.300 BLK 10” minor function issues

[LockedBreech]

Took my home defense 10” .300 Blackout pistol for a function test today. 60 rounds of Hornady TAP Patrol 110-grain GMX. 4 rounds didn’t cycle the bolt all the way forward. Each time it was a quick rap on the forward assist and it was back in action, but that level of reliability doesn’t work for me, so I guess the 16” Daniel Defense 5.56 stays in the home defense slot for the time being.

Relevant components: Aero 10” .300 upper, PSA SB3 EPT pistol lower, Magpul .300BLK Pmags, Toolcraft nickel boron BCG, Radian Raptor CH.

BCG was lubricated 5-6 weeks ago with what I thought was a pretty good amount of Slip2000. Traditionally I’ve used Miltech TW-25B grease in my ARs. Waiting 5-6 weeks was intentional as I wanted to simulate a home defense use in less than ideal readiness.

No double feeds, misfires, or other issues, just those 4 times with the bolt not going all the way forward.

Could it be as simple as just thinking I had enough lube when I didn’t? I don’t know what other issue causes the bolt to stop just shy of entering battery.


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[JCN]

@LockedBreech

How new is the charging handle?

How many rounds total on the bolt to barrel combination?

[757_Magnum]

How many rounds have you shot through this build before? If it's been shot before, what load/s were primarily used? Is this the first time putting Hornady TAP through it?

[LockedBreech]

Everything is brand new. These were the first 60 rounds. I am waiting for a good deal on 1-2K rounds for a real test, today was just proof of function.


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[Caballoflaco]

Have you compared the recoil spring length to a known good recoil spring?

[JCN]

Everything is brand new. These were the first 60 rounds. I am waiting for a good deal on 1-2K rounds for a real test, today was just proof of function.

I would think you’d want to break it in with cheaper ammo to mate the bolt to the barrel before even considering it for home defense?

I think I recently bought 300 BO for 55 cents per.

[LockedBreech]

This conversation has already made me realize I don’t know much about long guns. I had no idea about mating the bolt and I don’t have a pistol lower to compare recoil spring length too (unless it’s just a normal carbine spring in which case I have two). 90%+ of my AR rounds have been fired through my Daniel Defense DDM4V1 that I got off the rack in 2011. It never needed any particular break in.

I will hold off on the pricier ammo until I can grab a large chunk of bulk basic ammo to run and break it in. Sorry if I jumped the gun error reporting, I’ll report back and bump the thread if 500+ rounds and more lube doesn’t fix the issue.


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[Caballoflaco]

Your 5.56 AR should have the same buffer spring as the pistol lower as long as the pistol lower has a standard carbine length receiver extension (the part the stock or arm brace mounts to). Specs for a carbine buffer should be between 10.0625 inches and 11.25 inches in length if you just want to measure the spring that is in the pistol.


FWIW I’ve also never heard anyone worry about mating the lugs to the receiver extension either and I would expect an AR to work out of the box with no break in.

[JCN]

Your 5.56 AR should have the same buffer spring as the pistol lower as long as the pistol lower has a standard carbine length receiver extension (the part the stock or arm brace mounts to). Specs for a carbine buffer should be between 10.0625 inches and 11.25 inches in length if you just want to measure the spring that is in the pistol.


FWIW I’ve also never heard anyone worry about mating the lugs to the receiver extension either and I would expect an AR to work out of the box with no break in.

I would hope it to work perfectly when new and dry… but when a mish mash of various manufacturer’s pieces are put together and run with a short barrel….

Might need parts to break in.

I’ll bet after 300 rounds there will be shiny spots on places where there weren’t before and it’ll cycle with less resistance.

[757_Magnum]

The first thing I would suggest is to try standard 5.56 mags. As far as I know, the 300 BLK specific mags are mainly to accommodate the ogive on certain subsonic rounds. I've had great luck with standard Lancers on my two 300 BLK builds. I haven't tried my gen 3 Magpuls just because I'm reserving those for my 5.56 rifles.