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Posted: 1/5/2011 3:19:07 PM EDT
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I wanted to see what other people's experience has been on this one...
Background: I have been reloading for about 2-3 years now with a RCBS Rock Chucker using RCBS competition dies for .223 and .308. My question is, what is typical for deviation in overall length after seating the bullet? With the .223 die and Hornady 75gr HPBT bullets I typically see ±.003" deviation. In some cases it will be .010" from the target length. For the .308 with 175gr SMKs or HDY 168gr BTHPs, I have seen about ±.002" with an occasional ±.005" I have also notice that the seating die does not always contact the bullet the same distance from the tip on every round. Now I have to assume that since the diameter of the seating die does not change, then the die is contacting the bullet at the same diameter on every round. When I first started reloading and was building up test rounds, I adjusted the die with every round so the overall length was the same to within .001". Nowadays, I set the die for a nominal overall length and ignore the deviation if it's within .005". The thought being that the die is engaging the bullet at the same diameter on every round, so when the round is fired, the bullet travels the same distance to engage the lands and grooves. Does this make any sense? |
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You should never readjust the seater to get every cartridge to the same COAL. That means the bullets are inserted into the case at different depths.
The seater touches the ogive of every bullet at the same diameter, except for some old seater stems taht were too short inside for modern high BC or VLD type bullets and they contacted the meplat - that's no good. By now you should have noticed the great variation of the length of HPBT type bullets - measure a few. This is caused by the process for closing the jacket, and it's not real precise. If your measurements are good, you've been buying exceptional bullets. Adjust the seater to reach the desired COAL. A tweak might be needed for a magazine, so they cartridges will run through correctly. Then don't touch the seater. |
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Not that I measure from the tips but I checked some 75gr BTHP loads I loaded in new Hornady brass with my Redding Comp seating die for you just to get an ideal of the tip length variation. I'm ordering a melplat trimmer soon just to see what it does if anything for accuracy.
2.258" 2.261 2.257 2.260 target length by the way(Sinclair comparator length 1.8160" on all rounds) 2.260 2.260 2.261 2.259 2.2605 2.258 2.260 2.2605 2.261 2.258 2.261 2.260 2.260 2.261 2.261 2.260 I thought I picked the longest bullet to set the seater die but it looks like I was .001" shorter than the majority of the longest ones, they still feed and function from my p-mags fine and are only for range use so it doesn't bother me with these rounds(I usually seat at 2.255" don't remember why I picked 2.260" that time). ETA again: Sinclair bullet comparators measure to the bullets bearing surface(why the length is so much shorter than the Hornady comparator) and are really for bullet sorting but that is also a consistent length on most all match bullets(hence why they use it to sort match bullets) so I use it as well for a bullet seating comparator. |
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Quoted:
Quoted:
I'm ordering a melplat trimmer soon just to see what it does if anything for accuracy. Be sure to get a meplat trimmer that references to the ogive. I bought the David Tubb. http://www.davidtubb.com/tcom_images/reloading/bmu_one.html I was going to get the Sinclair model, I'm sure it will be correct but thanks for the tip. |
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