Gunsmithing Barrel timing questions

#54
Re: Barrel timing questions

I'm not understanding all the controversy. If the barrel is timed at 3 o'clock, the bullet will track slightly to the right. If you zero at 100 yards, you'll need additional windage to compensate if you move out beyond 100. Am I missing something that makes this more difficult than it seems to me?
 
#55
Re: Barrel timing questions

I dont believe you will need additional compensation past 100.
Ok if you really want to get technical it's a VERY small amount. Not worth talking about.
You've already compensated for it.


Once you sight in at 100, runout does not matter any more IMO.

That bullet if flying straight. It isnt arching unless youre in the movie WANTED
 
#56
Re: Barrel timing questions

Yes, the bullet is flying straight and not arching, but that straight line isn't consistent with your line of sight. The windage it takes to put your round on target at 100 yards will be insufficient at greater distances.
 
#58
Re: Barrel timing questions

If there is any common ground that can be reached in this "discussion" it's that compensation is needed for a barrel not timed to 12:00, or 6:00...regardless to what degree it runs out.

The question is, why would anyone purposely install a barrel that would needlessly use up otherwise useful windage adjustment........

That said, Triple6 did my latest rebarrel just recently, and will do the next one as well when the time comes, and the one after that too. He indexed my barrel like we've talked about here and it's one of only a couple I've had over the years that didn't need windage past the zero in a no wind condition. My reticle is centered and I have full use of the windage range on both sides.

I'll take that any day of the week...........
 
#59
Re: Barrel timing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tripwire</div><div class="ubbcode-body">If there is any common ground that can be reached in this "discussion" it's that compensation is needed for a barrel not timed to 12:00, or 6:00...regardless to what degree it runs out.

The question is, why would anyone purposely install a barrel that would needlessly use up otherwise useful windage adjustment........</div></div>

I can agree completely with this
laugh.gif
 
#60
Re: Barrel timing questions

Can anyone provide some numbers? Or a graph to show it matters?

As far as I can tell, once you zero at 100, it makes no difference past that.

By no difference, I mean around 1/10th MOA, maybe far less.

Can you provide anything to prove otherwise? I dont know the math, but I can picture bore runout in my head, and a bullet leaving it 20" down a tube with it meeting the scopes LOS at 100. My brain tells me it will be extremely close at further distances.

We exaggerate barrel runout in our heads to make easier logic of discussion, but there isn't as much as I guarantee some people are picturing right now.
Its a pretty fuckin straight tube, with a scope at the rear of it, pointing at the exact same point at 100 yards. The key there is that the scope is pointing at POI at 100. This corrects for 99% of the "fake wind" youre thinking is there.
If the scope wasnt adjustable, and just pointed straight ahead of the action, then yes runout would matter a lot. But after zeroing at 100, I dont see how it can.

My shooting ability can not tell the difference. And Ive never been in a day with so little wind, I could perform this test.



If the scope was over the muzzle, there would be zero effect from runout right?
 
#61
Re: Barrel timing questions

Picture zeroing at 500 yards. Perfect zero. No wind. No gravity, spin drift, no nothin.

how far left of LOS do you think the bullet would be at 250 with RH bore runout? How far left at 100? or at muzzle where itd be the most??

Cause youre saying it will be right at say 750 right? How about 900? Wont it be as far right at 900 as it was left at 100, with a 500 yard zero??

Bullets do fly in straight lines right? No WANTED movie effects due to runout right?







Another way to look at it:


Say your LOS is "Y" axis.

After compensating for runout, your bore has moved over 1" at muzzle to the left because you have a TON of Right hand runout. More than any barrel, anywhere, period. You also have an amazing scope..

Now, you zero'd at 500 yards.

Remember, your bore is 1" left at muzzle off "Y" axis, zero at 500 on "Y", how far right of "Y" do you think it is at 950 or 1000? If bullets fly straight.

Seems like itd be 1" right of "Y" at 1000 yards, with more barrel runout than any barrel ever has anywhere, and a 500 yard zero, being 1" left at muzzle.

Now use reasonable runout and say the muzzle is only .050" or less left of LOS to compensate for runout and achieve a 500 yard zero. It would be how far right at 1000?


Is that correct thinking? Doesn't seem like it matters if you zero your rifle.
 
#62
Re: Barrel timing questions

If you put a range rod into the muzzle end of a barrel and indicate it in to .000" TIR at the muzzle and have another indicator 6" out from the muzzle that is showing .005" TIR then your bore is curved at the muzzle. Having .005" runout 6" from the muzzle multiplies itself to .010" 1' from the muzzle, .030" 1 yard from the muzzle, 3" at 100 yards and 30" at 1000 yards. What does this mean? Probably not much, but it will buy you 3 moa of scope adjustment (from mechanical center) by clocking it at TDC, 12 o'clock, 6 moa more than same barrel clocked at 6 o'clock. Everything else being <span style="text-decoration: underline">EXACTLY</span> the same, take two rifles with one being clocked at 12 and the other at 6, with .005" TIR of runout 6" from the muzzle and the one clocked at 12 will be shooting 60" higher than the one clocked at 6 @ 1000 yards......given identical scope adjustment from mechanical center. Soooo, I can see that there IS advantage to having the barrel clocked at TDC, but no advantage to having it clocked in any other direction, particularly at extended range.
 
#63
Re: Barrel timing questions

Youve just shown that in an extreme case comparison, the difference between 6 and 12 o-clock with a bore that has .005" of runout in 6" is only a difference of 6MOA. Only 3MOA of correction is needed to be on zero.

3MOA of correction needed for .005" runout in 6".

3MOA, big deal. Seriously. You use up more correction to make up for fucked up scope base holes.


Can anyone comment on my above post from last night?
If bullets fly straight, and you say it will be right past zero with RH runout, then it must be left of LOS before zero. Right??

How much left do you think it is at 10 yards with RH runout and a 100 yard zero? Too small to measure?
Cause its that much right at 200, and continues in a straight line out.

Runout doesnt seem to matter.

People dont worry too much about their scope base holes most of the time. Dont see too many builds with the base holes re-aligned to bore. But it looks like scope base holes make about 10x as big a difference as bore runout.


Hmmm.
 
#65
Re: Barrel timing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body">I bend barrels straight over my knee cause I drink Ensure and smoke Marlboros.


Then I go to "Didney Wand." </div></div>
laugh.gif
Don't you just love it!
laugh.gif
 
#67
Re: Barrel timing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: triple 6</div><div class="ubbcode-body">True, these things can be compensated for with most scopes. And I also believe that the bullet travels in a stright line if you take out the effects of wind, gravity etc. But I also strongly believe the run out of the bore to the OD of the barrel has an effect on which way that stright line may be. To compensate for it hitting say 1 inch left at 100 yrds you just dial in some windage, but if you only dial in elevation at say 500 yrds, you will see it start hitting left again, that is if you were in a place where wind and the earths rotation or the spin of the bullet played no effect. That is my story and I'm sticking to it. </div></div>


Dont forget, you arent adjusting your scope 1" at 100 yds, you are adjusting it 1 MOA, meaning at 500 yards, without touching the scope again, you have compensated for 5" of drift not 1".
 
#70
Re: Barrel timing questions

I dunno just made sense of it in my head. If its wrong I just wana know.
If bullets make a straight line and dont curve, the bullet can only be as far right at 750 as it was left at 250 with a 500 yard zero. Think about that. How farleft do you think it was at 250??

Like I said I dont know the formula. But to the best of my ability giving it thought, I come up with a very small difference at all yardsges other than zero distance.

If its wrong I wana know. Cause I used to think it mattered.
 
#72
Re: Barrel timing questions

Can look the formula up pretty easy if you want.

Pictures the triangle your los and bullet path makes to the target at 100 yards, with your distance from scope to muzzle being the third side. Now mirror it out to 1000 yards

Assuming .010" runout per foot, lines intersect 3" over at 100 yards from the scope to muzzle axis
 
#73
Re: Barrel timing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Keith at PCR</div><div class="ubbcode-body">Also it seems barrel length matters.
And if the scope was attached over the muzzle, runout would have 0 effect. </div></div>

There's a new product opportunity for you.
Co-axial scope mounts.
They put the scope perfectly inline with the center of the barrel.
All you have to figure out is how to get the glass out of the way while the bullet passes through...
 
#74
Re: Barrel timing questions

OK, I did the math. I was using the above example of a 60" bore run out at 1000 yards. I don't know if this is the max, but I don't feel it is unreasonable to demonstrate my point. Assuming the above, if you zero the scope at 1000 yards, and then come back to 100 yards without touching the windage knob (assuming no wind yada yada..) you would be off by a whopping .0296".. WAY less than 1/10 MOA. I had to extropolate the first equation to the 6th decimal place to find a difference in the distance equation. Feel free to check over my math!

2a69s9c.jpg
 
#75
Re: Barrel timing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Keith at PCR</div><div class="ubbcode-body">Ive done the math to the best of my ability.

Runout dont mean shit. Less than 1/10th MOA.
Anyone who can prove otherwise feel free to.
</div></div>


Care to share what numbers you are dealing with? And you know this to be true for ALL barrels how?

By my math, in order for there to be .1 moa, there would only need to be .00017" of runout 6" from the muzzle.....thats 17/100,000ths.

