I finally got my RRA lower recieved and finished assembling my SPR-B type rifle.  It's a Bushy V-Match 20" upper, and RRA lower.  

I function tested the upper a few weeks ago on my Colt lower and it function flawlessly.  On my RRA lower however, it sometimes doesn't strip a round from the mag and the bolt closes on an empty chamber, OR it barely catches a round but skips over the top when it gets halfway closed and crunches the round as it jams.

@*(#@$%!!!  I have a different mag catch I can try.  The upper/lower fit is very tight (which I really love), I am willing to bet that the mag (COLT 30 rounder) is not high enough relative to the bolt and carrier by a couple thou.  Any other suggestions?  NO I am not selling it cheap!  

Anybody?  Does it sound like I am on the right track with my diagnosis?  Bueler?

Sounds like its the magazine.  Did you make sure it was seated properly?  

Try slapping the mag from the bottom to ensure it is seated all the way up into your lower and try again.  If you inserted a full mag with the bolt closed you will have to push the mag in harder than you would if the bolt was open in order for it to catch properly.

Also try a different magazine.  Check your magazine catch to ensure that you have it screwed into the mag catch button enough to engage the mag properly.

I seriously doubt that the RRA lower is out of spec.

Quoted: Sounds like its the magazine.  Did you make sure it was seated properly?   Try slapping the mag from the bottom to ensure it is seated all the way up into your lower and try again.  If you inserted a full mag with the bolt closed you will have to push the mag in harder than you would if the bolt was open in order for it to catch properly. Also try a different magazine.  Check your magazine catch to ensure that you have it screwed into the mag catch button enough to engage the mag properly. I seriously doubt that the RRA lower is out of spec.

Thank you for the reply!
Now that I am not so tired, I have had some time to think about the weapon's behaviour.
I always slap the bottom of the mag hard enough to make sure it is seated.....Tap Rack Bang/SPORTS.....if there is no loose round floating in the reciever, then I release the bolt and try again.
When charging by hand, it works great.  I only have 10 mags, and they all are visually perfect and function 100% in my other AR.  I think it may be short stroking, and the friction of the bolt riding against the round in the mag is sometimes bringing it halfway forward to wedge partially in the chamber.  I noticed that my buffer spring is really strong compared to my Colt, but more likely is that I am losing gas pressure somewhere.  I had the gas block off and changed float tubes before I put it on the new lower.  

I am going to check the gas rings (make sure the gaps are staggered), and flush the gas tube, then try it again today.

Try not fully loading your mags, download 2 or 4 rounds, sometimes that helps.

That RRA lower is Probably cut better than a Colt.

Colt= Overpriced Junk

Puts flame suit on and walks away laughing.

Since you messed around with the gas block, try it again on your colt lower.  Then if it still doesnt work in your RRA, switch the buffer springs and try again.  Only then would I start dissasembling the upper.  

There should be no way it should short stroke on a 20 inch upper unless you didnt have the gas tube fully inserted in the gas block and drove the roll pin in front of it.

Something else you may want to check is the straightness of the gas tube along the top of your barrel.  Did you have to bend it a little in order to get it in the gas block?  If so your barrel nut is not indexed correctly.  The way you check it is to insert the gas tube into your carrier key and insert that assembly through the receiver until there is at least 8 inches of gas tube exposed over your barrel.  The gas tube should lie dead center of your barrel.  Once this is confirmed you pull the assembly out and insert the gas tube for final assembly from the barrel side.  If it doesnt lie dead center you will have to adjust the barrel nut until it does.  The prefered way is to initially torque the barrel to about 35 foot pounds and loosen 3 times before torquing the final time.  This process seats the threads and ensures proper mating of the two assemblies.  Then check the barrel nut to ensure that you have it indexed correctly.  Chances are that you will have a "tooth" in the way.  Never loosen the barrel nut to obtain clearance for the gas tube.  Since you only torqued to 35 foot pounds, it is safe for you to tighten the barrel nut to the next slot to obtain proper clearance.

