View Full Version : VLTOR MUR Issue
I've had this upper for over a decade. It's been on multiple different brands of lower receivers. 3 different Spikes lowers, a BAD (forged) lower and a few other brands I am probably forgetting. Issue is the rear takedown pin on all lowers is extremely tight. On some it required a punch to get it out it was so tight. I should also mention that this has been with any takedown pin as well. I have used BAD, Lantac, KAK, YHM and a few generic milspec sets as well. If this was just an issue with one particular combination of parts I would lean towards it being a case of tolerance stacking. But I have not found a combination of parts where it doesn't do this. I have stopped using it and set it aside on my bench but am wondering what, if anything, I can do to correct this or trouble shoot it further. A shame to waste it. So open to any other trouble shooting ideas.
davidjinks
08-18-21, 14:49
Maybe take an undersized wood dowl with some super light weight sand paper and run it through a couple times. Not so much you go through the anodizing, just enough to remove some of the surface finish.
I've had this upper for over a decade. It's been on multiple different brands of lower receivers. 3 different Spikes lowers, a BAD (forged) lower and a few other brands I am probably forgetting. Issue is the rear takedown pin on all lowers is extremely tight. On some it required a punch to get it out it was so tight. I should also mention that this has been with any takedown pin as well. I have used BAD, Lantac, KAK, YHM and a few generic milspec sets as well. If this was just an issue with one particular combination of parts I would lean towards it being a case of tolerance stacking. But I have not found a combination of parts where it doesn't do this. I have stopped using it and set it aside on my bench but am wondering what, if anything, I can do to correct this or trouble shoot it further. A shame to waste it. So open to any other trouble shooting ideas.
Maybe take an undersized wood dowl with some super light weight sand paper and run it through a couple times. Not so much you go through the anodizing, just enough to remove some of the surface finish.
Reaming it out to some extent is certainly on the list of options. I'm just trying to find out if there is something else I am missing here before I start removing material. But it's a good thought. I do think its going to take more than just removing the anodizing. It's that tight.
Inkslinger
08-18-21, 17:10
I have a MUR upper that’s tough to push the pin out. It’s never really bothered me. If I have the rifle in my hand, I’ve yet to find myself in a situation where if I was struggling to get it out that I didn’t have something easily accessible to push it out. You can certainly remove material. Just take it slow and keep testing fit.
Check to see if bottom/back of upper takedown lug has clearance to fit into recess in lower.
I’ve found that occasionally that lug just needs back/lower edge lightly broken to allow upper to fit into lower more easily.
Check to see if bottom/back of upper takedown lug has clearance to fit into recess in lower.
I’ve found that occasionally that lug just needs back/lower edge lightly broken to allow upper to fit into lower more easily.
Ding, ding, ding... winner!
Thanks for the suggestions. I will see if I can clearance it a bit. BTW, when I say the pin is hard to take out, I mean I have to use a punch and hammer to break it free. It's not coming out any other way. You guys have given me some ideas to try. Thank you
I've had this upper for over a decade. It's been on multiple different brands of lower receivers. 3 different Spikes lowers, a BAD (forged) lower and a few other brands I am probably forgetting. Issue is the rear takedown pin on all lowers is extremely tight. On some it required a punch to get it out it was so tight. I should also mention that this has been with any takedown pin as well. I have used BAD, Lantac, KAK, YHM and a few generic milspec sets as well. If this was just an issue with one particular combination of parts I would lean towards it being a case of tolerance stacking. But I have not found a combination of parts where it doesn't do this. I have stopped using it and set it aside on my bench but am wondering what, if anything, I can do to correct this or trouble shoot it further. A shame to waste it. So open to any other trouble shooting ideas.
I have multiple receivers which are that way. It is what it is, tolerance stacking just pops up as an issue at times.
So I spent some time screwing around with it tonight. Took an assortment of takedown pins and checked fitment in both the rear lug and the receiver separately. All fit both with no issues. So it's not hole dimmensions.
Next I married the upper with a lower and checked dimensions. Right side holes mated up fine albeit a little tight. Left side not so much. So I used a pick to see if I could feel the misalignment. The hole in the lug is riding high on the left side causing a ridge where the pin contacts the upper inside edge of the receiver hole. The lug isn't interfering as the upper and lower are mated up tight with no daylight between the contact edges.
I repeated this on a few different lowers with the same results. My conclusion is it's either tolerance stacking or the pin hole in the lug wasn't drilled square with the lug. It's functional. My experiment is done. Thanks for the input and ideas everyone.
So I spent some time screwing around with it tonight. Took an assortment of takedown pins and checked fitment in both the rear lug and the receiver separately. All fit both with no issues. So it's not hole dimmensions.
Next I married the upper with a lower and checked dimensions. Right side holes mated up fine albeit a little tight. Left side not so much. So I used a pick to see if I could feel the misalignment. The hole in the lug is riding high on the left side causing a ridge where the pin contacts the upper inside edge of the receiver hole. The lug isn't interfering as the upper and lower are mated up tight with no daylight between the contact edges.
I repeated this on a few different lowers with the same results. My conclusion is it's either tolerance stacking or the pin hole in the lug wasn't drilled square with the lug. It's functional. My experiment is done. Thanks for the input and ideas everyone.
If it's a quality thing, get ahold of Vltor's CS. I found them to be excellent.
If it's a quality thing, get ahold of Vltor's CS. I found them to be excellent.
I can't say that is the case. In fact I'd say that is the least likely cause by a mile. Either way it works fine and I'm ok with it.
Sorry if that last post sounded abrupt. Just want to make sure no one thinks I am calling the QC of VLTOR into question and not contacting them to "make it right." It's not a "fatal flaw" regardless of the cause. I will keep using it and be happy with it. I posted this thread more out of curiosity than anything else and to understand how to trouble shoot this issue if it happens again on another upper to lower marriage.
I have an upper with a pivot pin hole that is too tight for pins that measure 0.248, but takes 0.246. This is the pins alone, uninstalled. What is the specified size and tolerance for the pivot pin hole?
I have an upper with a pivot pin hole that is too tight for pins that measure 0.248, but takes 0.246. This is the pins alone, uninstalled. What is the specified size and tolerance for the pivot pin hole?
The print I saw shows the pivot and takedown pin holes dimension as .251 +/- .001
ETA: http://www.biggerhammer.net/ar15/cad/ar15_receiver.pdf
Interesting drawing, but that's the lower. I suppose the upper could be tighter?
Interesting drawing, but that's the lower. I suppose the upper could be tighter?
Same source (had to dig a bit) has both the front and rear takedown pins at a diameter of 0.248 and
The upper receiver holes can be anywhere from 0.250 to 0.316 depending on which lug and which variation of upper and year of manufacture. It took me a few passes of this material to get a handle on it and Im still not sure I am up to speed
http://www.biggerhammer.net/ar15/uppers/
Where is that? This image from that site shows 0.246 for Colt small-pin.
http://www.biggerhammer.net/ar15/uppers/aruppercomparison.jpg
Where is that? This image from that site shows 0.246 for Colt small-pin.
http://www.biggerhammer.net/ar15/uppers/aruppercomparison.jpg
Scroll down further. So my post was sort of wrong but definitely incomplete. The rear lug pin hole is standard at 0.250 (across all receivers) but the front pin hole is either 0.246 (small hole Colt) or 0.316 (large hole Colt) or 0.315 (large hole Armalite) I don't see a front lug spec for an Armalite small hole so am assuming it doesn't exist?
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