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Posted: 1/2/2015 9:22:27 PM EDT
I threw this together tonight, had four Barden Precision bearings from a previous project. Just need to get a dial indicator now.
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Nice work, and on a budget! Will be interested to see your results, be sure to upload pictures 
I've often wondered what the right datum is to measure runout against, if using it to optimize accuracy. It seems to me that unless the brass is a pretty tight fit in the chamber (like bolt gun brass that's been neck-sized only for three or four firings), there will always be a tilt of the case body away from the ejector in the chamber itself of a couple of thousandths with respect to the axis of the bore; I wonder whether that sets a threshold for the noticeable effect of runout on accuracy. I would suspect that one would get a greater benefit from minimizing runout using neck-sized cases than using full-length-sized cases in the same firearm. In that case, I figure using the case body would probably be downright decent, actually. ETA: You might benefit from a stop against which to place the head of the case being measured, to keep it from moving axially. Should be doable with a simple little block or bent tab. |
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Nice work, and on a budget! Will be interested to see your results, be sure to upload pictures
I've often wondered what the right datum is to measure runout against, if using it to optimize accuracy. It seems to me that unless the brass is a pretty tight fit in the chamber (like bolt gun brass that's been neck-sized only for three or four firings), there will always be a tilt of the case body away from the ejector in the chamber itself of a couple of thousandths with respect to the axis of the bore; I wonder whether that sets a threshold for the noticeable effect of runout on accuracy. I would suspect that one would get a greater benefit from minimizing runout using neck-sized cases than using full-length-sized cases in the same firearm. In that case, I figure using the case body would probably be downright decent, actually. ETA: You might benefit from a stop against which to place the head of the case being measured, to keep it from moving axially. Should be doable with a simple little block or bent tab. I have tried to explain this concept several times but heads were too thick, this is why I size to zero headspace, so the case is forced centered into the taper. The cases come out of the gun quite straight and come out of the full length sizing die the same, body, shoulder, neck ID and OD run all with in a couple thou of one another at the same ..."index" mark. Of course some of the brass was born messed up so that is for foulers etc. If you were trying to match the gun by neck sizing only you would have to index it in the gun the same every time to see the benefit. If it was fired at a 12:00 positioned headstamp it would have to fired again indexed at 12:00. Which may really help but it would be impractical. |
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ETA: You might benefit from a stop against which to place the head of the case being measured, to keep it from moving axially. Should be doable with a simple little block or bent tab. Good point. Which end of the case would provide the useful results? Said another way, which end of the case would provide the worst/worthless results? Depending on size and location of the stop the case head might rumble the indicator reading a little due to metal stamping whereas the case mouth would more likely be smooth (all points of the case mouth in the same plane)? A stop at the case head would have to be at least as large as the case head to minimize indicator reading problems from stamping, rim nicks, etc. |
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Good point. Which end of the case would provide the useful results? Said another way, which end of the case would provide the worst/worthless results? Depending on size and location of the stop the case head might rumble a little due to metal stamping whereas the case mouth would more likely be smooth (all points of the case mouth in the same plane)? Quoted:
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ETA: You might benefit from a stop against which to place the head of the case being measured, to keep it from moving axially. Should be doable with a simple little block or bent tab. Good point. Which end of the case would provide the useful results? Said another way, which end of the case would provide the worst/worthless results? Depending on size and location of the stop the case head might rumble a little due to metal stamping whereas the case mouth would more likely be smooth (all points of the case mouth in the same plane)? Here is mine, I have indicated 1500 rounds with itso far and it works well with the stop at the back, and of course at the front you could not indicate the neck ID or seated bullet. 
I hook the rim with my two finger nails and press against the stop pin with my thumb assuring the case cannot move forward. If it moves either direction you wont get a good reading due to the changing diameter of the ogive and/or case taper. 
