Gomu Gomu no Rifle is an extremely dangerous technique used by Monkey D. Luffy in the One Piece series. The attack is a variation of his very own signature Gomu Gomu no Pistol, which is basically stretching one's arm to quite far distances to deliver a punch. The difference with the Rifle technique is to add a quite literal and figurative spin to this basic concept.
To fire a Gomu Gomu no Rifle, Luffy stretches out his arm, somewhat like how one would do when preparing a Pistol strike. Of course, the difference comes in when Luffy launches it forward with a rotation applied to his arm. It is this spinning motion that gives the attack its name, as it is similar to the rifling in a gun barrel that causes a bullet to spin, increasing its accuracy and power.
The technique has gone through several variations across the series as Luffy's powers evolve. One of the more famous variants is the Gomu Gomu no Ougon Rifle, otherwise known as the Golden Rifle. This was used in one of his memorable acts in the Skypiea Arc, where Luffy was able to ring the golden bell to prove the existence of the golden city. It was a moment that left an even deeper impression due to its emotional and narrative impact.
The impact of the Ougon Rifle visually has been so much that it has made its way into merchandise, including wall scrolls featuring Luffy using this technique. This shows just how much of an iconic technique it is within the One Piece fandom.
As Luffy's powers have grown, so have the permutations for his techniques. Most of Luffy's normal attacks while in Gear Second state have higher variations of themselves added before their names with "Jet" attached to the beginning. While this hasn't been depicted for the Rifle, it is possible that a "Jet Rifle" could exist due to the trend set by other techniques such as the Jet Pistol.
That is what makes Gomu Gomu no Rifle so formidable: not in its power but in its sheer unpredictability. This spinning motion might make the attack harder to dodge or counter for opponents since the trajectory will be much less predictable than a straight punch. The second feature of the technique falls more in line with Luffy's general fighting style, which often relies on creativity and an unconventional approach to win over powerful enemies.
Luffy's techniques throughout the series have only become more complicated and powerful. Recent arcs have introduced techniques such as Gomu Gomu no Bajrang Gun, much more on the large side of the power scale. These techniques, however—like Rifle—are still relevant simply because they represent his growth from budding pirate to one of the strongest in all the One Piece world.
Any discussion relating to Luffy's current strength compared to the ones from the past includes techniques such as the Rifle that were taken into consideration on how they would become empowered with Luffy's improved Haki mastery and Devil Fruit capabilities. This perpetual evolution of abilities keeps the fans on their toes while speculating exactly how his classic techniques might be used in new and more powerful ways.