(covers information from several alternate timelines)
24th century phaser rifles had sixteen power settings, fully-autonomous recharge capability, multiple-target acquisition, and gyro-stabilization. They were slightly less powerful but much more sophisticated than Cardassian phase-disruptor rifles; some, such as Major Kira Nerys, considered them less effective in the field as their complexity made them less robust. (DS9: "Return to Grace")
In 2256, phaser rifles had at least two settings: stun and kill. Although both settings fired single blasts, these weapons could also be utilized to fire a yellow-colored cutting beam. (DIS: "Context Is for Kings")
In 2256, Captain Philippa Georgiou discharged a type 3 phaser into a water well on the Crepusculan homeworld, shifting the water table and allowing water to reemerge from the well in a large geyser. (DIS: "The Vulcan Hello")
Type 3 phasers were also occasionally used by officers aboard the USS Discovery. For example, in 2256, a couple of officers in the ship's mess hall were equipped with phaser rifles; one of these officers was even about to use his when Michael Burnham began attacking Cold and Psycho using Suus Mahna, though he was stopped by Commander Ellen Landry, who instead brandished a type 2 phaser to persuade Burnham to cease and desist. Phaser rifles were also carried by Landry herself and Kowski when they were part of a boarding party that traveled to the USS Glenn. There, Landry and Kowski used theirs, switching the weapons to the kill setting, to repeatedly fire at a creature which survived the phaser fire and chased the group, causing them to hurry to refuge in engineering and killing Kowski. In engineering, Landry fired a cutting beam from her phaser rifle to cut through a door that was otherwise jammed closed. (DIS: "Context Is for Kings")
In the 2260s, phaser rifles were not standard landing party equipment aboard Starfleet vessels. Typically, rifles were equipped only when firepower heavier than that of the type 2 phaser was required. Spock, for example, had to file a special requisition for one to be brought down to Delta Vega in 2265. (TOS: "Where No Man Has Gone Before")
23rd century (alternate reality)
James T. Kirk used a phaser rifle to try to take out Khan's jumpship 208 when it was firing on the Daystrom Conference Room at Starfleet Headquarters. When fired, this rifle only had a bright muzzle flash and recoil and did not appear to fire a visible phaser beam or a phaser burst.
Also, in 2259 of the alternate reality, Section 31 of Starfleet used rapid-fire phaser rifles that fired red phaser bolts. Khan brought one of these rifles along with him to Qo'noS and used it to defend himself and Kirk's away team from Klingon soldiers. One of the Section 31 security personnel on the USS Vengeance also carried one of these rifles. (Star Trek Into Darkness)
Facsimile phaser rifles were created by the Romulan Star Empire in 2367 and given to rebels on the Klingon planet Krios, in an attempt to destabilize relationships between the Federation and the Klingon Empire. Both the facsimile and Federation rifles had an output of 1.05 MW. The only physical difference to the standard Federation rifle was an emission crystal efficiency of 94.1%. This was eight percent above the standard model. Another difference was that the initial output spike of the phaser beam was inverted, a sign that the power cell had been charged with a forced pulse in the terahertz range – a method used in Romulan disruptors. (TNG: "The Mind's Eye")
The 2360s version of the rifle could be modified with the use of a tracking light mounted on the central body, as well as a shoulder strap designed for ease of carrying. (Star Trek: First Contact) A phaser rifle could be set to fire an expanding energy pulse. The pulse could be set low enough to avoid damaging equipment, but high enough to affect changelings. It also heated up the air it was fired through. (DS9: "The Adversary")
In the early 2370s, the compression phaser rifle began to be distributed to Intrepid-class, Nova-class, and other starships, including the USS Voyager and USS Equinox. (VOY: "Caretaker", "Equinox", "Message in a Bottle")
More advanced phaser rifles capable of firing phaser bolts as well as the standard beam were also used in the 2370s. These rifles had a pistol grip in back and either an underbarrel grip or a second vertical grip underneath the barrel (similar to conventional firearms of times past), and were capable of being modified with various types of scopes, barrels and power cells. The rifle variant with the underbarrel grip was used during zero-gravity EVA-operations in the Borg incident of 2373/2063. This variant was also able to be magnetized against a surface, further proving its usefulness in zero-gravity environments. (Star Trek: First Contact; Star Trek Nemesis)
When Worf's rifle ran out of power on the Ba'ku planet, he improvised and swung it, like a club, at a Son'a drone that was firing transporter tags at Ba'ku villagers and Starfleet crew. (Star Trek: Insurrection)
- Beam control assembly
- Discharge crystal
- Emission aperture
- Energy cell
- Power pack
- Prefire chamber
- Rapid nadion pulse
- Safety interlock
- "The Maquis, Part I"
- "The Maquis, Part II"
- "The Die is Cast"
- "The Adversary"
- "The Way of the Warrior"
- "Paradise Lost"
- "Return to Grace"
- "To the Death"
- "The Ship"
- "Let He Who Is Without Sin..."
