Velo Dog
After I bought my .30-06 (ZG47) I purchased 120 rounds of PMP 150gr flat-base ammunition which achieved a 10-shot average measured velocity of 2,671 fps in the 600mm/23.6 inch barrel. I developed accurate handloads with 150- and 165-gr Hornady flat-base projectiles but velocities were somewhat lower than expected.
I was loath to push too far because my rifle appears to have a full size chamber whereas my Hornady New Dimension full-length die (supposedly machined to SAAMI maximum dimensions) sizes the base to less than military dimensions. If you are only shooting to 200m you may as well maximise your case life!
I was getting 2539 fps with 55gr of AR2209 (also sold as H4350) and the Hornady #3031 150-gr flat-base but one day I decided to load some Sierra 150-gr Game King factory seconds (and yes they were cheap) with the same seating depth and powder charge. Average measured velocity increased by 140 fps to 2679 fps. Coefficient of variation (sd divided by average/mean velocity) dropped from .98% to .84%.
I slugged the barrel and came up with a bore diameter of .300 and a groove diameter of .3082. When you have traditional rifling with equal width lands and grooves the groove diameter should be in the .309 to .310 range, to avoid pressure issues with flat-base bullets in the .30-06. YES, the 1903 rifle barrels made at Springfield and Rock Island had nominal .308 groove diameters (some were as tight as .3075, the same diameter as every .30 cal bullet I have ever measured) but they also had wide grooves with correspondingly narrow lands which burned out more quickly than the P17 barrels with their equal width 5-groove rifing and nominal .310 groove diameter. If anyone doubts me, read Hatcher's Notebook, Ch. 1 and 2.
I checked the PMP website and found that the factory test velocity from a 24 inch barrel was 2822 fps, 151 fps higher than my measured velocity. I purchased a packet of Federal Power Shok 150-gr boat-tail ammunition and achieved an average measured velocity ( always 10-shot) of 2,859 fps, 51 fps less than the factory test velocity of 2,910 fps.
Yes, I would be happy to try flat-base bullets in a .308 groove diameter barrel with 5R (as in Russian) rifling but my current .30-06 is best suited to boat-tail bullets and that is that!
Boat-tail bullets minimise drag over long distances but, most importantly, reduce disturbance in the transonic zone which causes so many problems with .22lr HV ammunition when you try to shoot past 30m in the wind and ... that really matters with long range reverse slope firing of machine guns. Look at the problems that the British had, trying to use the inadequate 7.62x51 in the Falklands, instead of the .303 Mk VIII 174-gr boat-tail ammunition that closely matched the German sS 198-gr boat-tail ammunition, introduced in late World War One.
Boat-tail bullets are also good for shooters who cannot afford case cleaning kit like a tumbler, because they feed more easily into dirty cases.
And thank you for your common sense and tendency to stir things up a bit!