Hp38 ... temp was 37 degrees F.
Will these rounds chrono higher when summer temps reach 85-90?
Yes. W231/HP-38 is more temperature sensitive than other powders like Titegroup. And there are even "reverse temperature sensitive" powders like WST/Promo/WSF -
https://www.thehighroad.org/index.p...s-and-discussions.778197/page-7#post-10117881
Look at the difference in velocities between 56F and 79F from my 9mm PCC testing -
https://www.thehighroad.org/index.p...n-9mm-40s-w-45acp.799231/page-4#post-10338994
- 9mm 115 gr RMR HM RN 4.8 gr W231/HP-38 @ 1.130": 1275-1263-1253-1290-1248 fps (56 F - JR carbine)
- 9mm 115 gr RMR HM RN 4.8 gr W231/HP-38 @ 1.130": 1303-1289-1298-1311-1323 fps (79 F - JR carbine)
230gr zero fmj at 1.255 ... Hp38 5.4gr velocities avg 837
Anyone think I might run into pressure issues?
Probably not if using FMJ RN at longer 1.255" OAL which is essentially loading at start charge. (Hodgdon load data uses shorter OAL with FP bullet):
I'm going to buy a new chronograph soon to verify the one I'm using currently, it's a caldwell cheapo.
I am also using the "Caldwell cheapo" chrono and use CCI SV and 10/22 as reference test for the chrono (It's been consistent for several years as long as I use fresh 9V battery and shoot closer to sensors on top of chrono
10-15 feet away from muzzle/expanding gas which can confuse the sensors ... If using remote cable and Caldwell app, consider using steel deflector plate protection).
Weird that a bullet change and changing to a winchester lpp would increase my velocities 50fps across the board compared to my data with cci 300 and rem 2.5 primers. Have any idea to why this is happening?
Yes, bullet and primer change could affect pressure. And I am assuming you are using same brass? (If you are using mixed range brass, you are "tolerance stacking" another variable to your chrono testing). While most 9mm FMJ bullets are sized at .355", I found Zero 9mm FMJ to be sized larger at .356". (You could measure the bullet and see if it is larger) And I thought Winchester LP primers were for both Standard and Magnum loads. (ETA: Just checked and
new packaging still says for "Standard or Magnum pistol loads")
BTW, have you checked neck tension/bullet setback? That's another variable that will affect chamber pressure/velocity.
Another factor to consider is actual powder charge temperature and not just ambient temperature. Like how "finished OAL" may not matter if you experience significant bullet setback when bullet nose bumps the feed ramp to affect "chambered OAL", ambient temperature may not matter if rounds are left out in direct sun to get warmed up or chambered long enough inside hot barrel to "cook" and raise powder charge temperature (Both will affect measured velocities and could display suddenly different numbers).
For chrono testing, I try to maintain the temperature of loaded rounds consistent (Keeping them out of sunlight inside cardboard boxe/insulated ice chest on really hot/cold days) and not allow chambered rounds to "cook" inside the barrel (Cold vs hot rifle barrel variable alone can affect group size/scatter).
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