.300 BLK
Seekins SS 10.5" barrel with .750" block seat (pistol length gas system)
BCM KMR 10" rail

Set screw? Clamp on? Adjustable?

Barrel is NOT drilled for gas block pins

Also, on a non-pinned gas block, how does one properly align the block?

I used a SLR Sentry clamp on adjustable...

That what I had read, but that block's specs say 1.40" height. KMR states 1.30" inside diameter...

Is the KMR taller than wide? Ie: is the 1.30" spec for the KMR at its narrowest point?

I have mine under a SLR Solo Lite rail which is 1.3" ID and have plenty of clearance...

The 1.3" ID is the tubular part of the handguard.  The top piece that the gas tube sits inside adds a good bit.

SLR .75" set screw version works perfect with plenty of room in there. Here is mine with a 11.5" 300 blk barrel. If you put a 10.5" barrel your muzzle break will be partially inside the rail.

http://i81.photobucket.com/albums/j203/anibal999r/lw-5.jpg

The rear screw hole is concentric with the gas port in the gas block.  So knowing that, you can rotate the gas block upside down on the barrel, then visually center the barrel gas port in the rear screw hole of the gas block.  This will tell you how far the gas block must be set back, if any, from the step on the barrel (because some are made to accomodate the thickness a standard hanguard cap and some are not).  It will also tell you if the gas port in the barrel is top dead center, because if not, then the gas block will appear slightly crooked when sighting down the top or bottom of the receiver when the barrel is inserted.   If it is slightly crooked, remember how crooked it was and repeat that same crookedness when you rotate the gas block around right side up for the install.  

If you don't have calibrated eyeballs, you can use little bubble levels and a sandbag style shooting rest to assist you in getting things lined up.  Or use little pencil marks or tape when you find the center as described above.

JAston, Scarr and VBC, thanks!

Looks like I'll be going with the clamper SLR Sentry 7.  I don't own a suppressor, but figure that if I ever do and want to shoot subs, an adjustable block is the way to go.

Thanks for the advice!

Personally i went with the "old reliable" YHM set screw .750 lo profile gas block for $22 or whatever it costs. I have several and never have any issues; it fits the kmr fine.

More info on that rail and what all you did to it, more pics if you got em. Very interested. How much does it weigh now?

The rail's stock weight was 6.3 oz after I machined it it was 5.7 oz. I didn't do it too much for the weight, I just wanted a slimmer profile.

http://www.ar15.com/forums/t_3_124/643624_2A_Armament_BALIOS_lite__Billet_7075___6_5oz_lower_receiver_.html&page=15

I'm running the YHM clamp gas block on mine and it fits fine, I little tight in there but works great

wareagle:  I used a clamp on Vltor GB under my SLR Solo HG, which is similar in size to your BCM KMR.  It was a very tight fit, I had to grind off some metal to make it fit without touching the inside of the handguard.  I suggest you stick to the set screw type and avoid any interference.  Getting it aligned on the gas port with just your eyeballs and some pencil marks is not particularly difficult. good luck - CW