PS90 Barrel Swap (How To W/Pics)

[jhs27275]

Instructions provided by CMMG.

Disassembly instructions. For qualified gunsmith only!

Unload and disassemble the PS90 and secure the barreled receiver in a drill press.

I used a #43 carbide bit and drilled out the blind pin.





Using barrel blocks, clamp the barrel into a vise. You can then slip a 15mm wrench onto the chamber end of the barrel.
A stardard size wrench will not fit, so you have to thin it down a bit in order for it to work.





The barrel/flash hider is left hand thread, so turn the wrench clockwise to break it free.
The barrel is now loose from the hider/sleeve and you can now slide it off.







There are 3 springs used in conjunction with the barrel.
Here is the charging handle spring which is inside the receiver and is visible when you take your receiver off of the stock.
There is a spring inbetween the sleeve and receiver (pictured below). And lastly, there is a spring and the takedown button near the chamber end of the weapon.
I didn't take pics of the handle or takedown spring as I didn't remove them for installation of the new barrel.



Instead of sliding my old barrel out of the rear of the receiver and having to mess with reinstalling the takedown and charging handle spring,
I choose to to a dowel rod (or old PS90 barrel) to push the old barrel out (front to back). This keeps the springs captive.
That way, when the new barrel is installed, you just push it in back to front and the springs are still there.

Short barrel assembly instructions. For qualified gunsmith installation. All NFA rules apply!

Place the flash hider in a 19mm wrench (wrench has to be thinned like the 15mm wrench mentioned above).
I position the wrench on the left side of the vise as pictured so when you install the barrel/hider counterclockwise (left hand thread),
the wrench will bottom out on the vise shaft. Barrel is to be torqued to 30-35 ft/lbs.





That should be enough detail for anyone to see how a barrel can be salvaged and a new barrel installed on the PS90/P90 weapon system.

The results.

[jhs27275]

And the short method.

Just cut the barrel with a hack saw.

Slide a .223 cleaning rod through the old barrel so when it slides out the back of the receiver everything is held in place.

Then slide the new barrel over the cleaning rod and through the receiver.

It only takes about 20 minutes to remove the old barrel and install the new CMMG barrel/flash hider. Torque hider to 30-35 ft/lbs.

[ick]

Excellent post man, great work. Keep in mind the change was VERY easy... a caveman could do it.... except I was totally unable to remove the pin and separate the sleeve from the barrel. I eventually GAVE UP and cut the barrel with a hacksaw just before the threads.

VERY EFFECTIVE.

I am pretty sure most barrels cannot be removed even by a skilled machinist or gunsmith for two reasons.

1. It is almost impossible to drill out ONLY the blind pin. Invariably when you don't get a perfect and clean drill the resistance of this to the internal threading makes removal impossible.

2. If you have shot many rounds.... and I had shot A LOT before I attempted to remove the shroud after ATF approval months later... I think the blind pin and barrel threading on the civilian version sees some "stresses" that also make a clean removal difficult if not impossible.

All in all there is no question, for me the thing to do was to simply cut it off. Once I went SBR I never was going back to the long PS90 barrel anyway. Furthermore once I had approval for my SBR and the proper engraving I had little desire to wait to send the weapon away to a shop.... where they wouldn't be able to salvage the barrel anyhow.

You can get a barrel and flash hider from several places, but CMMG was top notch. The salesperson spent some time with me on the phone to make certain I was getting the correct twist and the proper flash-hider for what my plans were for the weapon…. The inclusion of the Gemtech G5 with bi-lock flash hider.

[SONYtec]

To make life easier with torquing the barrel you'll need a 15 mm crows foot wrench to fit onto your torque wrench.

This is what I bought that fits great without grinding. Snap-on part number: FCOM15A

http://buy1.snapon.com/catalog/item....e=&dir=catalog

[jhs27275]

Your link does not work.

[SONYtec]

Your link does not work.

Hmmm, works fine for me. I added the part number to my post.

Let me clear cookies etc, and try it again...

[SONYtec]

Link works after clearing cookies, history etc.

Even tried on my laptop, that has never been to that site.

[jhs27275]

Got it now.

The custom set of skinny wrenches made for me by member Hoover 1 already has that. Two wrenches, no waiting.

[rev9]

just got me stamp back (5 months from when I mailed the forms) and am going to start on my SBR.

For the CMMG barrel and hider, do I need to prep the treads with anything before tightening them down...?acetone, lok-tite?

[jhs27275]

As long as it's torqued to 30-35 ft/lbs you should not need anything.