Unfired SD/ES better than 1x Fired SD/es
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Mikecr
Well-Known Member
This is why you should never load develop with new brass.
Fired brass is different in capacity, so it makes sense the load performance would be different.
46.2gr with new brass is probably higher load density than 46.2gr in fired brass. So if you increment up in powder with the fired brass, you should regain the original load performance.
Fired brass is different in capacity, so it makes sense the load performance would be different.
46.2gr with new brass is probably higher load density than 46.2gr in fired brass. So if you increment up in powder with the fired brass, you should regain the original load performance.
Unfired vel: 2909
Fired: 2927
I would have thought the fired would be slower than unfired because of greater case capacity.
Same lots of bullets, primers, powder but different boxes from those lots.
I agree the the performance should be different but in my case the fired brass is faster. I did the initial dev. w/ 1x fired brass but tested the load w/ unfired after settling on a 1x fired load because I have a bunch of unfired brass.
FYI, all brass was uniformed, deburred, trimmed, neck turned and weight sorted into .5gr lots.
I used to think that too. It's not the virgin case capacity. Case capacity is only relevant when measured against your chamber dimensions. You should only care about fireformed case capacity.
The reason why fireformed case velocity is higher is because the powder does not have to expell energy to fireform the case to the chamber. That amount of energy is instead used to propell the bullet. Hence, the velocity is higher.
Why is the ES higher? It could be your scale is not repeatable and the initial low ES was a fluke. Could be that the neck is no longer as clean and soft as when it was new and the tension on the bullet is not as consistent. It also could be that particular powder charge does not generate a small ES in fireformed brass. You may need to tweak it.
A lot of variables influence ES. It's not just powder charge consistency.
That's interesting about virgin vs fire formed and pressure. I use a prometheus to measure powder so I doubt its the scale. I'll have to retest the velocity with that charge.
Not sure if it matters but I just had the barrel set back after 4500 rds. My pre-set back LR load was 46.4gr. that gave me SD/ES of 2/6. I was hoping to regain those numbers.
I do have a charge (45.8gr) that gives me a 1x fired SD of 4. I tested it this weekend from 100-300 yds. group size at 300 was about .8". The reason that I didn't just call it good with that is that 100 yard groups are better with the 46.2 and I was hoping to make that charge work for long range as well.
I bet if you stainless tumbled, then annealed, then FL sized using a small base die, then stainless tumbled again you would end up with similar to virgin brass. It would have nice clean soft necks and almost the same dimensions as new.
That's what I do. The best ES I have seen in my 308 was 11, but my RCBS scale is not accurate to one kernel, just three kernels, and it doesn't always happen. I can usually keep it under 20 though.
Setting back your barrel creates a brand new sharp leade. That will affect your load also.
But virgin velocity being lower is a fact. Can't get around that. A lot of people don't see it cuz they don't chrono every shot. By the time they get around to it the brass is reloaded. And there might not be any POI shift.
That's what I do. The best ES I have seen in my 308 was 11, but my RCBS scale is not accurate to one kernel, just three kernels, and it doesn't always happen. I can usually keep it under 20 though.
Setting back your barrel creates a brand new sharp leade. That will affect your load also.
But virgin velocity being lower is a fact. Can't get around that. A lot of people don't see it cuz they don't chrono every shot. By the time they get around to it the brass is reloaded. And there might not be any POI shift.
Thanks. Ill ha e to try as tumbling and annealing.
Capt. D
Well-Known Member
Kind of a related question. Will you see pressure signes sooner in virgin brass or once fired brass. From this discussion leads me to believe that load developement, including finding max pressure should be done after fireforming.
No intention of hijacking a thread, seems related in my mind. Thanks
No intention of hijacking a thread, seems related in my mind. Thanks
Bill123,
I suggest we back up a little here.
First of all, how many shots did you take to determine that your unfired brass SD was 4? Or that your fired brass SD is 9?
We need to understand what SD is really telling us before we use it to investigate our reloading process. This bit me when I was load developing for a 7mag and if I new then what I know now I could have saved myself some frustration.
I'm going to skip to the end and save some suspense and just tell you that with a small sample size of 5 or 10 rounds you really don't know what your true SD is for whatever reloading technique you are using.
To make a long story short, if you fired a ten shot string to calculate the SD, then mathematically we would have 95% confidence that the REAL standard deviation of your load would be somewhere between two thirds and approximately two times your sample SD. So if you fired a ten shot string to collect your sd data, with a perfect chronograph, with 95% confidence the true SD of your unfired brass loads is somewhere between about 2.5 and 8. It could be anywhere in there. For the fired brass with same assumptions it is somewhere between 6 and 18. It is quite possible that the fired loads do have a true sd that is better than the unfired. If you only used five shot samples, then we have far less confidence since the distributions we would expect would overlap even more.
