My understanding is that no barrel is perfectly straight and its best to time the curvature to 12 oclock. If the natural curvature of a barrel is off in another direction, rather than 12 oclick, does it really matter that much? Specifically, how far off are most quality barrels and then what does this bias mean at 500 yards? 1000 yards? Especially when we're shooting at ~2-3MOA targets. I've wondered this for a while and kind of had an ignorance is bliss mindset since I shoot AI prefits and I don't think all AI action threads are timed the same.
Gunsmithing Timing a barrel - how much does it matter?
- Thread starter Aaron47pb
- Start date
The "curvature" in a barrel is no where near as extreme as some people make you believe. There are ways to fit a barrel where it doesn't matter. There are also ways people use that I personally feel have a high possibility to exaggerate the runout at the muzzle end, which would be a good idea to time them north or south. On your AI prefit barrels, I am betting there's nothing to worry about.
Well...this is probably one of those topics that is subject to a lot of differing opinions.
IMO, the theory behind this practice- as I understand it- has a "flaw" in that, IMO, every barrel has different harmonics and will "whip" in a manner that cannot be predicted. The point is space of the bore at the exact moment the bullet is released cannot be predicted nor quantified- and as long as the harmonics are positive (bullet released when the shock wave is at the barrel breech) and consistent that's what matters; and that's a function of load development, not chambering/fitting methods.
With a match-grade barrel and honed bore, I suspect they are true "enough" that clocking is unnecessary, and there are countless rifles fitted with barrels chambered without indexing- including prefits- that shoot bugholes to support that opinion. Just because a rifle with an indexed barrel that shoots one ragged hole, doesn't mean it's due to the indexing.
I wonder if this has been "tested", as in chambering without clocking, assessing results at the target; then clocking/setting back as needed to clock the muzzle, and see if it makes a difference. There would be a small change in barrel length but I can't see that affecting harmonics from the baseline significantly.
Looking forward to reading others' opinions on this...
IMO, the theory behind this practice- as I understand it- has a "flaw" in that, IMO, every barrel has different harmonics and will "whip" in a manner that cannot be predicted. The point is space of the bore at the exact moment the bullet is released cannot be predicted nor quantified- and as long as the harmonics are positive (bullet released when the shock wave is at the barrel breech) and consistent that's what matters; and that's a function of load development, not chambering/fitting methods.
With a match-grade barrel and honed bore, I suspect they are true "enough" that clocking is unnecessary, and there are countless rifles fitted with barrels chambered without indexing- including prefits- that shoot bugholes to support that opinion. Just because a rifle with an indexed barrel that shoots one ragged hole, doesn't mean it's due to the indexing.
I wonder if this has been "tested", as in chambering without clocking, assessing results at the target; then clocking/setting back as needed to clock the muzzle, and see if it makes a difference. There would be a small change in barrel length but I can't see that affecting harmonics from the baseline significantly.
Looking forward to reading others' opinions on this...
I think the idea of “clocking” is intended to give a little extra elevation for longer range shots. I think there’s just so many variables that come into play it’s hard to hang it on just one thing. Bore clocked at 3 o’clock vs 12 or 15 mph wind at 1000 yards, which would matter more? It’s hard for me to say with any confidence at all.
I’ve clocked barrels and 12 and I’ve just let it land where it will and I haven’t seen any difference at least in groups at 100yds in my hands.
I’ve clocked barrels and 12 and I’ve just let it land where it will and I haven’t seen any difference at least in groups at 100yds in my hands.
For me, if you are having a smith fit a new barrel, why not time it? That's sort of what you pay for in having a professional fit a barrel as far as I'm concerned. I'm sure I could screw a new barrel on, but I prefer to have a pro do it for this, and other, reasons.
Yes, it may not matter, but when we are measuring powder to the 1/10th of a grain in every cartridge, why would we let anything that could be controlled, out of control?
And, if it's a hunting rifle, for larger game (deer etc.) within 200 yards it probably also doesn't matter.
Yes, it may not matter, but when we are measuring powder to the 1/10th of a grain in every cartridge, why would we let anything that could be controlled, out of control?
And, if it's a hunting rifle, for larger game (deer etc.) within 200 yards it probably also doesn't matter.
Part of this technique is a result of the stock inletting.
With a close fitting stock, which some prefer, an unclocked barrel may cause fitment issues.
R
With a close fitting stock, which some prefer, an unclocked barrel may cause fitment issues.
R
Wannashootit has an idea with the harmonics that I had not put any thought into. A good point to ponder on!
My last rifle I had built, the bbl was timed.
