Drill bits for enlarging a gas port.

[LorinB]

I am going to enlarge the .076 gas port in my Shilen stainless barrel to .096.  Would it be advisable to use inexpensive Harbor Freight numbered drill bits or would more expensive high speed steel bits or even a carbide bit be safer in regard to leaving a burr on the riffling or breaking in the hole?  Also, I had the idea of driving a lead slug into the barrel so that it obturates in the lands and grooves to serve as a backer to advoid making a bur on the riffling when the bit penetrates the bore.  Then I would blow all of the shavings out through the gas port with compressed air before driving the slug out the muzzel so no steel shavings would be drug along the riffling.  Is this a good or bad idea?  Has anyone ever made a burr or taken any measure to avoid making one?

Thanks!

Lorin

[Matt.Cross]

On 2/1/2023 at 6:28 PM, LorinB said:

I am going to enlarge the .076 gas port in my Shilen stainless barrel to .096.  Would it be advisable to use inexpensive Harbor Freight numbered drill bits or would more expensive high speed steel bits or even a carbide bit be safer in regard to leaving a burr on the riffling or breaking in the hole?  Also, I had the idea of driving a lead slug into the barrel so that it obturates in the lands and grooves to serve as a backer to advoid making a bur on the riffling when the bit penetrates the bore.  Then I would blow all of the shavings out through the gas port with compressed air before driving the slug out the muzzel so no steel shavings would be drug along the riffling.  Is this a good or bad idea?  Has anyone ever made a burr or taken any measure to avoid making one?

Thanks!

Lorin

As it will likely be done in either a drill press or by hand with a drill, I don't recommend a carbide bit, standard high speed steel bits will work just fine. Don't get them from Harbor Freight though, you don't want to try to remove pieces of drill bit from your barrel. Buy a single numbered standard HSS bit from your local hardware, use a suitable cutting oil and a hand drill and go slow, letting the bit do the work. Midrange on the RPMs, nothing crazy, mild pressure for the drill. It will follow the existing hole and the burr in the bore will disappear with the next shot that goes downrange. Easy peasy.

[98Z5V]

Ace Hardware carries the Irwin numbered bits.  Ironically, all the professional extraction sets on workshopt tool trucks (not including Snap-On, they're unique, and way more $$$)...   Most of those tool truck guys that hit shops have extractor sets that are pretty sweet.  Matco, Cornwell, MAC Tools, etc.  All those sets are made by Irwin, for them, and private labeled.  Oooohh, insider info - very true.  Off the truck, whatever truck that's not Snap-On, lifetime guarantee.  I break something, hand it to the tool truck guy, he gets me another for free-fiddy-free, next week when he's here again. 

Those are all Irwin extractors , left hand bits, specialty extractors, etc - all made by Irwin then private-labeled for whatwver tool-company truck that hits your shop.

Long story longer - you can trust the Irwin numbered bits that you can find in any Ace Hardware, in the blue and yellow packaging. 

[MikedaddyH]

Lowe's also has those high speed drill bits.

[LorinB]

Thank you all for the info.  Now there us a proper size gas port.