- "Nor the Battle to the Strong"
- "Empok Nor"
- "Call to Arms"
- "Rocks and Shoals"
- "Change of Heart"
- "The Siege of AR-558"
- Star Trek films
- ST: "The Trouble with Edward"
- PIC: "Stardust City Rag"
Matt Jefferies is accredited with drawings for the original series type 1 and 2 sidearms which fitted together in a modular fashion. The said drawings also mention a mysterious "UNIT 4" for which no drawing or design was ever made public nor featured in the original series. Possibly this UNIT 4 was meant to be a phaser rifle, but never made it onto the show as explained below. (Star Trek: The Original Series Sketchbook, pp. 92-93)
My Type III rifle blueprints don’t show an obvious button on either the fore or aft grips. One of the postings [on TrekBBS] talks about buttons being hit at the wrong times, which I do recall as being an issue during production. Made for slight VFX headaches. Perhaps that affected how I drew the thing.
My in-universe rationale for the grips having no obvious buttons is that (also similar to one posting) the actual firing studs are buried under the ribbed poly-elasto-squishy grip material. (TrekBBS)
The modified phaser rifle that first appeared in "The Adversary" was designed by Jim Martin. A new feature was the addition of triggers, although on the prop they were buttons. Joe Longo commented: "Ira [Steven Behr] said that when he was watching people shoot, they hadn't been activating anything, so we made them more realistic. It gives the actors something to do". (Star Trek: Deep Space Nine Companion)
While Voyager originally only used compression rifles, they later also used the First Contact variant – indicating that weapon had been part of the ship's stores since they left DS9 in 2371. This seems anachronistic since that weapon was not introduced in other productions until around 2373, after Voyager departed. Even so, Deep Space Nine used two designs (the TNG rifle and the First Contact rifle) concurrently, indicating that no one design was "replaced", establishing that Federation postings could use two types simultaneously.
According to the It's A Wrap! sale and auction, the Star Trek Nemesis version of the phaser rifle (with flashlight) uses "a pair of C123 3-volt batteries... the bulb housing is inscribed '6v Lamp, Laser Products, P60'." A Surefire brand P60 designation lamp is capable of outputting 65 lumens of light. A stunt version from Star Trek: Nemesis was sold off on the It's A Wrap! sale and auction on eBay. 
The Original Series phaser rifle
In the final revised draft of the script for "Where No Man Has Gone Before" (dated 15 July 1965) (scenes 134 and onward), this type of phaser was referred to as "heavy," "large," "lethal-appearing," and "lethal." Also, its discharge was described as "a deep, fiery-red beam." The rifle, while carried by Kirk, was said to be "slung across his shoulder."  However, this is not shown in the episode's final version, the weapon instead being carried by hand.
