measurement poll

[98Z5V]

3 minutes ago, Lane said:

Did I say something the wrong way?

I certainly didn't quote you in that, man.  No, that was not you... 

[98Z5V]

I tuned out a 0.640 on my Matrix tonight.  That thing runs like a champ. I also measured a few 0.660s and a 0.670 from the same exact manufacturer, with the only difference being - matched sets versus rack-grade parts.  Is there a difference on what they make?  I don't know, but that 0.670" measurement was from the first AP that I ever built, quite awhile ago. All the ones I bought after that were matched sets, but were all at 0.660".  Did a machining operation change, somewhere?  I don't know.  But they all run - because the builder of the lower, with that mag catch-height spec that they made - also machined the height in the upper for the BCG placement. 

That's the only rational way I can explain why I have a rifle with a mag catch of 0.640" that runs like a champ (same upper), and multiple rifles running 0.660" and running - another with a 0.670" and running... And the distance listed earlier in this thread was 0.687"...

So, in one gun, I can be almost 50-thou off of a published number - but that thing runs like a champ, with the exact same mags as all the other ones, with a spec that doesn't meet that number of 0.687", and is under by about 30-thou - but they work?...  Great!...  One of those 0.660s is my hybrid-bastard-from-hell, too - the 13.5" Armalite/DPMS/Aero gun.  That thing will eat any ammo I can fit in a mag.

The issue here is the different manufacturers of the parts you're using - and the blatantly obvious fact that there is no "spec" on these things.  That's the real problem here.  Pick a lower.  But pick the same upper.  Stick with what "is supposed to work" instead of piling parts together.

I'm off my on this - but I still want the details on the parts you've tried.  That will tell future members what to stay away from, on combinations that don't work.

Edited April 3, 2019 by 98Z5V

[Lane]

3 minutes ago, 98Z5V said:

That's MY observations on this mess...

Totally valid. My MagPul 10s work in everything I've ever built. 

Still curious about how to modify a mag catch to work in this way (as I think I understand it). Wouldn't the mag catch need to be thickened with a weld; and also the lower modified to fit?

[98Z5V]

From @panel77s history, he started with a PSA upper, and machined his own lower from Blitzkrieg or AMT, if I'm not mistaken. 

So, right off the bat, you've attempted to adapt a self-proclaimed proprietary upper onto an 80% lower, that you machined (or someone machined). 

And, there's a question as to why there are issues now. 

[Lane]

9 minutes ago, 98Z5V said:

So, in one gun, I can be almost 50-thou off of a published number - but that thing runs like a champ, with the exact same mags as all the other ones

If you tried this, and it works; I'm not even going to ask.

I have been looking at those distances in my caliper for more than a day trying to figure out " how " this could be an issue. I know the angle of the magazine could mediate in that way. Also the feed lip angle on the mag (but that should be static with MagPul magazines).

[Lane]

2 minutes ago, 98Z5V said:

And, there's a question as to why there are issues now. 

Nope. Been down that road once or twice. I appreciate the clarification.

[98Z5V]

11 minutes ago, Lane said:

If you tried this, and it works; I'm not even going to ask.

I have been looking at those distances in my caliper for more than a day trying to figure out " how " this could be an issue. I know the angle of the magazine could mediate in that way. Also the feed lip angle on the mag (but that should be static with MagPul magazines).

A manufacturer can put that mag catch placement anywhere they want, within obvious limits of the platform, brother.  As long as they account for that "higher or lower" placement in their exact placement of that BCG channel that they bore in the upper - on their own upper that mates to that lower.    They can literally do what they want, within functional limits.

When people try to match different uppers and lower from different manufacturers - is when we see these issues.

Or, you try to by an IRA billet machined matched set that never worked from the get go, because the dimensions were off, fundamentally...  

Edited April 3, 2019 by 98Z5V

[98Z5V]

I was only stating the measurements of the guns I could easily get to, and reported exactly what I saw on the guns I have.  They all run, or I'd chop them up and sell the scrap, man.  Personally, I was shocked at the differences I saw, because they all run like mad.  The numbers I got were way off that first print number or 0.687", too.  But they run...  

I don't have a single one that has a different upper than the lower, though.  Same manufacturers, but way different numbers in mag catch placement.   

Of note, on measuring AP lowers - you can't accurately measure that lower if you don't disengage the mag catch, and rotate it out of the way.  The AP lowers have a taper/chamfer on the top side of the lower shelf, that you can't accurately measure, if that mag catch is seated... 

Edited April 3, 2019 by 98Z5V

[panel77]

1 hour ago, 98Z5V said:

You seemed a little pissy in that post.  I understand, kinda - but you need to understand that we're here trying to help you out.

