RiverRider, lots of this discussion looks familiar.
Chad another screen in quickloads that shows some more good information is use the Table instead of graph representation in the default lower left hand corner. Save the file and compare some. That one will show pressure, velocity and burn percentage as the bullet travels down the barrel. Peak pressure happens within the first 2 inches of bullet travel then starts dropping off. Remember by the time a bullet has traveled 2 inches it has gone from stop to being in motion and has had the rifling engraved into the bullet. With most powders the amount of powder burned is many times more in the first half of the barrel than the last half of the barrel, like RR pointed out most is burned in the first 10 inches with very little the rest of the way. for example
Cartridge : .308 Win. (CIP)
Bullet : .308, 168, Nosler CC HPBT J4 53164
Useable Case Capaci: 49.301 grain H2O = 3.201 cm³
Cartridge O.A.L. L6: 2.800 inch = 71.12 mm
Barrel Length : 22.0 inch = 558.8 mm
Powder : Hodgdon VARGET
Charge : 45.0 grains = 2.92 grams
Estimates of the progress of combustion:
NR.: x(in.) Z(%) v(fps) p(psi) t (ms)
0 0.00000 1.31 0.0 3626 0.0000
1 0.00002 1.34 0.7 3726 0.0015
2 0.00007 1.42 2.2 3927 0.0045
3 0.00019 1.47 3.3 4077 0.0084
4 0.00044 1.56 5.1 4326 0.0132
5 0.00087 1.67 7.3 4625 0.0190
6 0.00154 1.81 10.0 4998 0.0254
7 0.00255 1.97 13.3 5443 0.0326
8 0.00398 2.16 17.3 5972 0.0405
9 0.00595 2.39 21.8 6583 0.0488
10 0.00857 2.66 27.2 7299 0.0578
11 0.01197 2.97 33.5 8129 0.0671
12 0.01630 3.33 40.8 9081 0.0768
13 0.02170 3.75 49.2 10162 0.0868
14 0.02834 4.23 58.8 11388 0.0971
15 0.03641 4.78 69.8 12757 0.1075
16 0.04608 5.40 82.3 14280 0.1181
17 0.05756 6.11 96.5 15968 0.1288
18 0.07106 6.90 112.3 17809 0.1396
19 0.08681 7.78 130.1 19801 0.1504
20 0.10504 8.77 149.9 21942 0.1613
21 0.12600 9.86 171.8 24217 0.1721
22 0.14995 11.07 195.9 26607 0.1830
23 0.17716 12.39 222.3 29090 0.1938
24 0.20792 13.83 251.1 31637 0.2047
25 0.24252 15.39 282.2 34222 0.2155
26 0.28127 17.07 315.8 36804 0.2263
27 0.32448 18.87 351.7 39353 0.2371
28 0.37249 20.80 390.0 41829 0.2478
29 0.42564 22.84 430.7 44202 0.2586
30 0.48428 25.00 473.6 46432 0.2694
31 0.54879 27.27 518.6 48496 0.2803
32 0.61953 29.65 565.7 50363 0.2912
33 0.69690 32.12 614.7 52012 0.3021
34 0.78130 34.69 665.5 53428 0.3131
35 0.87314 37.34 717.9 54602 0.3241
36 0.97285 40.08 771.7 55525 0.3353
37 1.08087 42.88 826.8 56200 0.3466
38 1.11751 43.79 844.9 56365 0.3502
39 1.17739 45.19 872.5 56498 0.3560
40 1.20797 45.88 886.3 56533 0.3589
41 1.22343 46.23 893.2 56544 0.3604
42 1.23900 46.57 900.1 56549 0.3618
43 1.24291 46.66 901.8 56550 0.3622
44 1.24683 46.74 903.5 56550 0.3625
45 1.24781 46.76 904.0 56550 0.3626
46 1.24879 46.78 904.4 56550 0.3627
47 1.24977 46.81 904.8 56550 0.3628
48 1.37922 49.50 960.1 56401 0.3744
49 1.51675 52.13 1015.3 55976 0.3860
50 1.66313 54.69 1070.5 55305 0.3977
51 1.81920 57.18 1125.7 54416 0.4095
52 1.98587 59.60 1181.0 53333 0.4216
53 2.16415 61.94 1236.2 52080 0.4339
54 2.35516 64.22 1291.4 50680 0.4464
55 2.56014 66.43 1346.7 49153 0.4594
56 2.78046 68.56 1401.9 47519 0.4728
57 3.01765 70.63 1457.1 45797 0.4866
58 3.27344 72.63 1512.3 44002 0.5009
59 3.54975 74.55 1567.6 42151 0.5159
60 3.84875 76.41 1622.8 40259 0.5315
61 4.17288 78.19 1678.0 38339 0.5479
62 4.52491 79.91 1733.3 36403 0.5651
63 4.90797 81.55 1788.5 34464 0.5832
64 5.32564 83.13 1843.7 32532 0.6024
65 5.78198 84.63 1898.9 30616 0.6227
66 6.28166 86.07 1954.2 28726 0.6443
67 6.83003 87.43 2009.4 26870 0.6674
68 7.43328 88.72 2064.6 25053 0.6920
69 8.09854 89.95 2119.8 23284 0.7185
70 8.83411 91.10 2175.1 21568 0.7471
71 9.64965 92.18 2230.3 19909 0.7779
72 10.55649 93.19 2285.5 18313 0.8114
73 11.56793 94.14 2340.8 16781 0.8478
74 12.69972 95.01 2396.0 15318 0.8877
75 13.97053 95.81 2451.2 13926 0.9314
76 15.40266 96.54 2506.4 12607 0.9795
77 17.02286 97.20 2561.7 11361 1.0328
78 18.86346 97.80 2616.9 10190 1.0920
79 19.87836 98.06 2644.5 9632 1.1242
80 20.14286 98.13 2651.4 9496 1.1325
81 20.27679 98.16 2654.9 9428 1.1367
82 20.34418 98.18 2656.6 9394 1.1388
83 20.36108 98.18 2657.0 9386 1.1394
84 20.36953 98.18 2657.2 9382 1.1396
85 20.37376 98.18 2657.3 9380 1.1398
86 20.37481 98.18 2657.4 9379 1.1398
87 20.37534 98.18 2657.4 9379 1.1398
88 20.37561 98.18 2657.4 9379 1.1398
Muzzle
To see an example of powders burning more efficiently under pressure, look how slow a charge of powder for a load burns when just poured into an iron skillet and not contained by anything, even fast handgun or shotshell powder will burn very slowly and produce a lot of smoke for a "smokeless" powder.