My thots are if you “time” the bbl to 12 o’clock, you take out unaccted for windage. When you zero your scope ur taking out unaccted for elevation and making it a known.
Am I a good enough shot to prove my theory, no I am not.
If you measure powder to 1/10gr, seat bullets to .001”. If you specify squared receiver and squared bolt face, and use custom ground reamers, it sure does not hurt to “time” the bbl.
Now exactly how much it helped, that is debatable! Good luck with your build
My last rifle I had built, the bbl was timed.
My thots are if you “time” the bbl to 12 o’clock, you take out unaccted for windage. When you zero your scope ur taking out unaccted for elevation and making it a known.
Am I a good enough shot to prove my theory, no I am not.
If you measure powder to 1/10gr, seat bullets to .001”. If you specify squared receiver and squared bolt face, and use custom ground reamers, it sure does not hurt to “time” the bbl.
Now exactly how much it helped, that is debatable! Good luck with your build
I remember seeing some guys shooting smallbore that had their barrels timed. Not sure if it made a difference on a .22rf but I would really like to see a comparison of two or more guns that have been timed. and shot from at least 600yds. I have not had any barrel timed to my knowledge and I would really like to see this and what the outcome is. Voodoo magic ? Who knows.
We timed my bbl with a precision ground range rod from PTG. Like you use setting up center to thread for suppressor. OD of bbl and OD runout of bbl is irrelevant
I’d like to know how many people have verified their muzzle TDC while set up on the lathe cutting the tenon/threads/chamber is the same TDC while being hung from the receiver threads, free of the stress of being jacked around by chucks and screws 20”+ apart...
Maybe do all your chamber end work and mark the muzzle TDC. Then put some stock in the lathe and bore/single point thread a female thread to match your barrel. Without changing the setup, screw the barrel into your female thread and measure the runout at the muzzle end. Is your TDC mark the same? Really?
Maybe do all your chamber end work and mark the muzzle TDC. Then put some stock in the lathe and bore/single point thread a female thread to match your barrel. Without changing the setup, screw the barrel into your female thread and measure the runout at the muzzle end. Is your TDC mark the same? Really?
While we are trying to pick the fly shit out of a pound of pepper... If the bore was perfectly centered in the blank at both ends of the barrel what are the chances it is centered in the middle of the blank? Slim to none? Same chance it is perfectly centered anywhere along the barrel. Clocking may be worth the effort if you know the barrel has a hook in it. My point is.. how would you determine if the bore is straight?
Most guys indicate off of the first couple inches of the bore at 2 points then assume that any eccentricity on the muzzle end is "bend". Measure the high then the low, subtract and divide by two is how far it bends. This also assumes that there is just one slow progressive bend that ends up at the muzzle.
I tend to think it doesn't matter. More of that theory peace of mind.
I suppose it depends on the setup. I have two lathes. One big lathe with a true bore chuck on it (zero stress), and a smaller lathe with an outboard spider. I use a steel wire around barrel at the inboard side on the small lathe, which allows the outboard end to be steered around without much imparted stress. I’d agree the amount of runout on the lathe would be more severe than when it’s hanging off the action, but the direction would be the same or very similar. Im not claiming I dial it out to absolute zero, but I like it to trend to “up” as opposed to off to one side. By the way 300, do you use grizzly rods. I seem to remember that from somewhere, and need some help with mine.
Barrels seem to vary so much, I just deal with it on a case by case basis. I did a 30” heavy palma bartlein recently that was so straight I didn’t give any of this a second thought.
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Well, if the bore is not straight then bend it. Barrel bending devices of this type were on the factory floor of Holland & Holland, Purdey, etc. They were used on both shotgun and rifle barrels and are still in use. I remember a picture of the Anschutz factory floor from the '50s showing the craftsman using the device. They are always placed so the operator can point them towards natural light and operate them while standing.
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I time the barrel to 12 o'clock high for the two reasons already mentioned. First to ensure that the barrel is perfectly aligned with the stock's barrel channel. And second to apply any banana curve so it increases the available elevation. It is also nice that I don't have to change my windage when swapping to a new barrel.
I purchased a TBAS to avoid the issues that Robert mentions above. This allows the barrel to be stress free coaxially aligned to the lathe's centerline.
Cheers,
I purchased a TBAS to avoid the issues that Robert mentions above. This allows the barrel to be stress free coaxially aligned to the lathe's centerline.
Cheers,
With the TBAS, can you dial in a barrel at the throat and the muzzle while the muzzle is unsupported?
My jaws dont mar barrels or receivers at all. Everything I’ve done so far with mine didn’t have a finish on it though, so it didn’t much matter. You could use any method you like though to isolate the jaws from the part. Tapered parts get shimmed.
