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 My PSA Dissipator AR isn't stripping the next round UPDATE 
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I took my newly built PSA DIssipator to the range today to try it out. Loading the first round from a magazine works fine, the gun fires, but I had three stove pipes, and only got it to strip and fire the next round from the magazine, maybe three times out of fifty rounds (a 20 round Bushmaster magazine, and a 30 round Magpul). I kept having to cycle the bolt by hand. At first I thought it was because the bolt was very dry, so I lubed it up with some TriFlow, then I found that the bolt was very stiff in the carrier, so I lubed that as well. That seemed to help a bit, but I still never got more than two rounds off without having manually cycle the bolt again. This was with cheap ammunition, probably Tula 55 grain stuff (which my other two AR & my Mini-14's eat up). I suspect it's probably just a break in thing, but wanted to see if you guys had any other thoughts. I can see scrape marks along the top of the rounds that weren't getting stripped into the chamber, but it's almost like the bolt is moving too fast for the magazine spring to push the rounds up fast enough for the front of the bolt to catch them.

Thoughts?

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Last edited by delliottg on Sun Jun 25, 2017 7:39 pm, edited 1 time in total.



Sat May 20, 2017 10:11 pm
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Sounds under-gassed to me. What is the distance between the gas port and the muzzle? Those dissipator uppers look like they would be prone to the same issue as 7.5" AR barrels...a very short distance/period of time for pressure to build behind the projectile after it passes the gas port and before it exits the muzzle.


Sat May 20, 2017 10:22 pm
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So, maybe more like it's short stroking the buffer spring? I'd guess it's 6" or so from the end of the barrel?

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Sat May 20, 2017 10:51 pm
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delliottg wrote:
So, maybe more like it's short stroking the buffer spring? I'd guess it's 6" or so from the end of the barrel?

It sounds like it is definitely not getting enough gas pressure to cycle the BCG, thereby short stroking. First I want to ask if you put an adjustable gas block on it or a standard gas block. I've found that adjustable gas blocks, even when placed in the fully open position, don't allow as much pressure (or gasses) through as a standard gas block. If it's an adjustable, switch it to a standard to increase the gas pressure. If you already have a standard gas block installed, just insure that the port hole in the GB is properly aligned with the hole in the barrel. It should be aligned correctly and you should be sure there are no obstructions in the gas tube or block that could be blocking the gasses. Blow some air through to be sure. Once everything has been checked and confirmed good here we will move on to the buffer and spring.

So the gas tube, block alignment and everything from the gas block to the BCG checks out okay? What weight is your buffer? What length is your buffer spring? You will want a lighter buffer if you are currently using anything heavier than a standard weight carbine buffer. If you are using a rifle length buffer spring instead of a carbine length buffer spring it could be screwing you up too. You want the lighter buffer and the shorter carbine length buffer spring. You can google the difference. These are good to go? Move on.

Next I'd check the BCG itself. Insure there are no obstructions in the gas key. Make sure the gas key aligns and seats properly on the gas tube when the gun cycles. Insure the gaps in the three gas rings are not aligned. They should be staggered. Sometimes the highest precision BCG (expensive ones) or coated (NiB..etc...) will have the tightest tolerances with the upper receiver. They will need more lube and take longer to break in due to those tight tolerance specs. If you think the BCG might be the issue, try a tested BCG from one of your other AR's.

If all else fails, meet me up at MRC on Monday and I'll bring my tools. Good luck brother. Hope this gets you shootin' that thing soon!


Sun May 21, 2017 1:46 am
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What ammo are you running thru it?

My 10.5" pistol will do the same thing with Wolf 55gr steel case cheapo rounds. Throw in some Federal M855 or Speer Gold Dot 55gr and it runs without a hiccup. I'm fine with that, as the pistol was built for PDW purposes and not range toying around....my Spikes/Seekins Frankengun will will run anything and it serves my needs just fine....double duty and all.

