Threaded barrels......does it hurt accuracy?

V

varminter .223

Well-known member
Im guessing the larger 5/8 diameter doesn't hamper accuracy but my question is how does the smaller 1/2 inch threads over the larger 6 mm bore affect accuracy. I understand that different flash hiders suppressors and objects hanging on the front of the barrel significantly change harmonics and the way the pressure is released from the muzzle etc but I will be running a bushing only.
 
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We have not seen any change in accuracy from a threaded to a non-threaded barrel of the same manufacturer. We have seen that in some cases, threaded barrels were not crowned and THAT could effect the accuracy and may be why some people say that threaded barrels are not as accurate as non-threaded barrels. Of course not all barrels are created equal...
 
I had threads cut off my one and only threaded barrel and target crowned.. It made a huge difference on my rifle.. And it was from a reputable barrel company the barrel came from..

Can a threaded barrel with the thread protector on it be machined to have a target crown?? Dan
 
I have a heavy can ( 23 oz.) and the guns that I have used it on have shot smaller groups with it on. 2 of them never shot all that well before being threaded. These have 1/2 x 28 threads.
 
Originally Posted By: whyI have a heavy can ( 23 oz.) and the guns that I have used it on have shot smaller groups with it on. 2 of them never shot all that well before being threaded. These have 1/2 x 28 threads.

in all honesty - that probably has more to do with the suppressor acting as a freebore dampener for the barrel harmonics than it has anything to do with the threading. unless of course pre-threading the barrels had a bad crown and the smith who threaded your barrels fixed that for you as well.


i'm not suggesting that your results are fake by any means, just possibly attributed to something other than what caused the change.


it still solid proof though that treading - done properly - wont degrade accuracy. and could [beeep] well end up with improving what you've currently got
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All I can contribute is this...my non threaded barrels are far and away more accurate than my threaded barrels. BUT, there are other factors at work other than threading. That being said, I will not buy any more threaded barrels and will stick with White Oak post ban barrels.
 
We will only thread our light contour barrels to 1/2”x28 (.735” muzzle) and will only thread our medium contour barrels to 5/8”x24 (.860” muzzle) we don’t thread our bull barrels.

This policy is based on our experience and backed by the experience of Shilen, the folks that produce our blanks.

The reasoning behind this policy sounds a little strange, but I’m going to do my best to explain it. It is based on a machining phenomenon where removing metal from the outside of a tube actually increases the diameter of the inside of the tube. An analogy that I often use goes like this: If you take 5” shaft and bore a 1-1/2” pocket in the end of it for a bearing assembly. Now, you press that bearing assembly into the end of the shaft, under 1500 pounds of force. Now, start reducing the outside diameter of the shaft. After turning it down from 5” down to 4”, that bearing assembly will fall out on the ground! Simply by turning down the outside of the shaft, increased the diameter of the pocket by several thousandths of an inch.

You never want the muzzle to be “loose”. As the bullet is about to exit the muzzle, high-pressure gas will escape around the bullet causing it to pitch.

If you ask Shilen to thread a bull barrel to 1/2” x 28, they will do it, but it’s going to cost something north of $150.00. The reason being, that after reducing the diameter of the muzzle and threading it, they go back in and lap the barrel to bring the muzzle back to being the same diameter. Lapping is something we can’t do at our shop, so we just limit the amount of reduction in diameter to a minimum.
 
The mechanism with reducing muzzle diameter for threading to be concerned with is the bore opening up (reverse choke, bad ju ju for real accuracy). But the overwhelming majority of barrels that get threaded aren't accurate enough to know the difference. I doubt one AR in a thousand is that accurate. They don't normally start out with large muzzles to be reduced very much either. It's real though and why you wouldn't want to take any more diameter off the muzzle of a precision barrel for threading than necessary. It's why I went with a CB mount so I could use the same can on threads from 1/2 to 3/4, sparing my heavier barrels from being reduced to 1/2.

The harmonics thing is obviously separate, but can cut either way - if it can improve, it can also degrade. Tuners definitely work. Hanging a can is hanging a non adjustable, one setting tuner. It WILL affect harmonics. Period. Your barrel and load might like it, but it might not. Luck of the draw. Of the five centerfires I had threaded, none got any better, but a couple got worse and needed loads re-tuned. One was easy to tweak the load and get back where it had been. The other, I have not been able to get tuned back to where it was before being threaded and having a can hung off it. Now not totally sure it will ever get back with just load tuning, but if it does it's going to take a completely different new load, not just a powder or seating depth tweak. It was the most accurate one of the five, to begin with, naturally... Again though, I think the majority of barrels and loads that go this route, aren't accurate enough, or at least never get shot in a way to know the difference anyway. It's not the kind of thing you'll know about by shooting a couple three shot groups.

Concentricity of the whole job and quality of any re-crowning are important too. Crown doesn't get touched while threading unless the barrel gets chopped, then it needs re-crowned. Possible to screw it up, obviously, but anyone I'd trust to thread, I'd triple trust to crown. I'd be most suspicious of factory threaded barrels.

To the original question "DOES it HURT accuracy?". Impossible to answer. It can, for sure. Couple different ways. Done properly and intelligently, it isn't likely too though.

It really can't do anything to help accuracy either though. Simply can't. There's no plausible explanation for how it could (assuming a crown wasn't bad, but that would be obvious before starting). When you see noticeably improved accuracy after threading and hanging a can, you didn't have a very well tuned load to begin with and just got lucky on the harmonics and the non-adjustable tuner you just hung. No mystery.

