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I couldn't find the original thread that I owed a response to, so I'm creating a new one.
The original question was how much velocity is lost with shorter barrels, but then we got into whether slower-burning powders lost more or less velocity.
Today I tried four loads of H4895 with 95 gr SST in a 243 Ruger M77 Compact 16.5" barrel.
I found that there was a big jump in velocity going from 32.0 grs to 32.5 grs, but much shorter jumps after that. It appears that 32.5 or 33 grs is about what can be burned in that short narrow barrel. 33.0 grs is the published starting load in the Hodgdon manual. I have the same rifle in 260 REM, and the velocity peaks out at about .5 grs below published max.
Anyway, here are the averages and velocity spreads. Remember, these are from just 5 shots with each load, so more testing would be required for a good stats. This was just to give me an idea of what charge to load for the kids' hunting season starting in a month. Mission accomplished! (My goal was approx 2600 fps with a 95 gr bullet and decent accuracy for 50-100 yard shots. Group sizes below are 5 shot 100 yard groups. Last group was probably worst because I was getting a little tired and didn't let the barrel cool as much between shots.)
32.0 grs avg 2569 fps spread 88 fps group= 3.2"
32.5 grs avg 2651 fps spread 41 fps group= 1.9"
33.0 grs avg 2656 fps spread 60 fps group= 1.5"
33.5 grs avg 2679 fps spread 12 fps group= 3.5"
The published velocity for the 33.0 gr charge is 2865, from a 24" barrel, so my gun dropped about 28 fps per inch. Right on our other estimates of 25 fps per inch. Since the velocity with this slow powder peaks well below the max charge, I suspect the loss per inch when comparing the max load woiul;d be a lot more than 28 fps per inch.
The original question was how much velocity is lost with shorter barrels, but then we got into whether slower-burning powders lost more or less velocity.
Today I tried four loads of H4895 with 95 gr SST in a 243 Ruger M77 Compact 16.5" barrel.
I found that there was a big jump in velocity going from 32.0 grs to 32.5 grs, but much shorter jumps after that. It appears that 32.5 or 33 grs is about what can be burned in that short narrow barrel. 33.0 grs is the published starting load in the Hodgdon manual. I have the same rifle in 260 REM, and the velocity peaks out at about .5 grs below published max.
Anyway, here are the averages and velocity spreads. Remember, these are from just 5 shots with each load, so more testing would be required for a good stats. This was just to give me an idea of what charge to load for the kids' hunting season starting in a month. Mission accomplished! (My goal was approx 2600 fps with a 95 gr bullet and decent accuracy for 50-100 yard shots. Group sizes below are 5 shot 100 yard groups. Last group was probably worst because I was getting a little tired and didn't let the barrel cool as much between shots.)
32.0 grs avg 2569 fps spread 88 fps group= 3.2"
32.5 grs avg 2651 fps spread 41 fps group= 1.9"
33.0 grs avg 2656 fps spread 60 fps group= 1.5"
33.5 grs avg 2679 fps spread 12 fps group= 3.5"
The published velocity for the 33.0 gr charge is 2865, from a 24" barrel, so my gun dropped about 28 fps per inch. Right on our other estimates of 25 fps per inch. Since the velocity with this slow powder peaks well below the max charge, I suspect the loss per inch when comparing the max load woiul;d be a lot more than 28 fps per inch.
