measurement poll

[panel77]

2 hours ago, Lane said:

What kind of magazines are you using (others have asked too)? Never had a single issue with polymers, but have modified every one of my stainless steel magazines in some way or another.

The measurement on my Ceratac .308 is 0.650"; perhaps +/- 0.0005", but I measured it quite a few times and got the same numbers. 

Belt Fed showed the same thing 0.6500"; you just have to read the first digit off the slide; and the rest on the large dial.

So the mag thing can be an issue I am learning BUT... what I am leaning on is the theory that the 0.695 pushes the mag too far down to where a sub-par mag or a jostle is enough.

all mags are PMAG with less than 50 through each mag.

my next more scientific visit to the range will include a c-clamp to jam that mag as deep as possible and if it 'fixes' it, these lowers are going to be scrap while I replace them with ones more in spec.

[panel77]

got replies from vendors I emailed

results so far

5DTactical thinks they are too awesome to send me a spec. direct quote, 

"Customer Care Agent (5D Tactical)

Apr 1, 15:59 PDT

Great question!

I see you haven't placed an order with us! I can't just provide specs of our lowers of course, but I can tell you that they follow DPMS Generation 1 pattern! I would recommend ordering one, and then you would be able to measure everything you like!

Customer Care Agent"

-nope-never doing business with them.

----------------------------

-Noreen firearms asked for clarification-always been happy with their CS-update-they supplied a spec of 0.659

-Hellfire armory responded almost immediately with a picture AND a dimension of 0.685

-Broken Arms in San Jose responded with critical thinking and problem solving along with a phone number and request to call. He was great to talk to, helped with information, clarity and provided a spec of 0.6665 along with great customer service. They immediately got my business.

-0.650 from a forum member-brand unknown, possibly Diamondback

-Xantos @ 0.669 and PSA 100% @ 0.700 from forum member

-Fulton @ 0.671 from forum member

-Colfax doesnt make 80% anymore but forum member measured at 0.663

-Ceratac @ 0.650 and Belt Fed @ 0.650 from forum member

[shooterrex]

Did the 1st gen DPMS guns use a different magazine? I don't know the answer to that question but if they did that could be the answer to your problem. Just an idea seeing the reply you got from the 1 vendor.

[panel77]

-American Made Tactical measured at 0.695=fail.

 

 

[Belt Fed]

If you have the old style lower, that is your problem. I will measure my older Armalite and see what it reads and measure the catches on both style magazines.

 

[Toolndie7]

Not sure if this will help but all the info I have points to 11/16" or .687" with a nominal 1/4" .250" wide slot. Same goes for the AR15 as well so if you guys are getting .650 then I would think its buried in there enough.

[unforgiven]

11 hours ago, panel77 said:

So the mag thing can be an issue I am learning BUT... what I am leaning on is the theory that the 0.695 pushes the mag too far down to where a sub-par mag or a jostle is enough.

all mags are PMAG with less than 50 through each mag.

my next more scientific visit to the range will include a c-clamp to jam that mag as deep as possible and if it 'fixes' it, these lowers are going to be scrap while I replace them with ones more in spec.

Just rest the rifle on the magazine and see if it will function. My LAR 8 is a dangler.

[ARTrooper]

3 hours ago, unforgiven said:

My LAR 8 is a dangler.

oh is that what you call it? 😛 I doubt it is an 8 though, maybe a 5 or a 6 

[shooterrex]

6 hours ago, Belt Fed said:

If you have the old style lower, that is your problem. I will measure my older Armalite and see what it reads and measure the catches on both style magazines.

 

I know the 1st gen Armalite use a different magazine. I do not know if the 1st gen DPMS use a different magazine.

[panel77]

the 80% utilized that returned a 0.695 are recent and from AMT. also ordered one from Blitzkrieg and will be returning-it looks IDENTICAL to the AMT and measures identical.

 

I doubt this is gen 1 DPMS and its not Armalite.

Where my options are to shoot, bench rest is not an option

also I do not want a bench rest only rifle, unless a rifle works each and every time, its not a rifle, its a hammer.

 

You guys are great, keep the data flowing

[shooterrex]

Next question.  Do the uppers fit tight to your 80% lowers? No gap? Could the takedown pins holes be just a tad high ?

[panel77]

1 hour ago, shooterrex said:

Next question.  Do the uppers fit tight to your 80% lowers? No gap? Could the takedown pins holes be just a tad high ?

no measurable gaps, havnt thrown a feeler gage in there but its not a gaps issue.

based on data received so far its a design flaw in the lower, out of spec(as if there is an official DPMS spec) by 0.020 compared the average of other specs.

