I have been reading some mixed sentiments on this subject.  Is it really unsafe to mount a gas block with set screws as opposed to pins?

I ordered the YHM-9381A gas block from YHM (I liked the simplicity).  Can I expect it to move even if I machine flats onto the barrel and use Loctite?

Thanks

If you machine flats into the barrel then you should be fine.  It is when the has block is being used on an unmodified barrel that they will move.

Thanks, I will machine flats on the barrel for sure.

Actually, that leads me to another question... Should I machine an area that is already within the existing grooves (where the pins were) or should I try to machine an untouched area?  I've never done this before, so I'm not exactly sure how they will line up.  Also, how deep do the flats have to be?  I don't want to drill so deep that I compromise the integrity of the barrel.

Last question - In case I decide that this project is not for me ( hat
Thanks again!

Anybody?

The gas block must match up to the gas port that is drilled in the barrel so where you mill the flats is dictacted by the location of hte set screws in the gas block.

Quoted: does anyone make an aftermarket block that is already drilled for pins?

Can't be done.  There is no standard for the location of the pins so there is no way to pre-drill them.  That's part of why most gas blocks use set screws.  The other is that they are being used on a match barrel and drilling the holes for taper pins and pounding the pins in can reduce the accuracy of the barrel.  Not by much but if everything else is top quality then it might make a difference.

Also note that there is a diffrence between a block that uses set screws and a block that clamps on with screws.  

some info here: www.gswagner.com/arsight/arsightmods2.html

What about lining up the gas port with the block, tightening the set screws, then removing the block and dimpling the set screw marks on the barrel with the tip of an appropriate size drill bit? I think that, along with loctite might just take care of that problem. My buddy had a gas block slippage problem over the weekend with an M4 we built last week. I'm gonna give it a try, and will post results.

You don't really need to machine flats on the barrel to keep the block in place, but you need to re-torque the screws about 20 times before you finally set them for good.  This will get the screws to dig into the barrel deep enough that they won't move.  

Putting dimples in the barrel with a drill can also cause you some trouble.  If the dimples are not drilled exactly in alignment with the set screws, then as you tighten the screws down, the gas block will "walk" to the center of the dimple.  If you are not dead on, then your block is not going to be lined up with the gas port.

Also, always check the gas port alignment before you ever torque the screws down for the first time.   The port in the block is drilled through the same hole as the rear set screw.  So just install the block, remove the rear screw, spin it upside down, and look through the set screw hole to see if it lines up with the hole in the barrel.  Not all gas blocks have the hole drilled the same distance from the rear edge of the block.

Use Purple low strength locktite on any screws 10-32 or smaller.  If you use Blue locktite, about 50% of the time, you will not be able to remove a 10-32 screw without putting heat to it.  DO NOT put the locktite in the screw hole and then install the screws or it will force the locktite down between the barrel and the block and you will never get it off without putting  a lot of heat to it.  Put the locktight on the set screws first, then install them in the block.

Trust me on this one guys.  I have already made every mistake outlined above......I didn't read this shit in a text book.....I screwed stuff up.

Tony Rumore

Quoted: What about lining up the gas port with the block, tightening the set screws, then removing the block and dimpling the set screw marks on the barrel with the tip of an appropriate size drill bit? I think that, along with loctite might just take care of that problem. My buddy had a gas block slippage problem over the weekend with an M4 we built last week. I'm gonna give it a try, and will post results.

This is what I've done in the past, but like Tony says, you've got to be very precise about where you put the dimples.

One other problem I've seen is that some gas blocks come with very short set screws.  The shorter the set screw the less surface area of threads that are holding it in place.  If your gas block comes with short little set screws then take a trip to a hardward store and get some that are longer.

Thanks for the input. I'll keep in touch!



"Eagles may soar, but a weasel never got sucked into a jet engine." hippie.gif

tag for reference

By the same token, are the PRI flip up front sights really not that stable, either? Their primary design uses a clamp with screws for tightening.

Quoted: By the same token, are the PRI flip up front sights really not that stable, either? Their primary design uses a clamp with screws for tightening.

Just IMO, but what the PRI has that some other clamp on sights have is nearly 100% clamping surface area.  Now some wheanie math geek is going to argue this, but let them.  I'd bet that clamp on PRIs can and have moved when used in extreme environments.

I believe there was some real world thinking in the initial design when the tall FSB was initially installed with hard to remove taper pins.

The AMU DMR uses a standard FSB, drilled and tapped for setscrews that are secured in place with Loctite.  I'd trust a sight base installed in this manner "with my life".  Be honest here, anything else, other than taper pin installation, is suspect to movement.

As with many things firearm related, there's a reason some things are easy and a reason others are hard.  I think that applies in this situation.

As always, YMMV.

Quoted: Quoted: Just IMO, but what the PRI has that some other clamp on sights have is nearly 100% clamping surface area.  Now some wheanie math geek is going to argue this, but let them.  I'd bet that clamp on PRIs can and have moved when used in extreme environments.

I have seen a real OPS collar move under heat and high rates of fire.  The suppressor was not installed right then obviously.