I mostly run pencil barrels and currently have several that are threaded 1/2-28. since i've decided to go suppressed, it would be convenient to run one set of threads on all my rifles. only 2 rifles are a much thicker barrel profile and they are .223 and 6.5CM. is there any reason to keep those at 5/8-24 or can they be taken down to 1/2" without any negative drawbacks?
Gunsmithing Threading bull barrel down to 1/2"?
- Thread starter SB545
- Start date
You can have them both threaded 1/2-28. The more material you take off the muzzle, the higher the chance that there is some stress relieved affecting the bore dimensions at the muzzle. This can affect precision negatively. Chances are good you would never see any negative effects.
I spoke to white oak armory about this. The predator barrel I just bought has 5/8” threads However it’s a 223. Their response was that on their predator barrels where the focus is absolute accuracy they prefer more meat around the muzzle.
They definitely know a thing or 2 about accuracy
They definitely know a thing or 2 about accuracy
Why go through cutting a barrel when you can use a thread adapter....?
Takes every bit of 60 seconds to swap it out in the can.
Takes every bit of 60 seconds to swap it out in the can.
I know Ed Shilen doesn't recommend their heavy varmint contour and larger prefits to run a 5/8". I've done several with no adverse effects. But, they don't recommend it.
Last edited:
Can you expound on this? I was thinking of getting a .223 built and planned to thread it 5/8 so I don’t need to buy a new thread adapter for my can.
I'm just saying what Shilen says they don't recommend it. Like I said, I have turned several (most actually) 1" barrels down to .625" with no problems.
If I were to guess, they don't like it because turning that far gets into their 11 degree target crown. However, when I turn a blank down, I thread the barrel, THEN put my crown on (be it recessed or 11 degree or whatever the customer requests.)
My pencil barrels are threaded half inch and my target guns have no threads currently. The 6.5 is a true 1/3 moa gun with factory rounds. The 223 I could care less about it opening up to 3/4 but I'd be upset to lose the accuracy on my 6.5.
I prefer not to use a bushing but could buy another adapter for the sico harvester though.
But that 1/2-28 thread on a bull barrel leaves a nice shoulder for the suppressor to tighten against . I did the same on my small caliber prairie dog rifles threaded them to 5/8-24 so I could use a couple direct thread cans on them .
No issue. Done it many times on friends' weapons and on mine. Besides my dedicated Allen engineering AEM5, I use my Surefire 30 caliber can from 300WM to 5.45x39 AR and slew of 223s in between.
I never liked the 1/2 x28 on AR barrels for service rifle competition, when the A2 flash hiders for the 300BLK came out, I threaded all the barrels I did with 5/8x24. They are just for crown protection for the most part in our application.
so, is the consensus to not thread the barrel on the 6.5 at all and keep it shooting the way it is?
i'll likely turn down the 223 anyway since it is more of a convenience and i'm not worried about the accuracy. to clarify, the 6.5 is a savage 10FCP HSP and is not threaded currently. the choices are to keep it the way it is, thread it 1/2-28 to match my suppressor or get an adapter/bushing to go from 1/2 to 5/8-24. i'm probably overthinking it but would rather do it right the first time.
i'll likely turn down the 223 anyway since it is more of a convenience and i'm not worried about the accuracy. to clarify, the 6.5 is a savage 10FCP HSP and is not threaded currently. the choices are to keep it the way it is, thread it 1/2-28 to match my suppressor or get an adapter/bushing to go from 1/2 to 5/8-24. i'm probably overthinking it but would rather do it right the first time.
If you have a problem threading a .264" groove barrel to 1/2-28, you have a junk barrel.
Bore expansion from "relieving stresses" via turning down the muzzle to thread it require pre-existing stress from improper stress relief to begin with. It is ONLY a problem with button-rifled or hammer forged barrels that had improper (or no) heat-treat/stress relief done to them. The only barrel I've had it happen to me with personally was a Green Mountain "gunsmith special" 1.25 straight contour (A piece of bar stock with a button run through it, basically).
Any cut rifled barrel, or properly relieved button or forged barrel are A Okay to turn down for threading. Some general rules to follow:
1) Wall thickness no less than .100" (You're getting a little bit under that with a .264 groove, but not the end of the world)
2) Shoulder diameter no less than .100" more than thread OD
Muzzle exit pressures on barrels over 14" long are low enough that the radial elastic deformation is in the scale of .00001's or less. Not worth worrying about.
Bore expansion from "relieving stresses" via turning down the muzzle to thread it require pre-existing stress from improper stress relief to begin with. It is ONLY a problem with button-rifled or hammer forged barrels that had improper (or no) heat-treat/stress relief done to them. The only barrel I've had it happen to me with personally was a Green Mountain "gunsmith special" 1.25 straight contour (A piece of bar stock with a button run through it, basically).
Any cut rifled barrel, or properly relieved button or forged barrel are A Okay to turn down for threading. Some general rules to follow:
1) Wall thickness no less than .100" (You're getting a little bit under that with a .264 groove, but not the end of the world)
2) Shoulder diameter no less than .100" more than thread OD
Muzzle exit pressures on barrels over 14" long are low enough that the radial elastic deformation is in the scale of .00001's or less. Not worth worrying about.
Id just tread everythin 5/8-24 even my 223 is now that way to add extra meat between the bore and shoulder undercut for the trheads
I've been using 5/8-24 on 22 cal barrels since 2008 for that reason. I purchased 12 barrels from different manufacturers and tested all of them for accuracy. 1 shot much better than the others so I tried to figure out why. 11 barrels allowed a .219 inspection pin to slide in the muzzle apx 3/4"...just about the length of the thread. The 1 barrel that shot better would allow a .218 but not the .219". I cut the threads off a couple and recrowned them, both shot better. I called Steve at Krieger and told him what I thought and he confirmed it. He said they stress relieved the barrels a certain way to minimize the swelling at the muzzle with 1/2" threads but 5/8 would be better as long as it is stress relieved.
is the stress relief at the time of rifling or when the threads are cut post manufacture of the barrel?
It depends on who writes the specs for the barrel. Most companies do it after the rifling but before profile and threading, that is why most of the barrels with 1/2" threads have bores that are oversize under the threads at the muzzle.
About 25 or 30 years ago a friend of mine had a .30/.221 fireball barrel made up for his AR(before .300 Whisper and Blackout). He wanted to run an Ops Inc suppressor on it so I turned the barrel detail for him(Shilen Barrel) When I started cutting I was amazed at how much the barrel started running out as I removed material. I was told by an old time bench rest shooter and stock maker that he saw that from time to time with the Shilen barrels. Never bought one after that, but I have not seen any other barrel move like that when turning. I honestly don't think you need to worry about it.
The more meat the better. I only use 1/2-28 on 22lr. All my 223 are 5/8-24. You cant do 1/2-28 on 6.5cm. The wall thickness from bore to threads would be too thin.
i'm cutting off a factory threaded 22" 7/16-28 and moving back 5" on the barrel. i also have a factory 1/2-28 on the end of a 26"bbl of a 7mm mag. so far no issues on that one and she's a bug hole shooter. it's a fierce fury.
