I've been considering changing my P90 into a SBR for a PDW. Other than all the SBR issues I'd be interested in your thoughts. I like the size, weight and round count of this gun. I enjoy the pistol and for similar reasons. There are some new rounds for these that I find quite attractive. Are there choices of barrels? Length, materials, shroud, threading, etc. Is that a bird cage looking flash hider on the SBR's? Is there a better can than others for this application? And, how difficult to DIY change the barrel? I well understand stamps and legalities but would greatly appreciate keeping the thread to the sort of questions above. I see a lot of pro's but would be open to thoughts of con's. I have a 300 blk out as an SBR and with a can. It's a great PDW but the P90 takes up a lot less real estate with less weight and greater round count. Thoughts?
P90 as SBR
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C-grunt
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There was a local store that had actual FN 10.5 inch barrels for sale a few years back. So they are out there. No idea on your other questions.
What do you lose or gain by going with a shorter barrel? If I'm looking at the barrel right, there is a shroud that does not look like it should be threaded. The shorter barrel looks like it has options. Is the barrel threaded or is it the shroud or am I just wrong in how I'm looking at it?
barnbwt
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You lose six inches, and I want to say 200fps on the ammo (actually a good thing, as the bullets don't hold together quite as well at the higher speed, having been designed for optimum fragmentation/tumbling at P90 speeds). And the gun also looks a heck of a lot better; the PS90 looks & feels like it's half barrel. You do get a little more juice into the bullet from the extra length, but it's well into the diminishing returns region (the cartridge was designed around a 10" barrel and does not benefit from additional bore like 5.56, for instance)
FN Herstal not only made the gun 16" barrel length, they made it a royal pain to shorten it; they went to such lengths, I have to wonder if it was not done to satisfy either domestic or foreign export civilian sales restrictions (sort of like how semi-autos cannot be readily convertible to fully automatic).
-There is a shroud over the barrel which forms the flash hider. It is threaded on, but also pinned, with a 3/4" long pin hammered in blind around the circumference of the barrel threads. Very, very difficult to cut that pin out and not destroy the shroud or damage the barrel threads. I believe the threads are lok-tited, too.
-At that point, with the shroud off, new threads will be required to be cut into the barrel for a muzzle device. However, since the P/S90 action requires the barrel to slide forward/backward about 1/8" against a return spring as part of the extraction timing, the exact placement of the muzzle device and its shape are kind of important.
-Complicating muzzle device installation, is that the PS90 barrel has a removable barrel nut at the chamber end (necessary because the flash hider/shroud is permanently attached), whereas the P90 simply has wrench flats (and a threaded muzzle). This means that care must be taken while torquing down the flash hider or barrel nut so the other does not come loose. I believe the PS90 nut requires a special narrow wrench, too, or a modified box wrench.
So although it can certainly be done, cutting down a PS90 barrel involves cutting/damaging an expensive FNH barrel (~500$) and shroud, and still requires some careful gunsmithing on top of that. Which is why most folks just buy a reproduction P90 barrel, or an original if they have the coin and really care about chrome lining. I personally found even removing the PS90 barrel to be too much work, which made the EFFEN90 replacement receiver even more attractive (now I'll have two 'uppers' I can swap out of my stock at will with a push of the takedown button)
TCB
great reply. Does the shorter barrel support the use of the AP's? I see them in use for the pistol but wonder how useful and what's lost with the conversion to a SBR. Through a local show I picked up a case of green tips but have not chrono'd anything or field tested. So, in hopes that you have, what do you think?
Olympus
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I've always wanted to buy a PS90 and do the SBR conversion myself, but the cost is just so dang high. From what I've read in doing my research is that CMMG used to make aftermarket short barrels, but I think they might be a special order item now. I have never seen them available on their website. There a couple different companies that I can think that will cut down the factory barrel and thread it, but some have said that doing so will mess up the chrome lining of the barrel and accuracy will be affected. There are several videos on YouTube about doing it yourself, but they aren't all that great and the process isn't as simple as one would expect. Good luck with your project though. The PS90 in SBR form is oneo f the few guns that I really lust after.
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