For the actual construction of the rifle prop itself, Gene Roddenberry turned to an outside contractor, toy manufacturer and inventor Reuben Klamer, who was already renowned at the time for the Milton Bradley Company's now-classic board game, The Game Of Life. Roddenberry became aware of Klamer's work, as he spotted a prop gun in use at another television production, The Man from U.N.C.L.E. Contacted by Roddenberry, Klamer agreed upon designing the prop, the final version of 28 June 1965 being the version which Roddenberry approved. (Julien's Auctions presents: Star Trek)
Upon approval of the design, Klamer was given the go-ahead by Roddenberry to proceed with manufacture of the prop, admonishing him that time was of the essence as shooting was already scheduled to begin in July. In a video, shot for the below mentioned auction, Klamer recalled that he initially was only given a mere two weeks to come up with both the design and the prop. Already facing a deadline that he found nearly impossible to meet, Klamer, upon additional urging by William Shatner, who desperately wanted the prop, needed an additional staff of three, including employee Ab Kander, to complete the prop on time. Working around the clock, the weapon was constructed out of wood and finished with a blue/green metallic paint. Additional detailing included the hand-tooled aluminum barrel and spring-loaded trigger, a sliding switch to adjust the force setting, three plastic non-functional domed indicator lights, and inset plastic panels, as well as a telescoping antenna mounted to the top. Moveable pieces on the weapon included three acrylic turret tubes cylinders with what appeared to be copper painted metal conduit with ends painted to match the three force settings. The entire turret unit turned on a center axis. The black shoulder butt also rotated to be used as a handle or shoulder stock. According to Klamer, in the video, Roddenberry took possession of the prop in person, which measured 34×14×4.5 inches, in the second week of July, and was very excited about its end-result, reportedly exclaiming, "This is it! This does the job! Those guys at NBC will be surprised that we have this in the show." (Julien's Auctions presents: Star Trek)
In "Where No Man Has Gone Before", the phaser rifle's beam was reused animation from the impact of the laser cannon in TOS: "The Cage". ("Where No Man Has Gone Before" text commentary, TOS Season 1 DVD special features)
When it was announced – during the Watts riots of August 1965 – that the rioters were about to move to Desilu's production base of Culver City, California, the original phaser rifle from "Where No Man Has Gone Before" was one weapon that Herbert F. Solow suggested to Gene Roddenberry as a means of protection. (Inside Star Trek: The Real Story, p. 89) Apart from its use in the episode and its proposed anti-riot use, the phaser rifle prop was most notably re-utilized for well known official publicity shots, which featured William Shatner, in the guise of Kirk, holding the phaser rifle. (Inside Star Trek: The Real Story, pp. 117, 106, 190; et al.)
Roddenberry obviously reverted his initial enthusiastic stance on the phaser rifle, and it was retired from TOS after he decided that, in common with smoking, guns were not to be shown on the series, either. Regarding the TOS phaser rifle design, Bjo Trimble remarked, "The gun was just a little too lethal-looking for Gene's taste and he just didn't like it." (TOS Season 1 Blu-ray special features, Starfleet Access: "Where No Man Has Gone Before".) The phaser rifle prop was returned to creator Klamer, who kept it in pristine condition in his possession for the next half century. This made "Where No Man Has Gone Before" the only canon appearance of the design in the Star Trek franchise.
But the TOS phaser rifle became somewhat of an iconic piece in the Star Trek fan community, drawing the "The Holy Grail" analogy Star Trek-archivist Alec Peters; this prompted CBS Consumer Products to commission the manufacture of at least one copy for inclusion as a display piece in exhibitions, such as Star Trek: The Experience  and Star Trek The Exhibition. These reasonably accurate copies turned up in later (un)official publicity photographs and imagery of Dave Rossi and Elizabeth Dehner actress Sally Kellerman individually posing with the prop. (TOS Season 1 Blu-ray special features, Starfleet Access: "Where No Man Has Gone Before"; et al.) Apparently, a phaser rifle prop copy even ended up in Kellerman's possession after the 2010 Official Star Trek Convention in Las Vegas. 
Michael and Denise Okuda were both somewhat critical of the TOS-era phaser rifle. Although Michael Okuda found it "a cool concept" and particularly liked how some of the weapon's components moved, he also believed the phaser rifle had "kind of a funky design." He concluded, "I think they were right to retire it after ['Where No Man Has Gone Before']." Dave Rossi remarked on the opinions that the Okudas, who Rossi worked with on Remastered TOS, had about the weapon: "I'm told that my learned colleagues thought that the phaser rifle was a bit hokey-looking." Rossi's own thoughts on the TOS-era phaser rifle, however, differed substantially from those of the Okudas. "I love the phaser rifle," he raved. "The phaser rifle kicks butt! And I'm bummed that it only appears in ['Where No Man Has Gone Before'], because to have a phaser gun that can, you know, take the top of a mountain off, what did the phaser rifle do?! You know what I mean? I really wanted to see this thing in future episodes. I didn't think it looked hokey at all; I thought it was cool. It was bulky and it was mean and looked good in Kirk's hands a lot." (TOS Season 1 Blu-ray special features, Starfleet Access: "Where No Man Has Gone Before")
Creator Klamer eventually offered up the actual original phaser rifle itself, with the accompanying period studio paperwork, for auction in the Julien's Auctions firm's Hollywood Legends Auction on 5 April 2013. As lot 120 it had an estimate of US$50,000-$70,000, selling for over three times the high estimate at US$231,000, in the process becoming the most expensive Star Trek hand-held prop ever sold at auction to date, affirming Alec Peters' assessment.