Partly out of curiosity and partly because I'm going to attempt to machine a gasblock.
I have a piece of 4140 HT steel I was planning on using but the barrel is 4150.  Could this cause some kind of thermal expansion differential and cause gas leaks?  I could just as easily make it from 4150, but I would like to make it from what ever a mil-spec front sight base it made of because I know it works.

Thanks

I don't know.

whatever it is made of it is hard as hell. i tired to knock one down with a hack saw to save a few bucks and ended up using a grinder.
 gas blocks come in every manner of high end overbuilt nonsense and cheap ass alloy junk and, if gas blocks leak its typicaly because of block or barrel or both being out of tolerance just enough. don't think i have ever heard of one expanding but i guess it could happen.

Quoted: Quoted: ..don't think i have ever heard of one expanding but i guess it could happen. Dig up Zak Smith's old post on some of the major 3-gun matches he attended.  It was a serious problem with high-round-count stages IIRC.

no kidding.. learn somthing new everyday.  

thats was a good read. looks like that guy has alot of fun.
i guess when you shoot that fast the heat really plays hell with stuff.  i only get the taxpayers weapons that hot, never my own...well hardly ever.

Quoted: Partly out of curiosity and partly because I'm going to attempt to machine a gasblock. I have a piece of 4140 HT steel I was planning on using but the barrel is 4150.  Could this cause some kind of thermal expansion differential and cause gas leaks?  I could just as easily make it from 4150, but I would like to make it from what ever a mil-spec front sight base it made of because I know it works. Thanks

The thermal expansion coefficients of different steel grades are practically the same. You will not have problems with 4140 gas block on a 4150 barrel.

Aluminiums are a different story. Aluminium expands more than steel so the gas block will tend to loosen up when the barrel gets hot. The connection will naturally tighten again when the barrel cools down, so it's not easy to spot. However, if the gas block is held in place with just a set screw, you might eventually end up with problems. Taper pins are much less likely to come loose.

Personally I would not make a gas block out of aluminium.