Building out Your TAC-9 Receiver
The Tennessee Arms Company, LLC TAC-9 receiver is the lightest weight, most versatile 9mm receiver on the market. This blog entry is intended to avoid some of the pitfalls of building and fitting our receiver to your upper. Most parts will be assembled just like a standard AR build. The differences are below.
*The 9mm AR receiver, unlike the AR15 style, does not have any mil-spec standards for dimension or tolerance. Also the Glock magazine compatible style we market has additional requirements to ensure fit and function.
Our 9mm is designed to be tight. We did this because of the vast range of upper receivers on the market and the world of tolerance differences between them. We think that having a tight receiver is much better than one with lots of play between the upper and the lower. The space between the two front lugs (Pivot Pin) is .495" or a few thousands of an inch smaller than the .5" tolerance called for in the mil-spec dimensions. Most receiver will be a tight fit at first but will eventually mold itself to the exact shape of the upper within a small amount of use. Some receivers may fit exactly right; some may be a bit loose. If you find your upper receiver is exceptionally tight, you can slightly shape the inner walls of the lugs to an exact fit using an Emory board or some sandpaper. Remember you are only removing a few thousandth of an inch, don't go overboard, or you will have a wiggly upper. (FigB)
The top of the receiver just below where your charging handle usually sits or just along the curve toward the Takedown Pin are areas you may find a bit of tightness. Depending on the brand upper you use, some very light sanding maybe necessary to have an excellent fit. (FigC)
The ejector is the metallic hooked extension that sits just behind the magazine on the TAC-9. ( FigD) This part is designed to push the spent shell casing off the bolt face. As our receiver is designed for use with the Glock style magazine ( instead of Colt SMG), the ejector sits a little higher. Ensure your Bolt is cut for the higher Glock cut. The way you can tell is by flipping your bolt over and on the bottom front side you should see two grooves. The groove that the ejector would sit inside should be noticeably higher than the other side in a Glock cut 9mm bolt.
Depending on your upper you may need to alter the shape of the ejector some. For example, the Palmetto State Armory complete upper ( great upper by the way) needs about a hundredth of an inch sanded off the top of our ejector to make everything work correctly. This isn't a defect. It's just accounting for the normal variations in designs between manufacturers when there are no standards to follow. We recommend Sons of Liberty Gunworks, JSE Surplus, Guntec, CMMG, and Palmetto State Armory(with the alteration) uppers for use in our lowers.
* If you feel any tightness or grinding when charging the weapon or you see any wear mark in the groove of the bolt that the ejector sits in then take a little of the top tip of the ejector with some sandpaper or a file. You arent going to hurt anything. We do not recommend a grinder. We are talking a hundredth of an inch or so... not very much is ever needed
The Buffer and Buffer Spring
Many build kits offer a 5 ounce buffer for the 9mm. This simply wont work unless the spring is upgraded. This is true for any 9mm lower build not just on our receiver. The top of the bolt will end up slamming into the back of the receiver causing over-travel and possible malfunctions. This is very similar to the common problem of over-gassing in the Ar-15. We recommend at least a 7 ounce buffer. If you are going suppressed, you WILL need heavier. The 9mm is a blow-back cycle of operations, which is why the bolt is counter weighted and the buffer/spring combo is so much heavier.
I have no idea why companies are sending out 5 ounce buffers for 9mm builds. Every kit I see has over travel issues using one.
Picture of the result of Bolt over travel..
The Buffer Tube
I designed this receiver as a pistol receiver so any carbine buffer tube or pistol tube should work. We recommend using buffer tubes with the buffer retaining ears at the bottom because it just seems to go together easier in the end. We do not recommend the rifle A1 style stock. We have found the SB Tactical tubes are a bit short,also.
Lower Parts Kits
Any quality lower parts kit will work fine though drop in triggers may require some hand fitting. The magazine release will come preinstalled and includes the ambi-mag release.