Tech ?, What's the difference between .750 gas seat and .625

[SR-71 BLACKBIRD]

I have my lower built and deciding on an upper. I've narrowed it down to two.

Spike's Tactical 16" Lightweight LE Upper (5.56) and Spike's Tactical 16" M4 LE Upper (5.56)

On paper they seem nearly identical except for the light weight barrel profile and the difference between the .750 and .625 diameter gas seat.

My question is, what is the difference between a .750 and .625 gas seat?

http://www.spikestactical.com/new/z/spikes-tactical-16-lightweight-le-upper-556-p-467.html

http://www.spikestactical.com/new/z/spikes-tactical-16-m4-le-upper-556-p-384.html

Thanks in advance for any advice/help,

Gino

[Barbarossa]

About an 1/8" of an inch.

Here:

Barrel weight is controlled by barrel length and barrel profile. Lightweight typically means the barrel is .625" diameter. Gov't profile typically means heavier (.750" gas seat) and about .730" from the gas block seat to the muzzle and .625-.650" under the handguards. Then there's the mid-weight (currently the craze). And then HBAR, HBARs (heavy barrels) are thicker under the handguards than the gas seat (.750" gas seat).

[Bhobbs]

I have my lower built and deciding on an upper. I've narrowed it down to two.

Spike's Tactical 16" Lightweight LE Upper (5.56) and Spike's Tactical 16" M4 LE Upper (5.56)

On paper they seem nearly identical except for the light weight barrel profile and the difference between the .750 and .625 diameter gas seat.

My question is, what is the difference between a .750 and .625 gas seat?

http://www.spikestactical.com/new/z/spikes-tactical-16-lightweight-le-upper-556-p-467.html

http://www.spikestactical.com/new/z/spikes-tactical-16-m4-le-upper-556-p-384.html

Thanks in advance for any advice/help,

Gino

I believe it is the diameter of the barrel under the gas block.

[dieselpower]

It will determine what after market part can fit around the barrel. Its the size or diameter of the barrel under the gas block. So if you are buying another gas block you need to know that dimension in order to buy the right one.

[cmace22]

Ones for a .750 dia barrel at the gas block and ones for a .625 dia barrel at the gas block.

[SR-71 BLACKBIRD]

Light weight barrel

I see. Diameter of the barrel. That makes sense. Does anyone have any experience with the lighter .625 barrel?