Tap drill size for 5x8/24?

[soofley]

so i just found this out: Rainier Arms Ultramatch barrel + BABC = bad combination

RA just informed me that BABC was underthreaded, making tight and even impossible to install the BABC. Sadly they are still waiting for the tool to arrive.

Would a tap and die set work to loosen up the thread on my BABC? i don't know what size tap drill to use for 5/8x24. I cant find 5/8x24 on the drill bit size  :o

please help me not turn this $220 metal into a paperweight

[fr3db3ar]

Different options here.

http://www.silencertalk.com/silencer-forum/viewtopic.php?f=10&t=24326

A little bit of a math lesson as well.

[Jgun]

You would use a 5/8"-24 tap for a 5/8"-24 tread. You may just be experiencing a situation where either the external thread of the barrel is oversize or the internal thread of the brake is undersize. Your outside dia on the barrel where the thread is, should be just under .625". You have the choice of running a tap into the brake to chase the internal thread, or using a die on the barrel thread. I doubt that your brake ID or barrel OD will be off, more likely one of the threads is just tight. If you have another brake/flash hider, try it on the barrel to see if it goes. I don't know what thread Rainier uses for their .308 barrels, but 5/8"-24 is most common. The last BABC I installed was 5/8"-24. I don't think they offer it with any other.

[Dusty44]

Before something inadvisable is done to the expensive metal,  maybe pick up a nut and bolt from a hardware store threaded for 5/8"x24;  try these to see how that thread fits.  Then try chasing the threads on the nut and bolt as may seem desirable and use what you learn to chase or re-work the high-dollar metal?

Worst case,  don't forget there is a system to redo the threads with a stainless steel heli-coil.  My memory says not cheap,  but a kit can be purchased to cut the metal and install a coil that will be a new thread and will sustain pressure and last essentially forever.  In the years I repaired industrial machinery I think I did it once and saw it done perhaps one or two other times.  It does a great job when all else has failed.  Don't have a link:  my parts all came from the supply room.  Heli-coil is a standard industrial repair item,  however.  And,  I probably did not spell it correctly.

[hobbesgunner]

If your just chasing the threads you shouldn't need a drill....you won't find a nut and bolt to check it against at hardware store...it's a UN extra fine thread....for what it's worth to you..the minor diameter should be. 5800-.5900 for a class 2B thread...5800-.5869 class 3B..(tighter thread)...37/64 drill is. 5781,..14.75 mm drill is. 5807.........that's for your internal thread......if you mic the barrel thread it should be between .6178 and. 6250 for major diameter (The outside diameter of thread )....there's a handful of things that can be wrong with precision threads.....sometimes its something simple like hole not drilled big enough or OD too big.......good luck

[Dusty44]

Thanks for the definitive technicals, hobbesgunner.  My thought was to use something cheap and expendable before risking the high-dollar hardware. 

Heli-coil may not be,  is probably not,  available for the precision threads.

[Jgun]

You may be overthinking this a little. If you check the ID of the BABC and the OD of the barrel thread and they are within tolerance, You probably have a tight thread on the comp or barrel.  Without getting into checking the comp with a thread gauge or the barrel with pins, your best bet is to try a comp you know to be good on the barrel. If you PM me an address, I can send one for you to try on your barrel. If you're not feeling comfortable about doing this yourself, maybe you can take the barrel and comp to a local machine shop (that you trust), They should be able to run a tap or die on/in to the offending part for you, for less than what you'd pay to buy the tap or die yourself.

[hobbesgunner]

Midway has a tap for under $19.....didn't say in what manner comp wouldn't go on...wont start on ...goes on few threads then binds...goes most way then stops....that would be telltale of problem.....I'd get a tap. Chase the threads in the comp and go from there...Check for burrs on barrel threads. Especially the lead thread..it's thin and can get rolled over...you can use small preferably fine file to take out the first 1/4 to 1/2 of the first thread..then wire brush it...may just be barrel is at max material condition and comp is at min material condition ...both are good threads but close to interference fit

[98Z5V]

Chase the threads in the comp and go from there...

This is probably the offender in the mate-up.  Barrel threads are pretty much standard, at this point.

[soofley]

I just sent it back to BCE because shipping fee's hella cheaper than buying the tap, and faster turn around time too. thanks again helpful people. Knowledge about this kinds of thing's always good to have!