Getting My New .264 Winchester Magnum Ready For Elk Season
- Thread starter Llama Bob
- Start date
- Status
OP
OP
Llama Bob
member
- Joined
- Feb 25, 2016
- Messages
- 2,258
So I addressed all the issues I could without getting the FCD modified. I switched to the new Whidden seater, and loaded with new brass at a 64.8gr charge weight and the new base->ogive length. I ended up with a nightforce 2.5-10 compact on the gun and it was certainly more enjoyable to shoot. These are shots 29-31 on this rifle, and we now have our first sub-MOA group 
My objective was to get there safely from zero load data in less than 35 rounds, and it took 31. These are all quasi-cold-bore shots BTW. I made 10 shots of this, but I saved the last 7 for future use (including possible hunting) or teardown, since I know I'm going to be making some major changes.
It would be nice to have a new-brass and fired-brass load that shoot to same POI, but we'll have to see if that plays out or not.
The rifle is now in for pillar and skim bedding. I'm not necessarily expecting improved accuracy (although I might get it), but I do expect improved rigidity and a stock less sensitive to enviromental conditions both of which are important to me. The lee FCD and world's finest trimmer will be going in to get reamed out this week. Once I get the FCD back, I can make loads that headspace on the shoulder rather than the belt, which is likely the #1 thing I can do to improve accuracy at this point.
All in all, I'm happy with where I'm at now - this is a featherweight rifle with a non-match bullet in a not-so-accurate caliber and I've got a safe MOA load that's 150+ ft/s faster than book and should be completely temp-insensitive given the powder and that it's sitting on a velocity node. If I can improve on accuracy with better headspacing and bedding, that's great but it's not required.
I'll do another update when I get the rifle and FCD back. I need to do velocity spreads, and I might do a temp test as well. Both need to wait for the new crimp die. I'm not sure I'm going to go so far as to take the temp chamber to the range, but I may at least ice down some rounds as I'm more interested in low temp performance than high-temp.
My objective was to get there safely from zero load data in less than 35 rounds, and it took 31. These are all quasi-cold-bore shots BTW. I made 10 shots of this, but I saved the last 7 for future use (including possible hunting) or teardown, since I know I'm going to be making some major changes.
It would be nice to have a new-brass and fired-brass load that shoot to same POI, but we'll have to see if that plays out or not.
The rifle is now in for pillar and skim bedding. I'm not necessarily expecting improved accuracy (although I might get it), but I do expect improved rigidity and a stock less sensitive to enviromental conditions both of which are important to me. The lee FCD and world's finest trimmer will be going in to get reamed out this week. Once I get the FCD back, I can make loads that headspace on the shoulder rather than the belt, which is likely the #1 thing I can do to improve accuracy at this point.
All in all, I'm happy with where I'm at now - this is a featherweight rifle with a non-match bullet in a not-so-accurate caliber and I've got a safe MOA load that's 150+ ft/s faster than book and should be completely temp-insensitive given the powder and that it's sitting on a velocity node. If I can improve on accuracy with better headspacing and bedding, that's great but it's not required.
I'll do another update when I get the rifle and FCD back. I need to do velocity spreads, and I might do a temp test as well. Both need to wait for the new crimp die. I'm not sure I'm going to go so far as to take the temp chamber to the range, but I may at least ice down some rounds as I'm more interested in low temp performance than high-temp.
mpd61
Member
This is awesome. .....
Dr T
Member
This is a fascinating thread. It is always nice to see the term "least squares fit" used with a straight face (whenever I used it in a talk people's eyes began to glaze over--especially since I was working with data on a log scale. It was lognormal data......)
Going back to your post of 26 July 2019, your graph of velocity vs charge weight is very interesting. It looks like if you subtracted the least squares fit from the observations your data would look sinusoidal. I wonder if this has something to do with the barrel harmonics. I suspect that it is related to the flat spots in velocity you discussed earlier.
Going back to your post of 26 July 2019, your graph of velocity vs charge weight is very interesting. It looks like if you subtracted the least squares fit from the observations your data would look sinusoidal. I wonder if this has something to do with the barrel harmonics. I suspect that it is related to the flat spots in velocity you discussed earlier.
OP
OP
Llama Bob
member
- Joined
- Feb 25, 2016
- Messages
- 2,258
Your suspicion matches mine. There's only two large forces on the bullet - pressure and friction. The charge weight and combustion model has a lot to tell us about pressure and doesn't predicts big sweeping curves, so it stands to reason the friction is the cause of the sine-wave type behavior. And the friction is clearly related to barrel diameter. However, the actual dynamics must be complicated since the speed of waves in the barrel steel is much faster than the speed of the bullet and some of the meaningful dimensions like barrel wall thickness are very small (so waves in those directions are very, very fast).
I don't know if the way the barrel "breaths" can be understood with a level of technology anyone would be willing to apply to the problem.
Dr T
Member
And those waves will be reflected from the muzzle back towards the receiver. In effect you are trying to get a load that will generate a standing wave in the barrel.
OP
OP
Llama Bob
member
- Joined
- Feb 25, 2016
- Messages
- 2,258
It seems like there would be movement in several directions. I've seen finite element analyses that show fairly complex oscillations. They also didn't agree very much on what they might look like either.
Experimentally it appears that local velocity maxima corespond to a closed bore on bullet exit and thus accuracy. Why this might be, I have a hard time explaining from any sort of basic friction argument
Dr T
Member
Well, it is probably because the underlying data for those FE models was either not collected or analyzed properly (or both). (My cynicism has some basis in over 35 years experience in working in industry on data collection and analysis problems).
I did a thought experiment on the data collection apparatus needed to collect and analyze the data. Off the top of my head, I would like data collected simultaneously from at least 5 points on the barrel with non-contact vibration sensors capable of measuring things on a very small scale. I would collect the vibration waveforms digitized at a rate of about, say, 250 Ksps with 16- or 32-bit samples. My rationale for the sample rate is that the bullet is spinning at about 250000 rpm (or 4500 rps), and I would want to look at the harmonics of the impulse wave and the perturbations induced by the spinning bullet. Once, you get the waveforms are collected, the fun will begin with liberal applications of the Fourier transform and other waveform analysis things.
All very do-able, and similar stuff has been done in the communications industry for years. If it has been done in this context, the research is probably buried a research lab somewhere. It would make a nice masters or part of a PhD project (if you sorted out all of the physics).
I did a thought experiment on the data collection apparatus needed to collect and analyze the data. Off the top of my head, I would like data collected simultaneously from at least 5 points on the barrel with non-contact vibration sensors capable of measuring things on a very small scale. I would collect the vibration waveforms digitized at a rate of about, say, 250 Ksps with 16- or 32-bit samples. My rationale for the sample rate is that the bullet is spinning at about 250000 rpm (or 4500 rps), and I would want to look at the harmonics of the impulse wave and the perturbations induced by the spinning bullet. Once, you get the waveforms are collected, the fun will begin with liberal applications of the Fourier transform and other waveform analysis things.
All very do-able, and similar stuff has been done in the communications industry for years. If it has been done in this context, the research is probably buried a research lab somewhere. It would make a nice masters or part of a PhD project (if you sorted out all of the physics).
- Status
