Procedure, technique, question/evaluation (comments welcome)

N

NesikaChad

Guest
Oky doke. I have a Winny that a guy sent me to have a new crown put on. No biggy there. Through the course of the conversation he also mentioned that his scope base (adjustable style) is burning up the vast majority of it's travel range in order to maintain a mechanical/no wind zero.

I agreed to take a looker at his action and report what I found and correct it if needed.


So, here's what I got. I mounted by B/S .00005" resolution indicator to the bottom of the spindle on my mill. I mounted the action in the vise, inserted a mandrel that fits super snug and indicated down the side of it while banging away on the vise with a mallet till the mandrel (bore center) was running parallel to the X axis of the machine.

Next I got out the gauge pins and sorted through them till I found one that would barely go into the base hole. I have to really yank on it to get it back out.

I then just laid the stylus against it and zero'd the bezel on the indicator using the Y axis jog on the machine. Then I went to the next hole, inserted the pin and ran the machine in X only just to see what the deviation is on the indicator. I repeated for the remaining two holes.

I checked it twice two ways. Using the DRO of the machine and zeroing the position of the indicator each time with the Y jog and by just leaving the Y alone and moving in X only and taking a direct reading off the indicator.

They didn't mirror one another exactly, but it was pretty dern close. Within a couple gillionths. I don't expect absolute repeatability as I am dealing with moving parts. I do however feel pretty confident that I'm getting a reasonably close (within .0005") idea of just how parallel the base holes are to the centerline of the receiver.

With the front hole at zero the rear hole was +.0024" The middle ones just followed suit incrementally.

I've included a few photos to illustrate what I'm trying to explain.

I guess my question is, I've never done it this way before (I'd always swept the holes on pins prior) but I don't really see any reason why it's flawed or skewed. From what I can tell the problem does not lie with the receiver holes. The center to center distance on the outer holes is 5.25" inches for this particular action. At 1000 yards a one minute of angle deviation comes out at .0015" at this distance (5.25"). With the action at .0024" I'm going to call that 1.5 to 1.75 minutes at the most. (I'm too lazy to go back and figure it out)

What I'm getting at is the math isn't pointing towards the base holes as the culprit for why he's eating up most of his lateral adjustment on his base.

Just for giggles I left the action in the vise and ran the indicator across the face of the receiver. I get a deviation of .0004". Again, it's not looking like its an action problem.

I conclude either his barrel is a bit crooked or there's something wrong with the scope or bases.

2nd opinions are never a bad thing though so feel free!

Thanks germs!

C

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If you cut a tenon, with a slight taper, and shoulder on a piece of stock, by trial and error, to that the taper prevents the face of the action reaching the shoulder, leave it in the chuck, screw on the action, and then insert a tight fitting mandrel into the action from the rear, till it touches the tenon, what is the runout of the mandrel at the end of the tang, and how uniform is the Gap at the action face?

Once a long time ago, I was trying to bore site a factory .224 Weatherby, from the bench, on a private range. I can usually get on paper at 100 yards this way. With this one, the barrel was evidently so crooked that I literally had to walk up near the target, take an off hand shot, adjust the scope, shoot again and so forth, and then do the whole thing over at another intermediate distance, before returning to the bench to finish. Looking through the barrel, you couldn't see the problem.
 
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Chad, You could mount the base, with the action still in the vise, asuming it's a picatiny style and sweep that.

You could also look into the barrel issue by reinstalling it and measure the bore centerline at the muzzle, compared to your action after vised and indicated straight. Or based on Boyds idea indicate the barrel thru the headstock and screw the action on , plug in the manderal and take a read on it.

I agree a bit with your findings, in that many first assume the scope base holes MUST be drilled out of center if they are running out of windage! More often it can be somthing else.
 
Sticking a pin into a threaded hole is hardly an accepted means for taking accurate measurements. jus sayin
 
Greetings,
I would take a look at the barrel tenon and the receiver face. Factory barrels get their tenons turned concentric to the outside diameter not the bore center, sometimes the tolerance stacking gets out of hand. Toss in a little receiver face run-out and you now have yourself a “major malfunction” if those stack as opposed to cancel.

Nic.
 
Chad, it seems to me it has be in the the rings and or bases or the barrel is bent or possibly a scope problem. Good luck and let us know!
 
Niccolo said:
Greetings,
I would take a look at the barrel tenon and the receiver face. Factory barrels get their tenons turned concentric to the outside diameter not the bore center, sometimes the tolerance stacking gets out of hand. Toss in a little receiver face run-out and you now have yourself a “major malfunction” if those stack as opposed to cancel.

Nic.
Click to expand...


+1
 
Chad...I would install the base on the action and do all measurements...I doubt that .002" is going to give the results you described...my money is on faulty base/ring and scope combo...the scope may have moved the erector tube into the lower portion of the scope tube restricting windage adjustment...if the scope elevation is set for a long range zero...then it is time for some Burris Signature rings with (+ or -) inserts...also as you may know..some better quality hunting scopes just don't have the range of internal (windag/elevation) adjustments for long a range zero...
 
TRA said:
Sticking a pin into a threaded hole is hardly an accepted means for taking accurate measurements. jus sayin
Click to expand...

Chad's methodology is a hell of a lot more accurate than your silly little insulting comment implies, and anybody who bothered to read and comprehend (probably your biggest challenge) what Chad posted would grasp that.

