09-16-2013, 10:53 PM
I suspect the bore is a bit tight, which will build pressure faster. It could be a result of minimal lapping on an economy barrel, since barrels are traditionally drilled tight, rifled, heat-treated, then lapped, if lapped at all.
For those that lap, the lapping process opens the land inner diameter. Most barrel makers use a lead slug that's embedded with lapping grit, and cycle the slug through the barrel until the desired finish and bore diameter is achieved.
The main issues I have are with publishing dangerous loads that are 320fps faster than they should be, then suggesting that it's because 5R rifling helps make a barrel faster. That was with the 2820fps 120gr TSX, and AA2520, which is literally 320fps faster than the fastest powder max load from industry-tested 24" barrels with the 120gr TSX. Then taking that data and concluding that it's a result of a special, fast barrel and running with it.
2820fps with a 120gr solid copper bullet is basically a max load or near max load in the .260 Remington, which I and many other forum members own, load, and shoot. The .260 Remington is a 60,000 psi SAAMI cartridge, and uses charges of even slower-burning powders with 42.7gr - 44.5gr weights to generate 2800fps. All it takes is pressure to get those speeds, so it looks like XCR was at least at 60,000 psi with that 120gr TSX load, maybe even higher.
What we did, instead of what is done on many other forums where a new reloader is insulted and basically trashed so they don't want to ever log on again, was try to find out what the details were behind the charge weight and powder type. Once I saw what the load and powder was, I asked what starting load he had worked up from before he hit 2820fps. To my shock, no starting load was ever used, just that max load of AA2520 that was developed for a cup & core 120gr bullet-not the TSX.
This highlights the importance of some basic reloading principles:
* Have a good source of reloading data for your specific bullet, case, primer, and powder.
* Know your maximum COL in your chamber with the bullet you're using.
* Have a good starting load, usually 10% lower than the maximum listed load. Ex: max load = 31.2gr, start load should be 28.1gr
...........( 31.2 x .10 = 3.12, 31.2 - 3.1 = 28.1)
* Know what pressure signs to look for, and how they start to show up (erratic velocities, expanded case heads above the extractor groove, loose primer pockets, etc.)
* Understand what types of powder are temperature sensitive, and at what temp increments you will start to see noticeable velocity changes.
There is nothing wrong with being new to reloading. We all were or are at some time. For guys like Drifter, LR1955, JASmith, and many other members of the forum, some of them were new to reloading before Reagan took office in 1981, and have been active hand-loaders since.
Many of us have experience with loading for the AR15 and AR10 already, as well as bolt guns and hand guns. In my case, I learned to reload on the .308 bolt gun, then went to AR10 in .308, .260 Remington, 6.5 Grendel, .223 AR15, .270 Winchester, and .40 S&W. I started with knowledgeable mentors who had been reloading for at least a decade per, and had more than a box of rocks for brains. Some people mysteriously escape the Darwin awards, riding multiple stacked factors of safety built-in by the industry, but eventually they will have an appointment with Mr. Murphy.
Our goal is to make sure that doesn't happen.
For those that lap, the lapping process opens the land inner diameter. Most barrel makers use a lead slug that's embedded with lapping grit, and cycle the slug through the barrel until the desired finish and bore diameter is achieved.
The main issues I have are with publishing dangerous loads that are 320fps faster than they should be, then suggesting that it's because 5R rifling helps make a barrel faster. That was with the 2820fps 120gr TSX, and AA2520, which is literally 320fps faster than the fastest powder max load from industry-tested 24" barrels with the 120gr TSX. Then taking that data and concluding that it's a result of a special, fast barrel and running with it.
2820fps with a 120gr solid copper bullet is basically a max load or near max load in the .260 Remington, which I and many other forum members own, load, and shoot. The .260 Remington is a 60,000 psi SAAMI cartridge, and uses charges of even slower-burning powders with 42.7gr - 44.5gr weights to generate 2800fps. All it takes is pressure to get those speeds, so it looks like XCR was at least at 60,000 psi with that 120gr TSX load, maybe even higher.
What we did, instead of what is done on many other forums where a new reloader is insulted and basically trashed so they don't want to ever log on again, was try to find out what the details were behind the charge weight and powder type. Once I saw what the load and powder was, I asked what starting load he had worked up from before he hit 2820fps. To my shock, no starting load was ever used, just that max load of AA2520 that was developed for a cup & core 120gr bullet-not the TSX.
This highlights the importance of some basic reloading principles:
* Have a good source of reloading data for your specific bullet, case, primer, and powder.
* Know your maximum COL in your chamber with the bullet you're using.
* Have a good starting load, usually 10% lower than the maximum listed load. Ex: max load = 31.2gr, start load should be 28.1gr
...........( 31.2 x .10 = 3.12, 31.2 - 3.1 = 28.1)
* Know what pressure signs to look for, and how they start to show up (erratic velocities, expanded case heads above the extractor groove, loose primer pockets, etc.)
* Understand what types of powder are temperature sensitive, and at what temp increments you will start to see noticeable velocity changes.
There is nothing wrong with being new to reloading. We all were or are at some time. For guys like Drifter, LR1955, JASmith, and many other members of the forum, some of them were new to reloading before Reagan took office in 1981, and have been active hand-loaders since.
Many of us have experience with loading for the AR15 and AR10 already, as well as bolt guns and hand guns. In my case, I learned to reload on the .308 bolt gun, then went to AR10 in .308, .260 Remington, 6.5 Grendel, .223 AR15, .270 Winchester, and .40 S&W. I started with knowledgeable mentors who had been reloading for at least a decade per, and had more than a box of rocks for brains. Some people mysteriously escape the Darwin awards, riding multiple stacked factors of safety built-in by the industry, but eventually they will have an appointment with Mr. Murphy.
Our goal is to make sure that doesn't happen.