Stugotz Wrote:So who is at fault? The gas block manufacturer for incorrectly drilling the port in the block, or the barrel manufactured for incorrectly drilling the gas port in the barrel 1mm further down the barrel (closer to the muzzle of the barrel?!?[ATTACH=CONFIG]18346[/ATTACH]
Stug,
Neither manufacturer is at fault - your barrel has been machined to accommodate the 0.025" handguard gap, but your gas port manufacturer assumes a more modern free-floating handguard will be used.
Nowadays, civilian AR15 shooters prefer the free floating design handguards so don't need the gap. Barrel manufacturers accommodate this by machining the port closer to the shoulder so you can push the block neatly up against it (your previous builds). However, the old clam-shell handguards need a credit card width gap (.025") to align holes with the barrel. It's an old trick to use a credit card to align the ports. With your barrel you can configure it for either clamshell or free-floating handguards.
While the gas port will be machined carefully, many gas block holes are more generous to accommodate a slight lack of alignment. Not all however, and 0.025" is a lot of misalignment.
I recommend measuring the gap between the edge of the block and the centre of its hole; then the barrel shoulder and the centre of the port. If they are the same you can push it up against the shoulder.