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Old 05-01-2011, 09:48 PM   #1
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Default Pressure VS. Velocity

Tried out some .221 Fireball loads in my XP-100 over the chronograph. Alliant shows a load of 15.5 grains of 2400 at 2700 fps from the 10.75" barrel. My loads of 15.5 grains of 2400 (individually weighed) are averaging 3033 fps for eight rounds with 40 grain V-Max. Fastest was 3066 fps.
I have no pressure signs. Bolt is not sticky, easy extraction and primers look fine. Very small amount of soot on some of the case mouths. The powder is from a "new" can, meaning unopened, that had been sitting in my dad's reloading room for about 12-15 years.

Advice? Should I back off based on velocity alone or continue to monitor the pressure signs. I know none are an exact indicator.



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Old 05-02-2011, 12:44 AM   #2
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Quote:
Pressure VS. Velocity
Should be covered in your manuals, and they will do as good a, or a much better, job explaining it than anyone here.

Your load is probably fine though, Hornady 8th has 40gr V-Max, 15.4 gr of 2400 reaching 3300fps. COL could be a factor as Hornady has it at 1.830, if your loaded round is longer it would be slower and if you're not showing signs of over-pressure I wouldn't worry about it.


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Old 05-02-2011, 02:40 PM   #3
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Your load is fine. You should have no problems with it. How is the accuracy and shot to shot deviation ?

Jim........

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Old 05-02-2011, 02:55 PM   #4
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Your load is fine. You should have no problems with it. How is the accuracy and shot to shot deviation ?

Jim........
http://www.firearmstalk.com/forums/f66/xp-100-first-report-41915/

I am not too excited about the groups, but this was a shot in the dark choice for a load, everything from powder to bullet weight to charge weight to COAL. High to low deviation was almost 120 fps. I didn't record shot to shot.

Oh, The small holes horizontal to the bull are from my cat. I may see if the XP can hold "minute of cat"...
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Old 05-03-2011, 04:33 AM   #5
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Default Okay, I'll be the wet blanket.

If your velocities are higher than expected, the pressures probably are as well. There just ain't no free lunch in physics.

I don't think it's dangerously high. On the occasions I've run overloads - which shall not be further discussed, ahem - the maximum spread gets real small. This is due to the pressures being upper borderline high and the powder burns really consistently - as in fast. Your velocity spread is not all that tight to demonstrate that characteristic. However, no point in putting the extra wear on your pistol.

On the other hand, your groups are not as tight as you'd like. I'd suggest you start working down to find a load giving better accuracy, not working up.

If you can't get it to shoot as tight as you think it ought, you might try other bullets or another powder.

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Old 05-03-2011, 04:20 PM   #6
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It all depends.

I have a load in my 223 that produces 3600 FPS in a 26" VLS. The book says that load should be going 3300 fps. Some times it just happens. That load is in the middle of the load range as well and has at least 2 grs to go in either direction.

It is not just the load it is also the gun. If you have a tighter chamber that can increase the velocity if your barrel is lapped or worn out that will increase velocity as there is less friction.

You say the can in 12 or so years old. That may be part of it as well. Check out a load manual from 12 years ago.

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Old 05-03-2011, 06:45 PM   #7
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Thanks for the input fellas, I'll check out some other manuals.

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Old 05-03-2011, 11:05 PM   #8
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Are you using once or more times fired brass? The sooty necks may be an indication you need to aneal the necks.

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Old 05-03-2011, 11:58 PM   #9
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Quote:
Originally Posted by robocop10mm View Post
Are you using once or more times fired brass? The sooty necks may be an indication you need to aneal the necks.
I used brandy new never fired factory Remington brass. Tumbled it, checked the flash holes, trimmed to minimum length and FL re-sized. Giving me a bunch of stuff to read up on. Thanks again.
KB
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Old 05-04-2011, 01:53 PM   #10
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As well as watching your cases (which apparently you are doing) pay attention to your bolt face. With new brass you may get by with higher pressures for a loading or two, but as the cases get older gas seepage may develop and pit yur bolt face.
A number of years ago a friend was loading his .257 Weatherby with Serria 100 grain bullets and we started to see rips in the target much like what Mr. Kitty left you, Switching to a bullet with a heavier jacket fixed that problem.
Goon luck and have fun!



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