- DAA
 
I just noticed Mike's post above mine. It wasn't there when I was typing
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. He explained what I referred to as reverse choke very well. In a bore, it's on the order of a ten thousandth or two. But any bell mouth at the muzzle is a bad deal for precision accuracy.

- DAA
 
Originally Posted By: DAAI just noticed Mike's post above mine. It wasn't there when I was typing
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. He explained what I referred to as reverse choke very well. In a bore, it's on the order of a ten thousandth or two. But any bell mouth at the muzzle is a bad deal for precision accuracy.

- DAA both of you are spot-on!
 
In my earlier post I mentioned that we had formed a policy based on experience. I failed to convey the “experience” that prompted the policy.

Barrel threading requests in our shop have been on an exponential increase with one state after another legalizing the use of suppressors. Not only are we threading barrels as we build them, but we are also threading a steady stream of barrels from the field where the barrel has been in use, unthreaded, for some time.

Several years ago we received a .20 caliber upper with a bull barrel from a customer that wanted it threaded to 1/2”-28. We threaded the muzzle and returned the upper to the customer. A week later we got the news that his upper went from a tack-driver to a 1” shooter! He sent it back to us for inspection, but we couldn’t find anything wrong with it. The crown was perfect, the assembly was correct, nothing looked suspicious, other than the fact that we had made a drastic reduction in diameter.

After visiting with our customer, he decided he would opt for accuracy over suppression. We cut .600” of threads off of the end of his barrel, re-crowned it, and it was back to a tack-driver!

Where accuracy isn’t our only business, it is incredibly important to us. We hate to see someone spend good money on a great barrel, then make a choice we know will limit the accuracy they will achieve.
 
I've read about this quite a bit here and there but never quite explained in this detail. The local guy I use to thread my barrels said it can be an issue but claims if you cut slow enough it mitigates it some. I don't necessarily believe that, however, sample of 3 bull barrels I have had threaded to 1/2" are all very accurate, a Shilen 204 that would put 5 into .4" and a pair of Rem 700 take offs that are nearly that accurate. Maybe they would have been even better un-threaded? We will never know.

I'm not disputing the fact that it does happen as it makes perfect sense to me. Just that it hasn't bitten me yet.

So what is a good solution? Maybe thread to a large diameter, then make an adapter down to 1/2" or 5/8" as necessary that is slightly larger than bore diameter?
 
Imo, theres no such thing as a "good solution". There are things that can be done to help minimize the effects, but honestly in a benchrest accurate type of rifle, anything done to the barrel will/could cause accuracy problems. Some even go to the extent of not having the cartridge chamber enscribed into the barrel because it may change the interior deminsion of the bore.

Granted most of this is not important on a hunting rifle, but in benchrest where thousandths matter, it matters to some.
 
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How about a 5/8" thread protector sticking out about .030" beyond the muzzle when tight. Anyone seen that affect accuracy?
 
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Very interesting discussion. I always thought it might be gas pressure from the pressure inside the barrel that could cause the swelling of the bore at the end when it’s threaded and you don’t have much barrel wall left. Maybe cut rifling might be different? Maybe gas pressure might aid the bore swelling if it was close to changing. Anyways I heard of this just briefly and decided to have mike do mine with 5/8x24 thread. Matt also said it was a good idea when I placed the order glad I did.

Mike we need an April special, lol
 
Originally Posted By: steve garrettVery interesting discussion. I always thought it might be gas pressure from the pressure inside the barrel that could cause the swelling of the bore at the end when it’s threaded and you don’t have much barrel wall left. Maybe cut rifling might be different? Maybe gas pressure might aid the bore swelling if it was close to changing. Anyways I heard of this just briefly and decided to have mike do mine with 5/8x24 thread. Matt also said it was a good idea when I placed the order glad I did.

Mike we need an April special, lol

Actually, there is no where near enough pressure to swell the muzzle by the time the bullet gets within 1/2” of the muzzle. The same phenomenon takes place in tubes where they are never exposed to any pressure.

Glad you reminded us! We’ll come up with something for April.
 
Okay, after reading this I got to wondering if there is a 'fix' for this. As I recall, TC marketed muzzleloaders with a barrel that was "back bored" for about an inch at the end of the barrel. This allowed the bullet to be started more easily and they claimed it 'aligned' the bullet the same way everytime thus increasing accuracy.

Now, I am no kind of a machinist, so I realize it may be difficult or impossible, but could the same kind of thing be done with a center fire rifle barrel? In theory the barrel could be 'back bored' slightly further than the threads so that the threading would not affect the last part of the actual barrel in the way that has been discussed in this thread. I imagine the trick would be making sure that the crown was true at the end of the rifling where it met the back bore, and also getting the specs right for the diameter of back boring to be enough yet not to much.

Anyway, it may not even be possible, but was just wondering if someone with more machinist skill and experience had heard of or considered such a theory or idea?
 
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That is being done, and I have considered it, but after I did the math on the one I was considering, I abandoned the thought.

My specific example was a .223 Remington threaded to 1/2”x28. The minor diameter of that thread pattern is .476”. The thread-relief groove is slightly less than that. Now, in order to give proper clearance for the bullet I would open the bore up to .264”. That is only going to leave you a wall thickness of only .100”. There are probably bore-diameter/thread-patter combinations that give you more wall thickness, but it doesn’t seem to be a “fix” for one of the more popular situations.
 
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