How does the Geissele MK4 rail lock up?

[markm]

While they may be ok to use as barrel nuts, my strong preference is still steel.

Totally agree. On a combat gun, a real Colt steel nut is non-negotiable. I remember hearing Ken Elmore from S.A.W. talking about how he Squished aftermarket barrel nuts in a bench vise, and how they sucked compared to the real deal.

[Defaultmp3]

Barrels get hot, very hot, steel conducts heat, aluminum retains heat. Aluminum has a far higher thermal expansion rate than typical barrel steels and since it retains heat, it is susceptible to thermal expansion at lower temperatures than steel.

Huh? 7075 has far better thermal conductivity than steel, at 130 W/(m⋅K), while 17-4 is between 18 to 23 W/(m⋅K) depending on the external temp (barrel nut used by Griffin Armament), 4140 is at 42.6 W/(m⋅K) (USGI, Samson, Fortis, Daniel Defense, etc.), and 1018 is 51.9 W/(m⋅K) (Compass Lake Engineering, Anderson, etc.). Not sure how much the much higher thermal conductivity helps with mitigating the thermal expansion issue, but the thermal conductivity is definitely an advantage for 7075.

[HKGuns]

Huh? 7075 has far better thermal conductivity than steel, at 130 W/(m⋅K), while 17-4 is between 18 to 23 W/(m⋅K) depending on the external temp (barrel nut used by Griffin Armament), 4140 is at 42.6 W/(m⋅K) (USGI, Samson, Fortis, Daniel Defense, etc.), and 1018 is 51.9 W/(m⋅K) (Compass Lake Engineering, Anderson, etc.). Not sure how much the much higher thermal conductivity helps with mitigating the thermal expansion issue, but the thermal conductivity is definitely an advantage for 7075.

You are correct, I got it backwards.

[Disciple]

I admit I have a psychological preference for steel barrel nuts but lysander doesn't see aluminum ones as a problem.

You know they make aluminum barrel nuts for some free-float handguards that hold up just as well as steel. The weak point is the aluminum receiver threads. Aluminum is lighter that titanium.

[Disciple]

I remember hearing Ken Elmore from S.A.W. talking about how he Squished aftermarket barrel nuts in a bench vise, and how they sucked compared to the real deal.

How is that test of barrel nut performance? That seems about as useful as drilling holes in a 7075 receiver, finding it easier to do so than a steel one, and declaring AR-15's to be junk.

[TMS951]

Being that the barrel is slid into a aluminum receiver and very little of it contacts the barrel nut. The nut also screws onto the aluminum threads on the upper.

Based on this I don’t see how a steel nut offers anything over aluminum, unless the upper was steel.

Honestly I’d want the upper and barrel nut and rail all made from same material so they all expand together. Other wise you end up with a steel, aluminum, steel and then aluminum sandwich. That’s sounds terrible.

[markm]

How is that test of barrel nut performance? That seems about as useful as drilling holes in a 7075 receiver, finding it easier to do so than a steel one, and declaring AR-15's to be junk.

Not sure on the full back story of why he was even doing it. But the point was that the shit nuts were nowhere near the strength of a real Colt barrel nut.

Based on this I don’t see how a steel nut offers anything over aluminum, unless the upper was steel.

I'd guess that the TDP would allow for an aluminum nut if it were acceptable. It's beyond my expertise, but some of the torque values I've had to crank on to remove would not leave me sleeping well if the nut were aluminum.

Honestly I’d want the upper and barrel nut and rail all made from same material so they all expand together. Other wise you end up with a steel, aluminum, steel and then aluminum sandwich. That’s sounds terrible.

Not following this logic. That's exactly what the design has been for many decades. And it's worked/works great. Extension, receiver, and nut.... steel/aluminum/steel. I'm sure Stoner explored this extensively to come up with the design.

[Disciple]

Not sure on the full back story of why he was even doing it. But the point was that the shit nuts were nowhere near the strength of a real Colt barrel nut.

And my point is that a 7075-T6 receiver is nowhere near the strength of the same part milled from hardened spring steel. Will you be switching? lysander said "The weak point is the aluminum receiver threads" after all. It's kind of funny I find myself arguing this because as stated I prefer steel barrel nuts anyway, but I think the idea of squishing parts in a vise to declare them unfit is a joke.

[DoubleW]

I don’t think a Geissele barrel nut has ever failed or caused any problems. So this whole argument seems like a moot point to me.

[MegademiC]

And my point is that a 7075-T6 receiver is nowhere near the strength of the same part milled from hardened spring steel. Will you be switching? lysander said "The weak point is the aluminum receiver threads" after all. It's kind of funny I find myself arguing this because as stated I prefer steel barrel nuts anyway, but I think the idea of squishing parts in a vise to declare them unfit is a joke.

Yeah, a gi style nut made of aluminum would be bad, but the giessele design is designed with the strength of aluminum in mind and is very robust. Theres a lot more material involved to take the stresses.

Comparing materials is irrelevent without taking the design and stresses into account.

If you look at quicklinks, steel ones dont offer much strength over aluminum, only abrasion resistance.