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Posted: 8/6/2016 7:55:20 AM EDT
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I picked up a nice set of calipers last week and wanted to recheck some measurements I had taken with my Hornady calipers. I just got don't checking my lands measurements and found what I would call a significant discrepancy.
The old base to ogive measurements averaged 2.322". When I checked today, the base to ogive measurement averaged 2.346", so a difference of about .024". The first set of measurements was taken when the rifle (Tikka CTR 260) was brand new never fired. The second set today is after 60 rounds and 3 cleanings. Both times I used the Hornady OAL gauge, Hornady modified case, Hornady bullet comparator, Lapua 123 Scenar, with the only difference being the calipers to take the measurements. However the calipers tested side by side are only .001-.002 difference. Does this amount of movement sound right for this number of rounds? I can't think of any reason I would be getting this large a difference from my equipment or technique. |
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That's a really significant shift. I suspect most people only see that sort of erosion after at least a thousand rounds of barn burners, which leads me to believe that there's some operator error here. I've found that my Hornady OAL gauge is really finicky. On my 6.5, it took lots and lots and lots of measurements until I was doing it consistently enough to get measurements I was happy with. I can also tell you that the Hornady comparator with .264" bullets is easy to take a measurement with the bullet cockeyed in there, giving you wildly varying measurements.
If you've got a load you're happy with, keep shooting it until you have some real erosion. If you haven't picked a load yet, just go back through the load development process with your new calipers unless you just don't want to use them. Consistency in measurement is key to getting good results, and a big part of that is using the same equipment every time. Edit- I just thought about this. Load up a single test round to your new BTO length using your new calipers, and see if it chambers happily. If not, just use your old number. If so, then it's probably wise to start the process over. |
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Quoted:
That's a really significant shift. I suspect most people only see that sort of erosion after at least a thousand rounds of barn burners, which leads me to believe that there's some operator error here. I've found that my Hornady OAL gauge is really finicky. On my 6.5, it took lots and lots and lots of measurements until I was doing it consistently enough to get measurements I was happy with. I can also tell you that the Hornady comparator with .264" bullets is easy to take a measurement with the bullet cockeyed in there, giving you wildly varying measurements. If you've got a load you're happy with, keep shooting it until you have some real erosion. If you haven't picked a load yet, just go back through the load development process with your new calipers unless you just don't want to use them. Consistency in measurement is key to getting good results, and a big part of that is using the same equipment every time. Edit- I just thought about this. Load up a single test round to your new BTO length using your new calipers, and see if it chambers happily. If not, just use your old number. If so, then it's probably wise to start the process over. I took multiple measurements both times I did the check. I've checked six different projectiles and did each projectile a couple times to ensure a consistent measurement. The first time I did this I also checked multiple projectiles and did each one multiple times until I could get a consistent result. My measurements ranged from 2.321-2.324 the first go around and 2.344-2.347 today. |
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Quoted:
That's a really significant shift. I suspect most people only see that sort of erosion after at least a thousand rounds of barn burners, which leads me to believe that there's some operator error here. I've found that my Hornady OAL gauge is really finicky. On my 6.5, it took lots and lots and lots of measurements until I was doing it consistently enough to get measurements I was happy with. I can also tell you that the Hornady comparator with .264" bullets is easy to take a measurement with the bullet cockeyed in there, giving you wildly varying measurements. If you've got a load you're happy with, keep shooting it until you have some real erosion. If you haven't picked a load yet, just go back through the load development process with your new calipers unless you just don't want to use them. Consistency in measurement is key to getting good results, and a big part of that is using the same equipment every time. Edit- I just thought about this. Load up a single test round to your new BTO length using your new calipers, and see if it chambers happily. If not, just use your old number. If so, then it's probably wise to start the process over. Yeah I will definitely do this. I am also going to measure some 130 Bergers and 123 Amax and see if I have the same error. |
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Quoted:
Did you use the exact same bullet for both first and last measurements? If not that's a contributing variable. Throats always get long with use. Not the exact same bullets, but from the same box. I also measure bullet lengths base to meplat and base to ogive. The largest base to meplat variance I have measured is .005 and the largest base to ogive was .003 across three different bullet manufacturers. Even doubling those measurements would not meet the +.020 change between the two sessions. |
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I would expect about a thousandth of an inch erosion for every 100 rounds.
The Hornady comparator is tough to use and requires a lot of practice to develop a consistent touch. I think I would try sizing the neck of an empty case about 2/3rd's the length so it gets a good grip on the bullet, and then try that. If it sticks in the rifling, give it a really light push with a dowel or cleaning rod, just a feather touch to help it break loose. Polishing the bullet first will allow the origin of the rifling to leave tiny rectangular marks on the bullet. They are hard to see. |
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