6mm arc - what a frustrating weekend

AR15, AK47, FAL, Bolt, Hangun, etc... If I find we need it I will expand this forum.

Moderator: MudBug

6mm arc - what a frustrating weekend

Postby plant_one » Mon Nov 01, 2021 4:16 pm

tl:dr - i'm never buying another Ballastic Advantage barrel again.

--------

as paul harvey would say... and now the rest of the story...


so i finally got my hands on some 6mm arc ammo ( still cant find brass...) a few weeks back. been swamped with work (good thing) and finally got around to building the upper i bought a BA barrel for ~10 months ago.

what a hot mess this turned out to be in my adventures of ar gun-plumbering!

my donor upper - BCA 6.5 Grendel g1 sidecharger - two of the handguard screws are WAY over torqued in and/or must have a gallon of red loctite on them. the other 4 came out with some convincing... but not these two... nope.

couldnt break them loose by hand, tried my fat wrench at 60 in/lb and nothing but a click. threw a little heat on them. nothing.

broke the tip of my t25 off in one of them with my baby bosch ps42 impactor, and managed to strip a torque's screw head on the other with a brand new tip! 900 in/lb impact wouldnt break them loose!

so i grab another upper (18" 223 wylde g2 side charge) decide i'll cobble that together with the bolt from the Grendel upper - damn crush washer wont come off the barrel. wont slide over the threads, wont thread off over the threads. Just sits there in spins in the thread relief laughing at me. I'm guessing some ham-hand ovaled it torqueing the A2 birdcage on there somehow... :roll:

so on to upper #3 (i'm determined to get this thing assembled now, damnit!) - annnnnd success - this one actually disassembles properly.

i now have a upper, bcg, barrel nut, handguard to work with. sweet!

Image

play a little pin the gas tube into the gas block.

shim the barrel nut to get it to index correctly for perfect handguard alignment.

gas block lines up nice and clean.

clean the threads of packing oil to rockset the muzzle device on and... wait... what tha?.... there's no thread relief at the shoulder and the threads stop about a crush washers width from said shoulder. wtf? like you cant make this sh!t up.

Image



so i cant use my QD mount, and i cant use my direct thread mount either. thinking to myself "this has got to be a just before lunch friday barrel"

call BA this morning, get thru to the tech dept, explain whats going on...

nope. the barrel is full in spec. exactly how they designed it. i am the first person apparently thats EVER had this problem before with one of their barrels. the QD and direct thread suppressor mounts they've tested all work just fine. sorry we cant help you. thank you for calling have a great day.

i'm paraphrasing... but that was the gist of the conversation. dude was super polite. and about as useful as screen door on a submarine.


i own threaded barrels from a half dozen manufacturers, and have had several threaded by smiths. ive *NEVER* seen a barrel cut like this. i mean.. maybe a half turn thread worth left back there before the shoulder... but never anything like this.

they all either have a thread relief cut in before the shoulder or just threads all the way back.

0.096" gap - full thread diameter. just a RCH shy of 1/8".
Image

heck even BCA takes the extra 14 seconds of machine time to cut the thread relief in there.



so my barrel is heading off to the smith to get a proper relief cut added to it. thank god ADCO does that for only $30... but sheesh!

i highly doubt i'll have it back in time for being able to hunt this upper this season.
User avatar
plant_one
 
Posts: 1109
Joined: Sat Mar 19, 2016 8:58 pm
Location: Oakland County, MI

Re: 6mm arc - what a frustrating weekend

Postby Texas Sheepdawg » Mon Nov 01, 2021 4:28 pm

OUCH…
-Texas Sheepdawg

http://youtube.com/c/TexasSheepdawg21
NRA Life Member
User avatar
Texas Sheepdawg
 
Posts: 4731
Joined: Fri Nov 05, 2010 10:55 am
Location: North Texas

Re: 6mm arc - what a frustrating weekend

Postby Al in Mi » Wed Nov 03, 2021 4:02 am

Undercutting those threads is a simple thing to do when threading that muzzle, and I don't know why the brake or flash hider makers don't counterbore their threads to alleviate that headache when it comes up.
User avatar
Al in Mi
 
Posts: 1982
Joined: Sat Jun 20, 2009 8:24 am

Re: 6mm arc - what a frustrating weekend

Postby plant_one » Wed Nov 03, 2021 12:52 pm

Al in Mi wrote:Undercutting those threads is a simple thing to do when threading that muzzle, and I don't know why the brake or flash hider makers don't counterbore their threads to alleviate that headache when it comes up.


right... i agree... muzzle device builders should not only counter bore their QD mounts, they should also thread relief/counterbore the bottom of the hole too. There's plenty of thread to hold with a small counterbore on either end of the hole being that a typical thread on a barrel is ~0.625" long.


i'm just facing a scenerio where both manufacturer's basically said "ahhh screw it, the other guy will adapt their stuff to it, we dont need to spend that extra $0.18"

instead of both spending the extra 30 seconds of machine time to make sure that no matter what another manufacturer did, their equipment would be compatible for the end user. :roll:



i might even just shim it for now - i have proper shim kits in my ar-builder box - so that i CAN hunt it this season, and worry about getting it "fixed" after deer season ends.
User avatar
plant_one
 
Posts: 1109
Joined: Sat Mar 19, 2016 8:58 pm
Location: Oakland County, MI

Re: 6mm arc - what a frustrating weekend

Postby AR Sarge » Wed Nov 17, 2021 1:10 am

Hi Plant,

Well, that sucks! Adco does kick butt work. Hopefully you can get it done in time for late season.

I’ve built two ARCs, an 18” Odin and a 12” Monster. The monster is out for some work (stripped out screws in my handguard) so no idea how well it can shoot, but the 18” Odin shoots abso-friggin’-lutely great. If I can get up north it’ll go along for late season.
AR Sarge
 
Posts: 29
Joined: Sun Nov 16, 2014 12:31 pm


Return to Firearms

Who is online

Users browsing this forum: No registered users and 14 guests