View Full Version : About to drill gas port on Galil barrel but...

April 08, 2002, 10:14
I have run into an issue. Specs call for a 1.8mm hole drilled at a 28 degree angle. The only bits I have (or can easily find) are 1/16 (1.59mm) and 5/64(1.98mm). A search for a 1.8 bit both locally, and on the internet has proven futile.

The port areas of the sizes (pie*r2):

1.59= 1.986 square mm (78% of spec)
1.8= 2.545 square mm (spec)
1.98= 3.079 square mm (121% of spec)

It appears that I will aslo be locating this hole around 7-9mm further back on the barrel than on factory guns. I have access to a true IMI manufactured ARM .223, so I will have to see exactly how far from normal it truely is...

Based on this, I'm leaning toward going with the 1/16th (1.59mm) bit and making the hole a little sloppy. The problem is, that whatever I go with, I have to stick with, as I'm going to have to solder the gas block to the barrel before firing. I sanded the diameter of the barrel down to fit the gas block, as I don't have access to a press. The only way I can remedy a low pressure situation, should one exist, is to get a very long drill bit to enlarge the port through the gas block.

Your opinions?

Or, with your help, I can locate a Cobalt 1.8mm bit over the internet....

April 08, 2002, 11:28
a #48 is .700
a #49 is .730
1.8 mm is .709.

Spend the $3 and get the correct drill bit. from MSC, J&L, etc. I also suggest that you zero the rifle on single shot before drilling the gas port - in case you end up needing to adjust the timing of the block.

Gas port location relative to the bloc varies on model. Hadars, ARs, and ARMs have all shown different locations. most frustrating.

April 08, 2002, 11:42
A #50 is .0700"

A #49 is .0730"

A 1.8mm is .0709"

Look in your yellow pages under "Machine Tools" or "Tools" and buy from them instead of the internet.
I find Machine Tool distributors are usually cheaper than the tool stores, but for what you are going to pay, just choose the closest to you. The bits should be .69 to $1. If you go to the tool stores, they will probably twice that.
For what you are doing, a regular drill bit will work, unless you want to pay the extra for Cobalt.
Just go slow and use plenty of oil. The trick to drilling is to find that sweet spot between going too slow & rubbing away the bit's cutting surface and pushing it too fast & risk breaking the bit.

Good luck!

April 08, 2002, 12:16
Awesome information, and excellent advice!

Looks like I'll be going for a #50, which translates to 1.78mm.

In mounting/headspacing the barrel, I don't think I got anywhere near to the whopping 300 ftlbs that is spec. I might have gotten to the 150-200 range. To be safe, I plan to silver solder the barrel in place to prevent any potential movement.