A while back I built a pseudo-retro carbine. 16" pencil barrel, green triangular handguards reminiscent of the Colt 607 and a DPMS A1 upper. That is the retro part. The lower half is built on an Anderson Manufacturing lower, Timney trigger, green A2 grip filed down to look like the old A1, a mil-spec diameter buffer tube and a green MagPul CTR buttstock. Looks quite cool and it is pleasant to shoot - ArmaLIGHT. But I have been having some ejection issues.  

Long story short I took it to a gunsmith today after conducting some rather detailed testing, substituting of parts etc.  The lower side (inside) of the receiver end of the buffer tube exhibited some rather severe wear after only about 500 rounds.  The gunsmith did a visual examination and told me that the buffer tube was not parallel to the axis of the barrel. Measurement showed that the tube was tilted upward towards the butt plate. This might well account for the wear on the lower side of the tube.

Upon reflection it appears to me that the attachment scheme for the carbine buffer tube is somewhat lame.  The rifle tube has a machined flange which mates against the machined surface at the back of the lower receiver. The carbine tube, however, relies on the threads on the receiver and the tube, a stamped sheetmetal plate and the threads of the castle nut to attempt to put all of this in alignment.  The threads are rather coarse and of loose tolerance for a precision alignment.  If the endplate is not exactly flat and uniform (mine varied by .005" from top to bottom in thickness) and the threads are not perfect - the tube could project at any random angle.

So my question is... What is the proper method for assembling the carbine buffer tube to the receiver so that it will be in correct alignment?

TIA,

Ken

.005 is close enough for what it does. Just line it up as best you can and be done with it. Save the precision for the upper where it will do the most good.

I would start with good quality parts.  White Oak Arms comes to mind.
There is no secret to putting together a carbine (or rifle) extension and an in-spec lower.  It will be square and function fine.
Cheap parts are not worth the aggravation.  Start with better parts.

I'm having problems picturing this. Unless the threads on the lower receiver or tube are cut incorrectly it should be aligned straight when tightened. The end plate should not effect this to the point of canting the tube in any direction unless is grossly mis shaped. You hear stories of canted buffer tubes but I've yet to ever actually see this so called issue. Do you have any photos of the wear on your rifle?

The enhanced buffer tube from pws supposedly corrects this, advertises it anyway. It looks really cool if nothing else.

Colt and Viltor are good buffer tubes.

The buffer tube is essential to long term dependability of an AR.
I have seen buffer tubes as low as $5.  

How would you like to have a buffer smack into your shoulder at full speed.

Thanks for the feedback so far.  I hope it is not the Anderson lower. I have several more of them which have not been built out. The upper worked great on an A2 rifle lower. I guess I could try a rifle length upper on the malcontent lower or another 16" upper which is known to function well. However, my current plan is to swap an A2 rifle length tube and stock onto the Anderson lower and see how that works. I will then fit the carbine tube to the DPMS lower from which I am borrowing the A2 parts. If that works I may just leave them that way. On the other hand the Fayetteville, NC gun show is next weekend so perhaps some new parts are in order.

On the other hand, I have NEVER liked the carbine AR - and I bought my first one in 1980. The Colt tear drop butt plate is not tall enough for me to get a decent cheek weld on the bare tube.  The MagPul butt plate is about an inch taller but it seems more. It fits me much better but not as good as a plain old A2.  I restocked a 25 year old heavy barrel carbine a couple of years back to an A2. It is much nicer to shoot. I thought I would never build another collapsible stock carbine until I came across the 16" pencil barrel and the triangular handguards and I just had to build it.

I will see if I can get a picture of the wear.  I shimmed the plate with a cut up .22 rimfire case so the tube was aligned then painted the wear area with Dykem layout fluid, let it dry, lubed the tube and fired 20 rounds.  I need to clean up the mess and see what I can see. At first glance it looked like a wider, larger wear patch but then again I had not cleaned it to get a proper look.  I will post more info when I can.

Ken

The Vltor RE-A5 or A5SR are top-of-the-line!
LMT is good stuff.  And a Colt carbine RE is the definition of mil-spec.

