Has anyone drilled out 5.56 A2 flash hider to accommodate 9mm?  Threads are a match on an old one I have laying around, and I need one for my PCC.  I figure I’ll probably use a 7/16 drill bit.  Any tips?  Or, should I just go be poor somewhere else?

Are you going to drill it by hand, on a drill press, or in a lathe? I would be worried about it being off centered/crooked if drilled by hand. Also a 3/8" bit would be big enough since it is .375" and 9mm bullets are .355" - .356".

If it was me, I would just buy the correct size flash hider and be done.

I bet it will work with out drilling it.  I fired a 9mm pistol with a A2 style 556 flash-hider and it worked fine, well it didn't damage my pistol at least.

You can get a 9mm A2 style birdcage for $10 or so from several vendors...

This. I would run some drill bits through its bore, first. ID might be large enough, already.

Most likely drill press, as I'm also concerned about it being off center.
Thx

Just look out for copper jacket shrapnel. Shot a friends 9mm AR with 5.56 flash hider. Report seemed strange but it worked. Figured it out later. No injuries or damage, just dumb and dangerous.

Birdcage had copper jackets stuck in it.

Good idea, about checking the bore first with drill bits.  I'm not going to shoot without checking it first.


Both are 1/2 x 28.  Most of the cheaper ones I've found are 1/2 x 36.  I'm always learning new ways to skin that cat.  Work smarter not harder.

For just a flash hider as long as you can keep it fairly centered you should be good to go.  A step drill bit may help with accomplishing that with a drill press.  The smaller steps acting as a centering pilot in the existing bore.

The more oversized the hole the less any off centerness should effect accuracy.  So if after your first try it mics out a little off center opening up a little more might save you.

Actual muzzle breaks that aren't just simple flash hiders require greater precision.  I recently bored out one of this big chevron clam-shell tanker muzzle breaks for a 243-Win build.  They come in 223 and 30 caliber.  I didn't want to just use the 30-cal since the oversize bore reduces efficiency.  So I bored out a 223 to the slightly 243 caliber size.

I was initially going to use a beat up old manual lathe with a four jaw chuck but I got frustrated trying to shim the darn thing just right to be perfectly lined up and straight in the chuck.

So I made a self piloting pull through reamer and did it that way.  Basically took a length of rod stock of good hardenable steel in the soft and turned it down to the appropriate final desired diameter.  Then I left only about an inch at that diameter and turned the rest of the length to the current diameter of the hole with a good sharp square edge at the transition.  The smaller diameter to be the pilot and the larger diameter part to be the cutter.

Then used my shaper table with a jug to cut four straight flutes in the cutter portion at 90-degree rotations.

Then I hardened that steel up and after hardening hand sharpened the four little cutting flutes, keeping it all nice and even.  Lubbed up that pilot diameter with some grease and slipped it in one end of the muzzle breaks bore.  Chucked a hand held cordless drill on low gear onto the end of that pilot part on the other end of the brake.

Got er spinny nice and steady slow just pulling back only on the drill and kept squirted some cutting oil on the cutting tail and pulled her through cutting nice and steady.

When you pull a larger diameter cutter through a bore hole where the undersize pull/power shaft to drive the cutter is a tight slip fit in the existing bore hole it cuts a whole lot straighter and centered up rather then trying to push the larger cutter through the bore.

Pulling vs. Pushing, it makes a huge difference, even if both are piloted.



I don't think you will have to go to that extreme for a simple A2 flash hider.  But if you want too.  If you can figure out a way to setup a pull through cut where the pulling/turning shaft is the pilot for the cutter that really works well.

Piloting even when pushing still helps though.  You might try chucking up a drill bit in your drill press and geter spinning and carefully grind the first half inch of the drill bit down to a pilot size in the existing bore.  That ain't easy to do nice and even using improvised setup but I have done it in the past before I had access to a lathe.  You have to then also know how to re-sharpen at the transition edge that will be the new cutting edge.  That's hard to do by hand on the helical flutes of a drill bit, but it can be done.

As I said step drill bit may be your best bet with the smaller steps beliw acting as a pilot in the existing hole.

And of course, drilling unpiloted.  People will debate whether drilling multiple times with drill bits that are just a tiny bit larger each time or making one good drill that is carefully centered - which one in the end comes out centered the best.

For me doing the multiple drills using just the next larger bit size over and over and working up for unpiloted push drilling usually turns out better for me.

YMMV - just the babbling of someone who has tried all different improvised ways of making small holes larger and maintaining center and have yet to find the way that is both the easiest and quickest with the least work and also the most accurate to stay centered.

$9 plus whatever shipping

https://www.midwayusa.com/product/1021153344?pid=514736

Had a friend ream one out using a lathe,.....would be cheaper to buy one

Thx.