Advice on sbr

[woodline]

My interest in delayed blowback PCCs mostly exists because I’m left handed and don’t like how direct blowback guns tend to eject crud into my face when shooting suppressed. Having an RDB upper I can swap onto my normal SBR lower is great for training, as it lets me use the same gear as 5.56 and just swap in the 9mm RDB mags. I can use that in a lot more places than a 5.56 gun. I also have a Grand Power Stribog SP9A3 that I like a lot, but am hesitant to recommend without caveats.

If I was right handed I would probably not care nearly as much about using delayed blowback PCCs.

 

[teratos]

If I was right handed I would probably not care nearly as much about using delayed blowback PCCs.

I'm right handed. I am interested in reducing felt recoil, which is substantial in direct blowback guns.

 

[alucard0822]

I'm right handed. I am interested in reducing felt recoil, which is substantial in direct blowback guns.

One promising design uses blowback barrels and lowers, but a BCG with ball bearings that engage pockets in the rear of a specialty upper. A wedge in the tail of the BCG under the bearings has to move rearward against the buffer/spring to allow the balls to move inward and disengage from pockets in the upper, and slide into the buffer tube. It has a linkage to pull it rearward from the charging handle, so doesn't take much effort to rack the bolt, and works kinda like an MP5 roller delay, but better suited to ARs, just needing the BCG and upper with a spacer and AR15 buffers to run. In the next couple years figure most all of the PCC receiver manufacturers are going to have their own delayed blowback receivers out.

 

[outrider58]

One promising design uses blowback barrels and lowers, but a BCG with ball bearings that engage pockets in the rear of a specialty upper. A wedge in the tail of the BCG under the bearings has to move rearward against the buffer/spring to allow the balls to move inward and disengage from pockets in the upper, and slide into the buffer tube. It has a linkage to pull it rearward from the charging handle, so doesn't take much effort to rack the bolt, and works kinda like an MP5 roller delay, but better suited to ARs, just needing the BCG and upper with a spacer and AR15 buffers to run. In the next couple years figure most all of the PCC receiver manufacturers are going to have their own delayed blowback receivers out.

Similarities also shared by the Scheel system except the roller delay mechanism is in the buffer instead of the bolt. If they both give a similar result, I think I'd prefer the Scheel only because it doesn't require a proprietary BCG and upper receiver. Makes it more adaptable in my view.

 

[alucard0822]

Similarities also shared by the Scheel system except the roller delay mechanism is in the buffer instead of the bolt. If they both give a similar result, I think I'd prefer the Scheel only because it doesn't require a proprietary BCG and upper receiver. Makes it more adaptable in my view.

The Scheel looks cool, but doesn't work the same way. Still waiting to get one, and do have high hopes for it, but it basically uses springs under the rollers to add resistance for that critical initial powered movement when the bolt is blowing back. Still has that resistance when racking the bolt, and at least it's cushioning the first part of the BCG movement and not simply trying to cushion a bolt running too fast as it slams into the end of the receiver.

True roller or in this case ball bearing delays use a wedge and bolt carrier to increase BGC movement against the recoil spring. An MP5 bolt moving rearward has an angled block the rollers are forced inward against, as they are pushed inward, the block is pushed rearward forcing the carrier against the spring at a greater speed than the bolt. There is a ratio set by the angle of the wedge, say the bolt face moves rearward 1/4", the rollers push the wedge and carrier rearward about 3/4", so it's like the bolt has 3X the mass and 3X the spring rate it really does for this part of movement. Once the rollers are fully pressed in, and the wedge is fully rearward the bolt unlocks and is basically 1:1 with the spring to complete the cycle. Being the charging handle acts directly with the carrier, there is no added resistance to racking the bolt as there would be if it acted on the bolt face.

The ability to have an easily racked bolt, tune the ratio of bolt to carrier movement to unlock, and the bolt engaging directly with the barrel or receiver instead of applying that locking force to the bufffer tube, pins, and everything between the barrel and buffer, it doesn't have most of the downsides of the scheel system. Of course it requires a proprietary BCG with rollers and upper or barrel with pockets for them to lock into. The JP-5 system is straight MP5 roller delay, but $3000+. The ball bearing delay I was told about is in the works by a receiver manufacturer, but also most all PCC manufacturers are looking or actively R&Ding true delayed blowback as the next step in PCCs.

 

[outrider58]

The Scheel looks cool, but doesn't work the same way. Still waiting to get one, and do have high hopes for it, but it basically uses springs under the rollers to add resistance for that critical initial powered movement when the bolt is blowing back. Still has that resistance when racking the bolt, and at least it's cushioning the first part of the BCG movement and not simply trying to cushion a bolt running too fast as it slams into the end of the receiver.

True roller or in this case ball bearing delays use a wedge and bolt carrier to increase BGC movement against the recoil spring. An MP5 bolt moving rearward has an angled block the rollers are forced inward against, as they are pushed inward, the block is pushed rearward forcing the carrier against the spring at a greater speed than the bolt. There is a ratio set by the angle of the wedge, say the bolt face moves rearward 1/4", the rollers push the wedge and carrier rearward about 3/4", so it's like the bolt has 3X the mass and 3X the spring rate it really does for this part of movement. Once the rollers are fully pressed in, and the wedge is fully rearward the bolt unlocks and is basically 1:1 with the spring to complete the cycle. Being the charging handle acts directly with the carrier, there is no added resistance to racking the bolt as there would be if it acted on the bolt face.

The ability to have an easily racked bolt, tune the ratio of bolt to carrier movement to unlock, and the bolt engaging directly with the barrel or receiver instead of applying that locking force to the bufffer tube, pins, and everything between the barrel and buffer, it doesn't have most of the downsides of the scheel system. Of course it requires a proprietary BCG with rollers and upper or barrel with pockets for them to lock into. The JP-5 system is straight MP5 roller delay, but $3000+. The ball bearing delay I was told about is in the works by a receiver manufacturer, but also most all PCC manufacturers are looking or actively R&Ding true delayed blowback as the next step in PCCs.

As I said, similarities. Obviously the application is different and is therefore adapted to that difference, but the principal offers(or promises) similar results. Each has its advantages and drawbacks. Of main concern to me is, as you put it, " but it's more of trying to adapt the AR design to 9mm than adapt 9mm to the AR platform."

So down the rabbit hole I go. This year will prove to be a fun learning experience as I play with all these new ideas and find out which adaptations proves worthy in the end.