So the barrel will be pointing the right direction when you screw it into the action.
I had a conversation about this with another person recently, which is why I asked. I couldn’t understand his point. He doesn’t do gun work, so I’m thinking he has some gaps in his understanding.
If I grab the barrel at the breech end rigidly in a chuck, and steer the barrel around with that chuck(TBAS) until the bore(where my reamer pilot runs) is coaxial to the lathe centerline, what the barrel is doing on the other end is irrelevant to the task. Torquing the muzzle into some alignment on the outboard side does nothing. Upon releasing it, it would just spring back anyway. The shoulder, threads and chamber will have been cut on the bore, and assuming a crooked bore at the breech end to begin with, the barrel WILL be pointing off in some random direction. That’s where this thread topic comes in, indexing the barrel to 12 oclock. The other setup I use with a steel ring on the inboard side, and an outboard spider on the other end, I can steer things around just like the TBAS chuck, and the outboard end of the barrel will still be turning eccentrically like it will in the TBAS.
If you watch Nate’s(straight shot gunsmithing) video of him demonstrating the TBAS, he dials in the bore completely, then screws down the outboard spider to support that end of the barrel, not to dial it in to alignment.
i see no reason why you couldn’t have the throat and muzzle dialed in with the TBAS. Maybe after the throat and muzzle were aligned with only gravity acting on the muzzle, you could then use a spider to hold it in place and attach your flush system. There’d be very little stress on the barrel at that point.
When you have a barrel dialed in at the throat and the muzzle, if you move the indicator .150" to either side of your indicating points, how much does your reading typically change?
How does one go about that? It seems to me that any eccentricity at the outboard end of the bore is just a product of what’s going on at the inboard side, but projected over a great distance. I agree with you about bore curvature though, it’s very minimal in a quality barrel.
If the bore is truly curved, you can only have it running concentric at two locations without bending the barrel. Each builder needs to decide which two locations those are.
I make bushings out of 6061 tubing. Tapered bushings matched to barrel's taper.
Cheers,
Yes. My first step Is to true muzzle's OD while cutting a barb for the chamber flusher hose. Then flip the barrel and align the chamber. Now it is easy to indicate the muzzle to mark 12 o'clock. Only then do I lock up the out board spider.
Cheers,
How much eccentricity are you seeing on the muzzle end?
I just drew it out on a CAD program assuming a .007" runout over a 27" barrel and the bend has a radius of something like 0.82 miles.
Assuming the bullet leaves the barrel in a straight line in the same direction as the muzzle (tangent to the "curve") that would account for about 1.8" difference vs. a perfectly straight shot @ 100yd.
You would not notice any continual convergence shift down-range (for example, once you zero at 100, even if it's "pointed" straight to the 9 o'clock direction, you won't get 1.8" of shift every 100yd. Maybe like .005" shift every 100yd). It's so small it's negligible to everyone... not any more than if your rings push your scope slightly to the right or left of bore centerline or if you zero/level your optic at a slight cant relative to the rifle/rail for the most comfortable position.
Bear in mind this makes a ton of assumptions about the curve, that the barrel is rigid enough to point in the direction of the curve during firing, etc.
I just drew it out on a CAD program assuming a .007" runout over a 27" barrel and the bend has a radius of something like 0.82 miles.
Assuming the bullet leaves the barrel in a straight line in the same direction as the muzzle (tangent to the "curve") that would account for about 1.8" difference vs. a perfectly straight shot @ 100yd.
You would not notice any continual convergence shift down-range (for example, once you zero at 100, even if it's "pointed" straight to the 9 o'clock direction, you won't get 1.8" of shift every 100yd. Maybe like .005" shift every 100yd). It's so small it's negligible to everyone... not any more than if your rings push your scope slightly to the right or left of bore centerline or if you zero/level your optic at a slight cant relative to the rifle/rail for the most comfortable position.
Bear in mind this makes a ton of assumptions about the curve, that the barrel is rigid enough to point in the direction of the curve during firing, etc.
It varies from about 5 thousandths to 25 thousandths. It's worse when the barrel is cut down more than the nominal 1". The 25 thousandths run out happened after cutting 4" off the muzzle.
You can see the banana bore by looking through it while it's rotating. I never record the jump rope barrels. I see those too often. None of this seems to affect the barrel's accuracy. They all shoot better than I do. Here is a straight one: https://youtu.be/TxAie6Lr6W4
Cheers,
Has it been determined (via mapping somehow) that a bore is a true "curve", as in part of a radius; versus random wandering by the gun drill?
