[Bepe]

Blowbacks are usually dirty. Yours looks unusually clean!

I'll have to admit that the upper pic was when the gun was new. Although it probably looks identical now. I'll credit it to being a former Jarhead and OCD about clean guns.

I think I get as much joy cleaning them as shooting. Seriously...I have a routine and certain products that I use. Makes cleaning simple.

Bepe

 

[maddmatter1970]

The easy clean feature of the Rock River straight blowback design is a definite plus. No barrel extension with locking lugs or hard to reach feed ramps. Same goes for the bolt with its minimal parts. Minimal maintenance time adds to the joy of owning it. These rifles can get nasty fast.

Bepe
View attachment 212230
View attachment 212231

I am trying to decide why more 9x19 feed ramps are not done that way. I cannot make up my mind if I think its brilliant, or there is something wrong. I mean, here is the ruger feed ramp into the chamber:

So why do they do that if they could have just gotten away with a big chamfer off the lathe?
(Yes it is cleaner now, this was after a few mags)

 

[Bepe]

I'll take a WAG and say that the take down feature and bolt design might have something to do with it. Maybe not. I'll have to examine it more closely next time it is apart. The Ruger ramp is more traditional.

Actually, I was a little surprised when I first viewed the Rock River upper. I didn't know how the bolt was going to lock up. From what I can see, I don't think there is an actual lockup with the Rock River. Probably holds true for all blow back designs.

If you look at the bolt face after 500 rounds you can see the witness marks where it mates with the chamber / barrel extension. Evidently, it just butts up against the chamber, with headspace being set from the bolt face. It is held in battery by buffer spring pressure and bolt weight. The barrel extension / feed ramp is 360 degrees so no matter what position the round is at it will directed into the chamber.

Considering how deep the bullet case recess is in the bolt face, I was thinking that the headspace ledge in the chamber must not be in too far. I've never attempted any measurements. All I know is that it works.

Here's another pic of the bolt face where you can see the witness marks with the chamber.

I'm believing headspace is set correctly because primer indents are plenty deep. These cases are from the 6.4 grain Power Pistol load.

Both the Rock River and the Ruger work as advertised.....just a different design.

Bepe

 

[Bill837]

I'll take a WAG and say that the take down feature and bolt design might have something to do with it. Maybe not. I'll have to examine it more closely next time it is apart. The Ruger ramp is more traditional.

Actually, I was a little surprised when I first viewed the Rock River upper. I didn't know how the bolt was going to lock up. From what I can see, I don't think there is an actual lockup with the Rock River. Probably holds true for all blow back designs.

If you look at the bolt face after 500 rounds you can see the witness marks where it mates with the chamber / barrel extension. Evidently, it just butts up against the chamber, with headspace being set from the bolt face. It is held in battery by buffer spring pressure and bolt weight. The barrel extension / feed ramp is 360 degrees so no matter what position the round is at it will directed into the chamber.
View attachment 212288


Considering how deep the bullet case recess is in the bolt face, I was thinking that the headspace ledge in the chamber must not be in too far. I've never attempted any measurements. All I know is that it works.

Here's another pic of the bolt face where you can see the witness marks with the chamber.
View attachment 212286

I'm believing headspace is set correctly because primer indents are plenty deep. These cases are from the 6.4 grain Power Pistol load.
View attachment 212287

Both the Rock River and the Ruger work as advertised.....just a different design.

Bepe

I think you are right about the lockup. Definitely on the Ruger PC Carbine, it is the weight of the bolt and to a much lesser degree the recoil spring that provides the initial resistance to premature unlock.

I would not be surprised if a lot of the rounds are just headspacing on the extractor. I know in my handguns in 9, 40, 45 Auto, a large percentage of the time, headspacing is provided by it.

PS - In my ongoing cleaning journey I did get a chance to play with the bolt and barrel lockup and it works exactly as @Redhawk100 speculated. It rotates into lockup like a normal AR and the rotation to unlock is driven by the bevel on the back side of the bolt lugs. I think that is how they get away with such a light bolt and buffer and likely why it shoots so soft. Kind of a neat way to solve the problem. Takes a little of the sting out of how much I spent.

Thanks for the reminder on PP, I am going to load up some more 9's for a day of chronographing both the PC Carbine and the Banshee, I have a bottle of Power Pistol on the shelf, I will include a flight of that in the results.

 

[Redhawk100]

Actually, I was a little surprised when I first viewed the Rock River upper. I didn't know how the bolt was going to lock up. From what I can see, I don't think there is an actual lockup with the Rock River. Probably holds true for all blow back designs.

You're right--there is no lockup on your Rock River. I have a Hi Point pistol and carbine, both of which are straight blow-back designs. Neither of those has any sort of lockup, either.

Unless you see moving parts like a roller or rotary system in a blow-back action, only the weight of the bolt or slide, in conjunction with the spring, will keep the action closed. The weight of the bolt/slide provides the inertia necessary to delay the action's opening until chamber pressure drops enough to make it safe to do so.

The translation of force into a helical vector in the CMMG is what delays the movement along the X-axis vector, while the rollers in an HK delayed blow-back action translates force into the Z-axis as the rollers pinch inward against the locking block to delay movement along the X-axis.

With our straight blow-back weapons, all of the force is sent along the X-axis, so inertia from the weight of the bolt/slide is all that's available to slow them down.

Here's a three-dimensional axis diagram to put some context into my earlier X and Z-axis references.

In a nutshell, semi-auto actions all rely upon some sort of energy transfer mechanism to open the action, and how they safely operate involves redirection of kinetic energy along the different axes at one rate or another. The straight blow-back action just directs it all along the x-axis.

