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Old 01-19-2020, 08:07 PM
DesertRat9 DesertRat9 is offline
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Same Powder Same Bullet Weight Different Results

I load Missouri Bullet 200 gr LSWC (with their coating) with 4.0 gr Titegroup for shooting in my Colt GCT with a 14 lb recoil spring (Colt recommends that for lighter loads). OAL averages 1.236. Gun feeds, cycles and shoots well. No problems. Last chrono run was 50 shots thru my Chrony Beta. Average velocity 735 fps (sd=13.3 fps). I am happy with the gun and loads.

Yesterday while rummaging they my bullet bin I found several boxes of MB 200 gr LRN (same coating) with a groove (they call it Oddball). I loaded up 100 with 4.0 gr Titegroup and OAL average 1.235. Today I chrono'd 40 and got 680 fps (sd 15.9 fps). Gun fed and cycled fine. No problems.

I am trying to wrap my head around the lower velocity for the same bullet weight and power weight. The LRN is 0.030 shorter, so the case free volume is larger. The lateral surface area of the LRN bullet that engages the lands is 60% of the LSWC lateral surface area (due to the groove), so the LRN has lower overall friction. Titegroup is a fast burner, so I am wondering if its all the case free volume, that the pressure profile is different (with lower peak). Can the ballisticians please explain?

Second question. Once in a while when shooing the LSWC the slide seems to be perceptibly slower to move forward into battery. I was looking for it today with the LRN today but didn't notice any perceptible delays in cycling. Why would the slide occasionally be a bit slow moving forward with the LSWCs? Something the with way the rounds load in the mags?
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  #2  
Old 01-19-2020, 08:24 PM
david_root2000 david_root2000 is offline
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Same Powder Same Bullet Weight Different Results

Your reasons and a light crimp.

David
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  #3  
Old 01-19-2020, 08:27 PM
flechero flechero is offline
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Your velocity difference could be as simple as the sizing of the 2 different bullets... This is confirmation of why they always say to work a load up... no 2 bullets are identical.
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  #4  
Old 01-19-2020, 09:43 PM
Capt. Methane Capt. Methane is offline
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The slower return to battery can be caused by several things related to the external dimensions of the cartridge that is especially noticeable in reduced power rounds. I had one pistol that would periodically ding the cartridge rim on feeding. A half a thousandth more crimp and no more ding.

Also different COL due to minuscule variations in bullet profile, a slight eccentricity of the case due to a bullet that didn't seat squarely and a few other things including perhaps a bit of coating residue on the feed ramp from previous feed cycles or even being at the bottom end of the sd...
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