.300 BLK 10” minor function issues

[LockedBreech]

Again, thanks y'all for the contributions, it's good to have stuff to try. HCM, you're spot on that current .300 BLK prices have me wincing a bit at 500 rounds to function test. I am a bit mystified at the rest, birds and warmarks are totally new terms to me and I am feeling very out of my depth on rifle building. Unless you got autocorrected and it was burrs and wear marks. In which case no, the bolt and upper both looked nice and normal to me, but I'm certainly going to have a closer look now.

Let me ask...this is a Toolcraft C158 Nickel Boron BCG. Given that NIB is a thicker coating, and I also have a brand new spare Toolcraft C158 IonBond BCG...might it be worth it to just swap the Nib out for the Ionbond? If it's extra tight, maybe the minutely smaller coating would fix the issue?

If that's a dumb idea sorry, I am just spitballing.

[SecondsCount]

You can try swapping bolts. You might have a little tolerance stacking going on and swapping things around could help if headspace is the issue.

[LockedBreech]

Appreciate it.

Like most things in shooting life, I suppose nothing will diagnose issues like range time. Just might need to shelve the project for a minute until I find some affordable .300. Or bite down on the leather and spend the money for a 1000-round case.

[HCM]

Again, thanks y'all for the contributions, it's good to have stuff to try. HCM, you're spot on that current .300 BLK prices have me wincing a bit at 500 rounds to function test. I am a bit mystified at the rest, birds and warmarks are totally new terms to me and I am feeling very out of my depth on rifle building. Unless you got autocorrected and it was burrs and wear marks. In which case no, the bolt and upper both looked nice and normal to me, but I'm certainly going to have a closer look now.

Let me ask...this is a Toolcraft C158 Nickel Boron BCG. Given that NIB is a thicker coating, and I also have a brand new spare Toolcraft C158 IonBond BCG...might it be worth it to just swap the Nib out for the Ionbond? If it's extra tight, maybe the minutely smaller coating would fix the issue?

If that's a dumb idea sorry, I am just spitballing.

It was burrs and wear marks.

You could have a gunsmith check the headspace - again cheaper than 300 blk ammo. AR's are pretty modular but they are not 100% Legos.

Aero's receivers and scope mounts (the stuff they actually make) are OK but their complete guns / uppers are... lacking. Same with PSA. Both make OK range toys but for serious use:

Colt
BCM
LMT
SOLGW
Sionics
DD
Geissele
SIG

[JCN]

Aero's receivers and scope mounts (the stuff they actually make) are OK but their complete guns / uppers are... lacking. Same with PSA. Both make OK range toys but for serious use:

One of my first ARs was a cheapo plastic one that promptly sheared off the rear of the upper.

That one isn’t going to see SD duty lol.

Ammoseek has some quite decently priced 300 blackout but @LockedBreech, spend the money on an omega 9k and test once you get it.

[mmc45414]

Did you buy the upper assembled? Might be worth reviewing this thread, seems like gas block alignment could be another variable, especially if you bought it assembled.

If you assembled it and know it is right then cool. But I wouldn't fire any more rounds through it without a fresh spring, they are just too cheap.

[MistWolf]

Before getting all crazy trying this and that, do a lock back check. Load a single round in a known good mag and see if the carrier locks back when fired. If it does lock back, the next thing to check is the action spring. If the carrier is closing a bit slow, the round can bobble. Or the carrier speed can be too slow to close the bolt. Or both.

[HCM]

Are there any signed of birds, or unusual warmarks indicating something being out of spec?

What weight buffer and what buffer spring are you using ?

The interaction between the gas coming back the weight of the buffer and the spring or what run your cycle of operation.

One thing to check is to load a single round and see if the bolt locks back when fired. If it does that means the gas coming back is adequate.

You may need to use a lighter buffer or a stronger buffer spring.

Given current price and availability of 300 blackout ammo trying a slightly stronger spring from Sprinco might be cheaper than breaking the gun in with half a case of ammo.

Adding a suppressor may also change that dynamic. Adding a can will increase the back pressure making the gun cycle faster. Unless you keep a set of active hearing protection with your home defense gun a suppressor makes a lot of sense for an HD long gun.

Before getting all crazy trying this and that, do a lock back check. Load a single round in a known good mag and see if the carrier locks back when fired. If it does lock back, the next thing to check is the action spring. If the carrier is closing a bit slow, the round can bobble. Or the carrier speed can be too slow to close the bolt. Or both.

Yup.

[HeavyDuty]

Before getting all crazy trying this and that, do a lock back check. Load a single round in a known good mag and see if the carrier locks back when fired. If it does lock back, the next thing to check is the action spring. If the carrier is closing a bit slow, the round can bobble. Or the carrier speed can be too slow to close the bolt. Or both.

This. I’m no SME but I’ve wrenched a lot of my own and friend’s ARs over the years. Ten single rounds of perfect RTB and lock back is my initial run on a new or modified gun.

Unless the fuckin’ birds are messing with me.

[mmc45414]

Let me ask...this is a Toolcraft C158 Nickel Boron BCG. Given that NIB is a thicker coating, and I also have a brand new spare Toolcraft C158 IonBond BCG...might it be worth it to just swap the Nib out for the Ionbond? If it's extra tight, maybe the minutely smaller coating would fix the issue?

You would be able to feel for any unusually resistance by just slowly pushing the BCG closed by hand.

I do not have as much experience/expertise as others here, but IMO the whole system of these things is not exactly fragile. It gets blown open by 50k of gas and shoved forward buy that huge spring that is carrying the momentum of the BCG and buffer with a combined weight that probably flirts with a pound. If something stops all that 0.100 from being closed I might be inclined to look for something wrong rather than something that is not broken in. Shooting it until it works with a bunch of expensive ammo might just be masking a problem that will reemerge when it get a little grime.