I have a small stash of Colt carbine end plates and 1x Vltor convertible fixed loop. No complaints.  All square up with my lowers.

Some good news. I pulled the carbine length tube from the Anderson lower and placed the lower on a magazine block in the vise. With a little shimming and adjusting I set the machined surface on the top of the receiver - above the fire control pocket - so that it was level as measured by a machinist square.  By means of a second square I determined that the receiver ring was perpendicular to the top of the receiver - at least as close as I can determine without access to a milling machine.  So I will pronounce the Anderson lower OK.  

I then pulled the stock from a rifle length DPMS lower. I again positioned it in the vise, leveled the top of the receiver and with the aid of a square/level determined that the rifle length tube was level within 2.35 RCHs.  I removed the rifle tube and installed the offending carbine tube. By means of the same measuring technique I observed that the tube was canted upward in this receiver.  I guess the carbine tube needs to be suspended from a string for use as a swinging target and a new tube procured and installed.

Ken

The term "mil spec diameter" (as opposed to actually MIL-SPEC) is often code for "cheap" and "shoddy."  It sounds like you got a shoddy receiver extension, which is why it wore badly.

You can get a nice receiver extension from Anderson for $20.  It's not just MIL-SPEC diameter, but it's made from the MIL-SPEC material too.  It should be within spec, too.  And if Anderson's tube doesn't line up straight with one of their lowers, you can contact them for a fix.

I get a kick out of Mil-Spec when applied to semi-auto and other items which the military never used and thus would not have written a specification for. Anderson on Anderson would certainly put a crimp in vendor finger pointing.  Good idea. Thanks.

Ken

Make sure the 'tit' on the REP is fully going into the relief in the lower.  A cheap REP might be too big and not fully seating.  That would cause the cant you are seeing.

There's nothing semi-auto or full auto about a receiver extension.  It's either within specs for a MIL-SPEC part or it isn't.  The only things that cannot be truly MIL-SPEC in a semi auto AR are the lower and the FCG.

When discussing receiver extensions, there is enough fudging and going cheap.  There's no need to start the "that can never be MIL-SPEC" argument for this part.  Yes it can be MIL-SPEC.  If you doubt that, take it up with someone like BCM...

Update... A complete Anderson Mfg buffer tube kit is on its way from TX.  The tube, end plate, castle nut, spring and buffer. I will install it and if it measures straight and true I will give it a work out. If not, I will climb Anderson's tree. If I does not work... I have enough other Anderson parts in my spare stock to put together a complete Anderson carbine (except for the barrel and pistol grip).  If I have to go that far and it does not work... I will install a rifle length tube and epoxy the Magpul carbine buttstock in place so it LOOKS cool and works

The current end plate does fit flush against the back of the receiver. A good suggestion to check.

As to Mil or notMil spec... I realize the tube is not semi or full auto specific.  However, the tubes exist in at least 3 different diameters. The smallest "Mil Spec", the sightly larger "commercial" and a slightly larger still size in a stock kit I purchased 25+ years ago.  

Ken

The Anderson parts arrived today. I noticed that the threads on the tube fit much more snugly into the receiver ring.  I put it all together, lubed it and made a test run.  A 20 round mag followed by a 10 round mag - no problem.  Time to cool and replace the paint on the target.  Most of the next 20 round mag and then a stovepipe with 4 or 5 to go.  Ejection was a little more regular but not as good as with the rifle length lower.

For my next trick I installed the H2 buffer.  3 or 4 stovepipes in the first few rounds - lost count - and then the rest of the 20 round mag ran OK.  Obviously NOT the direction to go.

Tomorrow, after celebrating 100 years old for my Webley Mk V, I will mount a different 16" upper on the Anderson lower - with the regular buffer - and see what happens.

Ken

Good to hear that your new parts arrived, and that they worked.  What upper did you test with - the 607-ish upper from your original post?  What ammo were you running?

Yes, the parts arrived. 1 failure out of 50 I would not call success. I am using the DPMS A1 upper with 16" pencil barrel. The ammo is hand loaded - 55 grain ball over 26.2 grains of WW 784. Right out of the Winchester manual - a load I have used for decades, in many different rifles.

