Fitment concerns

[Wzrd]

I'm building my first 308 AR & having some fitment issues. I've sent an email to manufacturers of my parts. I've copy/pasted it here. Looking for some advice from experienced builders. Any & all advice welcome. 

I think I have it mostly figured out. 

The receivers are getting tight when closing because the top edge on rear of BCG is hitting the forward face of receiver extension "arch". I can see wear on this part of the BCG. I removed the buffer & spring so those are causing no interference.
I removed the gas tube but it made no difference, so it was not bottoming out in the gas key. Also removed CH & again no difference. 
As far as I can tell, the barrel is in proper position & the bolt is fully rotated & locked into battery, but the BCG is still too far back. The relief cut is not lining up with the dust cover detent assembly, so it won't close. This also would account for the BCG sticking out the back slightly too far & hitting the arch. So I know what my problem is, but not sure what the cause is. I know there are no real set specs for the 308 AR platform, but I thought all of my parts are considered DPMS compatible. I guess I was wrong to assume they'd be compatible? These are the parts:

-Spike's Livewire 308 billet receiver set 
-KAK LR308 BCG
-Faxon 16" medium taper, .308 Win., mid-length, 4150 QPQ (10A810M16NMQ)

So I'm not sure which of my parts are the problem. I'm thinking the BCG doesn't fit with the receiver/barrel combo. But I think it could be the barrel that's the problem. Or maybe the barrel/BCG combo are fine but the upper isn't. Regardless of which part(s) are incompatible I'm out a few hundred dollars if I have to replace them. Neither the BCG or barrel could be returned & resold as new at this point. Does anybody have any suggestions or advice? 

Does Spike's have any BCGs they suggest & know will work with these receivers?

Is KAK aware of their BCG being use successfully with these receivers or this barrel?

Has Faxon ever heard of any problems like this? Does this sound like a headspacing issue?

Again, I'm a complete novice to the 308 AR world, so I'm all ears. I'll post on some forums to see if I can get any advice. I don't have anyone locally I can go to. 

End email. 

I do not have go/nogo/field gauges so I have not tested that. Can get some if needed. Have not chambered a round yet either. 

[blue109]

Have you tried removing the bolt from the carrier and just seeing if the carrier will line up with the door or the rear that way? 

Snap some pics of those areas. Pics of the carrier in the upper from the bottom and from the ejection port for reference

[Wzrd]

The bolt is still in carrier in the photos. Will try removing it like suggested when I'm home later. Sorry the picture from under BCG isn't so clear. 

[98Z5V]

Get some pics of the interference and what's wearing, where... That'll help.  Sounds like it's all at the back of the upper receiver, or bolt-to-buffer.

 

Just so you know, the bolt DOES push the buffer off the buffer retainer pin, ever time you close the receivers.  When the rifle is closed, that buffer never touches the buffer retainer pin.  If it did, during operation, it would shear that pin right off as soon as you fired it, and it recoiled, and closed on the next round.

Edited February 15, 2017 by 98Z5V

[planeflyer21]

21 minutes ago, 98Z5V said:

If it did, during operation, it would shear that pin right off as soon as you fired it, and it recoiled, and closed on the next round.

There was someone here whose pin was bent all to hell due to there being something out of spec.  Maybe 2 years ago?

[Wzrd]

I understand that. There's no problem with the buffer or its retaining detent. I'll take photos later when I'm at home. The wear is at the back but as this is a brand new build it's very minimal- just from me opening & closing the receivers. I think I'll try to back the buffer tube out one turn to see if the BCG is actually hitting it (instead of the RE "arch") when closing the receivers. But that still won't have any effect on the dust cover not closing. I looked up images of other 308 BCGs & there seems to be many different shapes & widths of relief cutouts for the dust cover detent. Some that look like they might allow mine to close. I just don't understand this if all my parts are supposedly dpms pattern. KAK said they've had no reports of the dust cover being obstructed by their BCGs. But that's all they said. Haven't heard from Spike's or Faxon yet since that email. 

Ultimately I could deal with these problems if I know the gun is safe. I might be able to grind off some of the dust cover detent assembly enough that it'll close on the BCG. But I'd rather not have to resort to things like that. 

Edited February 15, 2017 by Wzrd

[98Z5V]

32 minutes ago, planeflyer21 said:

There was someone here whose pin was bent all to hell due to there being something out of spec.  Maybe 2 years ago?

Yep.  Can't remember who, though, but I chimed in on that, too. I had that issue on my Spike's 5.56 billet set. Had to install a Tubb CWS to cure it. Caught it when it started chewing the hell out of the face of my buffer.

