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Continuation of Gopher's issues


Gopher

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It's easy to see the difference between the AR15 midlength gas tube (bottom) and the AR-10 Carbine gas tube (top).  Remember that increased height over bore I mentioned earlier?  The Armalite gas tube accounts for that.  The AR15 gas tube has shallower bends, because it's made for a lower height over bore.

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Edited by 98Z5V
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Something else, as I'm disassembling and assembling.  I noticed that the rear lug on the PSA upper was longer than other things I'm comparing it to. So is the front lug, barely.  I noticed this immediately, when I set the pivot pin with an AP M5 lower, and tried to pivot the receivers open... They'll open just enough to get a BCG and charging handle out, but that's about it, and they bind.  When I pinned it to the DPMS LR308 lower, they would pivot even less - you couldn't freely open it to the point to get a BCG and charging handle out, you had to fight it a little to get it to open to that point - binding of that front lug, as it pivots, against the front of the lower receivers.

The rear lug is quite longer than the AP M5.  The front, just barely - but that's enough to cause it to bind. 

Aero on top, PSA on bottom - you can see the additional material below the takedown/pivot pin holes on the PSA.  Again, we always knew this was a proprietary design. We've never seen how proprietary, until now.

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Aero rear - I measured from the lowest point of the lug, up to the receiver mating area. 

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Aero front:

P1060582.thumb.JPG.ebf6d525ce4e7d4c57c2d6c48537dfb0.JPG

PSA rear:

P1060583.thumb.JPG.8559c9433e6dcb162c3cf250787d0c00.JPG

PSA front:

P1060584.thumb.JPG.a42a666a7762cee66145378764f0885f.JPG

 

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Strange. Found something else.

Steve shipped me this upper just as he received it - even in the same box, which is a badass box!  Anyway, has shielded round handguards, delta ring, handguard cap, etc.

So, I went down to the Gun Pusher and snatched a .750 lo-pro YHM gas block for this.  Since it came with a handguard cap on it, I put that back on the barrel, then put on the lo-pro gas block.  Wow.  The gas port in the barrel is right at that point where it's about to be covered up...

(They drill the 0.125" gashole in gas block by going straight up through the rear mounting screw-hole. You test gas port location-to-the-shoulder by installing these gas blocks, and roll them over 180 degrees - it'll show you where your gas port is in the barrel, in relation to the shoulder on the barrel)

WITH handguard end cap in place:

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Handguard endcap removed, gas block back on...

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Here's an Armalite AR-10 Carbine gas tube installed - I will certainly be taking advantage of all available gas pressure, instead of giving up some gas pressure.  Also, this is more of a gas TIMING thing, than it is about "pressure..."

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Here's how the rifle will get shot and tested first thing in the morning...

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If I had the rail in there, it would look like this...

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I won't have the rail on there - I want to be able to get to whatever I need to, primarily the gas block.  It's at 0.081" right now, and I want it to be easy to get to if I need to go up from there...

Edited by 98Z5V
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That wear in the upper from the BCG is unusual to say the least, I have seen it before on a very old Colt M16 that a friend owns.

My guess is that the BCG is being pushed up into the roof of the tunnel by the hammer/hammer spring, were there not a gap there, the cam pin cut out, you'd probably not even notice the wear, it more obvious on the front side of the cut out because the BCG has 'tripped' over it, in the pics it clearly sows the witness wear all along the top of the BCG tunnel beside the charging handle channel.

FYI the cam pin cut out is machined after the BCG bore in the machining process.

Below is a pic of the last upper I machined from a block of 7075 tool plate, first step was to bore the BCG tunnel.

ar4.jpg

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They have a dull cutter on that thing when they cut the cam pin cutout, and displace metal down into the BCG channel?  I can only guess, I don't know. 

That BCG slides easy in that upper now - it removed what it had to, via the force of .308 Winchester.  It also slides easy in the AP M5 upper I put it in...

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9 minutes ago, 98Z5V said:

They have a dull cutter on that thing when they cut the cam pin cutout, and displace metal down into the BCG channel?  I can only guess, I don't know. 

That BCG slides easy in that upper now - it removed what it had to, via the force of .308 Winchester.  It also slides easy in the AP M5 upper I put it in...

Quite possibly/likely.

You'd be surprised how much you can 'push' aluminium around when machining it, if your feed rate is higher than the rate that the cutter is removing the metal it'll just push it in front of the cutter like a bulldozer.

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8 minutes ago, 308kiwi said:

Quite possibly/likely.

You'd be surprised how much you can 'push' aluminium around when machining it, if your feed rate is higher than the rate that the cutter is removing the metal it'll just push it in front of the cutter like a bulldozer.

That's the other thing I was wondering about - speed.  Good cutter, too much speed.  I've watched my machinist go off about a part he's experimenting with, because the speed was too fast, and he jacked it all up. It's quite awesome when he does it - it's like a Tourette's Guy explosion...  :lmao:

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4 hours ago, 98Z5V said:

  I'm going to replace the gas tube with an AR-10 gas tube first, and just shoot it like that, before I even drill the gas port in the barrel.  I want to see what happens, before I drill it, and after I drill it.  Either way, it's getting drilled to 0.081".

I'm going to tell you guys right now that I straight-up contradicted myself.  I drilled that gas port already, to 0.081".  That port size of 0.073/4/5" whatever it was (under 0.076"), is just too small for an 18" midlength-ish gas system in the .308 Win AR.  I punched it already.  And, it may go north of that, for reliable function...

