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Posted: 5/14/2021 12:09:21 AM EDT
So I had a gunsmith cut down my barrel for my sbr PS90. I bought the cmmg barrel thread adaptor to go on my barrel so I can thread 1/2x28 suppressors on it. He put a spacer shim on the barrel so there is no play or wobble. Is this a good idea. He said it would help with accuracy. I don’t know anything about this so I was just wondering.
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Posted: 5/14/2021 12:13:03 AM EDT
[#1]
It sounds like he cut and threaded the barrel to the incorrect length and is using a spacer to take up space. You should be fine.
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Posted: 5/14/2021 12:22:06 AM EDT
[#2]
Quote HistoryQuoted: It sounds like he cut and threaded the barrel to the incorrect length and is using a spacer to take up space. You should be fine. He said he cut it to 10.4. Same as my paperwork and factory barrel. My question is should the barrel wobble a bit back and forth and front to back for reliability? Or solid is good? |
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Posted: 5/14/2021 12:22:28 AM EDT
[#3]
Rotational play is normal.
As posted below, some front to back play is normal. Got the PS90 out this morning and confirmed. |
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Posted: 5/14/2021 12:24:46 AM EDT
[#4]
Quote HistoryQuoted: Rotational play is normal. Shouldn’t be any front to back slop though. That’s what I want to know. I see this video and this guy heads front to back movement. Skip to the end.  PS90 Short Barrel Installation |
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Posted: 5/14/2021 1:19:19 AM EDT
[#5]
Yeah, i have about 1 mm of front to back movement in the barrel.
I'm using the CMMG 10.4" barrel and 1/2x28 thread adapter. Didn't need a spacer though... |
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Posted: 5/14/2021 1:26:06 AM EDT
[#6]
Yes, there should be a little movement back and forth (and rotational). Just did this for a customer as well.
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Posted: 5/14/2021 7:34:25 AM EDT
[#7]
Would the spacer hurt anything? The factory 16” always bugged me with the play,
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Posted: 5/14/2021 10:25:09 AM EDT
[#8]
The system is designed to have some pogo-stick action (back and forth) play to create a delayed blowback. If it wasn't intended to move back and forth, why would FN have a barrel return spring incorporated in the system?
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Posted: 5/14/2021 11:01:56 AM EDT
[#9]
It might work okay but, unless you're pushing for something specific (like trying to make a precision gun out of it), I'd pull the shim and make it work as-designed. Doing an R&R on that barrel is pretty simple. Might even be easier than doing it on an AR, just need to remember that it's reverse-threaded.
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Posted: 5/14/2021 3:20:39 PM EDT
[#10]
Are you still getting that forward/backward movement with the spacer currently installed?
I just checked mine and this is how much space I have between the adapter and receiver once the adapter is tightened down to the barrel. If I were you, i would remove the spacer and see how much space you have without it.  Attached File |
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Posted: 5/14/2021 3:37:54 PM EDT
[#11]
Quote HistoryQuoted: Are you still getting that forward/backward movement with the spacer currently installed? I just checked mine and this is how much space I have between the adapter and receiver once the adapter is tightened down to the barrel. If I were you, i would remove the spacer and see how much space you have without it. https://www.ar15.com/media/mediaFiles/145596/spacer_JPG-1942077.JPG  Attached File |
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Posted: 5/14/2021 4:39:50 PM EDT
[#12]
This is what happens when you don’t go with an EXPERT! Mark McWillis (TROS) has forgotten more on this platform than most of us will ever know!
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Posted: 5/14/2021 4:47:00 PM EDT
[#13]
Quote HistoryYeah, that is a lot of space between the adapter and the receiver. Have you actually measured the barrel length? |
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Posted: 5/14/2021 5:04:02 PM EDT
[#14]
I'd be skeptical it was cut to the appropriate length. I don't know everything there is to know about a PS90, but I've yet to see one with a spacer at all.
My TROS cut barrel has a few degrees of side to side rotation, and maybe a microscopic amount of forward and aft play.  " />
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Posted: 5/14/2021 5:25:41 PM EDT
[#15]
Well I got shoot it tomorrow without the shim and report back.
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Posted: 5/14/2021 6:59:53 PM EDT
[#16]
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Posted: 5/15/2021 1:13:44 PM EDT
[#17]
I just shot 100 rounds of the blue tip FN ammo. I shot it the way it is in the post above. Sandman K with no barrel bushing. The only malfunction I had was one fail to feed from the mag. Accuracy Was about 3 moa at 100 yards with a red dot.
