AR9: Anderson lower w/BCA upper

[GAAREDSTATE]

I built an Anderson AR multi caliber lower and a 16” BCA 9mm upper 1:10 with blow back gas system. I read the CMMG magazines are the way to go without modifying the lower. I also read that the STERN glock insert may have issues with the BCA upper. Anyone have any experience mating the two to operate properly?

 

[LongNose]

Get some endo mags from mean arms. They worked for me.

 

[DanKATL]

I built an Anderson AR multi caliber lower and a 16” BCA 9mm upper 1:10 with blow back gas system. I read the CMMG magazines are the way to go without modifying the lower. I also read that the STERN glock insert may have issues with the BCA upper. Anyone have any experience mating the two to operate properly?

I have experience with a Stern. Not sure why the upper would matter unless it's not standard in some way. What matters to the Stern is the bolt needs to have a "Glock cut" to allow the ejector and last round hold open to work without damaging the insert.

They will cut your bolt if it isn't already for a small fee. The only issue I see there is the cut would not have a protective coating, so you'd need to be diligent in keeping it oiled.

SHOP STERN DEFENSE - Services - Stern Defense

getstern.com

EDIT

From the Stern site, if your bolt is a BCA it's not a standard pattern.

"STERN DEFENSE DOES NOT RECOMMEND THE USE OF BEAR CREEK ARSENAL BOLTS. Due to multiple compatibility issues and variations from normal PCC bolt geometry; certain BCA bolts can create UNSAFE operating conditions. As it is hard to narrow down which exact run of BCA bolts can create these conditions, we recommend not using any BCA bolt with our products and will not cover damages caused by the use of these bolts. We are also not offering bolt modification or Glock cut services for these bolts."

 

[joeldworkin307]

Cmmg mags are for radial delayed blowback uppers only. The endomags are the same thing with an ejector for standard blowback uppers, and they do work well.

 

[ReservoirDawg10]

I have experience with a Stern. Not sure why the upper would matter unless it's not standard in some way. What matters to the Stern is the bolt needs to have a "Glock cut" to allow the ejector and last round hold open to work without damaging the insert.

They will cut your bolt if it isn't already for a small fee. The only issue I see there is the cut would not have a protective coating, so you'd need to be diligent in keeping it oiled.

SHOP STERN DEFENSE - Services - Stern Defense

getstern.com

EDIT

From the Stern site, if your bolt is a BCA it's not a standard pattern.

"STERN DEFENSE DOES NOT RECOMMEND THE USE OF BEAR CREEK ARSENAL BOLTS. Due to multiple compatibility issues and variations from normal PCC bolt geometry; certain BCA bolts can create UNSAFE operating conditions. As it is hard to narrow down which exact run of BCA bolts can create these conditions, we recommend not using any BCA bolt with our products and will not cover damages caused by the use of these bolts. We are also not offering bolt modification or Glock cut services for these bolts."

That would be because BCA is a hot mess and puts out trash. There is no spec. There is no QC.