I loaded 50 rounds, new laupua brass, 41.4 grains Reloder 16, 147 gr ELD-M for my 260 Rem. I shot about 25 and no pressure signs. Took a break and shot the final 25, most of the second 25 had an ejector mark on the base. OAL is 2.890. Any thoughts as to what is going on. Thanks
Pressure signs
- Thread starter Steelshooter842
- Start date
Ran some number's through my QuickLoad app and with the info you've stated above it shows the pressure to be quite high. Specifically, it shows cases filled to 102.1% with a pressure of 63,468 psi at a temp of 70°F (at 40°F it's 60,191 psi) and the SAAMI max is listed at 60,171 PSI. So, it's not much surprise to me you'd get pressure signs and don't know why the first half didn't show any unless temperature was a factor. And maybe something to do with your particular chamber configuration???
Thanks for the response, that would explain it as was cold in when I started but did warm up. Frankly, I didn't realize how hot that load is. Ill back off to 40 grains. I really appreciate it as I could not figure out what was going on.
If you want to know you are near/at pressure before exceeding it, measure your case diameter with a micrometer or dial caliper just above the extractor groove before firing then again afterwards. Record the measurements, subtracting the before from the after to get total expansion for a given charge weight.
If expansion is more than .0015”, your load is over-pressurized but you may or may not see physical signs until .0025” or beyond. That’s been my experience.
I do this for all my ladder tests so I know where my pressure point is on the charge weight curve for a given load recipe.
If expansion is more than .0015”, your load is over-pressurized but you may or may not see physical signs until .0025” or beyond. That’s been my experience.
I do this for all my ladder tests so I know where my pressure point is on the charge weight curve for a given load recipe.
Keep in mind that NEW Lapua brass has a case capacity about 1 gr H2O less than a fired-newly sized case. On my QuickLoad app its set at 53.5 gr H2O, so because you're using NEW cases, I reduced the case volume to 52.7 gr H2O and that was a key factor in the pressure numbers I posted. Now. . . once you size those cases, i'd expect the volume to be close to that 53.5 gr H2O and if it happens to be right at that number, then the QuickLoad app shows that 41.4 grs of R-16 producing 57,865 psi. So, once you resize those cases, you shouldn't have the pressure issue you're having with that load and the NEW cases.
Of course, I'm just guessing about your case volumes. The only way to know is to weigh them yourself to see what you're really dealing with. And note that there can be significant differences between lots of brass, though Lapua tends to be pretty consistent.
And note too, if you happen to only neck size your cases, those cases will have even greater volume resulting is lower pressure and MV's. Just thought i'd mention that to help keep you aware.
