the45er said:
Loaded some 4.5 grain SR7625 rounds. Shot them through the chrono. One FTF and an average velocity of 934 fps. 4.9 grain rounds - zero malfunctions and 1199 fps average. I'm not sure what "signs of overpressure" are in a 9mm. I guess flattened primers would be one like in rifles. No signs of that. Noticeable difference in recoil but the 4.9 grain loads felt much milder than the Remington Golden Saber factory home defense rounds.
My guess is that you are in +P territory. Probably won't blow up the gun, but above recommended maximum load. Remember, you are loading a bullet recommended to be loaded at a C.O.A.L. of 1.160" to a C.O.A.L. of 1.125" but you are still loading the maximum powder charge.
The velocity associated with the maximum charge from your data source is 1040 fps. Your load chronoed at 1199 fps. That's an increase of 15 percent. That increase didn't happen just because you have a "fast barrel."
An old Speer reloading manual I have published a SR7625 load for a 115 grain FMJ HP bullet at a max of 6.1 grains. Again, I just don't see any evidence of 4.9 grains of this powder over the 124 grain Berry's 9mm RN bullet flirting with the danger zone.
And your data source has a 115-grain bullet loaded with 5.1 grains as the maximum -- using a JHP bullet, so we shouldn't compare them. Lyman's 50th doesn't have any 9mm loads using that powder, so we get no help there.
I don't think I understand what it is you are seeking. Everything that has been contributed here in answer to your questions suggests that your 4.9-grain loads are above the maximum. Your own chony tests (to the extent that velocity can be used as an indicator of pressure) confirms this. Yet you appear to be determined to convince yourself that your load is safe.
Why?
There's a lot of room between 4.5 grain and 4.9 grains. If you got ONE failure to cycle with 4.5 grains ... why not try a few at 4.6 grains? If those still won't cycle the action, try a few at 4.7 grains. It's not logical to conclude that "My gun won't cycle with a starting load so I must immediately go to a load that exceeds maximum."
"FTF" can mean either "Failure to Feed" of "Failure to Fire." I don't see how either would in any way be attributable to the amount of powder behind the bullet.
To use the same approximate calculation process I described above, Hodgdon web site calls for loading a
similar Berry's bullet to a C.O.A.L. of 1.150". Berry's calls for loading your bullet to 1.160". You are loading it to 1.125" Let's use the 1.150 from the Hodgdon site, because they give us data. At that C.O.A.L. their maximum load generates a pressure of 31,800 and a velocity of 1,054 fps. You are loading it 11 percent deeper.
Compared to the available volume of .03000 cu. in. at a C.O.A.L. of 1.150, when you load the same bullet to 1.125" the available volume is reduced to .02739 cu. in. That's a reduction of 8.7 percent. Pressure is inversely (linearly, not exponentially) proportional to volume. That means if the volume decreases by 8.7%, the pressure increases by 8.7%. So, by this rough and ready calculation, your load may be generating a pressure of 31,800 + 8.7%. That's 34,567 psi.
According to SAAMI, the maximum recommended pressure for 9mm ammunition is 33,000 using the CUP system. Using the transducer system, it's 35,000 psi. Based on this, I'd say you are definitely in a grey area, between the maximum pressures developed using the two systems. If you like being on the ragged edge ... it's your gun, and your hand. Ultimately, it's you who has to live with your loads.
If it were me, I'd reduce the load to 4.6 grains and consider the next lighter recoil spring in my pistol. I don't feel any compulsion to live on the edge and to beat up my gun unnecessarily.