I'd be interested in seeing the science behind these discussions, gun drilling is above my pay grade.
I'd be interested in seeing the science behind these discussions, gun drilling is above my pay grade.
Any way you can imagine a gun drill wandering, that’s what’s possible.
I had a rock creek barrel years ago that had a corkscrew shaped bore, and exited way off center. Shot fantastic.
No matter how much wander there is in the barrel (well within reason, assuming it comes from a reputable maufacturer, etc..) it's a SUPER shallow angle and very gradual so it's practically straight in terms of bullet deformation. It's no surprise to me that even corkscrew barrels produce precision.
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If it were an issue, do you think everyone would gravitate towards prefits like they do??? With a prefit barrel it is what it is....
Not really the point. Prefits are popular because they’re simple for the end user, and they work well. If a builder asked you if you’d like you’re barrel indexed to 12 if that barrel has some eccentricity, for no additional cost, would you actually decline? It’s a super simple step that many do (myself included) as part of the normal procedure for a barrel Install.
No, it's not an issue. Like I said, if the math is exactly what happens you're looking at maybe 2 mils deviation from a perfectly straight barrel in whatever direction the barrel clocks. It's a nice thought, and maybe gives a warm fuzzy but with the optics available these days you're going to have enough travel to get you well beyond the point your bullets are subsonic. Might be worth looking at if you're building a 375 Cheytac or something to shoot 2000yd+ but for most of us it doesn't mean much.
Like I said above, even if it points straight sideways, the effect on your optics/adjustments is that there's a .005-.015" lateral offset between the LoS of the scope vs. the line of flight of the bullet. Not enough for you to adjust for, and my guess is a lot of scope rings or off-center M700 holes push the scope further off to the side than what we're talking about here. I don't know how to effectively draw this effect, to scale anyway, but if anyone doesn't believe me I can try.
Like I said above, even if it points straight sideways, the effect on your optics/adjustments is that there's a .005-.015" lateral offset between the LoS of the scope vs. the line of flight of the bullet. Not enough for you to adjust for, and my guess is a lot of scope rings or off-center M700 holes push the scope further off to the side than what we're talking about here. I don't know how to effectively draw this effect, to scale anyway, but if anyone doesn't believe me I can try.
I agree, there are lots of causes for misalignment. What if you had several of those things stacked together? I’ll add in an out of square action thread, or face. I’ve seen many guns that wouldn’t zero, or burned up much of their windage to get zeroed, for a number of reasons. An easy no cost step to tie up a potential loose end, nothing more.
Some people set up their barrels so the muzzle and throat are running true when chambering. There would be nothing to "clock" or index at that point.
Agreed. To you, doesn’t that seem like it’s masking and not addressing the curved bore. And if the bore is curved at the breech end, the bore will be put out of alignment on either side of the dialed in point. I guess I just like my two points to be in front of and behind my reamer pilot.
Here’s some SAC vids on this exact topic.
https://youtu.be/CdoyqhiSfvE
https://youtu.be/R1V66Dv35RU
If you check the runout .150" on either side of the dialed in point, how much curve will it take for the barrel to have more wobble than your machine has?
That would certainly depend on the curve. Why box yourself in to a .300” window? The narrower you make that, the straighter everything seems. A 1” window would provide more resolution, wouldn’t it? My priority is to make sure the reamer has the straightest possible approach to the bore. That will ensure the most even leads, and the roundest chamber IMO.
I've had discussions with my gunsmith about barrel clocking. He is a true believer in it, and says that some barrels that had otherwise good work but were not clocked shot significantly worse than after he re-cut the chamber and clocked them.
I know the last two rifles I have had chambered needed slightly less elevation to hit at 1000 than what the AB program said they were supposed to. Another benefit has been switching scopes between guns and having similar elevation settings.
I know the last two rifles I have had chambered needed slightly less elevation to hit at 1000 than what the AB program said they were supposed to. Another benefit has been switching scopes between guns and having similar elevation settings.
I’m a bit skeptical of that.
Of what part?
That your AB discrepancies are due to barrel clocking. Mostly. I'm a little skeptical that the direction the muzzle clocks has anything to do with accuracy but I'm going to think on it a bit there may be something subtle to that.
Similar POI with scopes I buy. More similar than if they were 180 out anyway.
Similar POI with scopes I buy. More similar than if they were 180 out anyway.
All if it.
That a rifle shot better because of “clocking”. That there is a flatter trajectory due to barrel clocking. That switching scopes between guns is easier because of barrel clocking.
Don't worry. It doesn't make sense to me either. I've just seen the results on two of my personal rifles so far.
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