You are also going to have to make sure the indicator is solidly mounted to the fixture, if the indicator can move independently from the fixture it will give erroneous readings. Looks like your 2 base angles are aluminum if you could bolt that to a rigid piece of steel then you can position your commonly found magnetic base indicator where you like. |
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Another fine question, would a case head stop that is square to the case axis give a more accurate indicator reading than a stop that is square to the roller axis? Might be a useful consideration when chasing .002" or less. You want the case to be riding on the rollers only the head shouldn't effect the reading. The stop is just to position the case. Now if the head was severely crooked it would push the case in and out of the indicator altering the reading but that is a case not worth loading and would have been tossed before this stage. I angled my rollers to the same taper as the case to help keep it in position and when the case is flat in the rollers the base is parallel with the stop too but still with a crooked base it would push in and out. I can easily discern between zero runout and .0005", those are very few but I have seen them. As with any fine measuring it takes a bit of experimenting with your tool to find a good repeatable method . |
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Another fine question, would a case head stop that is square to the case axis give a more accurate indicator reading than a stop that is square to the roller axis? Might be a useful consideration when chasing .002" or less. Theoretically, it doesn't actually matter. Between the two bearings, you are constraining a rotational axis in threespace, which reduces the DOF to 1. Essentially, the axial alignment serves as a primary and secondary datum at the same time, leaving only a tertiary datum, which will (again, theoretically) only be met at a single point. I have a graphic on my work computer that will explain this a LOT better than words can, I'll add it to this post later. tl;dr: No, you should only constrain a single point on the case head. |
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Just seems like it's a real puzzle to separate case neck wobble or seated bullet wobble from case head wobble or even wobble due to a banana shaped case body. Ohhhhhh I used "wobble" too many times in one sentence, it's past my bedtime......  You could do it with two dial indicators, one on the bullet, one on the case, orby 'clocking your readings and taking multiple readings for one rotation on the bullet, then doing so at other locations along the case. This gets into a discussion of GD&T that absolutely terrifies most of my students (and many practicing engineers, unfortunately) |
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I have tried to explain this concept several times but heads were too thick, this is why I size to zero headspace, so the case is forced centered into the taper. The cases come out of the gun quite straight and come out of the full length sizing die the same, body, shoulder, neck ID and OD run all with in a couple thou of one another at the same ..."index" mark. Of course some of the brass was born messed up so that is for foulers etc. If you were trying to match the gun by neck sizing only you would have to index it in the gun the same every time to see the benefit. If it was fired at a 12:00 positioned headstamp it would have to fired again indexed at 12:00. Which may really help but it would be impractical. Quoted:
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Nice work, and on a budget! Will be interested to see your results, be sure to upload pictures
I've often wondered what the right datum is to measure runout against, if using it to optimize accuracy. It seems to me that unless the brass is a pretty tight fit in the chamber (like bolt gun brass that's been neck-sized only for three or four firings), there will always be a tilt of the case body away from the ejector in the chamber itself of a couple of thousandths with respect to the axis of the bore; I wonder whether that sets a threshold for the noticeable effect of runout on accuracy. I would suspect that one would get a greater benefit from minimizing runout using neck-sized cases than using full-length-sized cases in the same firearm. In that case, I figure using the case body would probably be downright decent, actually. ETA: You might benefit from a stop against which to place the head of the case being measured, to keep it from moving axially. Should be doable with a simple little block or bent tab. I have tried to explain this concept several times but heads were too thick, this is why I size to zero headspace, so the case is forced centered into the taper. The cases come out of the gun quite straight and come out of the full length sizing die the same, body, shoulder, neck ID and OD run all with in a couple thou of one another at the same ..."index" mark. Of course some of the brass was born messed up so that is for foulers etc. If you were trying to match the gun by neck sizing only you would have to index it in the gun the same every time to see the benefit. If it was fired at a 12:00 positioned headstamp it would have to fired again indexed at 12:00. Which may really help but it would be impractical. Have you ever had any extraction problems doing that repeatedly (i.e.: do you wind up having to set back your shoulder a bit after a few firings because the cases are too tight in the chamber)? Wouldn't be too hard to put an index mark on the case head, then load the rounds in the mag with the index straight up. I've never thought to measure runout in one of my barrel chambers, might be interesting to see how much variation there really is. |
