PT, What an intriguing question! Of course, I think we have to consider at least four factors: a) calibre, b) brass manufacturer, c) type of propellant, and d) weight of the projectile. I, for instance, am deeply concerned with this problem as for the newest cartridge I shoot . . . the .338 Lapua Magnum. But I'm still not even close to a conclusion after having fired a 200 piece allotment 5 times at pressures I believe are pretty much full (industrial) strength. The load incorporates a 250 grain Match HPBT and 89.5 grains of Vihta Vouri N560. The MV averages 3065 fps from a 28" Lothar Walther barrel. What are you shooting?
Not shooting anything special really. Just a remington vls in 260. It was incredibly accurate, with consistant groups from .375 down to under a quarter inch. Recently though, the accuracy is suffering and I believe it is because of the brass. The chamber is on the loose side and I have to full length resize every time to get the cartridge to chamber. I am going to try new brass and see if it comes back. Anyone else have an idea when brass starts to loose its best accuracy?
You have phrased your question in a way that makes it a little difficult to answer. Strictly speaking there is no direct relationship between the amount of times a case has been fired and accuracy. If it is not work hardened at the neck a case can be fired many times with very good accuracy. The less pressure you apply during firing and the less you work the brass during resizing, the longer it will last. Cases have been known to be very accurate at 20, 30 ,40 and more firings. Some folks will anneal their case necks when they harden to extend the case life.
What makes a particular case accurate is it's uniformity of performance with regard to other cases. Case weight is important, case wall thickness especially in the neck is also important. Some benchrest shooters go to extreme lengths to insure case uniformity. This includes workhardening so cases need to be segregated according to how many times they have been fired.
As you stated that you are full length sizing for each reload, this is as important a factor in any case workhardening as the firing itself. Different manufacturers resizing dies work the brass much more than others. Also, your resizing die could be inducing errors with each use.
In short range BR shooting, it is common for competitors to shoot the same cases until they are substantially work hardened. Given these guys are looking for “ultimate accuracy” at 100 and 200 yards, it would seem the answer is that accuracy is not affected.
However in a recent interview published in “Precision Shooting at 1000 Yards” Bill Shehane is asked if case life makes a difference to accuracy in 1000yd BR. He answers that it does and that he only uses a case 4-6 times (I don’t recall the exact number and the book is not to hand right now) before he puts it aside for use as a barrel warmer. I find that pretty depressing news, considering how much work I put into prepping each case!
as far as i can see, ther´s no change if Brass is loaded several times. I´ve a Box of 50 Rounds that i only use for competition. It´s a .30-Cal.Wildcat based on the .338 Lapua. Looking to my reports i´ve loaded them 22 times and still able to keep all of them "in the Black" at 800 Meters. To me, as i´m using "hot" Loads (185grs.Berger´s at 3240fps ) the most important thing is the Quality of the Brass.And so the Lapua is just "outstanding"..