I did in fact obtain a second "generic" tube.  I am about to head to the shop to install that in place of an A2 buttstock on a DPMS lower. I will then try the DPMS upper on the DPMS lower and another 16" upper on the Anderson lower.

Ken

Good plan.  I'm looking forward to hearing how this plays out.

This is approaching the realms of preposterous

As per my prior post I assembled the new, generic tube on the DPMS lower. The fit was good, not the sloppy engagement of the threads on the original bogus tube into the Anderson lower.    Upon completion of the assembly I checked the alignment with machinist squares and levels and pronounced it good. The first 50 rounds (my normal test routine 20 round mag, 10 round mag, a little cooling and another 20 round mag) fired 100% with decent ejection enthusiasm. All but 3 or 4 cases were pitched clear of the bench and generally were from 1 O'clock to about 2:30.

Back to the shop and I decided to dedicate the DPMS lower to this build as the DPMS A1 upper seemed to like to co-exist with it.  I changed the green furniture to the DPMS lower (pistol grip and a MagPul CTR buttstock in place of the black MOE buttstock).  I thought I was done except for another test run which I would do the next day as some rain showers were passing through the area. But I got a break in the weather and impatient so I decided to have another go yesterday.  3 stovepipe failures out of the first half of the first 20 round mag, one in the 10 round mag. The second 20 round mag ran fine.

I spent some time last evening reviewing the Troubleshooting forum on this site and watching some nice videos by MBELL556. I got the impression that most of the posts in the Troubleshooting forum had to do with rifles which did not work, not occasional failures.  MBELL556's discussion of failures to eject pointed to worn out parts (the firearm in question has about 5 - 600 rounds down the pipe) or "out of spec" parts.  However, he offers no advice on how to verify spec on the various parts.

To help me think though this let me recap what has transpired and what I have observed.

Ammo - I do not think the issue is here - I have been loading .223 for more than 40 years, the ammo works fine in other rifles, it comes off a Dillon 550b which has been very consistent, rounds are sampled for OAL, case dimensions with a Wilson case gauge etc.

Changing the BCG had no effect.

Changing to an H2 heavy buffer made things WORSE.

The original upper/BCG worked GREAT on an A2 rifle length tube lower.

Cleaning/lubrication - no more than 200 rounds between teardown. cleaning, lubricating.

Magazines - 3 different ones/types/mfgrs which work in other rifles.

Some possible things to try...

Install a different 16" upper on the carbine length lower (DPMS) and test

Change the M16 BCG in the original carbine upper with a neutered Colt BCG (from the days of the sear block in the lower). This is the lightest BCG I have. The heavy buffer made things worse so perhaps a little lighter is a little better?

Say screw it and mount the original carbine upper on an A2 lower  Actually I am liking this more and more.  Just need a green stock skin.

Crazy idea... procure a Rock River "Entry" stock and mount it on a rifle tube with a rod below the tube for stabilization. It would not be collapsible but would LOOK like the Colt 607 stock.

Or... perhaps someone can help me here... is there such a thing as a rifle length carbine tube with the carbine rib on the bottom - perhaps to make a non-collapsible rifle for a compliance state?

TIA,

Ken

How many rounds/how old is your carbine action spring?  Measure, and if under 10 1/16" replace.
Springs are a wear item and I replace every other year or 5K rounds.

The carbine spring was new for this upper build - less than 500 or so rounds. Measures 10 1/2" +. But I do have good news...

I installed the neutered Colt BCG (by that I refer to the carriers which had the bottom cut off all the way to the back end to allow for the auto sear & M16 hammer block which Colt blind pinned into receivers some years back). This BCG weighs 28 grams or just over an ounce less than the full auto BCG. I ran my 50 round drill with NO issues. Ejection was very enthusiastic and all but 3 or 4 cases landed in a patch between 1 O'clock and 2:30. The only cases which ended up on the bench had struck the sandbag which deflected their flight path. I will be running some more rounds during the week but considering the much better ejection action... I think this setup is good to go.

As to my earlier test with another BCG... in that case I had the wonky out of alignment buffer tube installed.

