two different lot numbers
- Thread starter misser
- Start date
What are you measuring here? What does each bullet weigh in this example?
The point he is making is on paper it probably doesn't matter. Just go shoot and stop worrying about stuff that does not necessarily translate to results downrange.
Bullet lots have varied since the beginning of time and will probably continue into the foreseeable future. What matters is how they perform. Generally Bergers shoot great across lots same as SMKs. DTACS's (made by sierra) seem to be the exception and no one shoot hornady who cares about their scores so best to just ignore them.
Bullet lots have varied since the beginning of time and will probably continue into the foreseeable future. What matters is how they perform. Generally Bergers shoot great across lots same as SMKs. DTACS's (made by sierra) seem to be the exception and no one shoot hornady who cares about their scores so best to just ignore them.
What you are measuring is akin to the bearing surface but depending on the inserts it's probably not giving a true gauge. Small variations in the ogive radius or boat tail angle will case variations which have no bearing on the performance of the bullet. Small variations in boat tail angle or length has almost no bearing on internal ballistics. While many people profess to see the difference in jump it may not be as sensitive as some seem to see on small sample sizes. That said, consistency in jump is important. What we do know is consistency in CBTO will put the bullet in a consistent jump which does seem to be a very important parameter for precision, probably more so than consistent bearing surface (IMO).
A few years ago I ran a test to get some idea what a difference is bearing surface length makes as I saw a difference between two lots of my 168 SMK's of ~.034" (it being a comparator measurement and not exact measurement of the bearing surfaces). What I found when comparing 20 rounds of the shortest to the longest, there was quite a difference in MV and a shift in POI. But I think one has to have a big difference in bearing surface length to see any such changes. I don't think one going to see enough difference within a lot (at least, not with the higher quality bullets) that would result in something than can be seen on target. . . at least, I haven't seen it with any lot of bullets I've had.
Here's that data taken from my chrono (when my reloading process wasn't as good as it is now
):
You should do a test similar to the above….shoot 20 of each lot seated to the same CBTO and see if you get any difference in stats or on paper at….300 yards or so. I imagine that ogive-to-lands is more important in a same weight bullet than ogive-to-boatail, within reason.
I actually saw this for the first time not too long ago. It manifested itself on my AMP Press. I was seating bullets out of one box of a particular lot, ran out with about 10 to go. I grabbed another box of the same lot and they all exhibited about 10-15 lb more seating force (shown below in orange).
I kept them all separate, but these were for a trip out to the hills and didn't end up recording the difference in performance. But what I did do was contact AMP and asked for their opinion. They saw that the press engaged about 20 thousandths of an inch earlier, leading them to conclude that the new box had a longer bearing surface, so was engaging the case sooner and staying engaged longer, resulting in the plots shown. They suggested comparing the two with a comparator.
If only I had one of the original bullets to compare...
Fortunately, if you want to call it that, one of my rounds out of the original box failed to fire. So I used that as a baseline and measured it against a number of bullets from the new box. They all landed at .020" longer, give or take.
Again, same bullet, same lot, ordered at exactly the same time.
Honestly, I didn't realize the significance until after I got back. Since this was more of a fun trip, I wasn't taking careful notes.
y
yes, all so very true . I do have a box of Barnes 120 gr bullets .then doing a measurement test weight,leight,leight of bearing surface all very close to being the same . and I mean wow close. its the only box I have never tried any more because the gun did not care for them,did not print as nicely as the sierra'a did.
Nice analysis. I've seen the same variance in the 168 SMK )but don't remember the difference) but the rifle I'm shooting it in is a factory barreled Rem 700 so the bullet is jumping a country mile so its hard to compare it to a good competition chamber's effect.A few years ago I ran a test to get some idea what a difference is bearing surface length makes as I saw a difference between two lots of my 168 SMK's of ~.034" (it being a comparator measurement and not exact measurement of the bearing surfaces). What I found when comparing 20 rounds of the shortest to the longest, there was quite a difference in MV and a shift in POI. But I think one has to have a big difference in bearing surface length to see any such changes. I don't think one going to see enough difference within a lot (at least, not with the higher quality bullets) that would result in something than can be seen on target. . . at least, I haven't seen it with any lot of bullets I've had.
Here's that data taken from my chrono (when my reloading process wasn't as good as it is now
View attachment 8715994
This brings up something that has been bugging me for some time and I don't have the equipment to measure seating force. I've been playing with some Hornady 168 Match bullets from a 500 round box. Each 100rds is packaged in a sealed bag. I have noticed that once the bag is opened the bullets tend to tarnish with time as compared to the sealed bullets. Differences in the oxide layer will likely, in theory, change the seating force due to different lubricity. Has anyone seen the seating for change for a given "box" over time after opening?
Definitively a tarnished surface will have a different coefficient of friction than a polished one. I did some Google-fu and found that for copper on copper:
- Clean dry copper sliding on copper has a reported COF of 1.21.
- Oxidized copper, on the other hand, can have a COF of around 0.76.
Anecdotally, this makes sense. As most of us on this site know, clean brass and clean bullets exhibit much higher friction (and variability) during seating.
The question I've got is whether oxidation on the bullet makes much of a difference when you have lubricant in the mix.
I'd be happy to test with something like 20 rounds of oxidized bullets vs. 20 of clean - both with lubed cases and standard case prep - if someone can give me an idea on what would be a sound way to safely get oxidation on bullets.
Similar threads
