I've never been much of a fan of big magnums in short barrel lengths. However, a customer recently asked about the possibility of a 22" 7LRM. I thought it was a great idea. Of all the magnums, I thought the 7LRM would quite possibly be the best candidate. It is so very efficient, and predictable... so we went after it! TS Customs sent the barrel over the other day, and it was finally nice enough to get out and do a little work. We were very short on time, with the loss of daylight setting in quick.
70.5 - 2850fps
71 - 2860fps
71.5 - 2880fps
72 - 2930fps
It would seem my suspicions were correct! This thing is amazing in shorter barrels. Only losing around 20fps or so per inch from 26" to 22" is pretty amazing for a cartridge of this size. Started to see a hint of pressure at 72gr, and while I have no doubt there is another node there, it was kind of cool today so any load up there would not work in the heat of summer. 70.5 was centered on a node and was a laser. To put it in perspective, I'm using the same 70.5gr load in my 30" barrel and seeing 3020fps. Roughly 75fps drop from 30 to 26, and roughly 75fps drop from 26 to 22. That certainly demonstrates the efficiency! That is quite a lot better than what I've seen from 7rem mag and 300WM barrel comparisons, which are typically 125fps loss from 30" to 26, and 150fps loss from 26 to 22. Obviously these are "average" figures since the different individual barrels will all have some variance.
A 180gr VLD will only need around 7.3mils from 100yd zero to get to 1000yds. A 10mph full value wind will push it 1.7 mils. Still pretty impressive. My 30" tube is 1 mil flatter, but only 0.1 mil better in the wind.
It was a great experiment, and it turned out very well.
Here is the last 3 shots, confirming the 70.5gr load.
That is quite impressive, and would make a heck of a Hunting rifle.