[survivalshop]

 Sounds like the Bolt is not seating or locking correctly .

As Blue109 said , remove the Bolt & see if it all lines up correctly & the Receivers should have no issue closing together properly with out the Bolt in any AR .

 

Edited February 15, 2017 by survivalshop

[Wzrd]

   Ok so here's the update. I checked the buffer tube & saw the top edge was being worn. It wasn't actually protruding into the receiver, but was close enough to the edge that the BCG was catching it when closing. Backed it out one turn & its closing fine with no interference now. The photo showing the wear has the buffer tube in its current, correct position. So that issue is resolved & was all my fault. 

  That still leaves the problem of the dust cover not closing. These photos show the carrier only. It is in contact with the barrel extension. As you can see it made no difference. The relief cut still doesn't line up with the detent. But am I mistaken that the photos of the extension in receiver look normal? So if that's normal, & the bolt isn't causing any issue, then what's the explanation? Detent is in slightly different position than most in relation to BCG? Or it's a little larger/wider than normal? Wtf? If I grind down the forward bottom corner of detent it might close. As I said before I could live with that. I'm just worried it might be an indication of something being wrong. Any thoughts?

[blue109]

Glad you got part 1 figured out. Carrier looks like it's seated just fine so I'd guess the way they shaped the cutout just doesn't play nice with that upper? Maybe that ejection port is slightly further back on yours that whatever upper they tested with? Take a measure from the front of the receiver to the detent on the door and we can compare. 

 

[Wzrd]

It is 2-1/8" from front of receiver to front edge of detent. Detent assembly itself is 5/16" wide. It's just a hair over 3/16" deep

Heres a few pics of other 308 BCGs showing the various shapes & sizes of detent relief cutouts. In order: Rainier, EP, Black Rain, Aero, Anderson, Young, Lantac, Rubber City. Why so much variation?

[blue109]

Some of those definitely look like the cutout is closer to the bolt than yours. Several of them have the gas ports in the cutout, your gas ports are on the flat logo part. I'll check mine out when I get home.

[survivalshop]

 Can we see a photo of the Gas Tubes protrusion into the Upper receiver ?

 You may or may not have feeding issues with that Barrel Extensions feed ramps , you have an M4 feed ramp system on the Upper Receiver & std Feed ramps on the Extension . You won't know till you test fire , some are ok , some have issues .   308 AR's really don't need the M4 ramp system .

[Wzrd]

What do you mean standard feed ramps on the extension? I'm familiar with the whole m4 vs rifle thing, but my extension looks like it has m4 style ramps to me. Or at least they seem to line up with the ramps on the receiver. Maybe wider than m4, for the larger cartridge? The last photo of extension is one of my ar15s. Seems the same to me. It doesn't look like the classic comparison photos I included. Am I wrong? 

[blue109]

I've got that same 2 1/8 measure as you on my Matrix upper and the same Anderson carrier you have in your pic.. Looks like the KAK carrier just doesn't have enough relief cut into it. 

Edited February 16, 2017 by blue109

[98Z5V]

3 hours ago, Wzrd said:

   Ok so here's the update. I checked the buffer tube & saw the top edge was being worn. It wasn't actually protruding into the receiver, but was close enough to the edge that the BCG was catching it when closing. Backed it out one turn & its closing fine with no interference now. The photo showing the wear has the buffer tube in its current, correct position. So that issue is resolved & was all my fault.

Just make sure that receiver extension is screwed into the lower far enough to properly capture the buffer retainer. If it's not, that buffer retainer WILL shoot out, while shooting the firearm, and it will jam something up, causing you grief... 

On the other issue with the port door - I'd grind the leading edge of that port door ball-and-detent housing, if it was mine, and test it out. I think that's the issue, as pointed out by others.  Port doors are easy to replace... 

[Wzrd]

It's a PWS enhanced tube. I had it screwed in as far as it would go while still allowing the detent to retain the buffer. Obviously that's not the way to do it. I don't think there's any chance of it coming out. The tube is holding it down on left & right sides as well as the rear. 

I'll try to grind the door. I think it will work. It just seems really odd that no one has heard of this problem. From the photos the Aero BCG, the cutout looks same as KAK, & I know Aero is popular. I'd think people have used those in all types of receivers. Maybe my door detent sticks out too far.

Thanks all who responded. If you have anymore advice or suggestions I'd be happy to hear it. I'll report back when I'm done grinding. Now I just have to figure out how to remove the door. Don't see any c-clip or set screw. I'll ask Spike's. hopefully I'll have a finished, functioning rifle soon. 

