Velocity question


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Old 06-12-2012, 11:26 PM   #1
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Default Velocity question

I have loaded up a trial batch today of 55gr BT-fmj Hornady bullets with LC cases, cci sm primers and 21.7 gr or IMR 3031 @ 2.200 C.O.L.


All the books and reference I can find are saying these should be pushing 27-3000 fps depending on what reference you use.

I ran some through my Chrony today and the fastest I had was 2417 and slow or around 2350. I was using an older 16" AR upper I have that I know is pretty worn but functions ok. All the rounds cycled ok and seemed to have plenty of pressure. Why am I getting such difference from spec to chrony ??

The cases all look good also .



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Old 06-13-2012, 12:20 AM   #2
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Quote:
Originally Posted by ktmboyz View Post
I have loaded up a trial batch today of 55gr BT-fmj Hornady bullets with LC cases, cci sm primers and 21.7 gr or IMR 3031 @ 2.200 C.O.L.


All the books and reference I can find are saying these should be pushing 27-3000 fps depending on what reference you use.

I ran some through my Chrony today and the fastest I had was 2417 and slow or around 2350. I was using an older 16" AR upper I have that I know is pretty worn but functions ok. All the rounds cycled ok and seemed to have plenty of pressure. Why am I getting such difference from spec to chrony ??

The cases all look good also .
What rifle were the books using? I've noticed that most books seem to use something with a high rate of twist and a long barrel to get their data. Shorter barrels then come in at lower velocities. I think they intentionally use longer barrels just for a safety factor?


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Old 06-13-2012, 12:47 AM   #3
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Quote:
Originally Posted by ktmboyz
I have loaded up a trial batch today of 55gr BT-fmj Hornady bullets with LC cases, cci sm primers and 21.7 gr or IMR 3031 @ 2.200 C.O.L.

All the books and reference I can find are saying these should be pushing 27-3000 fps depending on what reference you use.

I ran some through my Chrony today and the fastest I had was 2417 and slow or around 2350. I was using an older 16" AR upper I have that I know is pretty worn but functions ok. All the rounds cycled ok and seemed to have plenty of pressure. Why am I getting such difference from spec to chrony ??

The cases all look good also .
Aren't the velocity numbers usually generated with a 20-22 inch bbl?
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Old 06-13-2012, 01:15 AM   #4
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Ya I know barrel lenghts affect it but I didn't think 4-500 fps

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Old 06-13-2012, 01:46 AM   #5
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Ya I know barrel lenghts affect it but I didn't think 4-500 fps
if i remember right its like 100-200fps per inch depending on powder burn rates. so that sounds right for test data from a 20" barrel
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Old 06-13-2012, 02:56 AM   #6
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Personally I dont use 3031. My Lee book shows a starting load of 22.3 grains with a max of 25.0 and 3165 fps for the IMR 3031. The owner of one of the gun shops is a competitive target shooter and he put me on to Varget. I use Varget or H335. I dont have a chronograph so I cant tell you what the speed is out of my 16" barrel.
http://www.ballisticsbytheinch.com/223rifle.html

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Old 06-13-2012, 03:14 AM   #7
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I had some I wanted to use up, thats why I was using it and I have read good results with it. I think I am going to stick with AR comp.

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Old 06-13-2012, 01:36 PM   #8
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Not sure what manuals you used, but Hornady #7 test barrel was 26 inches.

http://www.accuratereloading.com/223sb.html



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