I am assuming that since this is a new upper that you also have a new bolt?  If so the gas rings should be fine.

I am also assuming that you have lubed your weapon to facillitate the break in process on new parts (a light coat of CLP will help)

I'm not trying to insult your intelligence, but rather just going through the process as I would do it.

Hope this helps.

Just one more thing...if it short strokes in your RRA it should short stroke in your colt.  Otherwise its a mag problem.  If it short strokes in both...then check out your gas system as stated above.

Staggering the gas rings is a popular bit of misinformation stemming from the assumption that these rings must work as piston rings in an engine.  The fact is, once inserted into the carrier and seated, the gaps are negligible.  If the tension from the seated rings will support the weight of the carrier (cam pin removed) then the rings are not the problem.  Also, according to the factory, the rings have a tendency to move around a bit during operation so carfully spacing the gaps is all for naught even if it made a difference.

If you want to test for your weapon short stroking, load 1 round in a magazine and chamber the round.  If the bolt locks to the back after that one round, the weapon isn't short stroking.  If it is, you most likely have a gas system problem.  Check your carrier key first (small tube on top of carrier that fits over your gas tube)  It should be rock solid tightened and staked to the carrier.  Any movement at all can cause short stroking.  Beyond that, the gas tube is the most likely culprit.  Make sure that it is straight, and that the roll pin that secures it in your front sight runs through your tube, not in front of it.  If it does not run through the proper hole, the gas port will be at least partially blocked, and the function will be negatively affected.

One last possibility is ammunition.  Did the ammo you are using previously work on this upper / barrel combo?  Will a hotter load work as is?

I tend to agree with Bear Hunter, your lower is not at fault.  In fact, I can't imagine a scenario that would fault your lower with the problem described as long as your fire control function test passes.

Let me know if that helps.  If not, I'll see what else I can dig up.


Saleen

OK.  I disassembled and checked out the gas block, gas tube, and bolt/bolt carrier.  Everything A-OK.  The barrel nut was indexed properly as well.  Tried the upper on my Colt CAR lower, it functions perfectly. The buffer spring is much weaker however.  Hmmmm.  Colt 16" upper functions on the RRA lower.  Hmmmm.  I swapped buffer springs.  The RRA lower had a brand new spring that is a couple inches longer than the old Colt spring and much stiffer.  
With the old Colt spring in the RRA, the gun functions perfectly.  AND, to my suprise, my Colt CAR function awesomely with the brand new spring in it, and cycles faster than hell.
Oh, well at least they both work reliably now.

Any comments?

I moved on to shoot some groups, and had a kB with it.  That post is in the GD.  (sigh)

Thanks guys!

Let me get this straight.  Does your RRA lower have a A2 buttstock?  From your last post, it sounds like you put a CAR buffer spring in your A2 buttstock, and a standard buffer spring in your CAR buttstock.

Your CAR buttstock should have a CAR Buffer spring (shorter than standard) and a CAR Buffer (shorter than standard) Unless it is a fixed telestock with a standard buffer tube.  Then it should have standard spring and buffer.

A fixed stock such as the A2 should have a standard buffer spring (longer than CAR) and a standard buffer (longer than CAR)

Make sure it is set up as above and check for short stroking as per "Saleen's" post.

Well now that you have managed to KB the colt upper, you can go out and get a RRA upper for about half the price, like you should have in the first place.

Quoted: Well now that you have managed to KB the colt upper, you can go out and get a RRA upper for about half the price, like you should have in the first place.

LMAO....
Yes the Bushy upper/RRA lower was short stroking.  One shot, and the bolt does not go back far enough to catch the bolt catch.  

The RRA lower has an A2 stock.  It is functioning right now with the CAR spring and A2 buffer.  The CAR is functioning (and crazy fast I might add) with the A2 spring and CAR buffer.  

