Build Sheet
AR-10 / .308 Build Sheet
The big-bore AR, where everything you know from the 5.56 build applies, except that there are two incompatible patterns, and mixing them wastes real money.
7.62 NATO · Rifle · Intermediate · 3–4 hrs · Tools: Armorer's wrench, punch set, vise block, headspace gauge
What this build is
An AR-10 is an AR-15 scaled up for .308 Winchester and 7.62 NATO. The assembly steps are nearly identical and the tools are the same, with one addition: you should gauge headspace before firing it. That is why this build is rated intermediate rather than beginner.
The thing that actually catches people is not difficulty, it is compatibility. The .308 AR was never standardized, and two families exist. The DPMS / LR-308 pattern is the overwhelming majority of the market, and confusingly the widely used "SR-25 pattern" magazines belong to this family, not to the other one. The original ArmaLite AR-10 pattern is its own island. Receivers, barrel extensions, bolt carrier groups and handguards do not cross between the two. Buying half a rifle in each pattern is the most expensive mistake in this hobby.
Pick a pattern before you buy anything, and pick a chambering too. .308 Winchester and 7.62 NATO are close but not identical in chamber and pressure spec, and the choice determines which headspace gauges you need.
The parts list and what it costs
Every part of the firearm itself, with a ballpark price for each. Optics, mounts and extra magazines go on top of this. The estimated total for this build is $855–$1,155, the sum of the parts below with a ±15% band around it, because prices move.
| Part | Ballpark | Notes |
|---|---|---|
| Stripped lower receiver · FFL | $120 | The serialized part - pick your pattern |
| Lower parts kit (.308 LPK) | $60 | Trigger, safety, springs, pins |
| Rifle buffer tube kit + stock | $75 | .308-weight buffer |
| Stripped upper receiver | $110 | Must match the lower pattern |
| Barrel - 18" .308 | $220 | Nitride or 416R, mid-length gas on PSA 18" barrels |
| Gas block + gas tube | $40 | Match the barrel, mid-length for an 18" PA-10 |
| Free-float handguard (M-LOK) | $130 | .308 profile |
| Bolt carrier group (BCG) | $170 | Match pattern, HPT/MPI |
| Charging handle | $45 | Extended latch helps |
| Muzzle device | $35 | .30-cal brake or flash hider |
These are ballparks, not quotes. Prices move weekly and we do not invent them. The deal board links straight to the retailer's own product page so you see the live price before you buy.
The part that needs an FFL
As with the 5.56 rifle, the stripped lower receiver is the firearm and the only part that ships to a licensed dealer for a background check. Uppers, barrels, bolt carrier groups, handguards, and triggers all ship to your door. Note that the lower is also where your pattern choice gets locked in: a DPMS lower will not mate to an Armalite upper, so this first purchase determines every part that follows.
Where to save
These are the parts where the budget version and the premium version are the same material with a different roll mark:
- Handguard. Blem and raw M-LOK handguards in .308 profile show up regularly, same extrusion at a big discount.
- Stock and grip. These only affect ergonomics.
- Muzzle device. A basic .30-caliber flash hider is fine to start.
Where not to save
And these are the ones where cheap costs you twice:
- Barrel. More pressure, more heat, more money on the line. Buy 416R stainless or a quality chrome-moly barrel from a known maker.
- Bolt carrier group. It must match your pattern and your barrel extension, and it must be HPT/MPI tested. This is not the line item to economize on.
- Buffer and spring. .308 needs a .308-weight buffer. The wrong buffer beats the rifle up and causes cycling problems that look like ammunition problems.
- Headspace gauges. Not a part, but buy or borrow a set, and buy them for the chamber you actually have. .308 Winchester and 7.62 NATO are not the same chamber spec, and the gauges are chamber-specific.
Common mistakes
- Mixing DPMS / LR-308 and ArmaLite pattern parts. Receivers, BCGs, barrel extensions and handguards are all pattern-specific. Note that "SR-25 pattern" is DPMS-family shorthand, not ArmaLite.
- Skipping the headspace check: unlike a 5.56 build, .308 barrel and bolt combinations are not reliably drop-in. Gauge it before you fire it.
- Using an AR-15 buffer or spring. The .308 needs its own, heavier setup.
- Assuming rifle-length gas is automatic. Match the gas tube to the barrel's gas port position.
- Buying a handguard for the wrong receiver height. This trap is inside the DPMS family, not between patterns, since DPMS changed rail height around 2009, and a low-profile handguard will bolt onto a high-profile receiver with the top rail sitting proud.
Before you load it
Do all of this with the firearm confirmed unloaded and pointed somewhere safe, before it ever sees live ammunition. It takes a couple of minutes and catches almost every assembly error:
- Function check. The hammer or striker holds when cocked, the trigger releases it, and the trigger resets.
- Safety check. With the safety engaged, the trigger does not release the hammer or striker. Check every safety the design has.
- Hand-cycle dummy rounds or snap caps. Watch them feed, chamber, extract and eject. Do it slowly and watch, not fast.
- Headspace. If your barrel and bolt did not ship together as a matched pair, check it with go/no-go gauges for your exact chamber before firing.
- First live rounds one at a time. Load a single round, fire, and inspect the case, then do it again, then load a full magazine.
If anything on this list does not behave the way it should, stop and take it to a gunsmith. That is a cheap afternoon compared to the alternative.
FAQ
What is the difference between DPMS and ArmaLite pattern AR-10s?
They are two incompatible families of .308 AR parts. Receivers, bolt carrier groups, barrel extensions and handguards do not interchange. DPMS / LR-308 is the far more common family, and "SR-25 pattern" magazines and parts belong to it. Choose a pattern before buying anything.
Do I need to check headspace on an AR-10?
Yes, because unlike the 5.56 AR, .308 barrel and bolt pairings are not dependably pre-headspaced, so gauge it before firing.
Is an AR-10 harder to build than an AR-15?
Slightly. The steps are the same, but the pattern compatibility problem and the headspace check add real ways to get it wrong.
Which part of an AR-10 build needs an FFL?
Only the stripped lower receiver. It is also where your pattern choice gets locked in, since the upper has to match it.
Price this build out
The deal board tracks parts for this build across the retailers builders actually use. Every listing links straight to the shop's own page for the live price.
Browse the gear →Affiliate disclosure: Cold Bore Index earns a commission when you buy through links on this site, at no extra cost to you. We link to real products at retailers you already use; prices and availability are shown live on their pages. We're not a dealer and hold no inventory. Nothing here is legal advice. Firearm laws vary by state and by city, and checking yours is on you.