I've often pondered the real world performance of a short 22-250. Sadly, this is one configuration that is very difficult to find reliable data on. When doing research, you see people reporting every number under the sun. Most of the "data" isn't data at all, but pure speculation base on other speculation that they read somewhere and are now regurgitating. A sad state of affairs that seems to illustrate one of the core flaws with the internet itself and society as a whole. I spend more time shooting than talking about it, and I spend a lot of time talking about it. As per the norm, it soon became clear to me that if I wanted any real data on this, I was going to need to collect it myself. I sent a factory Remington 700 chambered in 22-250 with a 14 twist 24" sporter barrel over to TS Customs to get cut down so I could do some testing.
Hornady 50gr VMAX
38.5gr of Varget
The above load averaged 3800fps from the 24" tube, and represents a stout charge of Varget. No massive pressure, but there was a hint of it, letting me know I'd found the limit. I had Travis cut the barrel down to 16" and thread for suppressor, losing 8" of barrel. We then attached a new Magnetospeed chrono to the suppressor, and set my PVM-21 chrono at 10ft. The goal here was two-fold. First, to see just how much velocity we would lose, and second to see how accurate this new Magnetospeed was. My PVM has pretty well proven itself over the years, as I've proofed out countless loads and rifles through it with real world testing at distance validating my numbers. As far as optical chronographs go, I trust it more than I trust any other chronograph. I have had numerous other chronographs tested against the PVM. Some units I've purchased myself, and others that friends and customers had stopped by with to compare. To date, every other chronograph tested from every consumer brand you can imagine has been planted behind the PVM and been found desperately wanting. So much so that I've witnessed the owners of the chronographs in question shoot them upon the conclusion of the testing. Basically, they served better as targets than they did velocity collection devices.
For testing, I used the exact same ammo which was loaded at the time I took the velocity readings on the barrel at factory 24" length. This would ensure as real representation of the velocity lost as possible. I fired 20 rounds across the chrono's simultaneously to ensure the bare minimum of statistical significance to the data.
Temp - 44F
Station Pressure - 28.45in/hg
Humidity - 60%
As expected, the Magnetospeed recorded slightly faster velocities than the PVM-21 with an average reported velocity difference of 14fps. I can attribute this to the PVM being 10ft away from the muzzle, while the Magnetospeed is hanging right on the end of the rifle. The numbers for each individual shot were all very close to that average, with the exception of shot #2. It's very difficult to choose who to believe here. Both readings by the PVM and Magnetospeed for that shot are significantly lower than the rest of the rounds in the string, but there is no clear way to statistically break out which chronograph could be at fault. You'll also notice that shot #2 represents the largest disagreement between both units. With a spread of 45fps, it is nearly twice the spread as the next largest difference.
With both chronographs producing numbers that are this close to each other across a string of 20 shots, it is clear that both are quality units. Though interpretation of the data can raise some interesting questions. For instance, take a look at shots 15 and 16. Here we have an instance of both chronographs agreeing that two separate rounds fired had the exact same velocity, and each of them reported that same velocity on the nose. This brings up an interesting point about the magnetospeed. Had it not been for its display showing the last shot fired at the exact same velocity, one could assume that the shot may not have been recorded at all! This has happened to me countless times over the years when using chronographs that only displayed the velocity of the most recent shot. However when glancing at the Magnetospeed, it was very clear I had indeed fired another shot and it did indeed record it at the exact same velocity. Was this simply a strange statistical anomaly, or are some chronographs more accurate than we think they are?
There are many other questions which are outside the scope of this article, but lets take a second to recognize some additional talking points: Does the Magnetospeed change barrel harmonics and negate the possibility of load development with it attached? Which is easier to setup? Which produces the most accurate velocities? Which is less affected by conditions and environment? Which costs less? Which is easier to transport? The answers to some of these questions are very easy to produce, while others are much harder to quantify.
It's hard to say if the Magnetospeed affects harmonics or not. My time working with rimfires and tuners leads me to believe that it absolutely will. As little as 2 ounces added to a barrels end or moving the tuner in or out 2 thousandths of an inch can cause drastic changes in how they perform. However, I've not specifically tested on/off modes to see whether it does or not on a centerfire. So while logic and experience is telling me one thing, I have no proof. That being said, I will not do load development with the Magnetospeed attached. I will have it on when doing a pressure ladder, to see whether the components selected will even get me in the ball park velocity-wise, and then take it off for the actual OCW.
Ease of setup, use, and transport goes to the Magnetospeed without question. The PVM is decidedly european, and thus needlessly complex with a remote control being required for its operation. Very time consuming to setup properly as well. The Magnetospeed however is very intuitive and easy to attach and use. No fuss what so ever. The ability to handle adverse conditions would also go to the Magnetospeed. If a good wind is kicking, it is very hard to get the PVM to stay still on even the nicest of tripods. The PVM-21 will run you about $1000 by the time you get all the battery packs and chargers required for off-grid operation, while the Magnetospeed V3 can be had for $400. For these reasons, it would be foolish to overlook the Magnetospeed if you are going to buy a chrono.
Now lets take a look at what a short barrel does on a 22-250. When I collected the velocity on the factory barrel, it was done with the PVM, so that is the average velocity we will use. Coming from the 24" barrel we lost 258fps. Dividing that among the 8" of barrel removed, we come to a 32fps per inch of barrel lost on average. I would bet the fps per inch from 24-20 was considerably lower than that from 20" to 16". There it is, the hard data I was looking for! Now, when you take a look around and see people regurgitating that 50fps per inch number, you can realize just how terribly misinformed they really are. I've done similar testing with a 223rem and 308win... and both were closer to 25fps than they were to 50fps per inch.
Remember, the same load from the same exact lot numbers of components were used for each barrel length. I would bet 5 million illegal immigrants that I could squeeze some more FPS and much better ES out of this rifle if I went back and did a fresh load development. Better still, I'm going to get it back to Travis @ TS Customs to re-barrel it with a good Benchmark tube and go from there. This was a fun and illuminating exercise.