P.S.  I had the kB (split case) shooting the RRA not the Colt.  Is it because I have the CAR spring in it?  
I had the Colt first and got a good deal on it.  I agree the RRA parts are much tighter.....I am impressed with it.

The split case will typically be ammo related.  I doubt seriously that your buffer spring has anything to do with it.  On the issue of springs, change them back.  They are specific to the type of stock, and NOT interchangable.  If your A2 spring is out of spec, replace it.  If the lower is fairly new, call RRA and complain.  My guess is that you will have a better than average chance of getting a new one in the mail directly.

Now, on to the short-stroking problem:  Am I to understand that all things remained constant except for the spring?  Is the ammo the same? and what ammo are you using?  Have you checked the carrier key for tightness?  Have you checked the rings for sufficient tension?  What length barrel do you have?  If a tree falls in the forrest and no one is around to hear it, does it still make a noise?  Are you sure?

Okay, maybe I don't need the answers to the last two questions, but give me an idea of what we are dealing with on the malfuctioning rifle so I can help you diagnose it.


Saleen

The upper is a Bushmaster 20" HBAR V-match flattop with shaved gas block.  I got it from Jeff/CMMG.  Perhaps I have found why it was sold.  The gas block, gas tube, bolt and bolt carrier, carrier key, gas rings are all fine!  The ONLY think that I can think of is that the A2 spring is too long/stiff, since the gun will function with the CAR spring.  HOWEVER, my 16" WILL function like crazy with the A2 spring, so that tells me the 20" upper is not generating enough gas pressure.  

I think the problem is that the gas block is installed slightly off center.  I marked the location of the gas hole on the top of the barrel before I reinstalled the gas block.  After installation (yes the taper pins are tight) the gas block is slightly crooked/off center.  This would close off the hole in the gas block slightly and reduce the pressure pulse no?  

I will work on it again tomorrow.  One more thing I can try is to use the bolt group from my other rifle in it.  But I have a feeling it is that gas block.  I think I may ream the hole in the gas block a little and try it again.  From all indications, that should help.  

I didn't realize the gas block had been off.  You may have found out the hard way that these are not always interchangable.  If any reaming is to be done, do it to the gas block not the barrel.  I probably didn't need to tell you that, but just in case......

Good luck.


Saleen

Quoted: I didn't realize the gas block had been off.  You may have found out the hard way that these are not always interchangable.  If any reaming is to be done, do it to the gas block not the barrel.  I probably didn't need to tell you that, but just in case...... Good luck. Saleen

Thanks.  I put the same gas block on it that came off it, I am thinking that this upper came on the market due to the short stroking problem.  It looks like the gas block was installed off center from the factory.  

I didn't get a chance to play with it today, instead a poured a patio (ick).  Tomorrow I will shoot it with the other bolt group, and if that doesn't work, ream the gas block hole a little bit so the hole in the barrel is uncovered.  

Thanks again to everybody for the kind advice.

Well, well!  I think I have the problem solved!
I was wondering if the gas tube is supposed to be real tight in the gas block or not, as there was some visible blow-by on the gas tube at the gas block, and there was a bit of wiggle room as well.  I was pawing through the parts containers at the GPSS display at the BRC, and he had a front sight/gas block assy there.  I stuck a new gas tube in and it fit real tight.  Realizing that the gas block was probably the problem, I was going to buy the front sight and mill off the top, until Tommy pointed out that it was a CMP set screw unit.  However, he suggested using green "wicking" Loctite on mine, as it was likely part of the problem if it fit as loosely as I felt it did.

Well, to check it, I tamped in some JB Weld around the gas tube.  I then fired three rounds, and it cycled flawlessly, even though I got hit with a chunk of JB Weld in the forehead.

So, I cleaned it out, and applied some green wicking Loctite to the gas tube/gas block interface.   Should be good to go tomorrow!

Thanks again to everyone.  Life is good!