front guard mount moving on new AR

[rady8um]

I got into cleaning the M&P 15 tonight, after popping its cherry yesterday, and I notice that the retainer that holds the front of the handguard moves up and down about 3/16 of an inch. This translates into an obvious up and down motion of the entire handguard. Clearly this is not normal. I will be reviewing the pdf file that was recommended for maintanence and repair, but it is about 250 pages long.
In the mean time, what would be involved with getting into and removing the gas block and checking out why this mount is moving?

[Kaos]

should be a couple pins to remove the gas block/sight tower. You'll have to remove the gas tube too methinks.

Lycan will probably drop by to confirm

[arrrrgh15]

I had this happen on a bushmaster upper once. I shipped it back and they gave me a new upper.

When they attach the site base to the barrel they drill holes through the site base and barrel and pin it in place. It seems that they didn't snug the site base against the handguard retainer before they drilled and pinned it.

I believe the alignment of those drill holes, which are not the same from one rifle to the next, forever dictates the location and alignment of the site base. Maybe it would be possible to remove it, shim it, and reattach. Or swap out the site base for something different that clamps on and doesn't need to rely on the same drill holes. But that's a lot of work for something that should have been right in the first place.

[reels18]

I got into cleaning the M&P 15 tonight, after popping its cherry yesterday, and I notice that the retainer that holds the front of the handguard moves up and down about 3/16 of an inch. This translates into an obvious up and down motion of the entire handguard. Clearly this is not normal. I will be reviewing the pdf file that was recommended for maintanence and repair, but it is about 250 pages long.
In the mean time, what would be involved with getting into and removing the gas block and checking out why this mount is moving?

I think your best bet would be to contact S&W about your problem and let them fix it. Any unauthorized repair on the upper may come back to haunt you.

It is an inconvenience, but you paid good money for the rifle, why settle for a home remedy?

[SteveWag]

The front sight is held one of three ways; two tapered pins, four set screws or glue. If the front sight (or gas block) is removed the gas tube comes with it. In any event, trying to clamp the front hand guard retainer between the barrel shoulder and the sight will not remove the movement. The retainer needs to be replaced with one having a smaller hole. This kind of slop (not just the hand guard) is why I don't recommend S&W, R.R. or DPMS have been more consistent as to quality control.

Steve Wagner

[JayBell]

question here is:

is the GAS BLOCK moving, or is the metal HANDGUARD CAP moving?

if its the handguard cap, its possible the cap was made wrong, it should not move hardly at all...a tiny bit yes, but not much. The cap is held in between the gas block and the milled shoulder of the barrel, and kept in alignment by the gas tube. Thee should be the tiniest buit of play, but the cap should not allow the handguards to move UP and downto any great degree.

Have it replaced or repaired by the MFG if it is..

if its the gas block (I doubt it), send the rifle back now for replacement, thats BAD.

as a note, gas blocks are NEVER held on with just glue, theres not a glue available that will stand up to the temps that the AR barrel will produce around the gas block (700-900 deg F).

Loctite, or a fixative is often used to make sure the gasblock is held in place during the taper pin drillin/install process, but never glue by itself.

[Xringshooter]

Give Smith &Wesson a call and explain what you told us. They will take it from there. Their customer service is very good nowadays. Let them fix the problem.

[rady8um]

Thanks everyone, it is in fact the front retainer that is moving. The hole that the gas tube runs through is oval shaped, I assumed it was to allow for variances in the tube position during assembly. I guess if the hole was smaller, I would have never noticed the movement.
I'll be giving S&W a call on Tuesday, to se what they want to do about it.

[SteveWag]

Bushmaster manufactured CMP match rifles have the front sight/gas block held on with an adhesive ("glue"). I have rebarreled many of these, removing the sight with a heat gun. As these rifles have had 5,000+ rounds through each, many having been used in the "rattle battle" at Camp Perry, with no apparent sight movement, I would say that the "glue" works well. If I reuse the sight, I drill and tap for four set-screws, and mill four flats on the replacement barrel.

Steve