6ppc wedge speed ?

J

janderson0

Guest
Saturday a shooter let me run a few over his Chrony Beta. I have a 6ppc Hart 1:14 24 inch. Shooting 28.0 of n133 Fed 205M and the 68 Wedge. The average was 3324 fps. Is this possible?

Seems too fast for that load, oh about 70 degrees in the AM. Does the tight fit of the Wedge increase pressure that much? Or is the Guy's Chrony suspect?

Thanks,
Jim
 
Jim

A lot of different factors can add, or subtract, as much as 100 fps with a given case design.

We did a test a number of years ago with bullet designs such as the Barts Ultra as compared to the originol 7 1/2 ogive bullets such as the Watsons and Fowlers. With the exact same powder charge, the Fowlers gave almost 100 fps more velocity.

The big factor was, (it seems), the amount of shank length at full diameter. The bullets that tend to have more length ways shank diameter built pressure quicker.

Also, different barrels have different groove diameters. A barrel that is on the low side of the tolerance, (tighter) will probably give more velocity than one on the high side.

I have never measured a Barts Wedge, I was under the impression that they didn't have much shank at a full .243, sort of a "driving band bullet".

That velocity does seem a tad fast for just 28 grns, But heck, there are a lot of other variables involved. The only way to confirm is to shoot over another Chrono within a few minutes of the first.........jackie
 
Not picking on the equipment used but the Chrony Beta may be part of the problem. Many other factors like, sample size. powder lot, barrel condition, and the like can cause errors too.
 
I have a Shooter Chrony beta and an Oehler 35 and when I compare the two on any given day to get ballistic coefficients, the Chrony has been off as much as 75 fps above and below the Oehler. The Oehler is always spot on. I would bet the readings you got were slightly off reality as 28 grains shouldn't get that much speed, but like others have said, there are lots of variables.

Btw, the last time I ran a bc test on 66 grain flatbase Cheek bullets, the bc came out at .255 at 5000' and 90 degrees. The fowler 66 is real close to the same bullet so you could do a drop test from a ballistic program and compare the drop from 100 to 200 to the program. In essence, back checking the chronograph.
 
I think looking at any data I'd need at least 1.0gr more to approach 3300 fps. But I'd assume most data was from a barrel about 21 inches not 24. So that might add a little, and the difference comes from Chrony errror.

Thanks,
Jim
 
Bart's 65 boatails-

I had Roger Freeman chonograph a couple of rounds two Fridays ago, just before the Logan match. The average was around 3330-3340 out of a new Bartlein 237-4 groove. The load was about 28.8 grains of 133 and the temps were in the high 90's. I ended up backing the load down a little bit on Saturday. Roger uses a Pro-Chrono, don't know how this unit stacks up against the Ohler.

FYI-

Mike Paul
 
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