Loose fit between Upper and Lower reciever?

[raudi]

Anyone else have this problem? Mines seems to be a bit loose where it will wiggle a bit. Also if you look at the rifle from the side you can see a bit a daylight coming through the gaps. Shouldn't the fit be a bit tighter?

[IronEagle]

Mine is the same. Little bit of play between the upper and lower. I haven't had any problems with mine but I would like to know if this is how all xcr's are.

[Desert_StormTrooper]

I don't think it's uncommon.  When I open it up, it's a looser fit.  When closed, I also can see light through it.
I know I saw somewhere on here a simple fix to this.  Just have to dig through and find that post.

[beyond_visual_range]

 Yes, a little play is normal. Here is another thread on the subject.

http://xcrforum.com/index.php/topic,3379.msg50086.html#msg50086

Personally I used a little bit of Gorilla tape to tighten up the fit. But the play wont affect operation, It was just a small annoyance to me that I eliminated. Even with the play I still love the rifle. 

[DJ]

I found the play between the upper and lower of my XCR to be excessive for my comfort, but I have succeeded in completely eliminating it.

In my XCR the excess free play was largely rotational(about a lengthwise axis) and was traceable to excess clearance at the forward hinge between the upper and lower, i.e., the three holes there were all larger than the axle pin.  My XCR's hinge axle appeared to be an off-the-shelf clevis pin and the nominal industrial specification manufacturing tolerance range for such 1/4" clevises is about 0.243 to 0.246", wherein was mine.  The holes drilled in my upper and lower for that hinge were in the 0.250 to 0.251" range and thus there were several thousandths of an inch of excess radial clearance.  I measured my dimensions with a good micrometer to the ten-thousandth of an inch, but that level of precision, while reassuring, probably isn't required to fix the problem.

If you have a micrometer(everyone should!) to measure the existing clevis pin the problem is then how to measure the holes.  A decent hardware store selling clevises will likely also have in an adjacent small drawer having a 1/4" ground steel taper pins for sale($.50 or so) and then one just places the tapered pin in a hole, marks the point at which it stops and then measures the taper pin at the marked point with a micrometer.  That's how I found and then calculated the excessive radial clearance of several thousandths of an inch.

I sought a larger clevis and there were thousands about in town, but there weren't any larger than 0.246" nor any from typical online industrial suppliers.  So I looked around for a steel rod of the needed diameter(~0.2495" to 0.2500")). I found and then made one from the tail end of a close at hand six inch long 1/4" drill bit.  That closed the total radial clearance to about half a thousandth which solved the problem nicely.  Lubricated,, it hinges easily but has no discernible free play.

Out of curiosity, but only subsequently, did I find that some AR rifle parts suppliers had already addressed this problem(due to normal wear and tear) and that there exist screw tighten-able two-piece split clevis pins and other clever solutions to more easily take up such free play or excess clearance between the pin and hinge holes.  I've not had experience with any of them though.  Nor do I know if their lengths are correct for the XCR, but many are intended for 1/4" upper/lower AR hinge holes.  Better, they don't require the careful measurements.  Happily, I no longer have to contend with the problem, at least in the near term.

I will note that my random walk solution was tedious, took careful measurements, a Dremel with a cutoff wheel, several trips to a ACE hardware store, and some care in fitting, and, finally, good luck in the sacrificial drill bit find.
 

[MickeyC]

For me, I don't see the XCR as a precision weapon so it's not a big deal. Nice solution though.

[DJ]

Please don't let the small numbers, i.e. thousandths of an inch, mislead you.  The matter is not that of a precision rifle.  I have a Grip-pod vertical front grip attached to the underside rail of my XCR and a few thousandths of excess radial clearance is amplified by the length of that longish vfg to a very irritating angular rotation of several degrees, maybe a quarter inch or more at the base of the vfg-when the rifle was new. 

Maybe I exaggerate, I can no longer measure same.  Still I no longer have any such  annoyance and it did exhibit far too much play to be acceptable to most any other shooter I know.  Further, I am a committed believer in PM, i.e., preventative maintenance, and in this setting, excessive initial clearance will almost certainly grow worse with usage-because the clevis pin is hard steel and the upper and lower are both far softer aluminum.  Repeated friction and impact will and must, at some rate, further deform(i.e., enlarge) those holes in the aluminum and further degradation is the inevitable consequence.  Too, the vfg doesn't help matters.
YMMV.  
An added thought from another perspective:  My experience with my high performance auto engines that turn well beyond original specs as regards rpm, up to 8000, is that the typical total radial clearances on their rod(big end) and main bearings is nominally 0.002 inches (sometimes less) and are judged worn out at 0.0025, with pressurized lubrication of course.  So that 0.005 or 0.006 inches at the XCR's front hinge seems quite unnecessary(for hinge performance anyway) and that a final achievement of ~0.0005 inches is quite reasonable and close to the acceptable range for the thickness of an oil film.

