Don’t Get Benched: Must-Have AR Spare Parts for the “What If” Moments

Let’s face it — gear breaks. And when it does, it’s almost never at a convenient time.

One second, your AR 15 is running like a dream, mid-mag, mid-range day. The next? Click. Silence. 

You’ve just entered the “What If” zone — where one tiny failure can sideline your rifle, kill your momentum, or worse, leave you defenseless.

Here's the good news: With a few key spare parts, you can recover quickly, fix the issue, and get back on target.

At Bear Creek Arsenal, we focus on two things: building reliable rifles, and helping shooters prepare for the unexpected.

That's why we made this easy guide. It lists the most important and affordable AR parts. Every shooter should have these AR 15 parts on hand.

First up is the Bolt Carrier Group (BCG) — the heart of your rifle. It chambers, fires, extracts, and repeats. If anything’s going to knock your rifle out of the fight, odds are it starts here.

Having a complete, caliber-matched BCG in your bag is an easy way to troubleshoot issues fast. Drop it in and go. Whether you're packing a .223/5.56, .300 Blackout, 7.62x39, or 6.5 Grendel, Bear Creek Arsenal BCGs are rugged, reliable, and ready to ride in your range kit.

Right behind that, you’ll want to keep a spare bolt. The bolt alone takes a serious beating over time, and when it cracks, shears, or fails, your rifle stops working — fast. We recommend keeping at least one pre-headspaced spare that matches your caliber. At Bear Creek Arsenal, our bolts are MPI tested, precision-machined to mil-spec standards, and affordably priced, allowing you to purchase spares with confidence.

You might not think about your gas tube until you’re manually cycling rounds like it’s 1865. Carbon buildup, dents, or poor handling can cause failures. And when the gas system fails, so does your semi-auto functionality.

Always pack a spare gas tube that matches your system (carbine, mid, rifle) and throw in a couple of extra roll pins too. They're cheap, light, and easy to lose.

Speaking of small but essential ARparts, don’t overlook the firing pin. It’s critical for ignition, but it’s also surprisingly easy to bend, break, or misplace. That’s why we recommend stashing two or three firing pins in your toolkit. They take up almost no space and can turn a frustrating failure into a 30-second fix.

If you’ve ever disassembled a lower and watched a detent spring launch itself into another dimension, you understand having AR lower parts kit (LPK) spares is essential.

Takedown pins, detents, springs, and the bolt catch assembly are all small enough to lose and important enough to stop your rifle cold. Whether you build from scratch or just tinker, having a spare LPK or individual components on hand is a smart move.

The AR lower parts kit (LPK) is the unsung backbone of any AR build.

While the complete upper receivers and BCG get most of the attention, the tiny springs, pins, and plungers within the lower control how the rifle functions, how it feels, and its integrity when you rely on it the most.

Lose or damage one small detent or spring and your rifle can go from perfectly functional to a frustrating parts puzzle. That’s why a thoughtful LPK spares strategy is essential.

An LPK usually contains the small components that make the lower receiver operate. These parts include takedown/pivot pins, detents and springs, magazine catch and spring, bolt catch and plunger, selector (safety) detent and spring, trigger and hammer pins, trigger and hammer springs, and often the trigger and hammer themselves if you buy a full kit.

Each has a role:

• Takedown & pivot pins + detents/springs — These hold the upper and lower together and allow takedown. The detents are tiny and their springs launch easily during disassembly. Lose one and your rifle won’t stay assembled.
• Magazine catch & spring — Keeps magazines engaged reliably. A weak or broken spring can cause feeding or retention issues.
• Bolt catch, spring & plunger — Holds the bolt open after the last round — important for immediate-action drills and clearing malfunctions. A worn plunger or weak spring can cause intermittent bolt-hold open.
• Selector (safety) detent & spring — If damaged or missing, the safety won’t stay in position.
• Trigger & hammer pins/springs — They retain and tension the fire control group; damaged gun parts can change trigger feel or create unsafe conditions.
• Trigger/hammer (if included) — These should be treated as wear items: a bent pin or cracked sear will destroy function and safety.

