OK aren't both of these supposed to be milspec?  I have an A4 BM upper (complete BM upper) that will not fit on either my RRA lower or my brothers RRA lower.

Which one is out of spec?  I assume I'm not the only one who's had this problem.

Thanks!

RRA parts seem to be very tight tolerences. What is not fitting?

The RRA has a built up shelf that won't allow the rear lug on the Bushy upper to sit all the way down.  I've ran into the same problem myself.  


Your "not so simple" answer is either to lightly file down the bottom of the Bushy lug on the upper until it sits down properly or mill out the shelf in the RRA lower.

Unless you have access to a mill, then option one sounds like the solution for you.


Remember, the holes will line up properly, it the amount of material below the hole on the lug on the upper that is causing the problem.

Well I'll be damned.  This topic peaked my interest so off I went to the safe to get a Bushmaster M4 A3 upper, and a RRA lower.  Sure enough, the bushy upper does not fit on the RRA lower.

I did not get out the calipers, but it does appear that Frisco is right on the money.

I have long known that the RRA lowers were out of spec, because their high rear shelf keep accu-wedges from working.

I am surprised this has not been a big deal before?  Has this issue been taken to RRA?  The high rear shelf has GOT to go!

First we heard about the flat tops being out of spec. While it appears they have fixed that problem (after a large controversy), now the lowers look too tight for milspec uppers? In additon, there's a thread in the optics forum right now which may indicate their A2 handle is out of spec (sight channel is too narrow to accomidate a ACOG mount designed to fit inside milspec handles... whats next? They seem to have some nice stuff, and I sure do hope they can get thier stuff together.

You guys are all wet about RRA lowers being out of spec.

See... RRA lowers are the only lowers that are [i]in spec.[/i] You know... the new improved mil. spec that [b]all[/b] the other manufacturers will be moving to after the first of the year.

A [b]BIG[/b] announcement to this effect will be made at the next SHOT show.

I know all this because a friend of a friend's second cousins wife's hairdresser's brother knows about these types of things.

Oh... and if Bushmaster, Oly Arms, Armalite, DPMS, and Dick Swan of ARMS fame tell you anything different, they are misinformed &/or outright lying to you!!!


...but I ain't one to gossip.  [;)]

Could someone measure the depth of the RRA shelf that doesn't work?

thanks

I tried, mine, too; nogo.  The BM uppers won't fit onto/into the RRA lower.  The RRA upper, however, will fit on the BM lowers, although it's not a tight fit; it would definitely require an accuwedge.

BM upper rear lug width:  .0522"
RRA upper rear lug width:  .0519"

BM lower aft push pin interior width:  .0523"
RRA lower aft push pin interior width:  .0520"

BM lower aft push pin interior depth:  .0623"
RRA lower aft push pin interior depth:  .0523"

The last dimensional difference seems to be the culprit. (Hopefully Santa will bring me a new digital camera...)

J3_

That's exactly what I'm seeing on my 2 lowers.  So, in light of this recent observation I'm selling my RRA lowers and replacing them with either Eagle/Armalite or BM lowers.

If it's out of spec I just don't want to mess with it.

Is this truth?  Or are you just fucking around?

how many you got and what do you want for them?

These are AR15 lowers, so none of them are "spec."  I can tell you than FN ("spec") uppers will fit on RRA lowers fine.

Anyone tried a RRA lower & Colt upper?

In my experience, RRA uppers have tighter tolerances than BM.  But, unless you are building a target rifle, a little slop is good.

This is good info to know; thanks for the heads up.

Since FN doesn't sell uppers to the public how do you KNOW your upper is FN?  Some gunshow dealer tell you?

Hmmm and i was just getting ready to buy another RRA lower. Going home tonight and try swapping out some uppers to my RRA lower. I'll post my results.
R2K Out

Armalite M15A2 upper - check. [:)]
Tromix 440 upper - check [:)]
Tromix 458 SOCOM upper - check [:)]
RRA M4 upper - check [:)]

4 for 4 works for me [bounce]

My Colt AR15 uppers fit on my RRA lower.  I had to file the front pivot hole a litte on the 9mm upper.  It was a little tight.

Posted by SHIVAN...




I'm just poking fun. About a year ago,  RRA used the above assertions as a cover story for why a batch of their flat top uppers would not accommodate ARMS & other rail mounted accessories.

I called BS on them and started a two week thread thoroughly debunking their baseless claims.

I posted E-mails from Bushmaster, Oly Arms, Armalite, DPMS, and a response from Dick Swan personally, and all of them stated unequivocally that there had been no change in Picitinny rail specs., and that there  were absolutely no plans to do so in the future.  

Yet, even with a mountain of evidence to the contrary, some of the RRA faithful on these forums continued to insist that RRA rails were being machined to a new spec. (nobody could come forward with a named, reliable source besides RRA ), and that anyone who said different was either misinformed or was covering their ass!


So to answer your question... I as just having some fun at RRA's expense, because at this point, they deserve it!!!
 

Well, I have two different  Bush uppers.  One fits, the other does not.  When I get home, I will get the lug measurements and post back here.

I too once built a rifle out of a RRA lower and a BM upper.  What did I find?  The BM upper's rear lug fit too tightly to completely close the two pieces.  But I was GLAD!

Many pay extra for handfit upper/lower combinations, and that's exactly what you'll get when you marry a BM upper with a RRA lower.  It takes all of about 5 minutes to carefully file a "little" bit of the rear lug on the BM upper to PERFECTLY fit the RRA lower, with absolutely NO MOVEMENT!!!  A touch of Aluminum Black and NO ONE will ever be able to tell it was ever filed.  Not to mention you can adjust the rear pin tightness to your liking.  You can either make it so tight that you have to "tap" the rear pin into place, or you can make it as sloppy loose as a factory BM rifle.  It's up to you.