Im gonna mess around with creating a modified lower-specific mag catch just so the lowers arent lawn ornaments... nothing to lose at this point as using visegrips to jam a mag up the hole isnt a realistic or useful or viable option even though its the most appropriate redneck solution. 

hey-i resemble that remark!

[unforgiven]

3 hours ago, ARTrooper said:

oh is that what you call it? 😛 I doubt it is an 8 though, maybe a 5 or a 6 

I'll be dragging my nutsack before my dick 🤪

[shooterrex]

35 minutes ago, panel77 said:

no measurable gaps, havnt thrown a feeler gage in there but its not a gaps issue.

based on data received so far its a design flaw in the lower, out of spec(as if there is an official DPMS spec) by 0.020 compared the average of other specs.

Im gonna mess around with creating a modified lower-specific mag catch just so the lowers arent lawn ornaments... nothing to lose at this point as using visegrips to jam a mag up the hole isnt a realistic or useful or viable option even though its the most appropriate redneck solution. 

hey-i resemble that remark!

You are using plastic mags (magpul) jb weld is your friend. Modify the mags not the lower. Just a thought.

[panel77]

Just now, shooterrex said:

You are using plastic mags (magpul) jb weld is your friend. Modify the mags not the lower. Just a thought.

thanks-not interested in modding xxx mags when i can do one lower mod and if it doesnt work-its a throwaway anyway. or an extreme backup with bright neon sign that says only use with visegrips... LOL

 

pmags.... piles of...

[edgecrusher]

We have a thread on here somewhere where we compared parts kits. Armalite parts are structurally far beefier. Maybe an Armalite mag and bolt catch could help resolve the issue. I’ll get you some measurements from my Maten, LaRue and PWS in a few

[98Z5V]

0.670" on an Aero standard M5 lower, upper and lower not purchased together; purchased at different times.

0.660" on an Aero M5 matched set, limited edition ASO set.

0.660" on an Aero M5 matched set, Flag Edition set (the .260 Rem).

0.640" on the original Matrix Aerospace, that is the direct copy of the Ruger SR-762 receivers.  Matched set.

There's another AP set that's buried, and the original DPMS LR-308 "K-Serial" gun is buried WAY DEEP.  I'm not digging those out right now.

Those numbers tell me some things about attempting to measure this stuff against a known or published number.

 

Edited April 3, 2019 by 98Z5V

[Lane]

7 hours ago, panel77 said:

thanks-not interested in modding xxx mags when i can do one lower mod and if it doesnt work-its a throwaway anyway. or an extreme backup with bright neon sign that says only use with visegrips... LOL

I thought a lot about these modifications and haven't settled on any one yet. That's why I didn't reply sooner... I still don't know what the best course of action is; but you're totally right about not modifying every magazine to fit. 

1 hour ago, 98Z5V said:

0.640" on the original Matrix Aerospace, that is the direct copy of the Ruger SR-762 receivers.  Matched set.

Thanks for all these numbers Sir. I've been quite curious about how these differences play out in the real world. I never thought any of the bolt catches should be different; but clearly I was over-simplifying this .308 lower dimensions game in my mind. I always assumed there were minor differences in the FCG location because of the upper configuration. A few of those other numbers listed in this thread strongly indicate otherwise. This looks like about a dozen blueprints now?

Edited April 3, 2019 by Lane

[98Z5V]

1 hour ago, 98Z5V said:

0.670" on an Aero standard M5 lower, upper and lower not purchased together; purchased at different times.

0.660" on an Aero M5 matched set, limited edition ASO set.

0.660" on an Aero M5 matched set, Flag Edition set (the .260 Rem).

0.640" on the original Matrix Aerospace, that is the direct copy of the Ruger SR-762 receivers.  Matched set.

There's another AP set that's buried, and the original DPMS LR-308 "K-Serial" gun is buried WAY DEEP.  I'm not digging those out right now.

Those numbers tell me some things about attempting to measure this stuff against a known or published number.

 

One interesting thing I didn't mention about these guns - never had a feeding issue, not even one, from MagPul 20 rounders
, either 2nd Gen or 3rd Gen (there was no 1st Gen .308 mags from them), or from the Lancer mags.  So, with those difference specs on the mag catch placement, MagPul 20s and the Lancers work just fine. Zero feeding issues on those platforms listed above.

3 minutes ago, Lane said:

I thought a lot about these modifications and haven't settled on any one yet. That's why I didn't reply sooner... I still don't know what the best course of action is; but you're totally right about not modifying every magazine to fit. 

