Here is QuickLoad's answer on the barrel length question. When I reference the "image", I am referring to the image on Post #1. 12.9 grains of H4895 will generate 7230 psi of chamber pressure and an exit velocity of 1013 fps from a 24" barrel. A 16" barrel will be reduced to 917 fps. Chamber pressure is not affected by the length of the barrel. Fair agreement on the velocity (1057 fps) from a 24" barrel in the image data.
The maximum chamber/barrel pressure (7730 psi) is generated when the bullet has moved slightly less than an inch down the barrel. The vast majority of the powder has been burned at this point. The chamber/barrel pressure at the point that the bullet exits the barrel is 1469 psi. Any powder that is not burned at the point of the Pmax will be burned down the barrel. But it will not contribute to the acceleration of the bullet. As seen from the trace below, there is not enough gases generated from remaining powder to fill the increase of chamber/barrel volume as the bullet moves down the barrel and the pressure starts to drop off. The acceleration of the bullet, as it moves down the barrel is due to the momentum generated by powder burned up to the point of Pmax. See pressure trace below.
The chamber pressure presented for the four powders in the image is questionable. The image values range from 20,700 psi to 27,200 psi. For a 12.9 grain H4895 load for three of the four powders, the range is 7730 psi to 8166 per QL. The fourth powder, Trail Boss is a question by itself. The three powders are fairly close on the Powder Burn Rate Chart, 85-99. As such, you would expect equal charges of powders would generate close chamber pressures. And, in fact, that is what is seen by the QL Model; 7730 psi to 8166 psi. A review of the image shows the same trait for the three powders, but the range is much higher: 20,700 psi to 24,800 psi. The fourth powder, Trail Boss, is bulky fast burning powder (23), much faster than the other three. The image data presents a chamber pressure of 27,200 psi for a 12.9 grain H4895. This pressure is fairly close to the other three powders. The faster the powder burn rate, the higher the chamber pressure for a given load. The QL Model calculates a chamber pressure of 37,314 psi, which is easier to believe. It is questionable if 12.9 grains of Trail Boss can be contained in a 308 Win case. QL calculates a filled case volume of 111.7%. See table below. A couple of other slower powders have been added to the chart for additional information. The other three powders have filled case volumes ranging from 37.6% to 38.8%. The pressure data in the image are questionable, but the velocity data are fairly close.
12.9 grains H4895, 24" barrel, 70F
Powder-------------FPS---------PSI-------Filled Capacity--------Burn Rate
Benchmark---------1043--------8166----------38.2-------------------90
H4895--------------1013--------7730----------37.6-------------------99
H322---------------1111--------8071----------38.8-------------------85
Trail Boss-----------1482-------37314---------111.7------------------23
IMR 4064-----------1000-------7130----------39.9-------------------106
IMR 4350-----------958--------6083----------37.8-------------------130
Red Dot-------------1760------53717---------75.6--------------------9
I don't see the use of "fillers" in reduced powder loads have been mentioned. It is generally recommended that a case volume filler be used for reduced charge loads if the powder burn rate is higher than Alliant 2400 and the filled case capacity is less than 80%. The intent is to ensure that the powder is held against the primer and proper ignition of the powder is obtained. This is to prevent the somewhat rare Secondary Explosion Effect. The S.E.E. is the catastrophic failure of some rifles while firing seemingly reasonable handloads or reduced loads using slow-burning powders. It is somewhat rare but when it occurs there is a high probability of shooter injury. Just a word of caution.
Sorry for the long post. Hope this is beneficial.
The maximum chamber/barrel pressure (7730 psi) is generated when the bullet has moved slightly less than an inch down the barrel. The vast majority of the powder has been burned at this point. The chamber/barrel pressure at the point that the bullet exits the barrel is 1469 psi. Any powder that is not burned at the point of the Pmax will be burned down the barrel. But it will not contribute to the acceleration of the bullet. As seen from the trace below, there is not enough gases generated from remaining powder to fill the increase of chamber/barrel volume as the bullet moves down the barrel and the pressure starts to drop off. The acceleration of the bullet, as it moves down the barrel is due to the momentum generated by powder burned up to the point of Pmax. See pressure trace below.
The chamber pressure presented for the four powders in the image is questionable. The image values range from 20,700 psi to 27,200 psi. For a 12.9 grain H4895 load for three of the four powders, the range is 7730 psi to 8166 per QL. The fourth powder, Trail Boss is a question by itself. The three powders are fairly close on the Powder Burn Rate Chart, 85-99. As such, you would expect equal charges of powders would generate close chamber pressures. And, in fact, that is what is seen by the QL Model; 7730 psi to 8166 psi. A review of the image shows the same trait for the three powders, but the range is much higher: 20,700 psi to 24,800 psi. The fourth powder, Trail Boss, is bulky fast burning powder (23), much faster than the other three. The image data presents a chamber pressure of 27,200 psi for a 12.9 grain H4895. This pressure is fairly close to the other three powders. The faster the powder burn rate, the higher the chamber pressure for a given load. The QL Model calculates a chamber pressure of 37,314 psi, which is easier to believe. It is questionable if 12.9 grains of Trail Boss can be contained in a 308 Win case. QL calculates a filled case volume of 111.7%. See table below. A couple of other slower powders have been added to the chart for additional information. The other three powders have filled case volumes ranging from 37.6% to 38.8%. The pressure data in the image are questionable, but the velocity data are fairly close.
12.9 grains H4895, 24" barrel, 70F
Powder-------------FPS---------PSI-------Filled Capacity--------Burn Rate
Benchmark---------1043--------8166----------38.2-------------------90
H4895--------------1013--------7730----------37.6-------------------99
H322---------------1111--------8071----------38.8-------------------85
Trail Boss-----------1482-------37314---------111.7------------------23
IMR 4064-----------1000-------7130----------39.9-------------------106
IMR 4350-----------958--------6083----------37.8-------------------130
Red Dot-------------1760------53717---------75.6--------------------9
I don't see the use of "fillers" in reduced powder loads have been mentioned. It is generally recommended that a case volume filler be used for reduced charge loads if the powder burn rate is higher than Alliant 2400 and the filled case capacity is less than 80%. The intent is to ensure that the powder is held against the primer and proper ignition of the powder is obtained. This is to prevent the somewhat rare Secondary Explosion Effect. The S.E.E. is the catastrophic failure of some rifles while firing seemingly reasonable handloads or reduced loads using slow-burning powders. It is somewhat rare but when it occurs there is a high probability of shooter injury. Just a word of caution.
Sorry for the long post. Hope this is beneficial.
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