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Just seems like it's a real puzzle to separate case neck wobble or seated bullet wobble from case head wobble or even wobble due to a banana shaped case body. Ohhhhhh I used "wobble" too many times in one sentence, it's past my bedtime...... The casehead doesn't wobble for one, two the case head doesn't touch the rollers so no up and down and three, again, it would only be very slight when firing and sizing this is getting all straightened out it may not be perfect but it is negligible. Case are fire formed round, there are no banana shaped cases unless your rifle is banana shaped and then you size with a banana, say you step on a case or it has a gouge in it that is VERY apparent when you roll in on the device. With mine I can confirm all points, body, shoulder, neck od, neck id and projectile so if something feels weird or the runout is inconsistent on a particular case I can just check the body to see if that is the problem the body should always read zero runout because that is the part on the roller. |
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Have you ever had any extraction problems doing that repeatedly (i.e.: do you wind up having to set back your shoulder a bit after a few firings because the cases are too tight in the chamber)? Wouldn't be too hard to put an index mark on the case head, then load the rounds in the mag with the index straight up. I've never thought to measure runout in one of my barrel chambers, might be interesting to see how much variation there really is. Quoted:
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Nice work, and on a budget! Will be interested to see your results, be sure to upload pictures
Have you ever had any extraction problems doing that repeatedly (i.e.: do you wind up having to set back your shoulder a bit after a few firings because the cases are too tight in the chamber)? Wouldn't be too hard to put an index mark on the case head, then load the rounds in the mag with the index straight up. I've never thought to measure runout in one of my barrel chambers, might be interesting to see how much variation there really is. What is going to keep it indexed while being stripped from the mag and push into the chamber? It is basically loose during that time. No, when they come out of the gun they are 27 and when I size them they are 27. I let will let the 27.5 pass, 28 requires a bit of force to close the bolt so if I find a 28 I will size it again then it goes to 26.5 but for the most part I am keeping everything tights. Only time I have problem with extraction/bolt lift is when the load is getting near 70k psi. |
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I threw this together tonight, had four Barden Precision bearings from a previous project. Just need to get a dial indicator now. http://www.hotrodders.com/gallery/data/500/medium/DSC_0155.JPG - your homemade rig is OK but adjustments for other cartridges will be laborious. I use the Sinclair gauge that has quick adjust blocks front and back - I like to measure runout at the case neck for empty cases and at the bullet driving bands on loaded cartridges. The pic below from popinfresh shows the tip of the indicator riding on the bullet's ogive, which will produce a smaller TIR number than if placed slightly back onto the driving band - In my experience, with my dies, case necks are typically very close to zero runout, while bullet driving bands will show anywhere from near zero to .005" or so. Assuming the use of high quality bullets, this points to the seater die as the prime suspect when excessive runout is encountered. For me, cartridges with .003" of bullet runout produce about the same level of accuracy as those with near zero runout. good luck - CW |
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Vinny: Here are a few comments . The pic below from popinfresh shows the tip of the indicator riding on the bullet's ogive, which will produce a smaller TIR number than if placed slightly back onto the driving band good luck - CW Quoted:
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I threw this together tonight, had four Barden Precision bearings from a previous project. Just need to get a dial indicator now. http://www.hotrodders.com/gallery/data/500/medium/DSC_0155.JPG . The pic below from popinfresh shows the tip of the indicator riding on the bullet's ogive, which will produce a smaller TIR number than if placed slightly back onto the driving band good luck - CW Wrong, runout will show more the farther from the neck. On a true neck there will be a point inside that is zero runout, if the bullet is slightly crooked from seating, the farther out from the zero greater the TIR. If the case neck id ran out but the seater seated straight then the runout would be greater at the bearing surface/shank of the bullet. If you were using a "between centers" fixture that may also be the case but niether of ours are "between centers" fixtures because we are checking runout not trying to fix it. Posted Via AR15.Com Mobile |
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your homemade rig is OK but adjustments for other cartridges will be laborious. I use the Sinclair gauge that has quick adjust blocks front and back good luck - CW I do not have any investment in my home made unit, I doubt the Sinclair gage is as cheap as mine is.
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