"jus sayin" (sic)
 
I had the same problem on a rifle that i knew the barrel,receiver,and base holes were very close in line.
i did not have enough horizontal adjustment on a new weaver 36x scope.
i clamped a pretty straight piece of 1" aluminum round rod 3' long in the scope rings.
it was real easy to see that the rings weren't in line with each other (the rod was pointing off in right field).
another new set of rings and end of problem.
this particular 22lr rifle does not need any horizontal adjustment when changing from 50yd to 100yd targets.
 
Bill Ohio said:
Chad's methodology is a hell of a lot more accurate than your silly little insulting comment implies, and anybody who bothered to read and comprehend (probably your biggest challenge) what Chad posted would grasp that.

"jus sayin" (sic)
Click to expand...

Bill,
On the contrary, what TRA says is true. Taps can wander relative to the drilled hole so that the threads are deep on one side and shallow on the other (been there, done that, unfortunately). When this happens, a pin inserted into the threaded hole is not concentric with a screw threaded into the same hole. Still, indicating and comparing two pairs of holes lowers the chances that this possible source of misalignment is the problem (there is a smaller chance that both front holes, say, were tapped off in the same direction than one hole).

Chad,
Your setup is impressive and I admire your attempt to track down the source of the error. I will look forward to reading what you find. As you probably know, some scope rings are made offset on purpose, so that reversing one will often bring a scope back towards its center of adjustment. But when this works, you don't get the satisfaction of knowing what the problem was. Good work and thanks for posting.

Keith
 
I don't know where Chad was placing the stylus on the pins. The reading will be the most accurate if it is placed as close to the action as posible.
 
by the looks of the shadow on the reciever created by the stylus; very close to the reciever in the first couple pics. last pic looks like 3/16th or so up from the reciever, but that too will depend on the angle of the light creating the shadow. Looks like the last 2 pics are the rear reciever ring and thus it is lower than the front Reciever ring creating the extra space.
 
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1. How much was the base adjusted over. How much off center?

2. Where were the scope settings set at? And in what relation to the base offset?

3. At what yardage was this being checked at?

4. I've seen people start adjusting a scope base over, not knowing which way the shot will go and they adjust the scope the other direction. all the while calming the rifle is crooked.

5. The amount claimed off center would be quite obvious considering that .0024 is only about 1.5moa,

6. What you are looking for would be so obvious that it could be nailed down using a machinists scale, unless its the barrel then there could be many things wrong that your not gonna fix anyways

7. If the mount appearers to be straight on the action. and an angle plate and a scale could verify that it is, Then its more likely the scope, or barrel ,both items not readily repairable.

8. This could easily be one of those cases where someone misunderstood which way to move a base VS which way to move a scope.

9. The moral of this is, that unless thats a 1000yd group rifle, then your ultra precise
measurements may be a waste of time

10. Me thinks your going overboard to find a flaw or mis bored hole that will return this rifle to a winner. when the cause is more likley improper adjustment at the base and trying to balance it out with the scope adjustment.

Whatever you are looking for will be easy to see, it has to be bigger than thousands, to cause that much off target.
 
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First, thanks for the responses. By and large very constructive.

I don't have the base/rings/glass. He sent me the B/A to be recrowned. In a followup email he asked that I inspect the holes.

I agree for the most part that a pin in a hole is not the most accurate way to find location. However when the customer is talking about a minute of angle error to the order of half the target carriage at 100 yards I'm looking for a gross and blatant deviation. I can live with a pin being +/- .002" to .003" out of true position as I'm looking for values that are an order or two larger. As I showed the most I saw was .0024" and it was pretty linear from the first hole to the last. Considering the volume that these actions are produced I'm rather impressed it was that good to be quite honest. Once again a testimony to modern manufacturing.

I'm just doing what the guy asked and I wanted to make it as thorough as I could for the money I quoted the work at. I could have sent it to a metrology lab and had it dinged out on a CMM. Kinda silly though. After crowning the barrel I noticed that the bore is quite a bit off (concentricity) from the OD. It's favoring one side noticeably. Considering its a magnum and the customer shoots the gun often there may be several facets to this little problem. I personally too feel its residing mostly in the base/ring/glass combination. It may also be a barrel that has a curve to it. There is something to be said for timing a barrel in the vertical plane. I try to do this with all my barrel jobs.

Casting all this to the side for the moment, he's very pleased with the accuracy of the rifle (I didn't build it) overall. According to him it shoots very well. He just didn't like the crown because it's a working gun that he uses a lot. he was concerned it would take a beating in the truck.

So, I guess we'll really never know as I don't have the other components. I do feel pretty confident that my analysis was close enough to rule out the action being the culprit.


Thanks again.

C
 
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Could this not be cause by a barrel being set up in a headstock for chambering like Mr Gritters prescribes and then not being indexed properly so the "run-out" is either at 12 O'clock or at 6 O'clock?

I have a friend with a 270 Hunting rifle that has this condition. He used a set of Millett Angle Locks. Front set all the way left and rear set all the way right. It maintains "minute of deer" out to about 200 yards. Then all bets are off.......
 
RoyB said:
Could this not be cause by a barrel being set up in a headstock for chambering like Mr Gritters prescribes and then not being indexed properly so the "run-out" is either at 12 O'clock or at 6 O'clock?

I have a friend with a 270 Hunting rifle that has this condition. He used a set of Millett Angle Locks. Front set all the way left and rear set all the way right. It maintains "minute of deer" out to about 200 yards. Then all bets are off.......
Click to expand...


"There is something to be said for timing a barrel in the vertical plane. I try to do this with all my barrel jobs."

I think were saying the same thing. . .
 
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