The HTI is described as:
A long-range rifle in a compact package.
It can be found in Montuyoc province, inside the large base to the far east. The mission “The Instructors” is nearby. The weapons case is inside the armoury on the north edge of the base.
This base has a drone jammer, making recon difficult, but the easiest approach is almost certainly from the north-east, where there should be able to access the base and receive the least resistance. If you disturb the enemies here, remember this is a difficult province, and a large base. You’ll have helicopters on you before you know it.
The HTI is a bullpup sniper rifle, but with similar stats to the MSR. Both fire very slowly, but this is the slowest firing gun in the game. You cannot afford to miss a shot! It makes up for that with great range, accuracy and having the highest damage of all the sniper rifles.
Again similar to the MSR, it only has a 5 round standard magazine, but the HTI offers no extended magazine option. You may want to give this rifle a try, but the MSR is the better hard hitter.