I'm at a loss as to why you would want to practice shooting a different caliber then what you are actually hunting with? Back in the 80's and 90's, before the internet and when we relied on hunting magazines for information, I got caught up in the newest calibers, newest rifles, newest-bestest things out there that the writer would talk about, and bought stuff that I didn't need, and eventually learned, I didn't even want. An old timer that I first learned from said to buy a quality rifle in a popular caliber that you can find ammo for anywhere you go, and learn to shoot it. It took me decades to actually believe this, but now that I do, I don't have any need or desire to have any other caliber or rifle. Remingtion 700 BDL in 30-06 is 36 years old and still shooting less then one inch groups with factory 165 Federal Premium ammo that I buy off the shelf. I'm on my 3rd scope, but, but that's more from going cheap with the first one, and then finding a fantastic deal on the Zeiss that it has on it now.
To practice field shooting positions. To get better at breathing and trigger control. So save a ton of money in components. Much less powder, much cheaper bullets than ANYTHING larger than a .223. Brass is so inexpensive, shooters leave it on the ground at my range. So I have a steady stream of range pick-up .223 brass that I just have to clean and process. The "trainer rifle" also saves barrel life on your main rifle. My .223 A.I. has fired so many shots in the last year, I would have already worn out the rifle that it matches, a 6.5 Creedmoor. And every shot fired is probably half the cost of the 6.5 Creedmoor.
You bring up another thing that I don't understand. If you are at the range to improve your skills for hunting, should't you use the same equipment and conditions that you will encounter while out in the field?
Like shooting off the bed of the Mule, or the truck. Like kneeling, or using a barbwire fence for support, or a t-post? OR using your pack for support? Those are the shots made with the trainer. Long range practice is good because it trains you to identify distances, and to become competent at shooting an animal at those distances. It also lets you know what your limits are.
But its probably impossible to fire enough ammo through a rifle to wear out the barrel if you are shooting a cold barrel every time you shoot your rifle.
What about a cold bore shot from the positions previously mentioned? What about a cold bore shot from 500 to 800 yards? What about no matter if the wind is blowing 20 to 30 mph, go shoot anyway? Shoot 4 more rounds after that CBS, increasing the difficulty. 5, or even 50 rounds in 20 minutes, will wear out a barrel, I assure you. And every shot fired was a lesson
A lesson on what you did right as well as what you did wrong. Victory or defeat, learn from it. When you see a buck or a bull, your rifle barrel is cold. That first shot is all that matters, so your rifle and your skill needs to be based on that cold barrel.
I met a guy that said he needed to shoot a box of ammo through his rifle before it would zero in on the target. We where at the rifle range and he shot 20 rounds almost as fast as he could load them. I shot my rifle once, and that was timed while he was reloading his rifle. Those 20 rounds where all over the target. He didn't know where the first shot hit and he didn't care. Sure enough, after replacing his target, during the next shooting period, he shot a lot fewer rounds and most of them where in the bullseye. Probably a 2 inch group. The difference was significant. I shot my second round during that same shooting period and it touched the first one. He put another target up and did just about the exact same thing. My third shot was off a bit, but not enough to make me adjust my scope or change anything. I was done shooting, but he had another box or two of ammo. I left, he kept shooting.
He was wasting ammo, did not care, or was fouling in a recently cleaned barrel. The last scenario, I completely agree with. I NEVER trust a freshly cleaned barrel. After 10 rounds, of fouling, I might trust it.I've always wondered if he ever hit an animal where he wanted to when he went hunting?
To teach others to shoot, I rely on the .22 to get them into position, work on trigger control, and breathing.
Excellent tool 50 to 100 yards, but is an extreme range tool for 400 yards. You had better be a highly advanced rifle shooter to connect at 400 yards, with a .22 lr. And you had better have put in the research and testing to figure out the most consistent ammo to do it. Because we cannot handload .22 lr. Once they have the basics down, I don't know how shooting a small caliber like a .223 will have anything to do with my ability to shoot my .30-06 at a buck 200 yards away.
Once again, my Trainer, and many others exactly matches my primary rifles. Same weight, length, and barrel contour. It feels, and balances the same. Different stock, different trigger and different scope.
Then it is not a properly set-up trainer. In boot camp, they spent a week teaching us the different shooting positions, and dry firing over and over again, several hours every day. That sucked, but the reason they did it proved to be effective the next week. Those that struggled with the proper shooting positions also did the worse when given live ammo to shoot.
Completely agree, dry firing is invaluable, it reinforces breathing control, trigger control, and follow-through. But it does nothing for recoil management, and quickly getting back on target. That is where live ammo comes in