You think it’s good or is the space between the receiver and barrel too long? |
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Posted: 5/15/2021 6:37:37 PM EDT
[#18]
Quote HistoryQuoted: You think it's good or is the space between the receiver and barrel too long? I don't have the spec handy, but it should be around .020" to .030" and I think that's why you experienced a failure to feed. (I'm assuming your mags and ammo were good.) |
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Posted: 5/15/2021 7:05:24 PM EDT
[#19]
Quote HistoryQuoted: It's too much space. I don't have the spec handy, but it should be around .020" to .030" and I think that's why you experienced a failure to feed. (I'm assuming your mags and ammo were good.) Quote HistoryQuoted: Quoted: You think it's good or is the space between the receiver and barrel too long? I don't have the spec handy, but it should be around .020" to .030" and I think that's why you experienced a failure to feed. (I'm assuming your mags and ammo were good.) So I pulled the barrel out and measured it myself. It’s exactly 10.4 on the dot. Here’s a pic of the crown and threads  Attached File |
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Posted: 5/15/2021 7:11:51 PM EDT
[#20]
how long is the threaded portion? Does the adapter stop on the muzzle face or does it run out of threads?
The threads on the CMMG barrels start a little ways behind the muzzle. |
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Posted: 5/15/2021 7:30:35 PM EDT
[#21]
Quote HistoryQuoted: how long is the threaded portion? Does the adapter stop on the muzzle face or does it run out of threads? The threads on the CMMG barrels start a little ways behind the muzzle. It’s timing off the crown. So it’s stops on the muzzle |
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Posted: 5/29/2021 3:00:00 PM EDT
[#22]
So I shot 100 rounds today out of my sbr. I had about a dozen malfunctions with it. All I shoot is the blue tip FN ammo. Most were click no bang. I would pull the mag and there would be an unfired round in the chamber. Very odd. Maybe it’s not fully into battery when I pull the trigger? Any thoughts? I’m using a sandman K suppressor too. Some would be a fail to feed. I also have never cleaned the gun out of about 400 rounds.
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Posted: 5/30/2021 1:58:25 AM EDT
[#23]
Is that with or without the shim?
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Posted: 5/30/2021 9:11:07 AM EDT
[#24]
Quote HistoryQuoted: Is that with or without the shim? Without. All shooting has been done so far without. Maybe I should put it in. |
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Posted: 5/30/2021 10:49:18 PM EDT
[#25]
It not right with or without the shim. I would have the barrel fixed.
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Posted: 5/30/2021 10:59:21 PM EDT
[#26]
Quote HistoryQuoted: It not right with or without the shim. I would have the barrel fixed. What do you guys think I should do? I measured the barrel myself. It’s 10.4. Maybe the thread adaptor is out of spec. Take it back to the gunsmith and have him cut it more? I measured the gap last night. It’s 2.06mm. Install the shim and try shooting it with the barrel fixed? |
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Posted: 5/31/2021 1:22:19 AM EDT
[#27]
Just to reconfirm, there isn't any movement when you have the shim installed, correct?
Can you get a picture of the barrel outside of the receiver? Would like to see the entire threaded portion. |
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Posted: 5/31/2021 2:29:39 PM EDT
[#28]
Quote HistoryQuoted: Just to reconfirm, there isn't any movement when you have the shim installed, correct? Can you get a picture of the barrel outside of the receiver? Would like to see the entire threaded portion. With the shim it’s solid. Gunsmith thinks it would be more accurate with it but have not tried yet. I need to get a small wrench to take the barrel out. The one I used belongs to the gunsmith |
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Posted: 5/31/2021 5:48:45 PM EDT
[#29]
Capri Tools 14 mm x 15 mm Super-Thin Open End Wrench, Metric, 11850-1415
This is the one I used for mine and my buddies PS90. |
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Posted: 5/31/2021 6:43:32 PM EDT
[#30]
Quote HistoryQuoted: Capri Tools 14 mm x 15 mm Super-Thin Open End Wrench, Metric, 11850-1415 This is the one I used for mine and my buddies PS90. Thanks! Just ordered |
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Posted: 6/2/2021 7:09:36 PM EDT
[#31]
I went thru a situation with my and ps90 that resulted in alot of forced education. On a tablet so cant write the novel. In a nutshell someone messed up your ps90. The barrel free floats for a reason and you can look up the fnh patent. Tros might be able to fix but good luck with your situation.