[98Z5V]

^^^  You are WAY good on that receiver extension.  By FAR. 

[survivalshop]

15 hours ago, Wzrd said:

It's a PWS enhanced tube. I had it screwed in as far as it would go while still allowing the detent to retain the buffer. Obviously that's not the way to do it. I don't think there's any chance of it coming out. The tube is holding it down on left & right sides as well as the rear. 

I'll try to grind the door. I think it will work. It just seems really odd that no one has heard of this problem. From the photos the Aero BCG, the cutout looks same as KAK, & I know Aero is popular. I'd think people have used those in all types of receivers. Maybe my door detent sticks out too far.

Thanks all who responded. If you have anymore advice or suggestions I'd be happy to hear it. I'll report back when I'm done grinding. Now I just have to figure out how to remove the door. Don't see any c-clip or set screw. I'll ask Spike's. hopefully I'll have a finished, functioning rifle soon. 

 Thats one of their Anti tilt Receiver Extensions , they are assembled a little different for clearance .

 as far as your Feed ramps , you will not know till you test them . Its not where they sit , its how they are blended together . I have seen HP Match Bullets jam right where the two feed ramps meet , but as said I don't thin the 308AR even needs M4 feed ramps ,I have two with out them .

[FaxonNathan]

Correct. The 308 presents rounds higher and does not need (nor do we reccomend) any "M4" feed ramps. 

[Wzrd]

   So I ground on the dust cover detent a little at a time, testing the fit as I went. Eventually I got it to fit, however I had worn through to the spring by that point. The exposed area You see wasn't ground completely off, but the metal there was so thin that it just peeled away. I got into the spring a little too. Because of this I don't really trust using it. I'm worried the spring will break & I'll get bits of metal in the chamber, bolt, etc. at the worst time. BTW the white powdery stuff is just residue left from the flashing of electronics cleaner.

   I got one of the strike industries UDCs figuring it would be easier to alter, more forgiving & flexible, & I could complete the build & still remove/install it with the barrel nut in place. It too wouldn't close at first so using a razor blade I shaved off plastic, again testing fit as I went. In the photo you can see reflection off the detent ball as it isn't actually locked in behind the lip of the ejection port. If I shave off any more I think I'll compromise its integrity. At this point it is wedging closed tight enough for my purposes.

   This whole thing has been so frustrating. I know the dust cover has absolutely no effect on the functionality of the rifle, but I like to keep the covers closed when not in use. I'm a little OCD sometimes. I don't like the current state of it, but I can live with it. I just don't know how there's no info on this happening to anyone else. I'm thinking maybe my problem is the receiver/BCG combo. The relief cut not being deep or wide as some, & the receiver maybe having the ejection port just a tad tighter to the BCG than most. Does that make sense? Anyway, thanks again to the responders. Feel free to comment as long as you like, I will see it. 

[Wzrd]

[survivalshop]

 Do you know anyone with a 308 BCG , that you can swap Bolt Carriers , just to test another Brand ?

 I think you are right about the BC not being cut correctly , have you contacted KAK ? Maybe they are aware of an issue with some rifles .

Have you checked Head Space with this BCG ?

[Wzrd]

I know one guy who has a 308 AR. I'll see if I can use his BCG.

I haven't checked headspacing. Don't have any gauges. I can order some if necessary. I don't know if the BCG is cut wrong, or if it just isn't fully compatible with my spike's Livewire upper (the dust cover seems to be only problem).  I contacted KAK. All they said was they've had no reports of this problem. Same with Faxon & Spike's when I originally contacted them. The first post of this thread was a followup email I sent to all 3 & I also sent them a link to this thread. None of them responded with anything more. 

One of my earlier posts shows multiple 308 BCGs & there seems to be many different relief cut shapes. The KAK & Aero look the same. Others have wider cuts. Not sure if the depths vary. I'll test another brand & see what happens. 

[Wzrd]

Sorry it took me so long to get back here. Anyway my buddy's BCG has same relief cut as mine, so fit was the same. I don't know anyone else with a 308 AR. But I recently took it out to test fire for the first time. After some tuning of the adjustable gas block it is all working fine. No problems with anything through a couple hundred rounds. Feeding is good in spite of the feed ramps' presence ;) The alteration to the SI dust cover allows it to close enough to stay closed when not in use, & I don't feel I've compromised its integrity. So I'm letting it go. It would be nice to find out if anyone else has had this problem, but it doesn't affect functionality any so no big deal. I'm happy with the build. 

Thanks to all who replied.