[DJ]

Here is a link to one possible solution or at least an example of one approach to fixing a loose upper/lower due to free play at the front hinge/pivot.  The dimensions aren't given(presumably AR owners know these numbers) so an inquiry might be warranted for an XCR.  If you don't need one there's still a photo of the very clever gadget at the site, which took me a few moments to relocate. There also is a suggestion that accuracy may be involved.

http://www.jprifles.com/1.5.1.7_small_tp.php

 

[shortfal]

Same thing with my XCR. Made a .250 pin that took the slop out of the front.
Still needs the nub on the back of the spring guide made larger for a better fit in the hole in the lower rec.
Thinking I might turn it down and press a sleeve on it that's about .002 under the size of the rec. hole.
Yeah I know - but some things one does just because he can.
                                         Pete

[raudi]

Thanks for the replies. I'll try some of the suggestions.

[Dynamo55b]

 

[AR1516]

I posted about the fit a long while back when I got my XCR. I really like my rifle, but the gap does bother me. Even some of my low end AR's don't even come close to having such a large gap between the upper and lower. Since I'm not a machinist I guess I'll have to leave it as it is.

[bolster]

Please don't let the small numbers, i.e. thousandths of an inch, mislead you.  The matter is not that of a precision rifle.  I have a Grip-pod vertical front grip attached to the underside rail of my XCR and a few thousandths of excess radial clearance is amplified by the length of that longish vfg to a very irritating angular rotation of several degrees, maybe a quarter inch or more at the base of the vfg-when the rifle was new. 

Maybe I exaggerate, I can no longer measure same.  Still I no longer have any such  annoyance and it did exhibit far too much play to be acceptable to most any other shooter I know.  Further, I am a committed believer in PM, i.e., preventative maintenance, and in this setting, excessive initial clearance will almost certainly grow worse with usage-because the clevis pin is hard steel and the upper and lower are both far softer aluminum.  Repeated friction and impact will and must, at some rate, further deform(i.e., enlarge) those holes in the aluminum and further degradation is the inevitable consequence.  Too, the vfg doesn't help matters.
YMMV.  
An added thought from another perspective:  My experience with my high performance auto engines that turn well beyond original specs as regards rpm, up to 8000, is that the typical total radial clearances on their rod(big end) and main bearings is nominally 0.002 inches (sometimes less) and are judged worn out at 0.0025, with pressurized lubrication of course.  So that 0.005 or 0.006 inches at the XCR's front hinge seems quite unnecessary(for hinge performance anyway) and that a final achievement of ~0.0005 inches is quite reasonable and close to the acceptable range for the thickness of an oil film.

I don't see any problem in someone wanting to tighten up the fit. Thanks for posting what you found.  Both of my XCR's are what I consider good as far as fit goes, but I should take out my calibers and start measuring just for curiousity's sake.

[ougunnut]

I just got one.  Mine has to much play IMHO.

Other than that it is awesome.  If there was a larger pin I could just purchase and pop in I would be all over it.  It would fix the only flaw on my rifle.

[cyclesteel]

My gunsmith is making me one this week. I brought my XCR over yesterday and he measured the hole and pin and he made a test pin and it really tighten the gun up.  I think the whole thing is going to cost me $25-30

[MickeyC]

The front pin isn't really the isuse. The catch built into the rear of the recoil assembly simply has too much play in it.

For a battle rifle it's not too bad, but for a precision tool it sucks. Hopefully this is resolved on the XCR-M.

[WatchoutforStobor]

On mine, the front pin is definitely the issue. It fits tight in the lower but the hole in the upper is oversized. Sure it makes it easier to put the halves back together but it's not worth the slop that results.


 

[ougunnut]

On mine, the front pin is definitely the issue. It fits tight in the lower but the hole in the upper is oversized. Sure it makes it easier to put the halves back together but it's not worth the slop that results.


 

Mine is the same.  If the hole on the upper was a little smaller it would have a lot less play.  It's probably withing acceptable tolerances but it feels a little sloppy to me.

[cyclesteel]

The bigger pin tightened my XCR up. now a questions for the experts. Is having a bigger pivot pin ( I need a punch to remove my new one) going to cause more ware issues down the line like making the holes even bigger?

[Underground]

The bigger pin tightened my XCR up. now a questions for the experts. Is having a bigger pivot pin ( I need a punch to remove my new one) going to cause more ware issues down the line like making the holes even bigger?

I would think a looser fit would do that more than a tighter one.  Unless you're breaking it down and putting it back together 50 times a day for demos or something.

[WatchoutforStobor]

I think the tighter pin = less wear because there is less opportunity for recoil to mash loose parts back and forth.


 

[XCRmonger]

most of this can be chalked up to two words. Machining variances.

[ougunnut]

most of this can be chalked up to two words. Machining variances.

I don't disagree.  It does have a little more play than most ar15's I have handled though.  I like it alot that is just the one thing worth mentioning if reviewing the rifle IMHO for my particular rifle.  I don't regret my purchase.