I received my Colt M4 upper yesterday and put it on my Sporter Match HBAR lower.  How do I tighten up minor slop between the upper and the lower?

Thanks in Advance

I'd use an AccuWedge.

[img]http://www.cheaperthandirt.com/ctd_images/product_images/1221/ARR-005.jpg[/img]

Ya can get one from plenty of places like [url]www.cheaperthandirt.com[/url]

Mike

Mike--
I always wondered how those things fit. Could you tell me where it goes.  Thanks!

I have an accuwedge in my Colt.  It works great, tightened up the little bit of slop.  There wasn't much but with the A.W. there is absolutely none.  It won't do anything for accuracy but I think the rifle just feels better without any movement between the upper and lower.  Just my $.02

here is what i did to eliminate slop in my AR.

i bought some aluminum stick welding electrodes, and practiced plug welding 1/4 inch holes in some aluminum flat bar of the same thickness as the wall of my lower.

after i got it down good, i removed the finsh from my lower with a dremel tool, just about 1/8 inch around the take down pin hole, also use a piece of 1/2 inch carbon steel square stock to support the inside of the weld puddle, on the inside of the lower, this also does away with any post weld cleanup on the inside of the lower because the weld will be flat and flush, after you remove the square stock.

after you weld it up then just center punch the center of the take down pin hole and drill it out 3/16 inch and then tap for 1/4 20tpi.
this will give you supperior tightness, to any other method.

just go and get some 1/4 20 stainless steel bolts cut them to length, and install.

it work so well on my rear hole i went ahead and did the front also, and this did improve accuracy, but it takes a lot of work.

just be sure that your lower is made of stick weldable aluminum, 6061 t6 is what mine is made of, but the 70 series aluminum must be tig welded, and if you got a steel or stainless steel lower you can weld it also without, hurting your lower.

if you try and weld the 70 series aluminum with SMAW it will cause underbead cracking, not a good thing for a firearm or any other weld.

Sorry for the delay, the accuwedge slides into very rear of lower just in front buffer tube retaining pin and underneath the takedown pin like so:

[img]http://www.fulton-armory.com/accuwedge.jpg[/img]

Here's a link to info: [url]http://www.fulton-armory.com/AccuWedge.html[/url]

Mike

I use the acuwedge too, but I have found I get better results with a home made one. I used ureathane belting, about 3/8 round and cut with a razor. I left it a little long and just kept trimming the bottom until I could close and lock the upper.
One thing to watch out for; because of the increased pressure to compress the wedge, I found I was putting my weight on the upper to get the takedown pin to go in. I didn't realize it at the time, but I was pushing on the rear sight. Being a 1/4 moa sight with a glued on thread, I actually pushed the sight down in the sleve, greatly changing the zeros! This was the night before a leg match! When I discovered the problem with the sight the next morning, I went to my back-up rifle (that's what it's for) and got the third leg...(BSEG)
Regards, Ray

Thanks for all the info.  I plan on getting a AW but I figured that while I was at it I'd just replace the pins too, any thoughts?

Also, has anyone tried those expandable tensioning pins?

Or you can go the poor man's route and place a rubber band between the upper and lower receivers just behind the front take down pin. Close it up and you're ready to rock.