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  #1  
Old 03-29-2011, 1:04 PM
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Default DPMS LR 308 80% Blueprints? (and hole repair)

Does anybody know where I can get blueprints for an LR308 80% lower? Specifically, I need to know the hole locations for the safety selector, trigger pin and hammer pin.

I think I really screwed myself here and I might be holding a $200 scrapped part. I think I can fix it but I really need some dimensions. I'll post up pics and my repair if I can fix it, but until then I have to go take a chill pill because this lower is about to fly across the shop.......

Last edited by Lostsheep; 03-29-2011 at 7:29 PM..
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Old 03-29-2011, 1:25 PM
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Ive seen vendors selling .308 jigs to complete 80% lowers for around $130/set

Check with CalGun member: Roccobro
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Old 03-29-2011, 1:29 PM
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Originally Posted by rareair View Post
Ive seen vendors selling .308 jigs to complete 80% lowers for around $130/set

Check with CalGun member: Roccobro
That's one solution I have to my dilemma and it may be what I have to do. I totally dumb*****ed it and drilled the side holes in the wrong location. I am going to have to use an endmill to put the holes on location and make sleeves to get them back where there supposed to be. The jigs would work but I am hoping to avoid that as I am fairly impatient and don't want to spend the money if I don't have to.
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Old 03-29-2011, 4:19 PM
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What's your location?

[B]EDIT[B] I'm currently unemployed and I have an old style TM 10 Jig. Only thing it does'nt have is the selector hole.
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Old 03-29-2011, 5:59 PM
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CNC guns has AR10 files if that will help in any way.... drawing, IGES and solidworks...... I know there's some differences, but thought this might help you.
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Old 03-29-2011, 6:19 PM
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Quote:
What's your location?

[B]EDIT[B] I'm currently unemployed and I have an old style TM 10 Jig. Only thing it does'nt have is the selector hole.
I am in San Jose

Quote:
CNC guns has AR10 files if that will help in any way.... drawing, IGES and solidworks...... I know there's some differences, but thought this might help you.
That's the file I used that got me into this trouble. It's a dpms and I assumed (we all know what happens when you do that) that the fcg would be the same. Looks like it's off by aprox. .043" front to rear.

Everybody stay tuned I almost have it fixed,........ I think.
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Old 03-29-2011, 7:27 PM
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Okay,
Despite not being able to find any drawings, I am pretty sure I got it fixed. I won't know until I go and shoot it but I think I got it. Basically, what I did was drill all three side holes to far forward on the lower. By two different means, I determined the amount to be .043".

I used an end mill to put the holes where they were supposed to be and then I made some bushings out of 303 and pressed them in. The right side of the selector was a bit of a challenge as the detent has to pass though. I drilled the pass through hole undersized, pressed it in as straight as possible and then re-reamed it. I'm keeping my fingers crossed that it works.




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Old 03-29-2011, 8:46 PM
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That's a well done repair (if you got them in the right place)

Well done!
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Old 03-29-2011, 10:53 PM
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That looks like it's better than the original. What kind of metal did you use for the bushing?
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Old 03-30-2011, 6:43 AM
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Originally Posted by bigboy View Post
That looks like it's better than the original. What kind of metal did you use for the bushing?
It's 303 stainless. I suspect it is stronger than the original because of the increased diameter and because it's now steel on steel.

I assembled the lower last night and everything appears to be functioning properly.


ETA: range report soon

Last edited by Lostsheep; 03-30-2011 at 10:03 AM..
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Old 03-30-2011, 7:06 AM
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Sounds like the crisis may possibly have been averted! Being 303, those bushings should be ubber strong! Can't wait to see it in person! Well Done!
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Old 03-30-2011, 7:39 AM
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Sweet repair.
This repair has always been in my mind as a worst case fix whenever people worry about these holes wearing due to type II vs. Type III anodizing, or whatever other reason they can come up with for worrying about a non-issue. This makes it even more of a non-issue.
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Old 03-30-2011, 10:38 AM
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Well, for me, that bushing "repair" makes it look cooler! I might even ask you to make some for me to do it on purpose!
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Old 03-30-2011, 10:43 AM
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Well, for me, that bushing "repair" makes it look cooler! I might even ask you to make some for me to do it on purpose!
You have to believe me, being FORCED to do it really sucks!
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Old 03-30-2011, 5:45 PM
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Of course, but when the fix looks cool, it can take a bit of the sting out.
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Old 01-05-2014, 9:54 PM
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OP sayer "I assembled the lower last night and everything appears to be functioning properly.


ETA: range report soon"


I am getting ready to mill out my 80% lower off of those blue prints with your suggested adjustments and I was wondering how the range report turned out? and is it still operating today? over all good, bad, indifferent? would you say that if you move the .043 back for the side holes everything works as planned?