Or you can buy a RRA upper for your RRA lower and get a perfect fit without an fitting required.  That's what I've done.  I can attest to RRA's machine work as being the cleanest and tightest fitting around, bar none.  My BM's, Armalites and Eagle Arms NEVER were as well machined as my RRA.

Posted by ME [:D] ...


PPD, refresh my memory... you were one of the "RRA faithful" were you not ???  [thinking]

Few pics about the thing.
Lower lower[:)] is RRA
[img]http://www.printroom.com/_vti_bin/ViewImage.dll?userid=300whisper&album_id=103514&image_id=6&courtesy=1[/img]

[img]http://www.printroom.com/_vti_bin/ViewImage.dll?userid=300whisper&album_id=103514&image_id=7&courtesy=1[/img]
Lower in the middle is RRA
[img]http://www.printroom.com/_vti_bin/ViewImage.dll?userid=300whisper&album_id=103514&image_id=8&courtesy=1[/img]

MN

This is all really strange -- I just went and checked my RRA lower and yes, it is different in the area by the rear push pin. I got out my Colt and put the upper on the RRA lower just fine, then I got out my Bushmaster and put that upper on my RRA lower just fine -- what gives?
Pete-in-NH, what is the fixation you have for purple Bushmasters. I buy Rock River because I like them, I buy Bushmaster because I like them, I buy Colt because I like them and they each have their little oddities.

I ORIGINALLY purchased a RRA flattop upper BEFORE they changed their rail specs, and YES, it was not Mil-Spec BACK THEN.  But ALL current RRA flattop uppers have Mil-Spec rails and they accept EVERY accessory known.  In the interim, I used a BM flattop upper as a substitute.  And YES, there was some VERY minor fitting required.

Everyone keep this in mind... Commercially produced rifles are made for "general purpose use" and their tolerances aren't "precisely machined" as RRA's products are...

I'll put my RRA rifle up against any BM, ARMALITE, etc. - ANY DAY!  Like I said in my previous post, I've owned them all and can say RRA is the BEST!!!

YA! What Pete said.

My J&T upper fits my RRA lower fine.
My RRA upper fits my RRA lower great!

Sounds like BM is the outa spec company. My .02

It is not correct to say that Bushmaster is out of spec.  Their uppers would work fine on M16 or M4 receivers - those receivers do not have the big shelf.  The Bushmaster receiver is in spec.

It also does not make much sense to blame RRA for being out of spec, because all AR-15 lowers are out of spec.  Mil-spec uppers do apparently work fine on the RRA lowers.

The only thing that can be said is that BM uppers may not work on RRA lowers without some minor fitting.  If I was RRA, I would change my lowers to fix this "problem," because a lot of people buy Bushmaster uppers for the dry lube, chrome lined barrels, 5.56 chambers, etc.

Look on the bright side of all of this.  We now have a sure fire way to determine whether an upper from Gunsmoke is actually a Bushmaster.  [:D]

No problems observed here when swapping 3 BM uppers on 2 RRA lowers.  YMMV.  Never heard of this issue before.

This got my interest as I freely admit to being a big fan of RRA (sorry NYPAT.)...I have three RRA lowers and two of the PWAs they used before their own came on line.  I have access to a bunch of uppers so I thought I would try them all.  Results?
Uppers tried:
RRA A4:  Fit all five fine.
DPMS A4:  Tight going in to the RRAs, light tapping on flat-top with rubber hammer seated it nice and tight in all three.
Tromix (sorry, don't know which brand Tony uses) A2:  No problems.
BM A2:  No problem
BM A4:  Snug...same snugness as with DPMS on first lower tried...tapped it in place fine, when disassembled, showed a little exposed "silver" on rear bottom corner of upper's rear lug..after that, fit the other four lowers without problem.
Victor V22:  No problems.
2 more DPMS A4s:  No problems.
DPMS M37 flare launcher:  Tight in all five..also in every other lower available, which is weird.
2 "FN" A4s (the numbered ones supposed to be FNs at least)...one no problem, one tight in one of the RRAs and one of the PWAs, but again, closable with a light tap.  
Armalite A4:  This is the one that surprised me...it was sloppy in all three RRAs.  Rear (takedown pin) lug of upper appears to be chamfered (for lack of a better description)on all four lower edges..owner swears it's the factory original and hasn't been messed with, and finish does appear to match.
Not scientific by any means, and probably shouldn't have to lightly tap uppers into lowers, but I would much rather have tight fit than the sloppiness I got on the last upper.  You shouldn't have to use an accu-wedge, and I can't imagine I would ever have to with any of these except the Armalite upper, which again was surprising as it was a reasonably tight fit in the Armalite lower we pulled it off of.
Not trying to throw gas on the fire, I just thought my access to so many uppers might be useful.  By the way, I don't ever want to do this again as it took just under three hours to do in all the different configurations.
Sluggo  


               

Those numbered A4 flat tops you have can not be FN. I have no clue who did make them, but it wasnt FN. FN does not make flat tops.

Thanks![:)]

I've been collecting selling trading AR15s since the early 70's...
Carried one in Vietnam
Ive had four or five Bushys
Ten Colts
Springfield Armorys Version
PWA
EA Company
Eagle Arms
Rock River and a few more..
The Rock River I rank up with the best of them..if not the best...
My Bushy upper fits perfectly on my RR lower

I think the bottom line is that each manufacturer pays different levels of attention to fit and finish...

Nothing at all against other manufacturers such as Bushmaster, etc., but Rock River lowers are definitely not worth throwing out just because a few Bushmaster uppers don't fit without some filing on the upper. FYI, the Rock River upper and lower that I got from Pete have the best fit and finish that I have seen on an AR.