View Full Version : How does the Geissele MK4 rail lock up?
davidjinks
10-02-23, 15:57
I watched a bunch of installation videos.
My main question is; is it just the 2 cross bolts that hold the rail in place?
I’m used to KAC, Larue, Daniel Defense rails and am not familiar with the cross bolt type setups.
How secure is it? Loctite for the cross bolts?
G-Rail Instructions (https://geissele.com/amfile/file/download/file/e8b7b96f8463cbfd4292c2836935f6f7/)
I've only installed HK G-Rails. I do not use thread locker of any kind on those models. The instructions don't say anything one way or the other, that I can find, about thread locker.
However, some rails, that use a similar lock up method, with helicoils to catch the cross bolts, specifically state not to use thread locker, as removal can destroy the helicoils. The models with the dogbone nut are probably ok for thread locker, but I'd probably avoid it out of habit.
The two screw lockup system is very secure in my experience. But I've not fallen down a mountain with one yet, so YMMV.
A lot of companies use a similar lock up method, I'd imagine if there were issues, it would be bitched about on the internet and I've not seen anything.
davidjinks
10-02-23, 16:20
So if I’m understanding the installation instructions, the 2 cross bolts actually apply clamping force to the rail/barrel nut.
G-Rail Instructions (https://geissele.com/amfile/file/download/file/e8b7b96f8463cbfd4292c2836935f6f7/)
I've only installed HK G-Rails. I do not use thread locker of any kind on those models. The instructions don't say anything one way or the other, that I can find, about thread locker.
However, some rails, that use a similar lock up method, with helicoils to catch the cross bolts, specifically state not to use thread locker, as removal can destroy the helicoils. The models with the dogbone nut are probably ok for thread locker, but I'd probably avoid it out of habit.
The two screw lockup system is very secure in my experience. But I've not fallen down a mountain with one yet, so YMMV.
A lot of companies use a similar lock up method, I'd imagine if there were issues, it would be bitched about on the internet and I've not seen anything.
Yep, you got it. There appears to be roughly an inch-ish (Edit: it is closer to 2") of rail clamped around the nut on most rails I've installed.
After reading the instructions more carefully, I see the G-Rails use AL barrel nuts.....Not a fan of AL barrel nuts personally and would prefer a steel nut, given the option.
davidjinks
10-02-23, 16:37
Appreciate the info!
Yep, you got it. There appears to be roughly an inch-ish (Edit: it is closer to 2") of rail clamped around the nut on most rails I've installed.
After reading the instructions more carefully, I see the G-Rails use AL barrel nuts.....Not a fan of AL barrel nuts personally and would prefer a steel nut, given the option.
Appreciate the info!
Glad it was useful, most welcome.
ETA: Also, if you look at the G-Nut, you see two round indents circling the nut fore and aft, those bolts slide through those grooves to prevent the rail from sliding off as well. It is very similar to the way the HK rails and nuts work, if not a direct copy.
Mk 4 locks up solid. I wish they'd dump the Mlok crap and do some full pic rail models... (other than the 500 dollar camp Perry version)
The bolts go through two groves and the rail is going nowhere. It’s a very solid, well made rail. There’s nothing wrong with the G Aluminum barrel nut so long as it’s not over torqued. Once installed and covered with a rail it’s a non issue.
The bolts go through two groves and the rail is going nowhere. It’s a very solid, well made rail. There’s nothing wrong with the G Aluminum barrel nut so long as it’s not over torqued. Once installed and covered with a rail it’s a non issue.
Is Geissele's barrel nun Aluminum? I never checked. As you point out though, the nut is huge with a large bearing surface. Very solid.
Is Geissele's barrel nun Aluminum? I never checked. As you point out though, the nut is huge with a large bearing surface. Very solid.
5. Slide the aircraft aluminum Geissele barrel nut (Item 2) over the barrel and hand tighten.
Yep.......I didn't realize they were AL either, as I've never installed one on a scratch build.
While they may be ok to use as barrel nuts, my strong preference is still steel.
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.
AL barrel nuts may be just fine, but I've seen no data or analysis to prove they are as good or better than steel in this application.
Maybe we can get a materials science engineer to pop into this sidebar and offer some math as evidence my concerns are unfounded.
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
10-03-23, 10:44
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.
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.
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.
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.
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.
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.
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.
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.
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.
BufordTJustice
10-19-23, 21:31
If the GA barrel nut is designed with the material properties of AL in mind, then it's very likely fine. It would permit the handguard to function as a heat sink in a very effective manner.
I have used V7 Weapons Grade V Ti barrel nuts for my BCM KMR handguards for almost a decade now. Very pleased with them;l I employed them for weight savings, but they are BCM-approved and fit/function exactly like the BCM nuts with the sole exception that I have never had a V7 Ti barrel nut round-over using the wrench during tightening.
I think Bill Geissele very likely diid his homework on the AL barrel nut. I wouldn't sweat it one bit.
Sent from my iPad using Tapatalk
Geissele has a lot of problems…barrel nuts are not one them.
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.