We haven't even addressed chronograph error, since that will reduce our confidence (and is certainly present). Also an outlier can really skew our sd calculation in a small sample size.
Bottom line, statistical tools like SD really don't tell us much until we get to at least a sample size of ten, and even then we can only estimate that it is within a range of about two thirds to approximately double the SD calculated from that sample.
This is the reason that 3 shot groups can lead you astray as well. We shouldn't read too much into what SD is telling us for small sample sizes.
I found experimentally that the real sd of my 7 mag load is better than what I first measured with a small 5 shot sample, and I wasted a lot of time trying to improve what wasn't really broken. We shouldn't have too much confidence in either a really good or really poor result from a small sample size.
I suggest we back up a little here.
First of all, how many shots did you take to determine that your unfired brass SD was 4? Or that your fired brass SD is 9?
We need to understand what SD is really telling us before we use it to investigate our reloading process. This bit me when I was load developing for a 7mag and if I new then what I know now I could have saved myself some frustration.
I'm going to skip to the end and save some suspense and just tell you that with a small sample size of 5 or 10 rounds you really don't know what your true SD is for whatever reloading technique you are using.
To make a long story short, if you fired a ten shot string to calculate the SD, then mathematically we would have 95% confidence that the REAL standard deviation of your load would be somewhere between two thirds and approximately two times your sample SD. So if you fired a ten shot string to collect your sd data, with a perfect chronograph, with 95% confidence the true SD of your unfired brass loads is somewhere between about 2.5 and 8. It could be anywhere in there. For the fired brass with same assumptions it is somewhere between 6 and 18. It is quite possible that the fired loads do have a true sd that is better than the unfired. If you only used five shot samples, then we have far less confidence since the distributions we would expect would overlap even more.
We haven't even addressed chronograph error, since that will reduce our confidence (and is certainly present). Also an outlier can really skew our sd calculation in a small sample size.
Bottom line, statistical tools like SD really don't tell us much until we get to at least a sample size of ten, and even then we can only estimate that it is within a range of about two thirds to approximately double the SD calculated from that sample.
This is the reason that 3 shot groups can lead you astray as well. We shouldn't read too much into what SD is telling us for small sample sizes.
I found experimentally that the real sd of my 7 mag load is better than what I first measured with a small 5 shot sample, and I wasted a lot of time trying to improve what wasn't really broken. We shouldn't have too much confidence in either a really good or really poor result from a small sample size.
KYPATRIOT thanks for the great info. How many separate loads do you chronograph when developing? I've been OCW testing, finding a range of loads then chronographing 5 rounds of each load in the range to pick the best one. With 10+ rounds each, that's a lot of shooting. Any suggestions on shortcutting?
Well it depends on the confidence level you want. If you want to KNOW what the real SD is you have to shoot a lot...and like you said that adds up quickly. The point of my post is that with five shot sample sizes you can't really say with much confidence that the unfired brass is really shooting tighter spreads than the fired brass...it is very possible that it just happened that way for those two strings. So don't put too much effort into changing things just because of two five shot strings.
What I would do is to pick a load, shoot a string to get your velocity for the ballistic calculator, and run the load and see how it shoots. Instead of wasting rounds at 100 yards with a chrony shoot it at distance and get a feel for how much vertical you are getting. Collect this data the same way you would SD and ES and use it the same way. If you don't like the amount of vertical you are getting in your long range groups then go back and change something. You will have learned that your velocity isn't as consistent as you like and along the way you will have enjoyed the shooting a lot more and probably improved your wind calls.
Bottom line, shoot it at range for awhile and see if you really do consistently get the kind of vertical spread the SD would have you believe. To really know for sure, you need much larger sample sizes and you might as well get the data through real world long range shooting rather than data collection at the bench, unless that is just your thing. If you collect data and record all your shots, load development never really ends lol.
What I would do is to pick a load, shoot a string to get your velocity for the ballistic calculator, and run the load and see how it shoots. Instead of wasting rounds at 100 yards with a chrony shoot it at distance and get a feel for how much vertical you are getting. Collect this data the same way you would SD and ES and use it the same way. If you don't like the amount of vertical you are getting in your long range groups then go back and change something. You will have learned that your velocity isn't as consistent as you like and along the way you will have enjoyed the shooting a lot more and probably improved your wind calls.
Bottom line, shoot it at range for awhile and see if you really do consistently get the kind of vertical spread the SD would have you believe. To really know for sure, you need much larger sample sizes and you might as well get the data through real world long range shooting rather than data collection at the bench, unless that is just your thing. If you collect data and record all your shots, load development never really ends lol.