Common failure modes & symptoms

• Missing detent/spring — Receiver won’t lock to the upper; pins fall out; takedown becomes a guessing game.
• Worn magazine catch spring — Magazines won’t lock, or they pop out under recoil.
• Weak bolt catch spring/plunger — Bolt fails to hold open after last round, or bolt catch feels mushy.
• Selector detent failure — Safety feels sloppy or won’t reliably click into safe/fire.
• Bent/worn trigger/hammer pins or springs — Poor trigger reset, light primer strikes, or complete function loss in severe cases.

How many spares to carry (practical advice)

For an “Oh No” kit keep multiples of the smallest, most failure-prone items:

• Detents & small springs: 4–6 of each (they’re tiny and disappear).
• Takedown/pivot pins: 1 spare full set (pins + detents).
• Mag catch & spring: 1 spare mag catch assembly or at least a spare spring.
• Bolt catch spring & plunger: 1 spare set.
• Selector detent & spring: 1 spare set.
• Trigger/hammer springs & pins: 1 spare set (or a spare LPK if you prefer).

If you shoot a lot or operate in dirt/wet environments, double those counts.

Tools to carry with your kit

A basic set makes LPK swaps painless:

• Small roll pin punches (or a universal punch set)
• A brass/nylon hammer (or small mallet)
• Needle‑nose pliers or tweezers for tiny springs/detents
• A small bench mat or magnetic tray to keep parts from rolling away
• Optional: a small multi‑tool (with flathead/Phillips) for magazine catch adjustment

If you’re assembling or changing pins in the field, work on a flat surface. And use a pin tray — those small springs are easy to lose.

Nothing ruins a good day at the range like stuck brass. A worn or broken extractor or ejector is often the culprit.

These components endure wear and tear with each use and require to be replaced occasionally.

Keep a spare extractor, extractor spring, ejector, ejector spring, and a few O-rings in your “Oh No” kit. This will help your rifle cycle smoothly.

Gas rings are another part that wears out faster than most people realize. If your BCG starts short-stroking or feels sluggish, the rings might be worn.

Good news? You can replace them in under a minute. Keep 2–3 sets in your bag and stay ready.

Don’t forget the buffer system. If your buffer spring weakens or the retainer fails, your rifle won’t cycle correctly — or you might find your buffer flying across the range.

A spare buffer spring (carbine or rifle length) and a buffer retainer with spring should be standard in your loadout.

If you want to be prepared (and let’s be honest, that’s never a bad thing), consider adding a few extra AR parts to your gear.

A backup charging handle is a great idea — they can break under stress and you’ll be glad you had one. Back-up iron sights are another smart add if you run optics.

Optics may become foggy, fail, or be misaligned. For those who value versatility, having an additional complete upper in a different caliber gives you both a backup and an entirely new functionality.

Here’s the quick checklist of what to pack:

• Spare BCG (caliber-matched)
• Pre-headspaced bolt
• Gas tube + roll pins
• 2–3 firing pins
• LPK components (springs, pins, detents)
• Extractor, ejector, springs, O-rings
• 2–3 sets of gas rings
• Buffer spring + retainer & spring
• Bonus: charging handle, backup irons, spare upper

Store everything in a compact tackle box, tool roll, or zip pouch and keep it in your range bag, go-bag, or truck. You’ll thank yourself the moment something goes wrong.

At Bear Creek Arsenal, we believe in keeping shooters prepared and equipped without breaking the bank. That’s why we offer:

• Affordable, American-made AR 15 & AR 10 parts
• Caliber-specific components for your builds
• Full support for DIY maintenance and upgrades
• Proven, mil-spec performance you can count on

Whether you're on the range, hunting, or prepping for uncertain times, we’ve got you covered.