As to the offending BCG - I had not wanted to cast aspersions without some data - It is an AIM Surplus nickel boron coated item.  I purchased it at the time I was collecting parts for this built. I was not impressed with it and have had some discussion with AIM about the quality of the gas rings and the dimension of the flange on the firing pin .  For a super slick finish it does not seem that sick to me. It is hard as heck to clean and when it is dry - the lube having been removed with degreaser during cleaning - the finish seems to have a coating of greenish white corrosion. The BCG had some of this minge showing when I pulled it in order to install the other BCG.  Bottom line, the AIM BCG was unceremoniously tossed in the trash following the good results with the old Colt BCG.

I guess my ersatz Colt 607 buttstock project is relegated to the back burner as they say. I have a neighbor's CMMG dedicated .22 LR upper light strike issue to work on, the firing pin on my 100 year old Webly Mk V needs to be smoothed (perforates CCI primers - my Mk IV Webly does the same but ONLY with CCI primers) and a Kydex moon clip holder for my S&W J frame to prototype.

Thanks to all for your input.  I will probably make one more post towards the end of next week after I have run some more rounds.

Ken

Poor ejection with standard carrier and buffer, but fine with a lighter carrier sure sounds like a gas system problem.  Did the pencil barrel come with an installed FSB?

The pencil barrel did not have an installed FSB. I installed one which attached with 5 set screws. The gas tube was new. It is carbine length. I feel that it is aligned properly as the sights are centered and the ejection with a rifle stock lower was quite energetic. Ejection has been energetic with the other buffers although somewhat erratic with the AIM buffer and especially with the out of alignment tube.  I think this was due to friction between the BCG and the upper receiver and/or the wacky tube. The Colt has some age on it and is perhaps better broken in.

Ken

The second 50 round test of my "repaired" carbine was a disaster. 3 failures to eject from the first 20 round mag and 1 failure to extract. It the last case I must take most of the blame as I was trying to figure out if it was possible to clear the stovepipe jam without dropping the mag. It does not appear so. In doing this "manipulation" of the spent cartridge I believe I damaged the rim on the fresh cartridge which was attempting to feed.  Back in the shop it took only the slightest tap from a cleaning rod to pop the non-extracted case out. But it did finish my testing for the day.

I then took the carbine to a local dealer to speak with his in-house gunsmith.  We stepped through the list forward and backward and I had tried everything he could think of.  His conclusion "it must be a gas problem." As the firearm is gas operated and it is not operating correctly I guess that is true but not really helpful. I decided that only two components had not been replaced; the barrel and the upper receiver.  As the intention was to build an A1 carbine... if the problem was the upper - time to trash the whole project. So...

I pulled the Lothar Walther 16" "very, very light" stainless barrel from my prior build.  It is a super barrel. Heavier than a pencil but not as heavy as an M4 (and no grenade launcher groove for the launcher which I do not have :-)  I pulled down the offending carbine and this morning gave the upper a quick clean and installed the Walther barrel, the Del-Ton semi-auto BCG which has been used with that barrel and the gas tube from that carbine with an A1/A2 front sight base.

I fired 90 rounds from a collection of 6 magazines. NO PROBLEMS!!! Ejection was consistent and enthusiastic. I did notice that the spent cartridges were a lot cleaner than those from the prior barrel;  those were VERY smokey.  It has been my observation that the smokey crud on the spent cases occurs during the loading phase. When I single load an AR the cases are all shiny as is the FIRST case from a magazine.   Perhaps the pencil barrel setup was cycling the bolt too fast and shoving the new cartridge into the chamber while it was still full of fire. But then why did the heavy buffer not smooth things out?

Bottom line, the green furniture carbine will live on with a stainless Walther barrel and most importantly a polished stainless three prong flash hide (that bling is probably what really fixed the problem  The AIM nickel boron BCG has been retrieved from the trash can - it looks nasty but a buddy of mine claims he has some foaming bore cleaner which will clean up a nickel boron BCG to like new - I will have him show me.  The pencil barrel... perhaps something with a rifle lower. And my "sniper" carbine from which I liberated the Walther barrel... I have a mid-length free float tube on order to replace the carbine length one so as to cover the gas block. I will probably procure another Walther barrel.  A great deal for only $199.

Thanks again for all the input.

Ken