stubbicatt
Member
All. I've been experimenting with the RSI shooting lab and software etc.
This has been an eye opening experience. Until now I have relied upon things like primer appearance, case head expansion and velocities to tell me when I am approaching the top of a pressure curve. Always I have stayed within the limits of what the loading manuals call for, powder charge wise. I have yet to blow up a rifle, although I have had a couple case head separation on factory 40 cal ammo and on surplus 7.62x54r ammo. These experiences were not pleasant and I do not wish to repeat them again, hence the quest to find actual chamber pressures, or something close.
The guy on the other end of the phone at RSI is really super nice and knowledgeable. The kit I received was neatly packaged and consisted of the CED chronograph instrument, a series of strain gages that one super glues on his barrel, software for reading everything, and a grey box that holds the electronics necessary to make the whole shebang work. The only thing I had to purchase was a bluetooth "dongle" for my laptop so that my computer would communicate with the pressure measuring unit.
There are plusses and minuses to any bit of kit, and this is no different. The way one arrives at chamber pressures is involved, and requires measuring the thickness of one's barrel at the point where one glues on the strain gage, measuring the thickness of the brass one used at the same point in the chamber, and then inputting these factors in the software. Arriving at actual peak chamber pressures is sort of a SWAG using these methods, but there are other ways to get there... i.e. sending a couple loaded rounds to White Laboratories where they will get you a pressure you can work from, to sort of calibrate your setup.
Another method is to buy a couple of boxes of factory ammo to get pressure traces with peak pressure etc., and not exceed this value with handloads. Of course this requires the handloader to rely upon the factory as having done its job properly, but it is a failsafe of sorts.
The software package has two or three programs in it, one of which measures pressure and velocity, and has an interesting feature called OBT, or Optimal Barrel Time (IIRC). This feature will plot certain internal ballistic factors to arrive at a few points on the pressure curve where your barrel is most likely to be at the end of one of its vibrational nodes... the theory is that when the barrel is at the end of one of its vibrational nodes, muzzle deflection is kept more uniform, thus arriving at more consistently accurate ammunition.
I have fiddled around a bit with the OBT feature and it seems to work... however I am far from an accomplished bench rest shooter.
Even so, this is a really neat bit of kit that, while not entirely perfect, goes a long way to helping me to rest assured that my rifle will not kaboom due to an error in my handloading.
Oh... btw, some of the 308 loads I have found in reputable manuals exceed what seems to be maximum pressure in my rifle. The cause is probably in vagaries of throat dimension or some other manufacturing "features" in my rifle, rather than an error in the data in a test barrel. But it seems to me that this is the point of the RSI setup... not so much what a given load did in a test barrel, but rather what is it doing in my barrel?
I enjoy it.
DISCLAIMER
No warranties expressed or implied! I am not affiliated with RSI, and nothing in this post should be construed as warranting safety or anything else for that matter. Use at your own risk. Use carefully according to manufacturer's instructions and never exceed any safe loads in your firearms.
This has been an eye opening experience. Until now I have relied upon things like primer appearance, case head expansion and velocities to tell me when I am approaching the top of a pressure curve. Always I have stayed within the limits of what the loading manuals call for, powder charge wise. I have yet to blow up a rifle, although I have had a couple case head separation on factory 40 cal ammo and on surplus 7.62x54r ammo. These experiences were not pleasant and I do not wish to repeat them again, hence the quest to find actual chamber pressures, or something close.
The guy on the other end of the phone at RSI is really super nice and knowledgeable. The kit I received was neatly packaged and consisted of the CED chronograph instrument, a series of strain gages that one super glues on his barrel, software for reading everything, and a grey box that holds the electronics necessary to make the whole shebang work. The only thing I had to purchase was a bluetooth "dongle" for my laptop so that my computer would communicate with the pressure measuring unit.
There are plusses and minuses to any bit of kit, and this is no different. The way one arrives at chamber pressures is involved, and requires measuring the thickness of one's barrel at the point where one glues on the strain gage, measuring the thickness of the brass one used at the same point in the chamber, and then inputting these factors in the software. Arriving at actual peak chamber pressures is sort of a SWAG using these methods, but there are other ways to get there... i.e. sending a couple loaded rounds to White Laboratories where they will get you a pressure you can work from, to sort of calibrate your setup.
Another method is to buy a couple of boxes of factory ammo to get pressure traces with peak pressure etc., and not exceed this value with handloads. Of course this requires the handloader to rely upon the factory as having done its job properly, but it is a failsafe of sorts.
The software package has two or three programs in it, one of which measures pressure and velocity, and has an interesting feature called OBT, or Optimal Barrel Time (IIRC). This feature will plot certain internal ballistic factors to arrive at a few points on the pressure curve where your barrel is most likely to be at the end of one of its vibrational nodes... the theory is that when the barrel is at the end of one of its vibrational nodes, muzzle deflection is kept more uniform, thus arriving at more consistently accurate ammunition.
I have fiddled around a bit with the OBT feature and it seems to work... however I am far from an accomplished bench rest shooter.
Even so, this is a really neat bit of kit that, while not entirely perfect, goes a long way to helping me to rest assured that my rifle will not kaboom due to an error in my handloading.
Oh... btw, some of the 308 loads I have found in reputable manuals exceed what seems to be maximum pressure in my rifle. The cause is probably in vagaries of throat dimension or some other manufacturing "features" in my rifle, rather than an error in the data in a test barrel. But it seems to me that this is the point of the RSI setup... not so much what a given load did in a test barrel, but rather what is it doing in my barrel?
I enjoy it.
DISCLAIMER
No warranties expressed or implied! I am not affiliated with RSI, and nothing in this post should be construed as warranting safety or anything else for that matter. Use at your own risk. Use carefully according to manufacturer's instructions and never exceed any safe loads in your firearms.
Last edited:
