I want to upgrade my ar with the bcm kmr hand guard. my upper bcm 16" mid length has the standard A2 front sight post which i want to do away with. I was going to get a low profile gas block but i was thinking to just cut off the site post and keep the lower portion of it to be used as the gas block what do you think of that idea. 

I want to upgrade my ar with the bcm kmr hand guard. my upper bcm 16" mid length has the standard A2 front sight post which i want to do away with. I was going to get a low profile gas block but i was thinking to just cut off the site post and keep the lower portion of it to be used as the gas block what do you think of that idea. 

 

I've done that before.  Works fine, if you have a bench grinder you can even get the gas block really smooth and hit it with some paint.  Looks like a factory finish.

A Dremel tool works great to chop the gas block. I've done 4 that way. One with an angle grinder and three with the Dremel. The standard A-frame gas block that has been properly pinned to the barrel is the strongest gas block out there - IMO.

 

One thing to keep in mind - The BCM KMR uses a proprietary barrel nut, so you are going to have to remove the standard one that's on there. To do that, you are going to need to remove the muzzle device (possibly damaging or destroying it in the process, requiring replacement) and pull the gas block.

 

I have found that it is easier to pick a tube that uses the standard barrel nut, I personally like the Troy Ind. tubes (I think Rainer, Samson, MI, and Centurion use a standard barrel nut as well). That way all you have to do is shave the gas block, cut off the delta ring, and slide the new tube over everything without having to torque a new barrel nut, re-pin the gas block, and permanently attach a new muzzle device.

Here is what a started with:

 

Here's the cut down block:

 

Close up:

 

After cutting, everything got some Cold Blue and then hit with some High-Temp BBQ spray paint.

 

Here's what I ended up with:

 

All together, not including paint drying time, it took about 1.5 hours.

A Dremel tool works great to chop the gas block. I've done 4 that way. One with an angle grinder and three with the Dremel. The standard A-frame gas block that has been properly pinned to the barrel is the strongest gas block out there - IMO.

 

One thing to keep in mind - The BCM KMR uses a proprietary barrel nut, so you are going to have to remove the standard one that's on there. To do that, you are going to need to remove the muzzle device (possibly damaging or destroying it in the process, requiring replacement) and pull the gas block.

 

I have found that it is easier to pick a tube that uses the standard barrel nut, I personally like the Troy Ind. tubes (I think Rainer, Samson, MI, and Centurion use a standard barrel nut as well). That way all you have to do is shave the gas block, cut off the delta ring, and slide the new tube over everything without having to torque a new barrel nut, re-pin the gas block, and permanently attach a new muzzle device.

problem is i have an expensive battle comp pinned def dont want to destroy it once i shave down the front sight there still wont be room for the barrel nut to slide off?

The barrel nut should slide over the muzzle device, but the gas block won't.

 

Another option is to get a 2 piece clamp on gas block and chop the old gas block off altogether. They aren't as reliable as a chopped FSB, but they will work and you don't have to remove the muzzle device. Just make sure you line up the hole in the block with the hole in the barrel.

 

Personally, I would choose a different tube that uses the standard barrel nut, and shave the block to fit so you don't have to do anything with the barrel nut.

All of this trouble just because of a little pin or weld we have to abide by on the end of the barrel... 

 

I was dealing with the same situation a few months back, but ended up sourcing a used DD omega 9 rail (FF) just to keep it simple.  Looks aren't so pretty, but functionally the setup is very solid.

 

A vendor such as Tier 1 could probably get that KMR rail installed for you for a nominal fee as well if it's what you want and save the headache.  For a shop with all the tools, I can't imagine this process to cost more than around 150 (?) for 30-45min of work?  Remove pin/muzzle device, remove FSB & cut down to a gas block, re-install everything with the new rail and re-pin/weld muzzle device.  But then, in the end that $180 KMR rail will run a total cost closer to $400 or maybe more if you have to buy a new muzzle device.

Thanks guys for better or worse I have my heart set on the kmr I think I'll just sell my upper and buy a new complete upper with the kmr hopefully I want take to much of a hit

Check out arfcom's EE (equipment exchange). Theres usually a good amount of complete bcm uppers for sale both new and used. That site has been my go-to for quality used parts and ive had great luck with pricing.

Just a PSA, that KMR rail has a damn small inside diameter. You really need to use a low pro GB with it.

True dat.

 

Also, do some research and compare Keymod v. MLOK. Be an informed consumer