Thanks for all these numbers Sir. I've been quite curious about how these differences play out in the real world. I never thought any of the bolt catches should be different; but clearly I was over-simplifying this .308 lower dimensions game in my mind. I always assumed there were minor differences in the FCG because of the upper. A few of those other numbers listed strongly indicate otherwise. 

I had one hell of a bolt catch problem on one of these things, and I can't remember which one it was.  It certainly wasn't the original DPMS LR-308.  I think it was one of the Aero setups, but it could have been the Matrix.  I documented it here, but I don't know what one it was now... 

[Lane]

8 minutes ago, 98Z5V said:

I had one hell of a bolt catch problem on one of these things, and I can't remember which one it was.

This whole thing has me spinning. I don't really want to redraw every blueprint myself; but this is a substantial part of .308 issues as a whole. Measuring out the uppers is unfortunately even more difficult; so this isn't a short term endeavor. I appreciate your candor in these matters Sir.

[98Z5V]

I had to shave and cut and polish a bolt catch to get it running, on one of these.  I'll try to find the info on it. There are pics up and everything, with measurements of what I took off, and what finally worked.  I swear it was that first AP that I did, but I built that Matrix right after that one, too, within a month or two - it could have been that Matrix. I'll find it. 

I know a couple guys here saved my ass on that Matrix, and sent me the pivot and takedown pins for it - they're different from everything else.  @blue109 sent me one, and @jtallen83 sent me the other.  Those guys are the only reason that gun is pinned together right now. 

[98Z5V]

On 3/31/2019 at 9:01 PM, panel77 said:

Sorry

I thought this was the AR 308 Forum.

on a 308/large pattern AR lower.

 

Long story short, I am trying to eliminate variables in a feeding issue

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.

[Lane]

2 minutes ago, 98Z5V said:

I had to shave and cut and polish a bolt catch to get it running, on one of these.

Done the bolt catch cut and polish myself. Turns out I had a different issue in the long run that I didn't ferret out yet. Don't worry about finding that info; I saw it before and understood (fixed me up back then when I saw it).

The mag catch cut and polish is what I still can't work out in my mind. This isn't quite as easy. 

[Lane]

4 minutes ago, 98Z5V said:

You seemed a little pissy in that post.

Did I say something the wrong way?

[98Z5V]

On 3/31/2019 at 9:09 PM, panel77 said:

Sorry for not being more clear.

 

YES, I am having PITA with a 308 AR.

 

tried multiple complete uppers from 2 different vendors(PSA fail-fixed with help of 94x? member) but after swapping lowers with good uppers, mix/match, swap with about xx different combinations-the lowers appear to POSSIBLY be the problem and POSSIBLY not be allowing the mag to sit high enough into upper to get stripped(insert joke here) of the next round properly.

from all the online spec drawings I can find and attempting to do math(ouch) it looks like the spec(yeah i know there isnt one) is supposed to be .685-MAYBE... but thats the conclusion from drawings.

2 lowers that mo matter what upper is on get the bolt riding over the round too intermittently to be useful for more than a hammer(if it doesnt go bang E-V-E-R-Y time, its a hammer)lead me to see how deep the mag sits

hence the poll.

mag catch location dictates mage insertion depth which dictates how effectively the bolt will strip a new round.

'I think"

and since I can guarantee I know less about this sort of thing, I am working to get all your brainpower on it.

Thank you to all who supplied info, I am hoping to accumulate a statistical sample size to determine the folly or validity of my theory.

First - in red above - I certainly hope you're not talking about me.  But it you are, then let's just drag that out and get it done with.

Next - what upper and lower combination are you running, from how many different manufacturers, and what are you expecting to happen?  Please list, by manufacturer, what exact upper, and what exact lower, that you've tried to use here - and what the failure was, with each combination?  It's pretty common knowledge that you should use the same upper as the lower, when you build these things, and hoping for a perfect rifle when you mis-match this shiit it pretty much like playing the lottery. 

On 4/1/2019 at 8:06 AM, panel77 said:

Hellfire got back to me and stated they have a .685 distance

Colfax doesnt make 80% anymore but they stated theirs are .663 +/- 0.005

I have a theory that appears to be playing out to be at least a component of a problem.

^^^  This tells me alot about the combinations you've tried.

I have difference measurements in my lowers - with the different mag catch placement - but they all work with MagPul 20s over two different Gens, and with Lancers.  Because I'm using the same uppers, as my lowers.   That's MY observations on this mess...

Edited April 3, 2019 by 98Z5V