A Tale of Two Crush Washers, or Two Crush Washers One Barrel, and other AR oddities

[cmshoot]

Don’t know what’s going on at Wilson Combat. I’ve had my hands on numerous Wilson lowers that were seriously out of spec in critical areas. Out of spec to the point that parts wouldn’t fit. To their credit, they were easy to deal with and replaced the lowers, in the cases that I’m directly familiar with.

In the last SOTAR class they were gauging a brand new Wilson barrel. The barrel was bent and the bore was undersized. Headspace was short, and there was a bulge.

 

[cmshoot]

Brand new Colt CR6920.

Receiver extension was one rotation shy of being properly and fully installed. The buffer retainer was barely retained, and I was able to remove it with my fingers. With time and use, there's a 100% chance that the buffer retainer was going to launch into the guts of the AR. Pretty good chance that it would have ended up down in the FCG, where a piece that large has a solid chance of causing a malfunction. I've seen them wedge between the receiver and the hammer where the gun would not fire.

When I went to disassemble the Colt to repair it, I found that the receiver extension was installed very crookedly. This would not cause a malfunction, but it's a pet peeve of mine, and why I designed the green AR jig in the picture. There are AR manufacturers/builders that pay attention to the little things like this (SOLGW does), but most do not.

The owner purchased this particular CR6920 from us at TruPrep, so I repaired it for free.

 

[SpeedyR]

Don’t know what’s going on at Wilson Combat. I’ve had my hands on numerous Wilson lowers that were seriously out of spec in critical areas. Out of spec to the point that parts wouldn’t fit. To their credit, they were easy to deal with and replaced the lowers, in the cases that I’m directly familiar with.

In the last SOTAR class they were gauging a brand new Wilson barrel. The barrel was bent and the bore was undersized. Headspace was short, and there was a bulge.

bought two of the WC stripped blem lowers a few months ago. Two of my other uppers wouldn't fit on the lower (the others were fine). After some measuring, figured out the gap at the rear takedown pin was too small. Very slight filing of the two uppers made them work fine, one day when I find someone to do it, I'll have the lowers machined properly to fit correctly, but for now it was a small enough amount that it didn't bother me to take just a hair off the upper.

But yes, I was disappointed with the dimensions of the lower. Building the second one later this week and will see how the rest of the build goes. Would have been pretty pissed if I had paid full price for them. As it was, even though it was sold as a cosmetic blem, it didn't leave a good taste in my mouth. Hoping that the (older) 6.8spc WC barrel I have is GTG.

 

[cmshoot]

bought two of the WC stripped blem lowers a few months ago. Two of my other uppers wouldn't fit on the lower (the others were fine). After some measuring, figured out the gap at the rear takedown pin was too small. Very slight filing of the two uppers made them work fine, one day when I find someone to do it, I'll have the lowers machined properly to fit correctly, but for now it was a small enough amount that it didn't bother me to take just a hair off the upper.

But yes, I was disappointed with the dimensions of the lower. Building the second one later this week and will see how the rest of the build goes. Would have been pretty pissed if I had paid full price for them. As it was, even though it was sold as a cosmetic blem, it didn't leave a good taste in my mouth. Hoping that the (older) 6.8spc WC barrel I have is GTG.

If parts won't fit together, I wouldn't call that a "cosmetic blem". KAC does the same thing.

 

[SpeedyR]

If parts won't fit together, I wouldn't call that a "cosmetic blem". KAC does the same thing.

exactly. it wasn't cosmetic. it was an upper that won't get used on that lower, but didn't want to have to think about that at any point, so did the quick fix.

 

[jclem02]

Don’t know what’s going on at Wilson Combat. I’ve had my hands on numerous Wilson lowers that were seriously out of spec in critical areas. Out of spec to the point that parts wouldn’t fit. To their credit, they were easy to deal with and replaced the lowers, in the cases that I’m directly familiar with.

In the last SOTAR class they were gauging a brand new Wilson barrel. The barrel was bent and the bore was undersized. Headspace was short, and there was a bulge.

In the last two weeks I've had three Wilson Combat BCGs through my shop where the carrier was out of spec. Everything else was good, but the carrier body was bad. They made each of them right with no questions of course, but still annoying.

 

[cmshoot]

For quite some time now, I have regularly been “re-installing” muzzle devices that were improperly installed elsewhere.

If the muzzle device is not a suppressor mount:
-I recommend using a simple crush washer.
-Clean the male and female threads, apply a bit of grease to the threads, the crush washer, and the shoulder of the barrel.
-I prefer phosphated crush washers over nitrided ones, as the nitrided versions are oftentimes overly hard and difficult to “crush”.
-When applying a crush washer, the larger end of the washer goes towards the muzzle end.


