PS90 SBR Howto

Various howtos. Your mileage may vary. Use at your own risk. Do not blame me if you're unhappy with the results. Do not blame the original posters if you are unhappy with the results. Look to your own actions and own them and realize that happiness comes from within.

UPDATE 07/21/2006 CMMG has posted detailed instructions (with lots of pictures) on the FiveseveN Forum - READ THIS FIRST: http://fivesevenforum.com/forums/showpost.php?p=41652&postcount=1

JUST IN CASE YOU MISSED IT - READ CMMG's HOWTO in the link above.

Posted by tctrld:

Tools:

Dremel
15mm wrench
Vise
Punch

1. Disassemble PS90. Time for this: 1:00 minute

2. I used my dremel to reveal the other side of the pin on the shroud. (using a cutting attachment in an 'scraping' motion) - time for this 1:00 minute

3. Tap out the pin using a punch and hammer. Time for this: 0:10 seconds

4. I mounted the receiver assembly in my vise, vice jaws grabbing on to the flash hider. Use a 15mm wrench and apply force. NOTE! Turn clock-wise as it's reverse threaded. Barrel separated from flash hider after a few light taps with the palm of my hand. Time for this: 1:00 minute

5. Re-assemble with CMMG 10.3" barrel and P90 flash hider. Time for this 1:00 minute.

It is easier that it looks/sounds. The barrel has milled flats at the breach end for a 15mm wrench. The barrel screws into the flash hider only. Nothing screws into the receiver. The barrel assembly is under spring load between it and the receiver. That's why you can push on the muzzle and have it give for about 1/4"

Posted by fenemij:

Here is the info i have on the bbl/FH torque specs:

John at CMMG said 65FT LBS

FN manual says 40Nm to 50Nm
1Nm=0.737562149 FT LB

So if my math is correct that would be 29.5FT LB to 36.8FT LB

Posted by CMMG:

The thread is 12x1 LH. Secure the sleeve and chamber (15mm wrench) and unscrew the hider. Drill out the blind pin then unscrew the barrel. My first one wasn't pretty, I got the barrel and hider bound together because I didn't have everything secured like it was supposed to. You can do it a really fast way and just chop the old barrel off with a band saw and then the barrel will just fall out.

Posted by Halo Mfg:

When you do it, be commited to finish. In our case we followed jeffs instructions and ran into a snag. It wasn't his fault. The flash hider started to unthread then suddendly got stuck. We made the decision to continue and destroyed the threads on just under half of the barrel.

What happened was the threading on the hider bound and the pin ruined the rest of the threads. My gun was F---ked. I couldn't put the barrel cover back on (due to the threads) and now the only barrel I had to put on it was CMMG's (wich fit and functions perfect by the way). I finally designed a new fake suppressor to replace the barrel cover. So I wouldn't have to make it an SBR to take it home.

Everythings better now, but it won't ever have the original look again (FN will fix and re-pin it, but won't sell the barrel or extention.)
If anyone does change out there barrel (and has it and the cover with hider availiable). let me know ill buy it!

So the moral of the story is "I would suggest drilling out the pin, before doing anything"!!!

Posted by darkest2000:

Originally Posted by brazos609
So it looks like you just turned the wrench on the chamber area of the barrel and let the flat at the end of the sleeve stop against the receiver, kinda just chewed away the threads at the muzzle?

Nope, you might risk damaging the receiver that way, what I did was I threw the 15mm wrench on the chamber area then secure the wrench onto a vise, then you clamp down the flash hider/sleeve with a vise grip/slip joint plier and turn it clockwise (to unscrew), this way all the stress from the torque stays on the barrel/sleeve and not on the receiver.

The threads on the muzzle looks chewed away because I didn't completely remove the pin (long story) and that's just kinda how it turned out after I was done. It was a major chore for me because part of the pin got caught somewhere within the threads so it made unscrewing the sleeve extremely tedious. If the pin is completely removed like it should have been I don't think it's going to be that difficult at all as soon as the sleeve loosens.

Moral of the story: Be sure you completely remove the pin before you do anything or you'll have a tough life.

Posted by Brontes:


If anyone is going to post instructions on this forum and they are wrong, how could it not be their fault?

