I have an OSI Jig and made 2 receivers with good results, but drill bits shouldn't go anywhere near it.  Anyone know who makes the jig Tannery Shop markets?  I like the idea of replacable bushings and might buy one, or something similar.  

You know that OSI will rebuild yours cheap if you need?  Also, there are some jigs for sale on ebay by a couple of newcommers if you are interested.  dwj

[email protected] for osi questions.

I've seen some interesting jigs on eBay, but nothing that looks durable beyond one use.  I've seen a really nice aluminum one by a fellow from here (disremember his handle) who originally sold them as setup blocks.  Now he's added locator holes, but again durability is an issue, and it's a bit pricey for what essentially is a single use jig.  My major complaint with the OSI jig is the extensive hand file work needed in the mag well to fit the jig.  Even the EDM cut magwells on the forged receivers won't fit the OSI jig without work, although all USGI mags I've tried drop free.  This isn't really OSI's problem,. it's the lack of consistancy in the 80% cast receivers from Tannery for which OSI's jig was made for.  I have a mini mill and when I get a 3 axis digital readout, a jig won't be neccessary.  I think I just talked myself into going ahead with the DRO for the mini mill $$$ ;^)

[url=ar15.com/forums/topic.html?b=3&f=4&t=148435]BIY lower build sites[/url]

I bought some of the very first Tannery Castings and they fit quite nicely on the OSI jig. I ran the bits right into the jig - lubing the jig and being very careful not to hit the sides - to the point that the paint is still 360 degrees around the holes.

Bummer to hear that they're not so anymore.

The couple of Tannery castings I'm working on required extensive filing in the mag well, and not just to get Orlite mags to drop free...  

The casting pourosity is terrible, too.  I hope the parking will make it less noticable.

Those cast receivers dont take the anodizing coloration well. usually they need to be coated with something else after they have been completed.

I've had the same problem with the Tannery castings.  My first one was an early edition, and it fit the OSI jig with some filing and was actually fun to work on.  I've put 400 rds through it, and I have observed some receiver stretch.  I've twice had to refit it to the upper. It ran great without any trouble, but was always a B*tch to reassemble after a trip to the range. This leads me to believe that some stretch has occured after each session.  I have not taken any measurements, but I've since retired it for safety concerns.  It will work if the SHTF though, and I'm happy that I even got it to work, having made it with a Sears drill press, and alot of careful hand filing.  My second Tannery lower was a recent editon, and I found it required MUCH more work than the first.  The mag well required significantly more work, as well as the top plane.  The trigger group area was not correct dimension and required some tedious hand filing and dremel work.  Late into production, I found the rear of the receiver where the buffer tube goes had a distinct cant manufactured into it, resulting in the buffer tube hole being significantly off center and not leaving much meat on the right edge looking at it from the rear.  It runs fine so far, and I've got 100 rds through it to date. I'm taking measurements this time to documant any receiver stretch.  Unfortunatly I bought 12 Tannery cast receivers when they ran a special on them before William shipped out.  Right now they will sit on the shelf until I can rule out the possibility of my making an error in construction.  I have picked up some of the forged 80% receivers, and although they cost 50% more than a factory 100% receiver, I'm looking forward to trying my new mini mill on them.  The forged receivers look great and look very solid compared to the cast receivers.

I recomend against using a jig.

Either make yourself a template for the fire control and takedown holes, or use transfer punches and a factory lower.

Save your money for ammo.

I would like to see documentation on the lowers expansion. I'm very interested in your methods.

The lower receiver doesn't take any of the stress of firing the weapon - look at it - the bolt and bolt carrier glide into the receiver extension against the buffer and it's spring. It's a beautiful engineering solution.

Heck, we're shooting .50 BMG rounds with +13,000 foot pounds of energy though the little things [:)] - the "stress" is around the large and thick 1 3/8" ring that the receiver extension threads into - but as the upper presses against that same area they ought to recoil as one - there is no movement there.

The compression would take place between the upper's aft end and the shoulder stock - but the force is equal to the recoil felt by the shoulder - not much - a few pounds at best. Newton's laws of motion are just that - not suggestions or theories.

The fire control holes are very critical just +/- a thousandth here or there and you've got a $100 aluminum paper weight. I'm not a machinist and centering the pins in two dimensions is very difficult. I'm two for two using the jig and a drill press. Popping the detents, barrel extension, and pistol grip holes are easy enough with measurement - I would just land the safety, trigger, and disconnect holes with the jigs - or at worse another factory lower as a guide.

PS: I got more ammo than the 3ID [:D]

My theory is the buffer portion at the rear of the receiver which does take some stress is stretching the back end of the receiver some.  I'm sure it's minuscule, but after two 200 rd sessions, the upper and lower would not pin together.  I had to drive out the rear pin to get it apart for cleaning, and I figured it was just my tight hand file tolerances ;^) The rear take down pin just wouldn't line up.  A little work with a file on the rear curve of the receiver, and everything lined up again.  Receiver stretch is all I can come up with.  Any suggestions to a cause for this problem?  Who the heck knows for sure if the one I have is T6 or not anyway. May well be a bad one, plain and simple.  As I recall it was one of Wlliam's "grade 2" receivers, and a very early one at that. But this problem has happened twice with the same receiver after two rather short range sessions.

If you have access to a mini-mill then you shoudl try a 0% forging. The forging itself is much stronger and the forging will take the dye during anodizing. Much cheaper too at ~$22 a piece. Just a lot more work, but that is the fun part anyway right???