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Runs like a champ.  Nothing wrong with the extractor springs, as far as tension goes. It didn't chew up the brass at the rim any more than any other .308AR I have. I will include a spare extractor spring with it when I send it back, though, just in case you need it on your terrain, Gopher. 

I had it at 0.081" gas port size, and I'm shooting some "warm" handloads through it, and it should have tossed that brass forward on ejection (with those loads).  They went out to about 4 o'clock.  I don't use that "clock pattern for ejection" as a sole indicator of how the gun is running, gas pressure wise, but it is another tool you can use.  So, up in size the port went, to 0.083".  That was better, but not what I was looking for.  Up again, to 0.085".  THIS I liked.  Kicked the brass to the 1 and 2 o'clock positions, which is about what this load does on my others.  So, set up like this, it'll handle hot loads, weak loads, off-the-shelf whatever you find.  I have a box of CBC somewhere that's kinda weak, and should have used that, too.  Didn't grab it. I'll look for it and try it.

Here's the brass, as it landed from the rifle:

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Total changes: Armalite AR-10 Carbine gas tube, gas port went from 0.073" to 0.085".  It runs, well. 

I still need to test if with your front sight base as a gas block, and make sure it's not obstructing the pas port in the barrel, so there's still a little bit more to do to it, but it's not much.

Edited by 98Z5V
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On 7/15/2018 at 12:34 PM, 98Z5V said:

Same here  - it would be a riot, for sure...  :laffs:

In reference to the stuff I bolded above - your guns are only running because everything else is "right enough." As soon as you toss a gas port in there that's too small, no bueno.  Everything turns to shiit. As soon as you throw a stronger (correct) recoil system in there, again, no bueno.  Lack of gas pressure is fighting a proper (and not weak) recoil system.

It's exactly why I said this, in that other linked thread:

 

 

I don't have a dog in this hunt, BUT, I am familiar with the "minimum cost of manufacturing philosophy"  Engineering is charged to produce a product with just enough reliability to compete with the standard established product holding a reasonable market share.  Engineering reverse engineers a product and often purchases inexpensive  components that function well enough to pass their lab requirements Basically their main feature is lower price. From what I have observed here on the forum PSA may fall into this category.

Edited by mrmackc
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0.085" gas port size is where this barrel wanted to be, from the beginning.  Even with some "warm" ammo, there is no brass damage, at all.  All the case mouths are fine (I see two in here that got a little "out of round" during ejection).  Nothing out of the ordinary, at all, and MUCH better than some brass that comes out of overgassed 16" carbine 5.56 barrels, with 1/2 the case mouths squashed flat...

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Nothing to see here...   move along...   The bases look great, too.  No issues with ejector smears or ejector swipes (that would be more of an indication of a real hot load), nothing in the rims that would have indicated an extraction issue (that would have been an overgassed issue).  This much gas running through the operating system...  is where it's happy...

P1060593.thumb.JPG.21c0a9d40aaaab2ff44d56da73ca34ea.JPG

Edited by 98Z5V
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The PSA PA-10 barrel nut threading is DPMS-based, which saves my a$s.  I already threaded your Delta-Ring assembly back onto the M5 upper, so I can run your handguard and chopped/shaved front sight base (as a gas block). I have to verify that the FSB isn't restricting gas flow, with that handguard cap on there, which holds the handguards. 

Once I assemble it all and shoot it again - IF my ejection pattern changes to the "softer side," that means the FSB is partially covering the gas port, and restricting gas flow. Primary reason I watched the ejection pattern closely, and made sure I got a pic of it all.

If my ejection pattern doesn't change at all - your upper gets rebuilt and shipped right back to you.   :thumbup:

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Edited by 98Z5V
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While I'm at it - and since the PSA PA-10 Gen 2 thread pattern is the same as DPMS LR, I thought I'd toss this in there. PA-10 rail height.

AP M5s are set up at the old DPMS height (DPMS "High" vs DPMS "Low" - which is NOT that crazy "High-Rider" DPMS Shiit).

So, the PSA PA-10 Gen 2 is 0.050" lower than "DPMS High."

If there's a 0.060" difference between DPMS High and DPMS Low, that means the PSA PA-10 would be within 0.010" of the DPMS Low rails  - well within "close enough to work and make sight adjustments..." :thumbup:

You could even BURY a front sight post in a front sight assembly, and run it this way, if that's your thing.

Here's the Aero M5 rail on the PSA PA-10 Gen 2 upper receiver:

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Edited by 98Z5V
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4 minutes ago, blue109 said:

So you can only run PA10 handguards? Why the crap would they do that?

Because. 

 

Proprietary.

 

 

They knew what platforms were out there, and what accessories.  They had to DECIDE to do this...  

Edited by 98Z5V
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Oh, I might add, I don't see a single PA-10 Gen 2 rail for sale on their website.

Not one. :thumbup:

I'd just run the DPMS Low profile rails, eat the 0.010" through sight adjustment, and call it a day.

You could even get the DPMS High rails, and bury the front sight to make up for this.  You'll just have a rail-difference like I posted above, but your sights will work. 

Edited by 98Z5V
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3 minutes ago, Gopher said:

The PSA rail system has a triangle front that no one else uses I am guessing, I am going to replace that soon too to be able to put a picatinny rail system. 

If you want to do that now, brother - it's right here.  I can do that, make sure it's right, and test fire it.  Lemme know.

I'll give you that YHM lo-pro gas block I picked up.  You just need a rail that will mount up - and you probably won't find it as PSA.  Look for something in the "DPMS Low Profile" arena, and it'll be best on your gun. 

I can send it back already fixed, ready to mount to your lower...   :thumbup:

Edited by 98Z5V
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