Everyone knows you need to take out the pin first. CMMG simply posted the wrong instructions, you followed them and wrecked your gun.

Destructions:

1. Remove the pin (best thing to do is to drill from the other side and tap it out. The pin goes almost all the way through)
2. Clamp the sleve - brake loose hider. Hider goes on right hand thread into the sleve !!!! 1/2 turn is enough to loosen it (use torch to heat up parts)
3. Clamp the hider and turn out the barrel - barrel is in the hider left hand thread!
This is where you will most likely break the receiver - UNLESS - you turn the barrel on it's axis. The simplest way to do this is to have a custom 15 mm wrench with handles on either side, so you can turn on center and not bend the barrel. The barrel is chromoly steel, it flexes quite a bit. If you yank on it while the hider is in the clamp, you run the rick of stressing the receiver and cracking it (as some on this forum have done).

To make one of these, slim down an automotive 15 mm wrench (only the jaw part)and weld on a handle.

4. Separate hider from sleeve (they are already loose)

Contrary to popular belief on this forum - the barrel is NOT threaded to the sleeve - only to the hider.

You need:

1. Milling machine (heavy duty)
2. AR 16 barrel clamp
3. Heavy duty vise
4. Propane torch
5. Carbide Milling bits
6. Custom made 15mm wrench (slimmed down automotive with opposing handle)
7. Custom made hardened steel plate that you can insert trough the hider and whack it (to loosen the sleve from the hider)
8. Mig welder (for the wrench)

So, unless you have all the equipment above - give it to a gunsmith that does and knows what he/she is doing. Be were - there are quacks out there.

In Retrospect:

Many members here have been hacking their barrels off. Keep in mind - FN will NOT sell you a spare 16" barrel or a sleve or a hider (they are all going on guns).

If they did, barrel is $600.00, sleeve is $150 and so is the hider. Near close to $1,000 of replacement parts MSRP.

So, if you have destroyed the barrel, hider and sleeve with a hacksaw ($900), paid CMMG for a short barrel ($275) and a new hider $95 and a $200.00 for the ATF stamp - you just bought yourself another PS90. Instead, you have a weapon that Hillary now knows you have - and one with inferior ballistics to the PS90.

Posted by Sua Sponte:

OR --

you can take a $5 hack saw and just cut behind the pin on the sleeve about 1" -- the old barrel will then fall out the breech end, hit the floor, and go "ping-ping-ping" until it comes to a stop.

ohhhh, and while the ballistics may be marginally superior, the SBR version is way cooler looking!!!! let's be honest, the PS90 looks like a broom! LOL!

Posted by CLC3251:

First remove the pin holding the flash hider on. You can grind out a relief cut as Mark did or drill it out. Either way, remove the entire pin. There is no way to do it without maring the barrel extension. If you took a really long time, you cold carefully drill/grind away the opposite side of the sleeve from the pin and carefully drive it out. Once the pin is removed, don't try to unscrew the flash hider from the sleeve, it will not come out. Take a 15mm open ended box wrench and grind down the sides so that it will fit in the groove in the chamber end of the barrel. Most standard wrenches will not fit as the groove is tight and if you try to force it you will mar the barrel. Unscrew the barrel from the flash hider. It has left hand threads, so turn it clockwise to remove it. An easy way is to wrap the flash hider in a few layers of paper and clamp it in a pair of aluminum AR-15 barrel blocks to hold it without marring it. Watch the front of the receiver as once the hider/sleeve unscrews a certain amount, it can rotate and scratch the front of the receiver. Once it unscrews from the flash hider, you can pull the hider/sleeve off of the front of the barrel. Watch carefully as there is a spring between the sleeve and the receiver around the barrel that you will need to put back when you re-asemble or replace with a short barrel and hider. Pull the barrel out of the back of the receiver carefully as the recoil spring is around the barrel and the spring loaded takedown button is near the back That's it. You can separate the flash hider from ther sleeve by unscrewing it but it is right hand thread so unscrew it counter clockwise. The two different thread turns is what prevents you from unscrewing the hider first. The barrel only screws into the flash hider, but the flash hider screws into both the barrel and the sleeve which prevents it from being removed first.