Calculating OAL

[Bart B]

Andy, seems to me your chamber's got a long leade, so your best bet for those 155's is to set either one out as far as you can, then maybe add one grain to published loads for it. I doubt there's any difference between either 155 from Sierra; the newer one has a higher BC but that's all in my opinion.

IF your barrel's got a 1:12 twist, you may be in great shape if you load 190's with 42 grains of IMR4064 or 44 of IMR 4320. That longer bullet may just be the ticket to great accuracy in that long leade you've got.

David Tubb shot Sierra 250-gr. HPMK's in his .308 for long range matches one year. His 1:8 twist barrel had an extra long leade/throat so he could get enough IMR4350 in the case to shoot it out at 2150 fps. Bucked the wind very, very well. Very accurate, too.

[boomtube]

"the biggest window I've found to hold this performance has been around +/-3-5thou. Far tighter than 10-20thou."

Just out of curosity, what factory rifles, bulk bullets and cartridges have you found that narrow 6-10 thou seating window in?

[Bart B]

There's another part of the loaded round that'll increase any spread a bullet's reference ogive point measured for seating depth. If a bunch of rounds have a .003" spread in seating depth to that reference, the case headspace spread on rimless bottleneck cases will add to it. Case head to shoulder reference spread is hard to keep under .002". It often has as much as .004 or more depending on the case lube used, how much of it's on the case to be full length sized and how much the reloading press springs when the case is all the way up into the sizing die. After all, those rounds have their shoulder hard against the chamber shoulder when they fire.

[Mikecr]

Originally Posted by boomtube

Just out of curosity, what factory rifles, bulk bullets and cartridges have you found that narrow 6-10 thou seating window in?

This is mostly what I've messed with over the years;
*223- Cooper (1/4moa)
223- Browning
300wsm- Savage
*6br- Browning rebarrel (3/8moa)
6dasher-Savage rebarrel
6XC- Tubb2000 (McMillan)
*6.5wssm- BAT IBS LG (3/8moa)
6.53Scramjet- Savage (Lazzeroni)
*what I currently hold

Bart I have no problem holding headspace, fired or otherwise, to 1.5thou. MINE doesn't change on primer firing.
Boomtube I have no problem holding desired seating depth to lands under 1thou tolerance.
This, because I qualify bullet ogive radius, use only Wilson inline seating, and my neck tensions are measured & matched.
Also, my primers are set to the same depth at exactly the desired crush.
Man, I must be a miracle worker...

To me it seems ridiculous to generalize that these things can't be controlled. They can be, and when they are, it can payoff. If I were to let slip the seating for my Cooper by 6thou either way, grouping would immediately double in size.
Fortunately, I could not possibly be off by so much as 1thou & not catch it through measure.

[Bart B]

Mike, the 3/8th accuracy you're getting with your tools and techniqes, is that MOA at 100 yards?

If so, others have got that accuracy (often better) at 200 yards with no case prep, no load workup, and a few thousandths case headspace spread from standard full length sizing dies since the 1950's. Friend of mine shot his Win. 70 using a single case loaded 57 times full length sizing that case every time and put all of them in under 3/8ths center to center at 100 yards. He probably had 3 to 4 times the slop spread in any dimension you crave.

[boomtube]

"Friend of mine shot his Win. 70 using a single case loaded 57 times full length sizing that case every time and put all of them in under 3/8ths center to center at 100 yards. He probably had 3 to 4 times the slop spread in any dimension you crave."

And therein lies the message; it's usually not all that critical. What I posted about the seating window was just a generalization, not meant to be an iron clad standard for all times and places, amen; saying "I have one that requires ...." is statistically meaningless to anyone else. If we try to make every comment we post include the total of range of extremes nothing we could say would help anyone at all, would it??