Tapered reamer design for AR gas block pins....

I have had an AR kit lying on the floor for several years. In looking for a part that was launched by a contrary main spring, I moved all that stuff out of the corner, decided now was the time, my hands are getting worse every week. Typing is problematic now......

Installation of the front site/gas block requires (????) tapered pins.....at least that is what they included in the kit. The gas block already has correct tapered holes.
Brownells offers a hand held tapered pin reamer for the job..... It is pointed, wouldnt that tend to make it drift away from the barrel, surface needing the cutting, distorting the holes already in the front site/gas block??

PJH

You can get pin reamers from most tooling vendors, and will work just fine in a mill.

While these are slightly used, I won an auction on ebay for this lot of pin reamers, cost me $19.16 + $6.45 shipping. Most all are hardly used.

I needed the small ones to fix a South Bend bed turret.



I would just go search around ebay and see what is there. Wait, that's what I *did*...

Yes, it'll be really difficult to get a good ream - those tools are made for holes, not half (or closer to 1/3rd, IIRC) holes. I'd recommend making a steel jig block to fit to your barrel. Drill and ream in place so the reamer sees the same load around its full circumference.

GsT

Helical reamers are better for power reaming. but straight fluke reamers are better for hand reaming. You should own both and multiple of the most commonly used sizes. They are not expensive. Always drill and ream mating parts together, never separately.

I have used the Brownells tapered pin reamer before and it works well but I have only used it with sight towers/gas blocks that were undrilled. Getting the hole drilled in the barrel and having it line up with both sides of the tapered hole in the sight tower/gas block will be a challenge. Reaming it without making the tapered holes in the sight tower/gas block egg shaped or worse yet, breaking the reamer will also be a challenge as you have already considered. You also have to be sure your sight tower/gas block is properly aligned with the gas hole in the barrel and that your sight is not canted. I think I had this same problem once and ended up tapping the the holes in the sight tower and then used set screws to lock it in place from either side. You can also tap holes into the bottom of it for set screws as many of the low profile gas blocks are held on that way.
In your case, I would just ditch the front sight tower and use a low profile gas block with a free float handguard and some kind of optical sight. Free floating the barrel will help with accuracy and an optical sight will help realize that.

Gents....thanx for the input........

Try this on.....looks, remember, "looks", like 25% of the hole dia. is barrel. How about a very slowly advanced end-mill from the small dia. side for the first pass.??? This should remove 75% plus of that 25% before coming in the larger side w/hand turned reamer??

"Secured from the bottom with set screws".....very good idea. Why didnt Colt use that instead??? I will go to that if I am not satisfied w/taper pins. As to the handguards, Donna likes the old Colt triangular configuration & I have that design wood stock/grip/forend for this one. We have 4, one with round handguards & 4 pos. stock, two w/triangular handguards, and one original Colt machine gun from prior to mil. acceptance, M-614.

My hands are beginning to give out, whatever gunsmithing I have left will have to be done pretty soon........

PJH