Autopsy Of A Rifle: DPMS Oracle 5.56mm


Part 1: Overview

This is a factory new DPMS Oracle. And, it’s the first rifle featured in our “Autopsy” series.
This rifle was unboxed and fired for function. 60 rounds of M193 were fired to test for any obvious issues which would eliminate it as a candidate for this series.
This is an objective review, from an armorer’s perspective of the components and assembly procedures of this rifle.
This is not a knock at DPMS or their fans, but the purpose of Gun Plumbers Inc is to educate shooters on various platforms to help them make the most informed decision when buying a rifle or components.

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Part 2: Lower receiver.

Lower receiver appears to be in-spec and small lower parts are installed correctly and are of the correct materials. Then again, you have to really go out of your way to mess up a detent.

This rifle comes with a carbine buffer weight and milspec action spring. We’ll come back to this later on.
Castle nut is not staked, and receiver extension threads have not been treated with anti-seize. Castle nut broke loose at 22ft/lbs. (38-42ft/lbs is textbook). Coupled with no staking that could be an issue under a heavy course of fire.
Receiver extension is commercial. Although I cannot find any definitive answer from DPMS, commercial receiver extensions are typically made from extruded 6061 aluminum, as opposed to milspec forged 7075T6.
While there may be a debate if this is an issue, there is no debate that 7075 T6 has twice the tensile strength of 6061.
Milspec receiver extension threads are rolled which creates a 7% stronger thread, but more importantly the threads are deeper and interface with the receiver threads deeper, as opposed to commercial receiver threads which are cut.

Trigger pull was 6lbs 11oz. This is within the acceptable range.



Part 3: Bolt Carrier Group.

This rifle has a semi auto carrier.
Extractor spring is milspec with black insert.
Carrier key is fastened with inferior YFS screws as opposed to grade 8 torx fasteners, and very poorly staked.
Notice how the staking does not engage the fasteners. Fasteners broke loose with ease.
Inferior fasteners and weak staking are causes for short stroking due to gas leakage.
Bolt is marked MPI only.
I cannot find a definitive answer for what the material is, and I won’t speculate.
I’m always a bit suspicious of products when there’s ambiguity in the specs. Most quality companies are pretty proud of the testing and materials used…and they want you to know it. Detailed product descriptions help take the guessing out of component selection.

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Part 4: Upper receiver assembly.

16″ barrel, carbine length gas system.

First thing I noticed was the railed gas block is not on the same plane as the rails on the upper receiver. This will create issues with mounting BUIS…as they must be on the same plane. Some companies do make front sights that are elevated to compensate for this. Sounds like a lot of trouble to go thru to correct what should have been done right in the first place.
The gas block is made of aluminum. Aluminum gas blocks are quite problematic. Your barrel is made of steel… when your barrel gets hot (they do that sometimes), the steel barrel and aluminum gas block will heat and expand at different rates. This differential will cause leakage and short stroking under moderate to heavy use.
When I removed the handguards I noticed they did not have heat shields.
Removing the gas block revealed some kind of material to prevent the screws from backing out, but it was not red loctite (272).
The barrel was pin guaged at .070. This would be on the large size, and would be considered over gassed. Remember it also comes with a carbine buffer weight. This combination can be problematic.
Barrel nut broke loose at 90ft/lbs.
The acceptable range is between 30-80ft/lbs for a USGI barrel nut.
I can’t tell if it was over torqued at the factory, or if the 60 rounds I fired before tearing it down caused some carbon issues since the threads were not treated with anti seize.
Treating threads is critical to prevent carbon from seizing the barrel nut, and because USGI barrel nuts are made of steel and the receiver threads are aluminum.

Upper receiver appears to be in spec, and M4 feed ramps are present.

Barrel is 4140. No markings to indicate testing, and Barrel appears to be untreated, and not chrome lined.

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Michael Mihalski
Contributor at Primary & Secondary