There may be no TIR at the muzzle, I don't know, but I'll tell you that any smith that would say "It doesn't matter" wouldn't be screwing a barrel on any of my rifles. It does matter and for reasons already mentioned by several people. But the jist of it is this, if the barrel has runout at the muzzle then the bullet isn't leaving the barrel in an exact line with the centerline of the chamber. It is advantagous to you to know which direction the runout will cast your bullets for and use it in your favor. It's there, you can't do a damn thing about it, regardless of how small it is why would you not wan't to use it?
 
#77
Re: Barrel timing questions

I am in NO way suggesting that one shouldn't determine the direction of the bore run out and time it to the best advantage possible, I am saying that even with the run out timed at 3:00 or 9:00, that zeroing at any distance will compensate for that phenomenon.
 
#79
Re: Barrel timing questions

Since I've done it both ways with the same caliber, same scope, same barrel and the only difference in the chamber was to move it enough to time up the barrel once I did the untimed test; I'll chime in.

I had one with 0.009" runout on a 22" tube.

Groups at 100yd, untimed: avg under 0.33" for 5 shots, 3 targets.
Groups at 100yd, TIMED: avg under 0.3" for 5 shots, 3 targets.

Groups for both at 600yd are vertical under 1.5" and 2" wide on average.

The infinitessimal difference in the 100yd groups is more than likely my fault driving the rifle and not the rifle's fault. It is not uncommon for this rifle to cut a 3 shot group under 0.2" and 1 off 5 shot groups in the mid 2's.

The repeatability of the rifle is unaffected. It is a similar triangles problem, do the math and you'll find that gaslight is correct.

HERE'S WHERE IT COMES INTO PLAY:

The runout causes you to use more or less of the windage knob on the optic to zero the rifle. When you travel "up" with the scope not "optically centered" in the horizontal travel you will affect the internal travel that is so important to some people.

Here's my Razor untimed:

83 MOA of vertical travel left after zero, appx 27 MOA below even with the 20 MOA base on it.

Here's my Razor timed:

88 MOA of vertical travel left, appx 30 MOA below.

In this case it was a useful gain of only 5 MOA on 80+ MOA of useful travel. The projected range of a 140 Amax at +80MOA from my 100yd zero with THIS RIFLE is about 1600yd...with a 6.5 Creedmoor.

I don't worry about it because I ran the numbers, then I tried it, then I ran the results through the calculator to see if I was right, and then I went out and shot at the limit of the scope travel.

I don't lose sleep over it. If Keith doesn't do it except upon customer request then I don't think any less of him.

If a rifle builder makes a point to do it as an attention to detail that's great. It doesn't mean the rifle will shoot any better or worse.

The guys that get blue in the face telling the rifle builder how the pipe fitter should do his job are far more oft than not someone that needs to spend less time arguing about how it "might" affect it and a LOT more time out shooting.

ETA: The barrel I'm talking about is a re-use from my 6.5-06 after 1500rd. I chopped 4" off the breech and 2" off the crown, it finished at 21.8"

There was a lot of runout in the middle of the barrel and I knew that from the beginning but it shot so damn good with the 6.5-06 I decided to give it a reheat on the 6.5 CM.
 
#80
Re: Barrel timing questions

.010" @ 1' from the muzzle x 300' to the target = 3moa


Run out is run out, it doesn't matter where you zero your rifle in the run out is still there. If you and I have identical rifles, shooting identical loads and identical scopes and our barrels have identical run out at the muzzle at .005" TIR @ 6" from the muzzle with the only difference being that you clock yours at 6 o'clock and I clock mine at 12 o'clock, then your scope will run out of elevation adjustment 6 moa sooner than mine will. THAT is the difference. Does it matter? Prolly not, but why not take advantage of it? It has absolutely nothing to do with 100 yard or 1000 yard or 1,000,000 yard zero. Given the same rifles above, if we both have the same 100 yard zero, it'll take the same dope to reach a given distance. Where it would differ is where our zero points are in the scopes internal adjustment from its mechanical zero. In long range shooting which are you more likely to run out of, up or down adjustment? If you put a 20 moa base on said rifle and clock the barrel at BDC, your effective correction is 17 moa. Clock same barrel TDC and you've made 23 moa.

Maybe I'm just not getting it, how about showing the math?
 
#81
Re: Barrel timing questions

Bohem,

I'm speaking of taking advantage of what is already there. I know we are splitting hairs on this topic and as your real world example demonstrates it doesn't make a hill of beans differnce in it's effect, but my view is "why not"?


edit: this was in response to the post that was just deleted.
 
#82
Re: Barrel timing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body">The guys that get blue in the face telling the rifle builder how the pipe fitter should do his job are far more oft than not someone that needs to spend less time arguing about how it "might" affect it and a LOT more time out shooting. </div></div>

This.

