[jwtharpe]

Here is some real data from two completely different barrels.

ARP 16' Scout TC--- Bison 22" fluted heavy TC

Case- Fed.---------- Case-Fed.
Powder- TAC------- Powder-TAC
Primer- 450-------- Primer- 450
Bullet- 115CC ------Bullet- 115CC
OAL-2.33"---------- OAL- 2.33"
Temp- 75 -----------Temp- 75
Shim- .012"-------- Shim- .008"

32.0gr.-------------- 32.0gr.
Group- 1.2"--------- group-.4"
av.- 2589----------- av-2748
es- 29--------------- es-17
sd-14---------------- sd-6

32.2gr.-------------- 32.2gr.
group- .9"----------- group-1.0"
av.-2580 ----------- av-2757
es- 35--------------- es-40
sd- 15--------------- sd-18

32.4gr.-------------- 32.4gr.
group- .9"---------- -group-.6"
av.- 2581----------- av-2811
es- 35--------------- es-41
sd- 13--------------- sd-18

32.6gr.-------------- 32.6gr.
group- .8"---------- -group-1.1"
av.- 2599 -----------av-2801
es- 51--------------- es-18
sd- 21--------------- sd-8

32.8gr.-------------- 32.8gr.
group- .9"----------- group-.9"
av- 2633-------------av-2803
es-21---------------- es-29
sd- 9----------------- sd-11

33.0gr.-------------- 33.0gr.
group- .6"----------- group-1.1"
av- 2651------------ av-2807
es- 26---------------- es-95
sd- 9----------------- sd-25

33.2gr.-------------- 33.2gr.
group- .4"----------- group-.7"
av- 2638------------ av-2844
es- 37--------------- es-78
sd- 18--------------- sd-35

33.4gr. -------------- 33.4gr.
group- .4" ---------- group-1.1"
av- 2644------------ av-2847
es- 52 -------------- es-49
sd- 19 -------------- sd-18

33.6gr.-------------- 33.6gr
group- .5"----------- group-.9"
av- 2663------------ av-2863
es- 32--------------- es-97
sd- 12--------------- sd-47

33.8gr. ------------- 33.8gr.
group- .5"----------- group-1.0"
av- 2674------------ av-2854
es- 16--------------- es-43
sd- 7----------------- sd-16

34.0gr. ------------- 34.0gr.
group- 1.1"---------- group-.9"
av- 2694------------- av-2868
es- 54---------------- es-50
sd- 20---------------- sd-18

 

[jwtharpe]

That's some good data. The data seems to support an approx 25 to around 33 fps per inch change. Now need some posted for 16 and 12.5 maybe to see if that holds true for shorter barrels. I know there have been some 12.5 numbers posted on the site.

This is kind of misleading, Tac powder is on the slow side, when I shoot loads using lt-32 the difference is closer to 100fps for the same load. as you know, LT is a lot faster than Tac, so it tells me that Tac is using its slow burn rate to better effect in the longer barrel.

 

[jwtharpe]

So you're saying using Lt-32 the differences are closer to 100 fps vs the approx 150 to 200 you see with TAC? That would put it in the range of 20 fps per inch. Again looks like there are many variables so might only be able to come up with ballpark figures to cover all possibilities.

Yes, I think the burn rate of the powder has a lot to do with it, CFE shows even more than Tac.

Some of it could be the barrels, the only real way to be sure would be to run a test with a long barrel with a set of different loads, then cut it down and shoot the same test loads again at the same atmospheric conditions.