I am taking a 14.5" pinned barrel CLGS with standard hand guards out of a A4 receiver and putting it into a monolithic upper. The gas block has to be spaced about .032 forward of the step so that the gas key doesn't hit the gas tube. The old setup has a hand guard cap that will need to be dealt with. Should I cut it off (don't think it will go over the flash hider) or grind it down to stay on as a spacer for the new gas block (two piece yhm)? If I cut it off should I install some type of spacer to replace it or just install the gas block with the proper gap?
Are gas tubes available that account for this?
Thanks.

I'm not sure what you mean by this. Some gas blocks need a .025" gap so that the gas port is aligned. The gas tube could protrude an 1/8" further into the upper and still function.

If your gas block is relying on the spacer to not slide backward, it isn't a very sturdy installation. However, having it on there for installation wouldn't be a bad idea. You could also put it something in between the shoulder and gas block temporarily while you install it.

This isn't the thread I read about it originally but it touches on the issue. Dano's post.http://www.ar15.com/forums/t_3_66/714517_Gas-tube-movement.html&page=1&anc=7466619#i7466619

Basically the gas block journal is cut to allow for a spacer like a hand guard cap and putting the gas block all the way back without it can cause the gas tube to go too far into the gas key. This was a problem other people were having and the dimensions and a spacer were part of the discussion but I don't remember the exact thread.

I have to do something with the existing hand guard cap since it is there already and I'm not going to have a gunsmith remove the pinned flash hider to get it out of the way. I'm sure the new gas block would be secure, but other people were talking about using a space or something like a snap ring that is the proper thickness. I'm wondering if there is a preferred way to deal with this. If the 1/8 inch tolerance you say is there then it may be a non issue and I can just cut the cap off. I havent received all the parts yet to check. I was concerned having read about this issue others ran into.

The only time I use a spacer is when installing a virgin A2 front sight block and drilling the sight and barrel for tapered pinning.  Once aligned and drilled I slip the FSB off, slide on the front cap, reinstall the sight, and pin it.

In all other situations where the front cap is not needed, as with a low profile gas block and free float rail, I just push the block to the shoulder.  Most blocks have a large enough gas port that it does not matter and, as stated above, the gas key has plenty of room for the gas tube to extend back the extra .032".

That would make things simple then. Thanks.

I'm assuming it currently has std F marked sight on it?  If so I would likely remove the taper pins and slide it forward and cut off the hand guard cap, then I would cut the sight post off and the offending pieces underneath and use it as my gas block after I touched up my cutting/filing marks.  While it may not be Hollywood pretty, it provides for one of the best gas blocks on the market and it's already fitted to your barrel.

It does matter. Not having the gas port aligned correctly with the hole in the gas tube reduces energy into the system. This is the root of numerous malfunction/short stroking issues with home builds.

This. I concur with just cutting down your FSB into a low profile gas block instead of replacing it with a two-piece unit.

The current gas block is a clamp on 2 piece YHM flip up. No taper pins. At the time I bought it I was thinking I might need an adjustable gas block and it would mean cutting it off to get it out of the way. I would probably have to cut a pinned block off anyway just to get the mega installation wrench past the gas block area. The barrel is a Sabre CMV chrome lined in 6.5 Grendel. The upper is a Mega carbine length quad rail. This is a one-off build that puts two niche parts together in what should be the best way to get the most out of them. I would like to get this one right.


Then I will probably put the fluted 18" Sabre Grendel barrel in the Sabre receiver

To clarify, the flip up yhm is coming off, the planned replacement is a yhm 2 piece plain gas block. The optics won't be qd mounted so buis flip ups would be useless on this one unless angled anyway.