So, on that note, you need to give up alot of information.  Please allow me to respond, again, before you do - and I'll make my points.  I wanted to address this first, though.

sorry-my wife says i am terrible in writing and come across wrong. prob has to do with my dis-like of writing and expounding on thoughts in general...

sorry-you have in my previous PSA post been above extremely helpful and of a superior and scientific mind-I dont know if I ever got around to thanking you properly and publicly.

Thank you.

oh-and it looks like I didnt look up your profile properly-I wrote 94xx and what I meant was you-98Z5V-you got me pointed the right direction and now that ive found a more accessible spot to test fire stuff, im going to be a little more scientific this trip.

I can guarantee the PSA uppers had problems and you helped point me the right direction but what I am expecting to find is compounding errors all inside a non-standard platform.

[98Z5V]

Go hit my past posts here, man, and fire up some answers - what uppers and lowers are you working with here?  This is the ground-truth, right here, in mis-matching manufacturers.  I stand strong on this one - THAT is the major problem here...  

[panel77]

so to respond to 98Z5V who was super helpful in prior post, trying not to get too off-topic... 

yes I started with AMT lower and PSA upper assembly only to experience this problem almost all the time.

With his help and insight, I grabbed a matching AMT upper and used teh PSA barrel and handgaurd and parts with a new proper length gas tube and drilled out to i forget maybe 78 or so from 65? and put it back together, things worked better by a 10x factor but still had same problem but not as often.

then i got a little more measury with the calipers and able to look at 2 different lowers... long story short is i havnt been too scientific and thought the mag catch was too low and not allowing things to sit in proper place so i started the original post as a poll.

both the AMT and the non name but identical matching lower measured at 0.695 and the one i hadnt used in forever but worked 100%(in my memory) was at 0.665?

 

so I wanted data after digging in google and using a calculator-i asked you professionals for real world data and the consencus seems to be the 0.695 is wrong and a doorstop.

tomorrow will be a science day.

oh and based on 98xx i got a bear creek complete upper cause i was tired of the drama and it fits very very nicely with the existing lowers and it had the same problem. which led me to think it was a lower problem(not saying 98xx wasnt right about PSA p.o.s. uppers...)

 

 

[panel77]

7 minutes ago, 98Z5V said:

Go hit my past posts here, man, and fire up some answers - what uppers and lowers are you working with here?  This is the ground-truth, right here, in mis-matching manufacturers.  I stand strong on this one - THAT is the major problem here...  

Yep-you helped me make significant corrections to the upper setup and I got the correct matching upper and swapped all the good parts onto it with the same issue but slightly improved.

right length buffer spring, right length buffer tube, 5.4 buffer, right length gas tube, gas port size drilled out to 78 then 96...

mags are all 'brand new' pmags 10rounders. with less than 30 through each mag.

also went to local gunsmith who knows more than me and he drilled one of the POS PA-10 gas ports to 96 and it didnt help.

Edited April 3, 2019 by panel77
addition

[98Z5V]

So, is this thing solved, man?...  It functions now?...

[panel77]

1 minute ago, 98Z5V said:

So, is this thing solved, man?...  It functions now?...

I will find out tomorrow when I hit the hills.

got 3 boxes of gear and a yellow pad for notes.

 

if the redneck vise grips jamming the modified mag up into the POS lowers makes it run, im getting new lowers.

already ordered one from a vendor with superior customer service who provided a dimension.

[Toolndie7]

Call me a dick but shouldn't you be referencing the lower portion of that slot anyway? that is the surface that essentially holds the catch and mag up. Theoretically that slot width could vary quite a bit and not mean poop as long as the bottom wall of that slot was close. Print calls for a .250 finish width so Id be willing to bet most manufacturers just sail a 1/4' end mill in there and then clean up the walls to a slightly larger dimension. If they get carried away and drop that wall too far down it may be the problem you have going on. Just my .02

[edgecrusher]

Larue- .6560

PWS- .6550

Maten- .6555

[panel77]

so 100 rounds later and no definitive answer.

when i jammed mag up in and pushed HARD  on it while operating, it appeared to have zero issues with AMT lower and Bear creek (BCA) 18" OEM upper.

then i did a few mags right at teh end(limited timeframe) and without holding them in, it worked fine....

but now im skittish, i dont want to lug a hammer around the woods, a real hammer is lighter...

 

gonna mill the new 80 and see what happens.

in all cases- that slot is in the wrong place compared to everyone who has responded both here and via manufactures contacts.

wrong by at least 0.020 and most often wrong by an average of 0.030

 

im throwing up my hands for now-its a 45 minute drive at least to reach a place where i can test, no back yard range...

