I have used a similar load for 15 years and tens of thousands of loads. I have also shot a lot of actual Navy 262 ammo as well as the Black Hills commercial equivalent. Tested dozens of rifles of many makes in the 18” Mk 12 pattern.
Alan Brown from Crane who was instrumental in development of the Mk 12 shared a lot of information with me on the Navy testing.
Long to short is that the Navy utilizes a non cannister powder (we cannot get it) similar to TAC. It has flash suppressants and SLIGHTLY different burn rate. I cannot say if slower or faster.
According to my records the Douglas barrels are the second fastest. Proof barrels are fastest.
Over the long haul Navy 262 ammo shoots average 10 shot groups into 1.25 MOA. You will get better groups but this is long term average. Navy results were slightly less optimistic. They tested much more than I did of course.
If you load 24.x of TAC over a known consistent primer, VERY CONSISTENT POWDER METERING, seated to mag length and taper crimp you can reduce that to under 1 MOA average over a long series of 10 shot groups. The 77 SMK was not built as a 100 yard paper puncher. It does tend to hold up well at long range.
The area where the small scale hand loader can outperform Navy ammo is in consistent powder metering and a little judicious culling of brass.
BTW, accurate barrel life is 5200-5400 rds if not fired rapidly As mag dumps etc. Alan said 900-1200 rds full auto. This seems low but the Navy found the same thing I was told. Barrel wear shows up on chronograph or as vertical dispersion at 600 meters. Oddly bores will often appear ok to bore scope other than gas port area which will show great erosion.
So its not an SPR/1:7 but I do have an 18" WOA 1:8 twist. My favorite 77SMK load is 24.4gr of TAC which clocks in at a MV of 2751 with an SD of 5.4. Just a hair over MOA but also probably not my best shooting