Will OAL (9mm and 300blk) change velocity at all? - THR

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Old May 26, 2016, 04:14 PM   #1
Join Date: May 16, 2016
Posts: 24
Will OAL (9mm and 300blk) change velocity at all?

I want to load my rounds a little longer to test a few things now that I have learned a little more but dont want to rework my data (7-8 different bullets I've gathered good loads for).

Does this "usually" change velocity?
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Old May 26, 2016, 05:27 PM   #2
Hondo 60
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Yes, the OAL will cause the case capacity to change.
Shorter OAL in theory should go faster
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Old May 26, 2016, 06:20 PM   #3
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Can't speak for 9MM loads but....

This is my load info for my .300 AAC Blackout, 16 inch with carbine gas system.

It is 19.0 gains of H110 and Hornady VMax 110 grain bullets.

300 V-Max 110 H110 19 2302 DSA 5/8/2012 2.000in
300 V-Max 110 H110 19 2267 DSA 9/22/2012 2.065in

These velocities were taken at 10 feet.

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Old May 26, 2016, 07:01 PM   #4
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Anytime you change the case volume moving the bullet in or out the powder charge pressure will change and subsequently the velocity will change. How much it will change is purely a matter of how much you change the bullet seating depth. Will the change be apparent as to point of aim? The only way to know is to try it and see what happens. Depending on how much you change seating depth, when seating deeper you may want to reduce the load by a few tenths of a grain. Got a chronograph? Note the velocity before and after.

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Old May 26, 2016, 11:46 PM   #5
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Here are some #s from a test i did in 9mm with different powder charges and 2 OALs
Springfield 1911 9mm 5"
S+B SP Mixed brass
4.0 HP38 OAL 1.065
RMR 124gr FN Average ES SD PF
1045 1031 1040 1040 1033 1037.80 14 5.72 128.6872

4.0 HP38 OAL 1.10
RMR 124gr FN Average ES SD PF
1004 997 1021 1025 1021 1013.60 28 12.32 125.6864

4.2 HP38 OAL 1.065
RMR 124gr FN Average ES SD PF
1065 1088 1079 1066 1072 1074.00 23 9.62 133.176

4.2 HP38 OAL 1.10
RMR 124gr FN Average ES SD PF
1077 1062 1063 1055 1071 1065.60 22 8.53 132.1344

4.4 HP38 OAL 1.065
RMR 124gr FN Average ES SD PF
1116 1111 1103 1107 1109 1109.20 13 4.82 137.5408

4.4 HP38 OAL 1.10
RMR 124gr FN Average ES SD PF
1099 1113 1112 1098 1116 1107.60 18 8.44 137.3424
Didn't paste weel but 5 vels an average ES SD and PF

Note more velocity difference with the lighter charge.
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Old Yesterday, 12:38 AM   #6
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I found it interesting that changes in OAL have quite a noticeable effect on SD
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