I built a 243 on a 700 action and I clocked the barrel to 12:00.
After 1850 rounds, I chopped 2" off the back of the barrel and then fitted that same barrel into a surgeon action.
Again, I clocked the barrel to 12:00.
I took the same scope off the 700 action without re-zeroing it and mounted it on the surgeon action.

I only had to adjust the elevation about 1.5 moa to get the new gun re-zeroed.
The windage zero was perfect.

What this tells me is that the 700's scope mount screws must have been pretty damn centered and my truing job on the 700 action was pretty good too.
 
#84
Re: Barrel timing questions

I agree, "why not"...

However, I don't agree that if a gun builder says "I didn't do it" that I would tell him he's lost my business. My concern is that the thing shoots and I consider "shoots" starting at 1/2 MOA consistent groups.

If a guy can build me a rifle that day in and day out cuts paper at 400+ with groups under 1/2 MOA then we both did our job.
 
#87
Re: Barrel timing questions

Yaa "You're". Hey Im not too bad at spelling.


Speaking of shooting more... I havent got to fire my rifle in months
frown.gif



Bryan, I agree with "why not do it" since the barrel is already off and in the lathe anyways.
But I sure hope the guys that think its a must, also have their scope base holes trued every time and take every other measure out there to ensure a true rifle because they all matter more than barrel runout it seems.

I dont see many people with trued base holes and 8-40s in there. Of 25 guys at any given match, 17-20 will have Remys, and of those 17-20, I bet only 1 or 2 will have their base holes opened up and trued to bore.

Like I said I encourage this service and will try to talk every customer into it. It has to be done after the action is trued, but before the barrel is installed.
 
#88
Re: Barrel timing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Keith at PCR</div><div class="ubbcode-body">I dont see many people with trued base holes and 8-40s in there. Of 25 guys at any given match, 17-20 will have Remys, and of those 17-20, I bet only 1 or 2 will have their base holes opened up and trued to bore.

Like I said I encourage this service and will try to talk every customer into it. It has to be done after the action is trued, but before the barrel is installed. </div></div>

How are you determining where the true top of the receiver is when you re-locate the screw holes?
Are you using the 1/4-28 bottom holes as the true bottom and then just setting a receiver mandrel in v blocks to find the true centerline?
 
#89
Re: Barrel timing questions

No I go off the raceway, by going off the bottom of the feed lips.
I use a surface ground block that fits under the action, inside the mag port, with the action sitting on its feed lips. This keeps the raceway flat(if you set a parallel in there on it, it is flat is what Im talking about)...

So with the action sitting on that surface ground, parallel/flat to about .0003" block, I tighten it in the mill vise gently but securely keeping it flat down against it.

I then slightly loosen the nuts on our rotating table under the vise, screw my mandrel in that has a .650 shaft that is perfectly square to its shoulder that mates up to the lug abutments (which remember are square to the raceway, face, and threads by this point), then I indicate the action in using the .650 parallel(zero taper) shaft that is square to the receiver lug, face, and raceway.

Once thats done I use an end mill ground to the 8-40 pre-drill size to open the holes up. That way it doesn't follow the hole but creates its own.
After each hole is plunge milled I tap it using the spindle to guide it along Z without ever moving X or Y.
Then I move onto the next hole and repeat.

 
#90
Re: Barrel timing questions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Keith at PCR</div><div class="ubbcode-body">No I go off the raceway, by going off the bottom of the feed lips.
I use a surface ground block that fits under the action, inside the mag port, with the action sitting on its feed lips. This keeps the raceway flat(if you set a parallel in there on it, it is flat is what Im talking about)...

So with the action sitting on that surface ground, parallel/flat to about .0003" block, I tighten it in the mill vise gently but securely keeping it flat down against it.

I then slightly loosen the nuts on our rotating table under the vise, screw my mandrel in that has a .650 shaft that is perfectly square to its shoulder that mates up to the lug abutments (which remember are square to the raceway, face, and threads by this point), then I indicate the action in using the .650 parallel(zero taper) shaft that is square to the receiver lug, face, and raceway.

Once thats done I use an end mill ground to the 8-40 pre-drill size to open the holes up. That way it doesn't follow the hole but creates its own.
After each hole is plunge milled I tap it using the spindle to guide it along Z without ever moving X or Y.
Then I move onto the next hole and repeat.

</div></div>

Gotcha.
I don't have one of those rotation bases for my mill vise.
I do have a 1/2" ground rod and lots of bushings for my ptg 0.705 reamer though so I setup the receiver on v blocks.

I use a 9/64" endmill when I plunge the holes for the same reason you do.
It's within about 0.0001" of the nominal drill size for an 8-40 tap so I figure that will do...
 
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