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Posted: 6/2/2021 7:38:28 PM EDT
[#32]
Quote HistoryQuoted: I went thru a situation with my and ps90 that resulted in alot of forced education. On a tablet so cant write the novel. In a nutshell someone messed up your ps90. The barrel free floats for a reason and you can look up the fnh patent. Tros might be able to fix but good luck with your situation. What’s messed up? I got put on a instock notification for a cmmg barrel. All he did was take the barrel out and cut it down. |
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Posted: 6/3/2021 6:32:20 AM EDT
[#33]
The gunsmith’s work. We don’t know thanks what’s causing your issue, but we already know it’s not right.
The next step after getting the CMMG barrel is presumably avoiding that gunsmith, certainly for something specialized like this. You’d have saved your time, money and efforts if you knew what you know now. |
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Posted: 6/3/2021 10:57:31 PM EDT
[#34]
as mentioned when you have time, please take the barrel out and show us the OAL, and the threaded portion.
I used to have these measurements, but not sure where they are anymore Hey may have cut the barrel slightly too long? 
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Posted: 6/3/2021 11:10:35 PM EDT
[#35]
The wrench should be here on Saturday
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Posted: 6/5/2021 9:10:41 PM EDT
[#36]
Alright I took the barrel off tonight. Here it is.
@LuxorDeathbed @CJofFL  Attached File Attached File Attached File |
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Posted: 6/5/2021 9:24:58 PM EDT
[#37]
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Posted: 6/6/2021 9:46:04 AM EDT
[#38]
You’re better off comparing it to the CMMG barrel. Using manufacturer’s numbers to cut a barrel like this is hopeless because there’s too many variables. For example, how’s the barrel length measured? Chamber face? Bolt face? Another one is rounding off numbers or a bad conversion from metric to standard.
FWIW, the spec is 264mm. Edited to add: Here’s pics of mine, factory FN P90 barrel & flash hider... https://imgur.com/a/4FGp4vv Edited to add more: I notice your barrel has a shoulder where it shouldn’t and your thread adapter may be bottoming out on it. Or it’s too long. Or who knows what. Your best bet is probably to try to have it machined to mimic the CMMG barrel. |
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Posted: 6/6/2021 11:58:23 AM EDT
[#39]
Quote HistoryQuoted: You’re better off comparing it to the CMMG barrel. Using manufacturer’s numbers to cut a barrel like this is hopeless because there’s too many variables. For example, how’s the barrel length measured? Chamber face? Bolt face? Another one is rounding off numbers or a bad conversion from metric to standard. FWIW, the spec is 264mm. Edited to add: Here’s pics of mine, factory FN P90 barrel & flash hider... https://imgur.com/a/4FGp4vv Edited to add more: I notice your barrel has a shoulder where it shouldn’t and your thread adapter may be bottoming out on it. Or it’s too long. Or who knows what. Your best bet is probably to try to have it machined to mimic the CMMG barrel. It’s bottoming out on the crown of the barrel. Do you ever have any fail to feed or fire on your ps90? |
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Posted: 6/6/2021 7:16:33 PM EDT
[#40]
Quote HistoryQuoted: It’s bottoming out on the crown of the barrel. Do you ever have any fail to feed or fire on your ps90? No, knock on wood, never in 2,400 rounds of SS195 and American Eagle. |
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Posted: 6/14/2021 9:55:02 PM EDT
[#41]
I took it back to the gunsmith. He cut one mm off the barrel. It looks much better now. I just need to find some time to go shoot it and see if reliability improves.
 Attached File |
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Posted: 6/14/2021 10:15:06 PM EDT
[#42]
+subscribed, interested in the answer
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Posted: 6/15/2021 5:25:21 PM EDT
[#43]
That looks a lot more like it is supposed to.
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Posted: 6/15/2021 7:12:11 PM EDT
[#44]
So I just got back from the range. I had two 50 round mags with me. I shot 20 unsuppressed and 80 suppressed with my dead air sandman k. Hearing safe without muffs. Zero issues or malfunctions. Ran like it supposed to. Hopefully it stays that way. I really like this gun and want to use it in a few matches.
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Posted: 6/15/2021 11:29:31 PM EDT
[#45]
That's great! Sounds like he got you taken care of.
I'd do more testing to confirm.  |
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Posted: 6/16/2021 5:50:10 PM EDT
[#46]
+1 good outcome. Thanks for sharing your experience with this
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