Boresight Calibers Explained: .223, 300BLK, .44 Mag and More
By Optics Force | Published: 2026-11-03
Category: Handleidingen
Match the boresight to the exact chambering, not the bullet diameter. See how .223, 300BLK, and .44 Magnum laser boresights differ and which one to buy.
Quick answer
Buy the boresight that matches the exact cartridge your firearm is chambered for, not the nominal bullet diameter. For an AR-15 in .223 Remington or 5.56mm, choose the Firefield .223/5.56mm in-chamber laser; for a 300BLK rifle, choose the Sightmark 300BLK; for a .44 Magnum pistol, choose the Sightmark .44 Magnum.
Why chambering beats bullet diameter
A laser boresight works by sitting in the chamber or muzzle so its beam runs down the bore. If the body does not fit the chamber, the beam starts off-axis and your sight adjustments are wrong from the first shot. That is why a .44 Magnum boresight is not a substitute for a .44 Special or .45 Colt tool, and why .223 Remington and 5.56mm are usually treated as one fit family while 300BLK is a separate chambering.
The catalog facts for these three products describe chamber-style use: the Sightmark 300BLK chambers like a regular cartridge, and the Firefield .223/5.56mm is an in-chamber design. Treat the stated cartridge as the fit specification, not a suggestion.
In-chamber laser vs. other boresight types
In-chamber laser boresights are the fastest way to get a rough zero because the laser dot shows where the barrel is pointed before you fire. They are best for getting on paper and saving ammo, not for replacing a final live-fire zero at your intended distance.
The trade-off is caliber lock-in: one unit fits one chambering family. If you shoot several rifles, you either buy multiple in-chamber units or accept that the tool only serves one firearm. Also check battery type before you leave for the range; the supplied records show AG3 and AG5 batteries depending on the model, so keep the right spares on hand.
When a pistol boresight makes sense
Pistol boresights are most useful when you change sights, add an optic, or want a training aid for draw-and-point drills. The Sightmark .44 Magnum is built around that cartridge, so it suits a .44 Magnum revolver rather than a semi-auto in a different caliber.
Do not expect a pistol boresight to match a rifle zero distance. Use it to confirm the sight is roughly aligned, then verify with live fire at the distance you actually care about.
Decision rules for choosing a boresight
- Read the chamber stamp first: Check the barrel or receiver marking for the exact cartridge, such as .223 Rem, 5.56mm, 300BLK, or .44 Magnum. Match the boresight to that marking, not to the bullet diameter on the ammo box. If the stamp says 5.56mm, a .223/5.56mm in-chamber unit is the fit family to shop; if it says 300BLK, choose the 300BLK unit.
- Choose in-chamber for rifles you zero often: Pick an in-chamber laser when you want to get on paper fast and save ammo. The Firefield .223/5.56mm and Sightmark 300BLK both follow this pattern, so the deciding factor is your rifle's chambering.
- Choose a pistol-specific unit for handguns: For a .44 Magnum revolver, use the Sightmark .44 Magnum rather than a rifle boresight. It is also useful as a training aid for quick-draw drills, but confirm your revolver is actually .44 Magnum.
- Check the battery and kit before you buy: The supplied records list AG3 batteries with the Sightmark units and a carrying case with all three. Confirm what is included so you are not hunting for batteries at the range. Keep a spare set of the listed battery type in your range bag.
Product facts
- Sightmark .44 Magnum Boresight: Chambered for .44 Magnum pistols and includes a carrying case, three AG3 batteries, and instructions. You get a ready-to-use kit for a .44 Magnum revolver, but the included batteries are AG3, so buy AG5 spares only if your other gear needs them.
Sightmark .44 Magnum Boresight - Firefield .223/5.56mm In-Chamber Red Laser Brass Boresight: In-chamber red laser design for .223 Remington / 5.56mm rifles. It fits AR-15-pattern rifles in that chambering family and lets you adjust sights to the laser dot before spending live ammunition.
Firefield .223/5.56mm In-Chamber Red Laser Brass Boresight - Sightmark 300BLK (7.62x35mm) Boresight: Chambers like a regular cartridge in 300BLK (7.62x35mm) rifles and includes a carrying case, three AG3 batteries, and instructions. It is the correct fit for a 300BLK rifle, where a .223 boresight would not seat properly and would give a misleading beam.
Who should buy which
Best for
- AR-15 owners in .223 Remington or 5.56mm who want a fast rough zero
- 300BLK hunters and competitive shooters who want to save cartridges
- .44 Magnum revolver owners who change sights or practice draw drills
Not for
- Shooters who need one boresight to cover several different chamberings
- Anyone expecting a laser boresight to replace a final live-fire zero
- Firearms whose chambering is not listed for the product