Edited to see you tried what you guessed to be Tula.

Need moar coffee.

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Last edited by waglocker on Sun May 21, 2017 8:00 am, edited 2 times in total.



Sun May 21, 2017 6:18 am
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Tula is weak. Change ammo for the win.

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Sun May 21, 2017 6:37 am
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All good points above. My last build with 'high quality' -read tight- BCG and a billet upper acted similarly with my secret formula accuracy target reloads which chrono about 2900 fps.

A full wet down with Breakfree CLP ( what I had on hand) and a couple mags of brass 119 factory ammo and everything was nicely broken in.

My semi light target rounds then ran fine..
Hope your answer is as simple.

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Sun May 21, 2017 6:44 am
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Thanks for the replies guys, I think (hope) it's just a new upper that needs breaking in. I didn't build it, it came from PSA as a complete upper. I've got some good quality 5.56 I will run through it next time and see how it performs with that. I'll also strip the bolt down and make sure it's all nice & cleaned and lubed up. My lube job at the range yesterday was rushed and probably incomplete.

A final question (I hope), is there anything in the lower that could be causing this? I built up the lower, and it's only the third one I've done, so if there's a chance for a build error, it seems much higher that I did it, than on PSA's end for the complete upper since they do thousands of them.

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Sun May 21, 2017 10:42 am
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If it was just having problems picking up rounds, it could be a lower fitment issue but with the stove pipes probably not. I think the guys above nailed it. Under gassed.

Iirc the dissy uppers run a carbine or mid length gas system. The a2 front sight isn't actually a part of the system. Different ammo is the easiest fix. After that you could take apart the upper and check gas block alignment. Then fiddle with buffer weights. Polish the bolt and carrier. The list is long.

Hope you get it figured out.

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Sun May 21, 2017 11:18 am
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Guns4Liberty wrote:
Sounds under-gassed to me. What is the distance between the gas port and the muzzle? Those dissipator uppers look like they would be prone to the same issue as 7.5" AR barrels...a very short distance/period of time for pressure to build behind the projectile after it passes the gas port and before it exits the muzzle.



Its a midlength gas system on a 16" barrel with an extra front sight sight added at the rifle length position. There's only a couple of manufacturers in the last 15 years that have made a "dissapator" style 16" barrel with a rifle length gas system. It's pretty uncommon.

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Sun May 21, 2017 5:05 pm
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I haven't pulled the hand grips off of mine yet, but I'd be willing to bet that's pretty much exactly what it looks like without them right down to the sling swivel and bayonet lug.

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Sun May 21, 2017 6:12 pm
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NWRed wrote:
Its a midlength gas system on a 16" barrel with an extra front sight sight added at the rifle length position. There's only a couple of manufacturers in the last 15 years that have made a "dissapator" style 16" barrel with a rifle length gas system. It's pretty uncommon.

Ah, that makes. I just assumed the FSP was the gas block, so I thought it was an odd setup.

OP, I'd run some hotter ammo through it and see what happens.


Sun May 21, 2017 10:57 pm
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take the hand guards off and check the gas block if it wiggles. and has correct spacing at the neck

if you take a fully loaded mag and can hand rack all of them its more likely a gas issue.

put the upper on another lower see if it works, if so call PSA, since its not a serialized item send the upper back for a replacement.

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Mon May 22, 2017 6:17 am
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OhShoot! wrote:
Tula is weak. Change ammo for the win.
:plusone: when i built my first ar years ago i used wolf .223; it would cycle but never lock the bolt back in my mid-length. Something about mil spec gas ports and Russian powder burning so fast creating less pressure at the port. Buy a box of fed m193

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Mon May 22, 2017 5:16 pm
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I dunno about the ammo thing . . . if I had an AR that wouldn't run Tula, I'd consider it defective.

Blaming the ammo is too easy here.

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Mon May 22, 2017 6:32 pm
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