Surprising Reloading Result?

[rdtompki]

I've worked up 3.7gr WSF behind Bayou 147gr @1.15" OAL as a soft Steel Challenge load for my wife and myself. 3.6gr also works, but is too close to 3.5gr which does not reliably cycle our 9mm 1911s.

Based on a load in the Lyman manual (3.4 WSF (min), 147gr lead @1.058") and in concert with a clerical error I tried 3.4gr/147gr Bayou/1.12" OAL. The rounds were definitely softer, more accurate (likely) and cycled flawlessly. The shorter OAL would up the pressure at the same powder load, but reducing the load by .3gr is significant. Does this combined result at the shorter OAL, lower powder load makes sense?

Update: Chrono Results- the 3.4gr load chrono'ed at about 865fps average with a decent SD. We shot a bunch of this ammo (300 rounds) and it cycled flawlessly. The SD will improve when I switch to a conventional seating die; my micrometer die tends to drift if I don't watch it. This is officially or new to-to load for Steel Challenge until I come up with something better. I'm actually tempted to try 3.3gr.

My baseline load chronos at 900fps. I'm going to chrono the new load on Friday.

 

[RAT807]

I have tested this on 9mm with HP38 powder. The 125 gr hornady bullets passed the plunk test at 1.122. Load work ups found 3 areas that grouped pretty well at 25 yards. I ran some loads at 1.060 and dropped the powder charge. I found 1 group that had 3 holes touching. The other 2 bullets were not that great but more testing will be done. Overall the 1.060 groups were not as accurate as the longer 1.122 groups, but inside of 10 yards, it won't matter.

I got similar speed from 4.1grs at 1.122 and 3.8grs at 1.060

 

[Paddy]

Which would likely have more pressure?

 

[Blue68f100]

To answer your question, Yes. The shorter OAL at 3.4gr will greatly increase the pressure, being almost 0.1" shorter. This is why it's very important to workup your loads. With some powders the pressure doubles or more with a 0.050" short length. This is why some guns get KBOOMED due to bullet setback. Some powders are very sensitive to this others not.

 

[rdtompki]

I was safe at 1.12" since Lyman's had a 147gr lead load at 1.058" with the bottom end being 3.4gr WSF. I estimated by scaling the lead bullet drawing in the load manual (and measuring my Bayous) that my Bayou 147gr was a tad (.012") longer so I was going to bump up the OAL slightly. I could have loaded as short as 1.07" per the manual, but wound up with 1.12" - fatigue might have been a factor in arriving at the OAL, but certainly safe.

I'm going to stick with 3.4gr since it cycles a just try some variants on OAL, but I'm wondering if 3.3gr might even work in our guns.