If the muzzle device is a suppressor mount, but does not need to be timed, such as the Silencerco 3-prong:
-degrease male and female threads
-apply a thin layer of Rocksett
-torque to 18-20ft/lbs, or to the manufacturer‘s specs
-let set for at least 24 hours before mounting your can or firing the weapon


If the muzzle device is a suppressor mount, but is required to be timed/indexed, as most brakes are:
-measure/trial-and-error for whatever shims you are using. I prefer the shims from Precision Armament, as you’ll only use one. Whatever shims I use, I only use one. Sometimes a very slight amount of material can be removed from the back of the muzzle device so that it times without shims. Sometimes you’re very lucky and the muzzle device times perfectly without shims. Shims are not always required……they are only required if the device will not time properly without them.
-degrease male and female threads
-apply a thin layer of Rocksett
-torque to 18-20ft/lbs, or to the manufacturer‘s specs
-let set for at least 24 hours before mounting your can or firing the weapon


There are muzzle devices out there that have very specific manufacturer’s instructions, or use lock washers, etc. In these cases, use the manufacturer’s instructions and specs.

Lots of disagreements on how to apply and remove Rocksett. As always, when there’s a question on a procedure that’s covered in the TDP, that’s what I go to. When it’s not covered there, I go to the manufacturer. Who would know better than Flexbar (the company that developed and makes Rocksett) how to use Rocksett? Here are their directions, cut and pasted directly from their site.

Think of Rocksett as waterbased solution of glass. The instructions call for a certain time and temperature Which works well under perfect conditions. There are a few ways to cure Rocksett based on many different applications.

Rocksett works better with a thin or sparing application. This is because it tends to dry from the outside
in. Let us refer to that as “skin hardening”. By now you have applied the liquid adhesive and want it to harden to a solid bond. What must happen is that the water needs to evaporate leaving the silica behind. This is a physical process as opposed to a chemical one. The drying /curing process is benefited by forced warm/hot air movement across the surface.

One now wonders “Hey I’m using this as a thread locker.” Which makes it difficult to get the hot air into the threads or mating surfaces.” What needs to happen is total evaporation of the adhesive material.

This can become problematic because Rocksett wants to skin harden. Heating the part material does help by allowing heat to pass internally towards the adhesive. Based on part mass and geometry different heating methods should be used.

A light application can dry at room temperature in a 24-hour period, with good strength. Follow this up with 20 minutes of heat at 175 degrees, for a normal cure method.

If you applied a fair amount of adhesive you may get better results by a slow rise bake/ cook method, say from room temp to 300 F (linear steps) in say six hours.

If you were excessive in your application and goobed and screwed, this will not fare well.

What will happen if you air cure or heat cure, is basically the same. The Rocksett will skin harden and the uncured adhesive will be encapsulated. Then when any additional heat is applied the water boils immediately forcing its way out and destroying the bond.

Let’s review here. If your parts are a tight fit and you use the adhesive sparingly, you get good results. If you have a coarse fit and your using Rocksett as a filler and an adhesive, heres what you can do:

Apply a light coat of Rocksett on male and female portion of the mating areas. Let both air cure apart for 24 hours. Heat both to 175 degrees F for 20 minutes then let cool to room temperature. Then apply a thin coat to the male part and mate the two parts together. Let air cure for 24 hours. Heat the assembly to 175 degrees F for 20 minutes and you are done. This is the strongest cure method attainable for coarse bonds.

The only way to break a proper Rocksett bond is to soak the part in hot water for 20 minutes or more and then forcibly remove the components.

When applying Rocksett make sure parts are free of oils and contaminants. Acetone works well. Some brake cleaning products have been known to inhibit the Rocksett cure. Hope this information helps.

 

[Korndog]

Nice write-up. Thank you sir for passing on the knowledge!

 

[cmshoot]

Another note on muzzle devices. If overly torqued, it’s possible to stretch the threaded section of the barrel. This elongation of the bore will change the size of the bore in that area by making it smaller, and change the twist rate of the rifling.

Your bullet is trucking down the barrel, all nice n’ happy, then it hits the last quarter inch or so, and it all goes to hell. Does bad things to your accuracy.

When in doubt, refer to manufacturer’s specs on how to install the muzzle device. If you don’t have torque specs, I keep it to 20-25ft/lbs.

 

[cmshoot]

I won’t be using Griffin Armament QD receiver end plates anymore!

If you do, I’d recommend not attempting to stake it. Use Vibratite instead.

End plate cracked instead of staking, and it ruined the tip on my punch.