NOTE: See Warning on first post of this thread
Part One - Intro: Powders and ProceduresFirst, a quote from 28 January 2012 on a thread titled
Another Bolt Rifle under Construction.
Hoot wrote:[It might be interesting to load up some "suicide runs" that would not safely go in an AR, but just to see what you can wring out of the caliber with a 24" bull barrel. ...
Hoot's challenge about possible work with a bolt action rifle as quoted above was not a direct cause of the following work, but it may have played some subconscious role.
Be forewarned that the ratio of verbiage to actual fact is pretty large in this report.
Over the last few weeks I carried out some shooting projects that required regular trips to the local range. Since I had a couple hundred extra Hornady 200-grain FTX .452 bullets (SKU #45215) on hand, I decided to coordinate a "suicide run" with the other projects, to find what maximum velocities I could obtain with these bullets. I used the Winchester Model 70 bolt-action rifle that's been described previously on this site. The barrel is 26 inches long with a 1-turn-in-24 inch rate of twist. (For more about the rifle, see
A Second Bolt Rifle.)
Because this rifle is not constrained by the pressure limits of AR-type rifles using this cartridge, it can safely be loaded to pressures somewhat over the SAAMI 450B limits. Readers are free to judge whether the pressures that produced the velocities reported below were foolishly high.
This effort was not directed toward a serious practical endpoint, so I did not attempt collecting replicate data. I generally shot a series of increasing powder weights using only one trial cartridge for each powder weight, trying to find an estimate of maximum velocity for several powders for this particular bullet. Neither was it quite a hold-my-beer-and-watch-this type of endeavor. I stopped tests whenever excess pressure signs appeared.
I checked Hornady and Ramshot manuals for powders that seemed to me to be candidates for higher velocities with lighter bullets and settled on five powders:
- Hodgdon Lil'Gun
- Winchester 296
- Accurate No. 9
- Ramshot Enforcer
- Vihtavouri N110
I also consulted a dozen different lists of burning rate posted on various web sites. As usual, the rank order varied greatly among these lists for powders having reliably tested 450B data. I may have overlooked one or two candidate powders. However, at this point I doubt they would contain sufficient pixie-dust to exceed safely the velocities I found. (If you have actual experience with similar light-bullet applications using powders other than my five, feel free to suggest these other powders.)
I used Rem 7½ primers, and maintained a overall length of 2.200". Cartridges were resized with the Hornady FL resizing die for each loading. The pressures in these trials did cause the cases to increase in length after firing and resizing, so cases were trimmed then length exceeded 1.700 inches. I always used a taper crimp to 0.474" diameter at the mouth, and when necessary added a side crimp with the Lee 45-70 factory crimp die modified as described in early threads in this forum.
I measured velocities with the midpoint of the chronograph screens about 10-12 feet in front of the muzzle.
I started powder charges at about maximum manual amounts that produced pressure maximums for ARs, and increased powder charges by full- or half-grain increments. I generally worked with sets of five cases for each trial. After loading five, I'd try them at the range, watching for the traditional signs of excessive pressure, stopping trials short of real problems.
In this rifle, the first sign of excessive pressure is is pierced primers, but this phenomenon is inconsistent and did not always occur at elevated pressures. With more pressure, the bolt becomes difficult to operate near the end of the handle upstroke, indicating that the cartridge has expanded permanently in the chamber and is resisting the camming-extracting action of the bolt. With a further increase in pressure in this rifle, there is an extrusion of the case head into the ejector slot in the bolt face, resulting in the usual "shiny spot" on on the case head.
When you examine the resulting velocities and compare them to your own or to manual data, keep in mind that this rifle has a 26-inch barrel, and that the action and barrel are constructed for safety with pressures up to the SAAMI max for any sporting cartridge. Also keep in mind that I don't know what the pressures actually may have been. I do know that pressures in these trials were not sufficiently high to expand primer pockets, but that's neither a reliable nor realistic measure of pressures. Measuring case head expansion as a pressure indicator wasn't possible because the cartridge cases used in these trials had been fired multiple times previously with various loads, If I were to think seriously that these 200-grain bullets at velocities near 3000 fps were really useful, I'd use new factory brass and make replicate measures of expansion after firing. I'd also do a lot of replication.
edited to repair ratio