Check out this nastiness on a barrel someone sent in to get KGd. The threads are 18 thousandths undersized, 9 thousandths off center, and not an “edge” on a single one. The picture isn’t blurry; those are the “threads”! Surprisingly, it’s good enough to hold a flash hider in place.




If attaching a standard flash hider to your rifle, most any thread that will hold the flash hider in place “good enough”. If you are attaching a suppressor to your muzzle, the threads should be as close to perfect as possible, and perfectly concentric to the bore.

There is a lot of hype about POI shift, and too much regarding the shift is being credited to(or blamed on) the suppressor attached to the barrel. Production barrels are made to “spec” within allowed “tolerances”, and for standard applications that is just fine.

Is the hole in the middle of the tube – as in the bore through the barrel? Most often, the answer is NO. Standard barrels are off center an average of 3 thousandths, to 7thousandths on the extreme average end. With a suppressor attached, the POI shift will be significant with the bore off center only 4 thousandths. With a tightly mounted suppressor, on a barrel with a perfectly concentric bore, the bullet passes though the middle of the suppressor with the gasses distributed evenly around the projectile - that is how you get a minimal POI shift.

If someone wanted to demo 2 cans for POI shift, they should be sure to use good barrels. If brand “A” has .5 shift, but they are demoing brand “G” mounted to a barrel that is 6 thousandths off center – guess which have a significant POI shift – no matter what brand is attached to it?

The mount holding the suppressor is very important. If, when attached the suppressor has any play/wiggle, you will see more shift – even with a concentric barrel. If the suppressor droops down any when mounted, try to hold it up with sandbags or something. Take a shot with the suppressor supported and you will have a different POI. This applies the same to pistol suppressors. Some thread on only to be held square by the shoulder of the barrel(hopefully square), others thread on perfectly and are held steady by only the threads. AAC and SWR do the best job of threading their (pistol suppressor)pistons properly. I have seen some threads cut that work with one brand, but another wont fit at all – when claiming to be the same thread pitch.

The rifle mount itself should also be perfectly concentric to both the bore and the suppressor. So far, the only system I’ve seen that takes the time to ensure this detail is OPS INC. OPS may not be able to crank them out by the hundreds, but when the same person who makes the suppressors, is also the same person, in the same place making the mounts, it’s easily accomplished.

OPS INC has always had a great reputation for minimal POI shift. I don’t want to take anything away from the design, but a large part of that (known)reputation is owed to Gene Barnett. Gene is the guy who chambered, contoured and threaded the Douglas barrels used on the MK12 SPRs. I can promise you; those barrels were threaded as close to perfect as possible. A good majority of the suppressed SPRs in civilian hands have barrels also turned by Gene, John at White Oak, or Frank at CLE. Again, barrels that are properly made by people who do it the right way. There have been OPS cans in use on bolt guns for years, also earning a good reputation – but again, these are all custom contoured and threaded barrels.

Sadly, there are more and more “SPR Contour” barrels available which fall under the production tolerances. I recently saw a chrome lined one that was bored 7 thousandths off center. This has always been a concern of OPS, and part of his reluctance to sell to the civilian market. People start putting his products on poorly made barrels and it will start to effect his reputation.

Here’s another example of the right combination of parts. Finding a SBR barrel that is close to concentric is next to impossible (if you have a Colt barrel, good luck, the odds are REALLY against you). I found it was easier and cheaper cut 16” barrels down so I know the threads are perfect. Below is a picture of 20 shots from my SBR. This is 10 shots without the suppressor and 10 shots with the suppressor at 75yds with an Aimpoint. It was a 16” barrel, which was cut down to 11.5”, the threads are perfect.




I couldn’t ask for anything more – no shift that I can tell. How much of that’s the barrel, and how much is the suppressor? Not really a big deal for a short range weapon, but something to consider if any type of precision work may be involved.

You should have a permanent seat in the tech forums.  
Awesome insight as usual.

Holy crap...those threads are WAY undersized!WOnder if the operator fell asleep during operations and wasnt checking for tool wear!

Those threads look perfectly fine... FOR A SWING SET.

Seriously, when I was assembling my kids swingset I was a few bolts short and had to "fab" some myself in my garage.

Cut down a to desired length, and ran the trusty die down the shank. Ended up wtih a very similar threading results. The profiles being all flat like that.

DId this guy use a "Rigid" pipe threader. Hell, even a pipe threader would have had sharper threads than that.

That is sad... just sad.

tags

That ooks like my first try at cutting threads under the tutelage of my Grandfather in law.  Had to start over.

ost

So what barrel manufactures are better than others?

Ive got a couple questions. I have an 11.5" CMMG upper on order that I plan to mount a suppressor to and I was wondering, if I had the barrel checked and it wasnt concentric, could I send it to you (ADCO) to be cut and re-threaded? If so what would the new length of the barrel be and would that effect my SBR paperwork that reads "11.5in barrel"?

Thanks,

    BigHunter27

What a great thread!

GUYS LEARN FROM THIS!

Mike Mers

Very good info.  Thanks.

Convinced me to rethread a factory barrel I have with a can on it.  

Question is:  How much do you have to take off to rethread?  I have a factory 11.5" barrel.....how far back do you have to take it?  Could you get away with making it 11" or 10.75"?

Thanks

Most 5.56 thread are .625 long. So if we have to rethread your barrel we would cut off .625 and start over.

He already told us, Gene Barnett, John Holliger @ White Oak Armament and Frank White @ Compass Lake Engineering.

This worries me.
I'm doing an 11.5" urx II build, the last part I need is the dd barrel with low pro gas block.
Any advice? Id like to avoid the cutting and threading cost, but this will be a surefire suppressor host.

Hope it works out I guess

DD's are G2G. we've checked a few hundred.

Thanks,
Got my stamp today and ordered the last 11.5" DD barrel with low pro gas block I found anywhere.
All the parts will be comming to ADCO shortly.

Do the threads on sabre barrels tend to be decent?

I saw where you said most Colt barrels are not concentric, even as a government contractor. How concentric are other .gov manufacturers, like FN or LMT?  I know several people, including myself, that run LMT 10.5s on there SBRs. It would be hard to get them cut and rethreaded because it would not meet the typical 10.5" barrel limit on most suppressor manufacturers.