Have you seen powder adjustments affect grouping so much as bad seating depths?
I NEVER have.. Not even close..
Yes. That's been my common experience. I load with different powders and vary powder charges prior to tweaking seating depths. The only time I've seen seating depth affect accuracy to the same quantitative affect as varying powder charge, was changing from jammed into the lands compared to just off the lands. Other than that, I've not experienced dramatic changes to group sizes by changing seating depth.
I've about come to the conclusion that differing seating depths affect groups sizes due to the changes in muzzle velocity produced by changing the bullet seating depths. What I mean by this, is when bullet seating depth is increased, while maintaining a constant powder charge, MV decreases, and I wonder if this doesn't result in obtaining a good shooting load - in the same way that changing MV by varying powder charge can result in obtaining a good shooting load. I must admit that I've never heard or read anyone else express this concept though.
But changes in powder charge weights can obviously cause a much greater change in MV than changes in seating depths with any given (constant) powder charge. So I primarily alter powder charges in the search for the one-hole-group load. After I believe I've found an optimum powder charge which is yielding MV within the ballpark-range I'm seeking, I may or may not continue to play with different seating depths. The refinement of powder charge alone is usually enough to yield the accuracy I'm searching for.
Hope that makes sense. I mean, you may not agree, but I hope you understand my communication on the subject.
I see just the opposite.
I see optimum seating depth as a prerequisite to further load development, as best seating depth is so regardless of load.
That is, changing powder type or amount of it, does not change best seating. That remains right where it happens to be. So if you're going on to powder adjustments, you should do so at the right seating depth, as determined earlier.
Also, with atleast 3 of my guns, no amount of powder change can demolish grouping like seating changes. I can go from 1/4moa to nearly a full moa with seating adjustments. At the very ugliest, powder changes alone only take to me out to a bit over 1/2moa.
Even bigger still, can be primers, or I should say, incorrect striking of primers..
We try different primers with no particular plan or understanding of why. But a firing pin strike can be adjusted beyond 'adequate', and may be best or worst for one primer or another.
Personally, I think shooters have load development all backwards.
Maybe I'll prove this one day.
The above Thread contains my single experience wherein bullet seating depth caused a dramatic change in group size. Note that I did increase the powder charge slightly in the load with the bullet seated off the lands in the effort to maintain MV consistent with the load that had the bullet jammed into the lands. This was a 28" long lightweight barrel. Fact is, all of my rifles have lighter contour barrels than the majority of the rifles I've observed on display and discussed on this Forum. Simply because my hunting is backpack style - largely due to the terrain where the game is located and the utter lack of roads in Alaska. So I hike considerable distances in and back out.
Are the majority of your rifles in the 11 lb and heavier class (bare rifle - no scope, rings, bipod, etc.)? My primary hunting rifles are between 6 3/8 lb and 8 3/4 lb. I have a couple in the 10 lb range that rarely get hauled out on the backpack hunts. I'm convinced extra load development work is required to get these lighter profile barrels to shoot to their potential. More barrel movement requires honing in on a very stable/steady point within the barrel's motion. When I read of other's load development processes and efforts - or the comparative lack thereof - that quickly yield good accuracy, they are most often shooting rifles with a minimum bare weight exceeding 11 lbs.
So I toss out the barrel weight/contour idea, wondering if that could explain some of the difference in our experiences with bullet seating depth and its affect on accuracy. I'm not at all convinced that the bullet seating depth-caused affect on accuracy is independent of the MV changes caused by the differing seating depths. I have a firm suspicion that modified seating depths and powder charge weights both affecting group size in that common manner - by altering MV.
The way to test this out would be to maintain constant muzzle velocity while varying seating depths, to see if the varied seating depths then result in significant changes in group size. Powder charges would have to be tweaked and all loads chronographed. But I don't have the ammo, money, time, or barrel life to launch this experiment. Let alone that burning desire. So I use methods that seem to work in both a cost & time-effective manner - with my rifles. That's powder selection and powder charge weight, prior to seating depths. Primer brand, and magnum LR versus standard LR has been hit or miss with me. I can't say that I've seen any consistent accuracy affecting trends. I have seen some affects on ES & SD while testing over tandem and triplicate chronograph setups, but all in all it seems to be very rifle and cartridge specific, IME.
My rifles have generally been unique when it comes to load development. What worked with one has no greater than 50/50 odds of working on another. The most one can do is employ some systematic method of load development, keep a good record of the resultant flow of data, and go in the direction of improvement in group sizes. I find it relatively easy to identify and discard some load combinations that are a lost cause, and not deserving any further time and effort. I find it harder to figure out which components and combinations have the best potential to produce an acceptable and satisfying end result. Long range accuracy, while maintaining acceptably low ES & SD, and acceptably low MV variation with temperature swings. It's pretty darn satisfying when it all comes together.
