That's my take away, which has given me reason to re-evaluate my methods
Chasing the lands is stupid... What do you think?
- Thread starter Erik Cortina
- Start date
That's my take away, which has given me reason to re-evaluate my methods
kindabitey
Gold $$ Contributor
It all makes quite a bit of sense to me. This takes a lot of work out of the process. I have a 223 that shoots Fed. 77 GMM at around 1/2", and that is loaded to mag length.
https://bisonballistics.com/articles/optimal-group-size-for-rifles
"In no situation should you ever use 3-shot groups to get an indication of accuracy. It's just not an efficient way to spend your money or your time."
"In no situation should you ever use 3-shot groups to get an indication of accuracy. It's just not an efficient way to spend your money or your time."
Yeah, but, in most of these methods used for evaluating loads, we aren't just using 3 shots. As Erik points out, he's looking for consistency across at least 2-3 groups. That's 6-9 shots.
I'm sure there would be nothing lost by increasing to 5/10/20 shot groups, other than time/components/barrel life, but why do it if it isn't necessary?
CharlieNC
Gold $$ Contributor
Like the distance to the lands many significant factors are changing over time, many which we do not choose to or are not able to measure. The target should be the primary measurement which dictates something should be done, and of course a major shift in a critical measured parameter can prompt concern. I don't chase the lands but if I happen to check at the end of the comp season and find significant erosion, even if the target is ok I will do a small evaluation +/- charge and seating depth, just to be sure I'm optimized for everything which is changing. Only a few shots needed and it's still practice. On this topic we are dealing with RELATIVE measurements using a COMPARATOR, so the concepts of accuracy and precision are vague.
And neck sizing gives more accurate and consistent head space in my 223 bolt guns! Not so in any others; universal principles are difficult to come by
And neck sizing gives more accurate and consistent head space in my 223 bolt guns! Not so in any others; universal principles are difficult to come by
dcali
Bullet Maker
I shouldn't have worded that so strongly, as it has a specific context - that the groups being discussed in that article are *independent* groups - a simple test to decide if one group is better than another. In most (smart) load development, there is a trend that we can follow (accuracy changing with seating depth or charge weight) that contains information that is useful. That extra information can make multiple 3 shot groups more useful.
They're still inefficient relative to 5 shot groups, but sometimes it's helpful to trade off efficiency for simply getting more groups to look at. Sometimes being able to see a trend of 5 three shot groups is more useful than the extra confidence gained by shooting 3 5-shot groups.
My experience is that the very best loads are relatively insensitive to small variations in seating depth and are also insensitive to different lots of components. A new lot of bullets can always change the distance between where the seating stem makes contact and where the ogive touches the lands. The distance from where the seating stem contacts and the point can also change, which changes OAL.
If you are pulling your hair out over these measurements, I don't really think you're in a "sweet spot."
If you are pulling your hair out over these measurements, I don't really think you're in a "sweet spot."
I don’t want to speak for another man but that’s what I heard him say so as long as it shoots small - who cares where the lands are
stay .001 back from the inside of the seating window until it doesn’t shoot small @Erik Cortina
Correct me if I’m wrong
Ron Gorski
Silver $$ Contributor
I think what Eric is trying to say is after finding the jam measurement he will not measure this again. He will only adjust his seating depth from the accuracy node measurement. He doesn't care how much the lands have worn.
Is this correct, Erik?
DirtySteve
Gold $$ Contributor
Great video Erik. I agree with your method.. lol.. Now I bet you can sleep better.
CharlieNC
Gold $$ Contributor
I will reiterate a point you made because it is highly misunderstood. If you want to compare item A to item B ( group dispersion, velocity, sd, etc) then a significant sample size may be required in order to achieve statistical significance. On the other hand establishing a significant trend vs multiple increments of an adjustment usually requires less data. For example how much does 0.2gr powder affect velocity? Simply loading several bullets with 0.2 different charge may require 10-20 each to achieve significance. On the other hand loading 1 or 2 each at something like +/-0.2, +/-0.5 will provide a highly significant and more useful result. And if you don't care about statistical significance you will end up chasing your tail.
BoydAllen
Gold $$ Contributor
I disagree, with a qualification. Very well done rifles, shot off of the best rests, using flags well, on days where the wind is being kind, tend to be quite consistent. I have such a rifle. With it, I can do preliminary testing at 100 yards, for powder charge using what amounts to a sort of mini ladder test, noting how shots string out or cluster up as I advance through slight increases in charge weight, one shot per charge, on the same target, in the same wind condition for all shots. Once I have identified what I think will be a good charge weight that way (using a seating depth that has done well in the past) I shoot three and then five to verify, and if it checks out, start fiddling with seating depth. Doing things that way, loading at the range, I can sort out a load quite efficiently in an hour or so. I am always amazed at how difficult some seem to want to make this. Again, the rifle, rest, shooting technique, and conditions have to be right to use this approach.
dcali
Bullet Maker
I don't disagree with you, but I will point out that the net conclusion of my article is that if you have 15 rounds to confirm a load, shoot 3 five shot groups, not 5 three shot groups. That's just about the entire point of the article, and perhaps I should have been more clear when writing it.
That said, when I'm doing initial load development, I start with 2-shot groups. The odds of having a good load shoot two very poor shots right out of the gates is so low, that it's very much worth saving the ammo to look elsewhere. If a gun that should shoot in the 2s prints the first two rounds in the 5s, you can go ahead and move on. This is not at odds with the article - the confidence that those two shots represent the load well is still very low. But the probability that a 2 shot group in the 5s will suddenly turn into a 5 shot group in the 2s is low indeed.
CharlieNC
Gold $$ Contributor
Boyd you are saying the same thing Damon said and which I attempted to reiterate above. Looking at behavior across a wide range of some adjustment, such as charge weight, does not require much data for significance. For a ladder this is because the signal you impose (charge wt) greatly outweighs the variability of the response (poi). This is not the same as asking if 0.1 gr charge weight changes the poi of just loading up a few bullets with the 0.1 difference.
If a bullet touching the lands centers the cartridge better, causes a more uniform pressure curve and eliminates the vibrations caused by a bullet slamming into the lands, all three of which lead to less vibrations, why would a more accurate load with a seating that is less than touching be anything other than an indication of a wrong primer or powder charge? What's the reason an off the lands load could be best?
Erik Cortina
Team Lapua Brux Borden Captain
Correct. I only find "jam" so that I stay away from it. If I am limited by mag length, then I don't care where jam is ever. All I worry about is where the rifle shoots.
For example: "Erik, where do you seat your bullets in relation to the lands?"
Me: "I don't know, however, I know my rifle shoots well at 2.150, 2.153, and 2.156, so I seat at 2.155"
Upgrades & Donations
This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.