View Full Version : What is the difference in durability of Gas Blocks made from different materials?
PA PATRIOT
11-17-13, 17:00
I'm in need of a new .625" Gas Block for a new pencil barrel build and have noticed that there is a wide range of materials used to manufacture same. I have seen 6061, 7075 aluminum, High Grade Steel and Stainless Steel versions and had to wonder if construction material is a real concern for durability other then just the weight issue for use in a gas block.
I'll make it easy. Get a BCM one and you're finished. They are made to very exacting tolerances and fit most all properly machined barrels very well.
I'm in need of a new .625" Gas Block for a new pencil barrel build and have noticed that there is a wide range of materials used to manufacture same. I have seen 6061, 7075 aluminum, High Grade Steel and Stainless Steel versions and had to wonder if construction material is a real concern for durability other then just the weight issue for use in a gas block.
Suwannee Tim
11-17-13, 21:11
I would get a steel gas block because it has the same coefficient of thermal expansion as the steel barrel.
I would get a steel gas block because it has the same coefficient of thermal expansion as the steel barrel.
Interesting, never thought about it that way.
K.L. Davis
11-17-13, 22:05
Any serious gas block is not made from aluminum... the thermal expansion rate, risk of corrosion "under" the block and vulnerability of gas cutting pretty much rule it out for a service weapon.
Chome Moly steels (4XXX) are a good choice and there is no reason to not go with this material.
My personal preference is 17-4PH - it is a very good, precipitation hardened stainless material; its thermal characteristics are great, resistance to gas erosion... and it doesn't get all wonky out-of-round during machining (less fall-out).
What is probably more important than what steel (again, no aluminum) is used, is the machining and manufacturing - the main bore should be +0.0005 -0.0000 and finished with a honing, reaming, burnishing or boring process that leaves a good finish. If the main bore is bored so fast it looks "threaded" or overall looks like it was cleaned up with a chainsaw file, pass on it.
The hole for the gas tube also should be 0.180 +0.0005 - if the gas tube fits sloppy, wiggles around... pass.
The hole for the gas tube roll pin is often off center or crooked... this all too often makes the difference between *simply* driving the pin in... and whacking the shit out it, flaring out the end and slipping with the punch and gouging the shit out of the gas block.
There are a lot of good GBs on the market, go with a good name, expect to pay for quality and enjoy having to install it once and never worry about it again.
The new Geissele one went on great. I got the non-nitrided version. When you drill the pin for it (it comes with a rolled spring that acts as a pin), the hole provided is slightly undersized for the recommended 3/16" bit. So it creates a very clean barrel channel during the process, and leaves just enough margin for error that even if you didn't line things up perfectly you're still not egging a hole that was already drilled full size.
21490
The Geissele SGB is easily the nicest GB I've owned to date.
http://i888.photobucket.com/albums/ac81/trident1982/DSC09516_zpsf7a1a868.jpg (http://s888.photobucket.com/user/trident1982/media/DSC09516_zpsf7a1a868.jpg.html)
The Geissele Super Gas Block (SGB) is precision investment cast from 17-4 precipitation hardening stainless steel, which combines superior corrosion resistance with high strength.
The new Geissele one went on great. I got the non-nitrided version. When you drill the pin for it (it comes with a rolled spring that acts as a pin), the hole provided is slightly undersized for the recommended 3/16" bit. So it creates a very clean barrel channel during the process, and leaves just enough margin for error that even if you didn't line things up perfectly you're still not egging a hole that was already drilled full size.
Did you use a drill press and clamp it for drilling? Just curious if this is a free hand operation or if you need something a little more involved.
Did you use a drill press and clamp it for drilling? Just curious if this is a free hand operation or if you need something a little more involved.
I did use a drill press for mine. However, the design of the block would likely allow for a person with a steady hand to use a hand drill. The undersize pin hole gets reamed a little as the drill passes through, so as long as your at least clamp the barrel in a vise and keep a steady hand you'd probably be fine hand drilling.
PA PATRIOT
11-18-13, 16:29
Anyone know exactly what metal the USGI A2 FSA is made from?
Excellent advice here
Any serious gas block is not made from aluminum... the thermal expansion rate, risk of corrosion "under" the block and vulnerability of gas cutting pretty much rule it out for a service weapon.
Chome Moly steels (4XXX) are a good choice and there is no reason to not go with this material.
My personal preference is 17-4PH - it is a very good, precipitation hardened stainless material; its thermal characteristics are great, resistance to gas erosion... and it doesn't get all wonky out-of-round during machining (less fall-out).
What is probably more important than what steel (again, no aluminum) is used, is the machining and manufacturing - the main bore should be +0.0005 -0.0000 and finished with a honing, reaming, burnishing or boring process that leaves a good finish. If the main bore is bored so fast it looks "threaded" or overall looks like it was cleaned up with a chainsaw file, pass on it.
The hole for the gas tube also should be 0.180 +0.0005 - if the gas tube fits sloppy, wiggles around... pass.
The hole for the gas tube roll pin is often off center or crooked... this all too often makes the difference between *simply* driving the pin in... and whacking the shit out it, flaring out the end and slipping with the punch and gouging the shit out of the gas block.
There are a lot of good GBs on the market, go with a good name, expect to pay for quality and enjoy having to install it once and never worry about it again.
The Geissele SGB is easily the nicest GB I've owned to date.
The Geissele Super Gas Block (SGB) is precision investment cast from 17-4 precipitation hardening stainless steel, which combines superior corrosion resistance with high strength.
Do you mind expanding on what sets it apart from a BCM or Vltor gas block and makes it better? Aren't cast things typically not as strong, or accurate? is it machined inside to size, or is it just straight casting?
Do you mind expanding on what sets it apart from a BCM or Vltor gas block and makes it better? Aren't cast things typically not as strong, or accurate? is it machined inside to size, or is it just straight casting?
I think that the KAC gas blocks are also cast. The bore would be drilled and then finished smooth and to spec.
I like the Centurion gas block for it's extremely small size. Not sure what it's made of however.
Centurion's is steel. Not sure what 4XXX though.
TMS951: I dont know the intricacies behind it but investment casting is not your typical steel casting.
surfish95747
11-19-13, 02:08
I like my $24 Yankee Hill Machine gas block. It is made out of steel. Although I only have a few rounds through my newly built rifle, it hasn't been a problem and I haven't read one bad comment about their gas blocks. Just throwing that out there. Plus it fit nicely on my Daniel Defense 14.5" middy underneath my URX III. So I'm happy.
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