06-19-2009, 12:14 AM
Join Date: Mar 2008
Location: Contra Costa County
We will now drill for the Following (in the order stated).. Barrel retaining pin (1), RSB retaining pin (1),
GB retaining pins (2) and FS retaining pins (2).
Here are some measurements for the M70AB2.
Barrel Pin (1) - Pin Diameter is 7mm/0.2755"
RSB Pin (1) - Pin Diameter is 4mm/0.1575"
GasBlock Pin (2) - Pin Diameter is 2.5mm/0.0985"
FSB Pin (2) - Pin Diameter is 2.5mm/0.0985"
I highly recommend measuring your drills. Just because it says it is 5MM, does not mean it is.
Drilling takes skill - Know your cutting angle, speed and feed rate. These perimeters (will change) depend upon the work material, while using the same drill bit. Check out mmsonline.com/article.aspx?id=14722
i.e. While drilling the barrel retaining hole (7mm), my drill speed was 650 RPM and feed rate was .0015"-.003" per second (roughly as I am doing this on a drill press by hand) with a point angle of 140 degrees..
Here we start on the barrel retaining pin. Some measurements for your pleasure.
Scribe a line 5.5MM from the top of the receiver and about the center of the trunion tab. Drilling at this point at 7MM will give you a clearance of about 3mm+ at your chamber bore.
We don't want our drill hole to be uneven as it will lead to potential issues apart from aesthetics.
I position the drill off the drill point so i can eye-ball it. I adjust the barrel so the drill is equidistant from my designated reference points. Once this is done I am certain barrel retaining hole will be all square and not canted. On a lathe it would have not been an issue.
Use cutting oil liberally. I give a squirt every 15-20 seconds. After you are through drilling, use a reamer if you have one.
Measure 20 times, drill once!
Last edited by fredieusa; 07-08-2009 at 12:06 AM..