 

[Bepe]

Thanks for the reminder on PP, I am going to load up some more 9's for a day of chronographing both the PC Carbine and the Banshee, I have a bottle of Power Pistol on the shelf, I will include a flight of that in the results.

Bill...that 6.4 grains of PP and the 115 Hornady HAP is a fairly stout load. I think it is rated about 1200 FPS. Primers looked outstanding as far as pressure.

Bepe

 

[Bill837]

Bill...that 6.4 grains of PP and the 115 Hornady HAP is a fairly stout load. I think it is rated about 1200 FPS. Primers looked outstanding as far as pressure.

Bepe

All I have on hand are PD 124gr (FMJ/JHP), so I will take a look at Alliant's online manual and do a ladder from about 10% down from the max (Alliant aways lists max loads and expect you to read the fine print. )

 

[Bepe]

All I have on hand are PD 124gr (FMJ/JHP), so I will take a look at Alliant's online manual and do a ladder from about 10% down from the max (Alliant aways lists max loads and expect you to read the fine print. )

Just for reference the Hornady 124 RN FMJ max load is 5.7 grains of PP. I've shot a bunch of that load and it is nice.

Bepe

 

[Bill837]

Just for reference the Hornady 124 RN FMJ max load is 5.7 grains of PP. I've shot a bunch of that load and it is nice.

Bepe

Looking at Alliant's online guide, they list a load for 124gr Speer GD's at a max of 6.4gr at 1.12 COL. They list velocity at 1157 out of a 4" barrel.

I will start at 5.6gr and work up in like .3gr rungs. I will use some RN's at 1.125" (the PD JHP I have is shaped like a HAP, so I suspect may want to be loaded a little shorter for similar pressure)

 

[Bill837]

Just an update on what I have found regarding an effective use of a sling for support while shooting without shouldering the pistol. I have been playing with various options of using a sling to push against for support while shooting without the gun shouldered (even though there really isn't a great deal of it on this pistol).

My first reaction after shooting the Banshee for the first time was that a single point sling would work best. I had jury rigged a two point sling having both attachments returning to the dual loop end plate CMMG puts on the Banshee stock. It worked pretty well but was a little clumsy with the sling routing. Hence my assumption a single point would work best.

Having played with things quite a bit, including creating a sort of single point sling out of one of my adjustable two point slings I had spare, I have concluded, for ease of donning and getting to supported firing position quickly, a dual point will work best, with only one end attached to the end plate loop.

I mounted an extra M-Lok QD swivel attachment I had laying around to the M-Lok slots on the hand guard (mounting it as far back as possible on the hand guard). With the sling adjusted so it is perfect for locking into position with my arm while the gun is up in firing position with my cheek welded exactly where it needs to be, the sling can still be taken off and donned without adjustment (eliminating the need for quick adjustment apparatus on the sling).

I will post pictures of how I have it setup after the plain 48" sling gets here, along with the padded HK style clip that will replace my jury rigged mini carabiner which is beating the heck out of the parked buffer tube nut.

 

[Redhawk100]

Just an update on what I have found regarding an effective use of a sling for support while shooting without shouldering the pistol. I have been playing with various options of using a sling to push against for support while shooting without the gun shouldered (even though there really isn't a great deal of it on this pistol).

My first reaction after shooting the Banshee for the first time was that a single point sling would work best. I had jury rigged a two point sling having both attachments returning to the dual loop end plate CMMG puts on the Banshee stock. It worked pretty well but was a little clumsy with the sling routing. Hence my assumption a single point would work best.

Having played with things quite a bit, including creating a sort of single point sling out of one of my adjustable two point slings I had spare, I have concluded, for ease of donning and getting to supported firing position quickly, a dual point will work best, with only one end attached to the end plate loop.

I mounted an extra M-Lok QD swivel attachment I had laying around to the M-Lok slots on the hand guard (mounting it as far back as possible on the hand guard). With the sling adjusted so it is perfect for locking into position with my arm while the gun is up in firing position with my cheek welded exactly where it needs to be, the sling can still be taken off and donned without adjustment (eliminating the need for quick adjustment apparatus on the sling).

I will post pictures of how I have it setup after the plain 48" sling gets here, along with the padded HK style clip that will replace my jury rigged mini carabiner which is beating the heck out of the parked buffer tube nut.

Glad to hear that your setup is working out. A little time to experiment and customize your rig to your needs pays huge dividends.

 

[CDR-C]

A sling attached at the back allows you to stabilize by pushing it forward, so a stock is really not necessary. That's worked fine for lots of platforms (Uzi, MP5, etc) for decades.

Having said that, the whole pistol brace Cluster-F is still playing out. It'll go to the Supreme Court, I bet - as of this moment, the ATF rule is blocked by a federal judge (or two).

Personally, there is No way I would go the registered SBR route - and I already have registered silencers. The rules for SBRs are considerably more restrictive than silencers - notify the ATF to take it across state lines, notify local law enforcement, etc. It really is a bigger deal.

As far as CMMG - my only experience with a full build from them was a Banshee 10mm - it was wonderful. BUT, superfluous - so I sold it. I do have several AR-pattern (colt magazine) dedicated 9mm - two CMMG, some others. All work great. Both as pistols (formerly braced, no longer) and as carbines (I have both 8" and 16" barreled uppers).

Enjoy.

 

[RE Parker]

Freedom Ordinance FX-9 is similar. Nice items!

 

[VictorLouis]

I am A-O/K with the FX9 for value. However, it's not for the Left-Of-Hand crowd. IF you have, or can source one of the old military brass deflectors...you're all-in.