Perhaps other members will provide their experiences, observations, and conclusions.
Your linked observation is right inline with what I see with my guns.
And what I find from that point is that powder tweaks to normalize MV are not needed -to spot optimum seating. You see, I'm not trying to hit on the best load at that point. I'm not fine tuning the overall load. Just finding best seating, before continuing on with powder testing.
There is more going on with seating than we can see.
Many pick distance w/resp to lands right up front, and go through the load development motions as though carved in stone by a divine messiah. Then they tweak seating just a tad for further 'fine' tunning/timing, Then guess what? Optimum seating SEEMS very very close to that they chose right up front, after pre-conditioned with further development... Hell, it might be, for them(never am I so lucky). And their gun might shoot well enough with that process.
But there was no particular reason that chosen seating would happen to actually be the 'best'. There is no formula, rule of thumb, known reason, or rational basis with which best seating could be predicted up front like that.
So they got what they got, and it's canned carvings that they try other bullets, just in case these results aren't good enough. Oh, and we'll do the same thing with primers as well.
Talk about tail chasing..
But this is what I've noticed; Once best seating is actually determined it does not change with other loading parameters. You can go from IMR to VV, from Feds to CCIs, big changing of the whole ballgame, and a quick +/- seating check will show that best is still best.
Yes, adjusting seating affects velocity. It affects the pressure curve on engravement and possibly through tension change(with an extreme). But you'll also notice that those same velocity changes ALONE do not cause the same things that seating does. Targets show they are seperate, and different actions.
A chronograph won't.. PressureTrace won't..
Your MV normalized +/-8thou seating change(which is HUGE) caused a far bigger change to grouping than 5fps alone would cause. This was NOT a 'fine tune'.
I also agree completely with load development being different for longer/lighter contour barrels, over shorter/heavier barrels. And I've found through communications with many barrelmakers that they have no idea how to make an accurate barrel in light contour. They make em all the same, and they are not at all interested in R&D for accurate hunting barrels.
Ruined by the BR market...
This is how we've arrived to a point of so many barrelmakers, with none any better than another. A market so divvied up, and so assimilated, that a better barrelmaker could not profit from it.
Anyway, it won't change. Just recognize that LR hunters need to pay less mind to the ancient carvings, and think for themselves.
Phorwath and MikeCR, I am really enjoying your points. You both bring up some great methods of isolating variables and relying on your known constants. I wish I had both of you right here with me to work up the new .260 AI that is hopefully out of the shop tomorrow. I am pretty good at math and statistics. Loved calculus. Physics was a blast that is why I seem to pour over all of this stuff. But even with what you all have pointed out, there are still variables that have not been isolated or controlled. Hence the "work up" right? For instance I developed a load for my 7mm Rem Mag very much like the article and fell right on the sweet load and the "factory gun" will shoot < .310 outside diameter groups at 100 yds. Move to my Mark V in .270 Win and at how many months of development before I get to acknowledge that the factory load shoots better than anything I can come up with. Throat length? So my question is, considering that I totally agree with both of you and see your points depending upon my situation(how? because I can't get the ideal length of my cartridge in every rifle I own because of magazine length, and I know, I know I can change that), so what is the best way to start? Maybe like on my old 17 enfield that had been sporterized and reemed to 308 Norma Mag. I found the nodes and adjusted in the second node until, with the bullet I am going to use in Namibia, I am shooting sub MOA. Pretty good for a 92 year old lady(the enfield is 92), but factory 180 gr Oryx shoots 1/2 MOA. Again I was limited in my case length room. But the factory shoot better and are at a set length. I guess there are as many variables as there are shooters setting up rifles, shooting different types of targets or game, at different "long ranges?" So I guess it boils down to if we have the luxery of adjusting our OACL we want to find it before we ladder and if not, we can ladder and then tweak the case length? Thanks to you both for your input and keeping it interesting.
Also my quotation marks around long range acknowledges that some of the rifles mentioned above would not be considered long range shooters by everyone. And therefore load development not as exacting but it is done with the challenge of making each one shoot the best I can under the circumstances and in some cases the results are not bad.
Thanks every one that is what I was after I learned a lot. This is what I am going to do. The fcatory win ammo is .080 off the lands that just seams alot to me. So set it at .040 and find both nodds then play with seating depth. But what about the barrle being 20 1/2 " would using faster powder be the right move? thanks agine