight or if it goes in with ease. I think you have some problem with the ammo being to tight in the chamber, now find out if it is the chamber or the ammo. By the way you know if you use a collet die for reloading you should use that ammo in only the weapon that it was originaly fired in, because the cases fire form to that chambers exact size.
Good luck.

Quoted: So where is the Bushmaster Buffer Tube you are talking about? I looked and looked for it? I am waiting on a Stripped lower as we speak along with my lower parts kit. However I haven't ordered a buffer yet as I wanted to be sure about which one to get. Frankly I was a little worried about these pistol buffers anyway? However everything else is the same, right? You will have to get the short tube from them the "old fashioned way".  Call them on the phone, as it is not listed separately on their web site.  HTH. Paladin

I thought about doing that.... getting one of those butt stocks the tactical ones from RRA and using the tube only..... drilling out the threads so a stock can't be put...

I would ask BATF in writing if they really REQUIRE you to modify the extension to preclude installing a stock...as that would defeat the "purpose" of building a dual use pistol that can be converted to a rifle.

It is ILLEGAL to install a stock on a pistol.  The act of placing the stock onto the receiver extension is illegal when combined with a short barreled upper, not the "ability" to accept a stock.  And adding a stock when configured as a rifle is legal.  The mere "fact" that it is easy to remove/install the stock itself has nothing to do with the situation.

Think T/C contender.  It also has a protruding receiver extension of sorts, which the pistol grip attaches to.  And after removing the grip, "you only have to slide the stock onto the extension, and install a single screw to make it a stocked lower assembly".  JUST LIKE AN ARF PISTOL!

You DO need to stick something in the rear hole of the pistol extension to prevent air/oil blowback when the buffer cycles.  I use a sling attachment stud for a QD swivel.

Paladin

Paladin


That's a good point.... just like the stocks for the 1911's and Glocks.  The Glock stock is especially simple to put on.... just stick it in that hole behind the mag well...done.


I suppose since the AR pistol is "evil" or at least not "conventional" in most peoples eyes....  some owners want to play it safe.  On the other hand, owning M16 parts +  AR = unregistered machine gun in the eyes of the BATF..... so some people are "playing it safe" by assuming the same thing with the stock issue w/ the pistol/carbine conversions.

Well, I think I've done it. I removed the front sight base to get to the little gas port hole in the barrel and i bored it out alittle with a drill bit. I dont remember the size of the bit but it was the next size up from the bit that fit perfectly in the hole previously. I put it back together and fired it still useing model 1 sales pistol buffer tube and it ejected perfectly!!! It shoots fine continuously for the first 10 or so rounds until it starts to get dirty, then i encounter the bolt bouncing back after closeing and not locking again closed again. They say after it breaks in it will work better!