Edited April 4, 2019 by panel77

[Belt Fed]

So it never jammed again? that's weird. I know how ya feel thou. I wouldn't know what to to with it now.

[panel77]

3 hours ago, Belt Fed said:

So it never jammed again? that's weird. I know how ya feel thou. I wouldn't know what to to with it now.

I had one jam but it was an obvious error and related to flawed testing and a repeatable error.

Extreme... LOL redneckness to test theory-failed. used clamp with modified trash/test mag.

should tried clamp with reg mag but i just need 2-3 hours(only had about 15 minutes) and more ammo... 

[panel77]

lower

 

[98Z5V]

On 4/3/2019 at 4:03 AM, Toolndie7 said:

Call me a dick but shouldn't you be referencing the lower portion of that slot anyway?

The top of the mag catch is what holds the mag in place. Now, a slot that's way too wide (over 0.250") would allow the mag catch to "rotate" down in the too-wide slot, which would effectively lower the seated height of the mag.  But the top of the catch is what determines mag height - and retention. 

A fully loaded 20-rd LR/SR-20 PMag weighs 2 lbs.  The top portion of the mag catch itself, and the top of the indentation in the mag body, is what determines the height of the mag when it's seated.   That business is all determined by the top of the mag catch, and this - this is what the 2lbs hangs in the gun from:

 

[98Z5V]

There absolutely MUST BE a correlation to that slot in the mag body, and the centerline of the BCG.  No other way around it.  I have no idea what that measurement is, but you could find it from Armalite AR-10 prints - because it is the original, and it always works.

The reason there MUST BE a correlation to that, is - the bottom of the bolt face has to strip the next round out of the magazine during the cycling process, when the magazine is seated and locked. The bolt face takes this force, because of the cam pin - the cam pin isn't allowed to rotate until it gets to the cam pin cutout in the upper - that bolt is locked in place in the BCG body, extended, while the cam pin is traveling down your charging handle groove, in the upper receiver - it's solid, not moving into the BCG body - and stripping the next round.

Now, there will definitely be some variance, or tolerance, in what's too high and what's to low, in the relation of those two parts - but it can't be much.  20-thou?  30-thou?  I don't know. 

Within limits, manufacturers can do whatever they want for mag catch placement in the lower - as long as they are within that range or tolerance in BCG centerline over the top of that mag catch.  And it will work.  They are working within the limits of their own upper AND lower receiver dimensions to achieve that distance between those two parts. If a manufacturer fuks that up - your gun doesn't feed/strip the next round, OR the BCG slams into the back of your mag body.  It can only be those two things. 

This is the beauty of "not having a standard or pattern to follow..." 

I will measure the 4 previous rifles I listed - Top of mag catch to BCG centerline.  I'll bet it's pretty close on all of them, despite having a difference of 30-thou in mag catch placement over the 4 guns. 

Edited April 5, 2019 by 98Z5V

[ar-mountaineer]

This has nothing to do with the measurements (I provided my Fulton earlier) but do you got a pic of the upper and lower together. I’m curious about the width of the 2 and how they mate up. My 80 from Daytona tactical looks pretty much exactly like that AMT and I’m looking for an upper that mates up good (no overhang of the lower or upper). You said your upper was bear creek?

[Toolndie7]

On 4/5/2019 at 12:43 AM, 98Z5V said:

The top of the mag catch is what holds the mag in place. Now, a slot that's way too wide (over 0.250") would allow the mag catch to "rotate" down in the too-wide slot, which would effectively lower the seated height of the mag.  But the top of the catch is what determines mag height - and retention. 

A fully loaded 20-rd LR/SR-20 PMag weighs 2 lbs.  The top portion of the mag catch itself, and the top of the indentation in the mag body, is what determines the height of the mag when it's seated.   That business is all determined by the top of the mag catch, and this - this is what the 2lbs hangs in the gun from:

 

 

I totally get what your saying I was just thinking about the fact that some slots could be machined waay oversize.  My point is the bottom of the slot in the receiver holds the catch and in turn the mag UP.  The top location of that slot really means nothing as it basically just determines clearance and NOT location.  I was just thinking he should be getting reference numbers on the location of the BOTTOM of that slot as that is the surface that determines the final location of the feed lips.

EDIT: Maybe just get a measurement from the top surface of the lower receiver to the top of the catch would be a more relevant measurement?

Edited April 8, 2019 by Toolndie7

[panel77]

i will add a pic of the upper.

the AMT upper fits the AMT lower nicely.

i dont have any other lower and the PSA upper is for PSA lower ONLY and is useful for target practice only.

 

Broken Arms lower coming sometime

all slots are at 0.2500