RRA 9mm and PRI Gas Buster Charging Handle Problem.

[Paulinski]

I just picked up my 9mm SBR from my gunsmith. Its a factory Rock River Arms 9mm upper with Stag Arms lower and LPK, RRA 9mm hammer, Hahn dedicated magazine block

Here's my problem the upper work fine with standard changing handle when insert the PRI gas buster - it slides in and out fine without the 9mm carrier.

If I insert the carrier its very hard to pull the (charging handle / carrier) out of the upper finally when I assemble the upper on a lower the I can't charge the firearm. Everything just binds.

Once again everything works fine with standard charging handle. Bolt locks open on empty mag, charges fine.

Anybody encountered a similar problem?

Thanks in advance.

[Robb Jensen]

The carrier key on a 9mm bolt is different than on a 5.56mm bolt carrier. The 9mm probably just doesn't fit the PRI Gas Buster correctly. I'll measure a 9mm key at work, it's either taller or wider.

[rob_s]

Can you put a caliper on the carrier key of the 9mm and compare it to a 5.56?

It sounds like the key is too large on the 9mm and it's causing the GB to "swell" and fill the channel.

I'd be interested to know:
OD of the 9mm carrier key where it fits into the GB
OD of a 5.56 carrier key that works with the GB where it fits into the GB
ID of the GB slot
ID of the slot of the CH that works with the gun

[Paulinski]

Thanks for the replies.

Rob

I'm at work but I'll measure everything this evening and post it.

Paul

[SHIVAN]

I have a PRi on my 9mm upper and it works nicely.

Colt 9mm SMG bolt group, RRA 9mm upper, and Hahn dedicated block.

I bet the lower has the Hahn block setting up to high and is pushing the carrier key into the charging handle.

[Paulinski]

The only difference in my set up is that I'm using the RRA carrier group.

ETA I don't think the the height of the Hahn block because if I have the upper separated from the lower when the PRI goes into the upper all by itself its moves freely - when the PRI and carrier group go together it starts to bind (I can still move it but it has noticeable resistance.

Now If I assemble the upper and lower together it binds completely.

Could you measure the width and height of your Colt carrier key?

Thanks

Paul

[khc3]

On my 9mm, most of the blowback comes out of the ejection port, and the gasbuster I tried didn't seem to do anything. I put it on a 5.56 gun, and used the regular CH on my 9mm.

[Tim_FL]

I bet the lower has the Hahn block setting up to high and is pushing the carrier key into the charging handle.

I'm not sure that is his problem because he indicates that he has a Hahn dedicated magazine block (according to his original post). The dedicated blocks are dropped in from the top and are not adjustable unlike those adjustable blocks put in from the bottom and set and placed with an allen screw. Good suggestion though !

[SHIVAN]

...and yet my Hahn dedicated has creeped up under F/A fire just enough to create drag on my carrier.

[Robb Jensen]

I thought we had a 9mm RRA in stock so I could measure it's key, we sold it last Saturday. All these non Colt 9mm problems make me want to buy a Colt upper and use a Colt block and pin it in my lower when I get around to converting one of my SBRs into a 9mm.