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Solved: New Grendel build will not lock bolt back - Printable Version

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Solved: New Grendel build will not lock bolt back - Dt219 - 11-29-2020

Details. New 18” mid length gas Shaw barrel, non adjustable block has been checked several times it is lined up with port. The port size best I can tell from home is +-.072. Carbine buffer. The gun will lock back when cycled MANUALLY and pick up next round. Ejects between 3-4 o’clock but bolt will not lock back or pick up the next shell. I do not have a grendel mag have been using a 6.8 mag which shouldn’t cause the bolt not to lock back. Have tried different lowers/buffers. Shooting factory loaded hornady 123 sst. What should I try next, I’m no dummy but no genius either thanks Only 8 rounds have been fired. Fail zero bcg and no gas leaks I can find

Solved: New Grendel build will not lock bolt back - Dt219 - 11-30-2020

Problem found, LOOSE GAS KEY

Solved: New Grendel build will not lock bolt back - VASCAR2 - 11-30-2020

That’ll do it, thanks for letting us know you found the problem.

Solved: New Grendel build will not lock bolt back - Klem - 11-30-2020

Dt,

Is the carrier key staked?

Are you going to fix it yourself or return it?

Solved: New Grendel build will not lock bolt back - Dt219 - 12-02-2020

It was staked and it looked to me like it was good but I guess not. I took the key completely off, cleaned it spotless, and make a thin blue locktite gasket and a drop on the bolts. If I can come up with a good way to stake it I will do it

Solved: New Grendel build will not lock bolt back - Klem - 12-02-2020

Dt,

Fair enough.

For the sake of only one carrier it doesn't make sense to purchase the $70 Brownells jig. Staking from the top is a recognised method however. For this you only need a chisel and a hammer, so no financial outlay. I hear this was the original method used before the 'Revised' method replaced it (coming in from the sides). I am sure you know the drill. Just enough to stop the screws moving and not too much to break them.

I hear some manufacturers of cheap carriers don't bother putting a gasket seal around the flat of the key. The time I did three of these jobs we used Selleys Liquid Gasket to seal the bind. It's a silicone rubber for car engines. I am sure your Loktite gasket will work also.

Solved: New Grendel build will not lock bolt back - LRRPF52 - 12-03-2020

Use US Grade 8 fasteners torqued to 55inch-pounds.

Colt Armorer/Depot Maintenance and Repair Manual, No. CM102 dated 1991, specifies Permatex #3D Aviation form-a-gasket as a sealing compound for the carrier key.

[Image: ?u=http%3A%2F%2Fwww.2040-parts.com%2F_co...f=1&nofb=1]

[video=youtube_share;J_ObvWjV250]https://youtu.be/J_ObvWjV250[/video]

Solved: New Grendel build will not lock bolt back - LRRPF52 - 12-03-2020

You can use the OCKS Carrier Key fasteners as well, which really help prevent fasteners from ever backing out.

Loc-Tite vs Permatex, Thread Sealant and Threadlocker Comparison

Some companies use Red Loc-tite 272 or Permatex Red sealant, both of which are high strength.

The Aviation-grade Form-A-Gasket is meant for sealing two pieces together like that.

A weakness of the AR15 carrier and carrier key interface is that the fasteners are located to the rear of the gas hole, so torque is applied and maintained behind the hole, not on both sides of it.

POF actually made a carrier and carrier key that dovetail together and only use one fastener to deal with this design feature of the standard Mil-Std configuration.

[Image: 01650-1.png]

Solved: New Grendel build will not lock bolt back - Mad Charlie - 12-04-2020

LRRPF52:

Thanks for that info, I haven't had any issues yet, but I am going to change out at least one of my gas keys for a RCA key shortly.
I like using new fasteners for such jobs as this.

Solved: New Grendel build will not lock bolt back - Old Bob - 12-04-2020

Mad Charlie Wrote:LRRPF52:

Thanks for that info, I haven't had any issues yet, but I am going to change out at least one of my gas keys for a RCA key shortly.
I like using new fasteners for such jobs as this.

I got my OCKS carrier key screws from this vendor. They have some nice pics of the screws so you can see how they function...

https://www.forwardcontrolsdesign.com/OCKS_p_149.html

I had a loose carrier key on a M4 carbine. The key looked like it was staked before the screws were torqued. I replaced the key also & used the 3D aviation form-a-gasket as well.

Solved: New Grendel build will not lock bolt back - LRRPF52 - 12-04-2020

Remember when replacing the carrier key fasteners to toss the old fasteners. They aren’t meant to be re-used.

A lot of carriers come with Taiwanese-made YFS fasteners. In high volume where the temps get elevated in the carrier, these have been known to occasionally break and lose the gas seal between the carrier and key.

I’ve shot untold numbers of AR-15s in high volume that have YFS fasteners and didn’t fail, but there are some that have failed and were documented as the source of the problem.

Shows up as short-stroke malfunctions that otherwise can’t be diagnosed until you dig more deeply into the carrier/carrier key, or set the torque wrench and attempt to back-out the fasteners.

Also, the original torque spec for RLGS M16s was lower for the fasteners. A change was made for the M4 to increase the fastener torque value to 55 inch pounds, I suspect from the increased heat from higher port pressure coming from CLGS.

Something to think about. On 5.56 guns with the RLGS, you don’t see a lot of issues with bolts, fasteners coming loose, or anything really. As the gas system gets shorter, that’s when you really need to pay attention to setting the gun up more ideally.