Velocity Increases With Five Grain Powder Increases

[Semisane]

In addition to doing Underclocked's work for him last week end with the Great Plains experiment , I added three more data pointsto my earlier experiment of shooting the same bullet & sabot combination over a chronograph,starting at 65 grains weight of T-7 FFFGand working my way up in five grain increments.

In the first experiment I shotfour sets of weighed charges at65,70,75 &80 grain weight.

Last Saturday I shot85,90 & 95 grain weight charges.

Allcharges were loadedunder300 grain Speer Gold Dot Hollow Points and Harvester Crush Rib sabotsand setoff with CCI small rifle primers in a 25 ACP breech plug.

Here are the average velocities for each load.

Grains Of Powder Average FPS
Weight= VolumeFive-Shot Groups Group Size

6574.7 1635 3 1/8"
7080.51624 (-11 fps)4 3/8"
7586.21660(+36 fps)2 7/8"
80 92.01698(+38 fps) 3 1/4"
8597.81775 (+77 fps)4 1/2"
90 103.5 1822 (+47fps)3"
95 109.31829(+7 fps)3 3/4"

As said earlier, I really can't explain why 65 grains had a higher velocity than 70 grains.

[cayugad]

That is some excellent information there. It really makes me wonder what those big conicals I shoot are doing.

[Semisane]

That's the trouble with this kind of info - it gets you to wondering about other stuff.

The crush ribs load easily in the Mustang. In my "Same Load / Six Different Sabot" experiment I found that regular Harvester long sabotsshot better out of the Mustang than the crush ribs. Igot a four-shot average velocity of 1667 fps with 75 grains weight T-7 FFFG and the 300 grain Gold Dot - almost the same velocity as the crush ribs with that load - with a 1 7/8" group.

[Underclocked]

Semi, I may be workin' you too hard but you are doing some very interesting experimenting. I hope you are recording all this somewhere - I think a book might be in your future.

Or, you might just get away with it.

[bronko22000]

Semi - Now you have me curious. Did you record each velocity? I see you listed the average but it would be interesting to see what the velocity variation was for each load.
Keep up the good work.

[yeoman]

Semisane - interesting work.

From your previous posts I gather those are 3 shot groups @ 100 with a scope? What is the twist rate of the Lyman Mustang? How did you get such precise numbers on the "volumn" measurements? One thing your tests make me wonder is whether there are multiple performance points for a given combination. For instance, maybe a gun dislikes 70,75 grains, likes 80 grains, dislikes 85,90,95,100 then likes 105. Interesting stuff. Thanks.

[Semisane]

Hey bronco. Yes, I do record shot by shot velocities. They are generally pretty consistent. See the readings on the Harvester long sabot target below. That was a four-shot group because I had only 4 of those sabots on hand.

I usually shoot five-shot groups at 100 yardsyeoman. Sometimes I shoot at 50 yards when it's hot and I don't feel like doing a lot of walking.

I have a 3X9 Leupold on the Mustang (which I use for most of my experiments) and a 2X Simmons pistol scope on the New Englander, which was my "go to" ML before I got the Mustang last year. Lyman twist is 1 in 28".

The "volume equivalent" is derived mathmatically. A while ago, using my brass powder measure, I threw a bunch of 100 grain charges with each kind of powder I had and weighed them out.100 grains of T-7FFFG weighed 87.0 grains. So1 GV=0.87 GW and 1 GW = 1.15 GV.Therefore, when I'm working with weighed charges I just multiply it out to get anidea of the volume equivalent - i.e. 75 GW x 1.15 = 86.2 GV.

[dmurphy317]

Yeoman,
Your question about multiple performance points is not unusual to see. In reloading for CF's I have noticed similar grouping at different powder levels with a spread between. It can to some degree be related to barrel harmonics. Every barrel vibrates when shot in a circular fashion. The point at which the bullet exits the barrel during that vibration determines to a great extent where the group will end up and how tight that group is. If you find two loads that exit at the same point in the vibration cycle you will have a good chance that they both perform well compared to other loads in that gun.

[Johnmorris]

Semi
how do you protect your chronogragh from the sabot and powder blast? I have been going to do some of my loads but was not sure how to protect unit.

[Semisane]

Hey JM, I have a$99 Pro-Chronograph that I really like. I killed it last year with a sabot to the face that shattered the LCD screen. After I got it repaired I made a plexiglass shield. Took a 5" x 16" piece of 1/4" thick plexiglass and drilled a hole about 1" from one end, and (using a torch to heat it a little) bent about 5" of the other end up at about a 45 degree angle. The mounting bolt from a camera tripod goes through the hole in the plexiglass into the bottom of the chrono, and the bent up part protects the face. After I did that I found out that Pro-Chronograph makes a shield thats pretty much the same as mine, except it sits on top of the unit instead of under it.