I have an older KAC sr-15 m4 upper with the a2 style front sight post gas block. I wanted to replace it with a low profile gas block, so I ordered a troy and a pri ( for 2 builds I have going on ).  Both of the new low profile gas blocks will not fit on the m4 barrel without some good force. So I took the fsb that was pinned on the knights barrel and slid it on some extra barrels I have and it goes on and has a bit of back and forth play.

I grabbed the caliper but the battery is dead ( get a new 1 tomorrow). The gas bocks I bought are .750, did KAC purposely make their barrel diameter a little bigger than the .750?   I have had tight fitting gas blocks that go on by twisting back and forth, but will need to be hammered on pretty good to go on ( which I don't want to do to ruin anything)....  

I sent KAC an email, waiting to hear back.

thanks
steve

You want the gas block to be a good snug fit for a better gas seal.   Cool the barrel and heat up the gas block and it should go right on.

I'd consider maybe getting a couple dust-off cans and turning them upside down and chilling the barrel with them, then see if the
block goes on a little more easily.  It should.

I'd reject a gas block that has any play in it when it's placed in position on the barrel.  That's just TOO loose.

Snug is the minimum.

Why are you doing this to a KAC upper?  Please sell the upper/rifle and buy another PSA upper.

Go waste someone else's time

The older (before the Mod 2 gas system) guns that utilized LPGBs had them pressed on.  

My guess is they used a slightly larger diameter on the barrel’s gas block seat to facilitate that process and kept that consistent with all their barrels, even if they didn’t use a press on GB.

Sorry we couldn't work out a deal.  All on my end,  this guy is a great EE seller.

IIRC from my questioning of his upper in the EE, I believe he is doing this because the original FSB was cut down by a previous owner.

GL w/ your issue op

I have a knights URX II 10 3/4" rail I am installing, so I need to switch it over to a low profile gas block.  Knights must do their sizing different, If you drag your thumbnail up barrel, you can feel a lip about 1 1/2"-2" before where the gas block would sit. Its definitely a hair over the .750 diameter. and the a2 post gas block that came from factory goes right on ( both made to be oversized I guess).

I took 1 of the low profile block I have and slid it on till it got very tight, took a piece of delrin I have for a nice punch and can hit the gas block to go on perfect as well as being lined up perfect. but it takes a few pretty good whacks with a hammer on the plastic punch. I just was wondering if this is normal for the older knights barrels, or who knows.....

Will it cause any issues with the low profile gas block being so snug and needing to be hammered in place?  gas holes lined up perfect as I can feel air through the gas tube if I plug 1 side of the barrel. I will pick up a battery first thing in the morning so I can mic it up and see the actual size differences. I can always go back to the a2 post if needed.

You could consider chopping the already "hacked up" A2 fsb down to fit as a low profile gas block.  May take a little more time, but if you liked pinned gas blocks I have read of people doing this.

Btw that upper with the new rail combo shpuld look great.

No, the gas block being tight isn’t going to hurt anything.

thank you.....


**** just got back with and was able to mic it......

-- Knights barrel is .750  where the gas block should be
-- my noveske spr stainless 18" barrel is right at .746

-- knights a2 sight is .750
-- troy low profile gas block is .743
--pri gas block is .745
--dpms gas block ( .950 version ) is .945

I guess just knights is dead on, and all the gas blocks are a hair under......

Thanks guys,
I appreciate it...

Steve