By adding six feet to the cannon, engineers at Picatinny Arsenal, New Jersey, increased the chamber volume as well as the rifling length of the artillery piece.
"We were able to push the round harder for longer, so it goes faster and further," David Bound, M777ER team lead, said in a recent Army press release.
"Think of it like a guy with a really long arm. He can hold a ball longer and throw it faster than a guy with a really short arm. So we just integrated that longer 'arm' onto the howitzer so that the same bullet could get acted on longer and quicker. That in turn means more range."
The latest configuration of the M777ER weapon integrates a special, .55 caliber cannon tube manufactured at the Army's Watervliet Arsenal. Engineers tested the weapon at Yuma Proving Grounds, Arizona, in November.
"Several Marines and soldiers were at Yuma in November to witness the firings," Bound said. "I think they are all very happy and impressed with the fact that the M777ER did what it did so quickly, and they are definitely excited to see the next step."
Testing to date has been done with legacy ammunition, which is what soldiers and Marines currently use every day. A new rocket-assisted projectile is being designed, as well as a new super-charge, Bound added.
The next step is to see if the M777ER platform can take the force from the new ammunition since it would be going from a 7-kilometer increase in range to a 40-kilometer increase in range, Bound said.
If all goes well, a user evaluation will be conducted and feedback on any other modifications will be solicited, he said, adding that this step could happen in July 2018.
"The latest test is certainly an intermediate step," Bound said. "We saw a few different outcomes than we expected to see."
For example, the gun is very light, so it moves when it shoots -- especially at low angles. But engineers did not expect to see it move as much as it did, he said.
What engineers expected to see and didn't was an increase in tube whip, the bouncing of the cannon tube after firing, but it appears the elevation system can lift all the additional weight and still hold the tube steady, Bound said.
Another concern engineers are wrestling with is blast overpressure, Army officials maintain.
When the weapon is fired, there is a blast wave that comes out of the muzzle. The muzzle brake, located at the end of the cannon tube, takes the energy of the extra propellant gases and redirects it backward so that it helps slow down the tube during recoil, Bound said.
"Unfortunately, this redirects all that energy back at the crew and, if we redirect it too much, we hit the crew with a large blast wave that can hurt them," he said. "To reduce the impact on the crew, the engineers at Benet Laboratories are designing a muzzle brake that gets us the efficiency we require while keeping the crew safe and out of the way of all the redirected energy."
Army officials did not say when the M777ER will be ready to fire 155mm rounds. The engineers have planned additional incremental improvements with several demonstrations over the next few years, according to the release.
"The main point of the [November] test was to build confidence," said Bound, adding that the team expects to see increasing range during future tests.
-- Matthew Cox can be reached at firstname.lastname@example.org.