RR lower won't fit.....

[Boomer]

issue....

I have a complete RR lower that fits on my Bushy upper, and my Ruger upper just fine.
It will Not fit onto my DD upper. Very tight and a cannot get the front pin to make into the upper.
The DD upper fits fine on the Bushy lower. I have an Aero lower that the DD fits on just fine.
I've looked at this for an hour now and I am stumped.

To put it another way.... Every upper and lower combination fit fine except the one combination of the RR lower on DD upper. What's the magic ?

I have to leave for some afternoon work and won't be back until 7PMish

Thanks

[Svickstc]

Just how it is sometimes...take a punch and hammer those pins in(unless they are clearly not in line)...a tight upper is not always a bad thing (accuracy)...it will loosen up overtime a bit

[Gun]

It will Not fit onto my DD upper. Very tight and a cannot get the front pin to make into the upper.

The pivot pin will not pass thru the DD upper? Are you holding the upper open, as in perpendicular to the RR lower, or are you trying to push the pivot pin thru with the upper and lower mated.

[ViperHummel]

Have you tried having the upper angled when putting in front pin? Like a break action shotgun. I had a Para Arms lower that I had to angle (find the sweet spot) to pop the pin out and put it back in. Give it a shot. Change angles so see if you too find a sweet spot.

[Fragger]

Long story made short.

Just last weekend was putting a 10" barrel on a friends upper receiver along with a FF tube. At the same time he was building his virgin lower for a pistol build.

When it came time to mate the two together it just wasn't going to happen.
You could get the front pin in but not the back.

So I put a different pistol upper that I had on his lower with out a problem.

I put his short barreled upper on my pistol lower and no problem.

After looking a lot closer and a good bit later we found the buffer tube was just catching the upper not allowing it to drop FULLY into place. It was just so close and very hard to see.

So after removing a little metal from the Buffer Tube everything pinned up nice and easy.

I'm just glad we decided NOT to go pounding on the pins.


Picture is used as an example and is not the actual tube we worked on as it was a pistol Buffer Tube and this is a rifle tube.
Metal removed (very small amount) was along the Red Line.



The rest of the story is originally before this went down was the front pin of his lower would not fit thru his upper.
Seems the guy that installed the FF HG (me) had it screwed on just a tad too far and made a slight contact with the lower.
It was hardly noticeable but was an easy fix. LoL

That thing ended up to be a 3 hour build which was twice what we figured.
On top of that it didn't run right on the range.
It's a 7.62X39 and we're working on buffer weights at the moment.

[Boomer]

Thanks for the input.......... Correction...

I said I could not get the front pin in.... Sorry.... I can get the rear pin in fairly easy, tight fit but noting I haven't seen before.

The rear pin by the stock does not fit. I am not sure what is holding it up from fitting. Tried with and without the buffer/spring.

I do not think the buffer tube is making contact as best as I can see.

[dlm84]

Some times when you add all the tolerances up s&@t just don't fit look it over again. I had a buddy have the same problem as fragger and he didn't realize it. Long story short he grinder the hell out o the upper trying to make it fit and I had to weld and machine the upper to save it for him. Good luck and check everything before you make a decision.

[Fragger]

Thanks for the input.......... Correction...



I do not think the buffer tube is making contact as best as I can see.

We didn't either until we backed it off a tad.
It's an easy check.

[Fragger]

Some times when you add all the tolerances up s&@t just don't fit

Got to figure you have a range. If everything is on the high side or low side well you may have a tight fit. Not suppose to but I guess it could happen.

Nothing to do with this but reminds me of a time when a construction company I know figured they would save some $ and took a crap load of large bolts to have them plated themselves. Cut out the middle man kind of thing. Then wondered why the guys on the job site couldn't get them to screw in the holes.

[iamtommyboy]

Rock River lowers have very tight tolerances. If you look at it compared to another lower (such as a Stag) you will see that the channel where the rear ear of the upper slides in is slightly smaller.

When helping my brother put his AR together, we ran into this issue. We bother were using aero precision uppers and he had an RR it wouldn't fit into. His upper fit my stag lower no problem. My upper would not fit his RR lower. We had to file a small (very small, a little at a time) amount of material off of the upper receiver's rear ear. It then slid right in with no problem.

I saw an earlier post about removing some material from the buffer too. With his build, we also had to remove just a little bit from the buffer tube, but I do not know if this was the tube or the lower causing the issue.

In building my AR, I had no fitting or alignment issues. With his, these were the only two issues we came across. Nothing wrong with your parts, just have slightly different specs. All should function well with slight modification.