Casey
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Old 01-05-2014, 10:13 PM
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Maybe these will help ??


http://www.calguns.net/calgunforum/s...d.php?t=756641



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Old 01-06-2014, 4:39 AM
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unless the receiver is a QD I would not use those dimensions on any other lower.
the hammer pin is .020 further back then the prints I have.
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Old 01-06-2014, 5:02 AM
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Old 01-06-2014, 5:03 AM
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Being a machinist,I have to say your fix looks great.

The only other thing I may have done is to use some Loctite but probably not needed.

Last edited by 1flhtk4me; 01-06-2014 at 5:15 AM..
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Old 01-06-2014, 6:27 AM
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Sorry for the Necro range report

Quote:
Originally Posted by caseyhoward View Post
OP sayer "I assembled the lower last night and everything appears to be functioning properly.


ETA: range report soon"


I am getting ready to mill out my 80% lower off of those blue prints with your suggested adjustments and I was wondering how the range report turned out? and is it still operating today? over all good, bad, indifferent? would you say that if you move the .043 back for the side holes everything works as planned?

Casey
The lower is still functioning no problem. It has a little over 1000 rounds through it and the bushings have not moved.


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Originally Posted by kcstott View Post
unless the receiver is a QD I would not use those dimensions on any other lower.
the hammer pin is .020 further back then the prints I have.
^^^X2. The hole pattern is the same distance from the top of the lower as every other lower I've seen. The 3 holes should be the same distance away from one another and you can locate the front to rear location of the selector hole by aligning it with the selector detent hole.
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Old 01-06-2014, 7:06 AM
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Originally Posted by Lostsheep View Post
Sorry for the Necro range report



The lower is still functioning no problem. It has a little over 1000 rounds through it and the bushings have not moved.




^^^X2. The hole pattern is the same distance from the top of the lower as every other lower I've seen. The 3 holes should be the same distance away from one another and you can locate the front to rear location of the selector hole by aligning it with the selector detent hole.
I'm not talking about the over all patern. I talking about the paterns distance from the front take down pin. QD has that dimension at 4.190"
Every print I have shows that dimension at 4.170" or less
Granted this only effects at what angle the hammer impacts the firing pin. There really seems to be no consistency of any of the 308 AR's out there. And that is what I take exception with. It like the holes were laid out arbitrarily
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Old 01-06-2014, 7:56 AM
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Quote:
Originally Posted by kcstott View Post
I'm not talking about the over all patern. I talking about the paterns distance from the front take down pin. QD has that dimension at 4.190"
Every print I have shows that dimension at 4.170" or less
Granted this only effects at what angle the hammer impacts the firing pin. There really seems to be no consistency of any of the 308 AR's out there. And that is what I take exception with. It like the holes were laid out arbitrarily
What a coincidence, so am I.

The holes are the same distances apart as AR15's. It is there location fore and aft that is different on the LR308.
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Old 01-06-2014, 8:06 AM
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Originally Posted by kcstott View Post
There really seems to be no consistency of any of the 308 AR's out there. And that is what I take exception with. It like the holes were laid out arbitrarily

One big difference in this respect is that AR-10's have a 3 degree angled magwell passage while KAC patterns (Dpms etc...) have a straight magwell passage.
This moves the location of the bolt stop, mag catch and fire control pocket.

The advice above about locating the selector hole from a pre-drilled selector detent X axis location and then following AR-15 relative dimensions is solid advice.
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Old 01-06-2014, 8:10 AM
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Originally Posted by Lostsheep View Post
What a coincidence, so am I.

The holes are the same distances apart as AR15's. It is there location fore and aft that is different on the LR308.
And different for every Non AR10 out there.
The thing is i am trying to figure out why. There should be no difference in where the hole patern lands between all the different non AR10 308 lowers.
And with all the screw ups in the selector detent location id like something a little better then just line it up and call it good. Now somewhere there is a correct dimension and all these prints need to be corrected.
For the most part I've only seen a few thousandths of an inch difference which is no big deal. But .020" it may not be enough to foul things up but it is enough to make me wonder what else is incorrect. And it's enough to make me question every dimension on the print.
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Old 01-06-2014, 8:13 AM
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Quote:
Originally Posted by kcstott View Post
I'm not talking about the over all patern. I talking about the paterns distance from the front take down pin. QD has that dimension at 4.190"

Every print I have shows that dimension at 4.170" or less

Granted this only effects at what angle the hammer impacts the firing pin.

It's not JUST what angle the hammer impacts the firing pin.
As the pins are moved forward in the fire control pocket, we come to a situation where the hammer is impacting both the bolt stop and the firing pin.
Keep moving those pins forward and we get misfires from more hammer energy going into the bolt stop than into the firing pin.

When troubleshooting misfires in new 308 AR's, my first test is to feel for easy bolt stop movement with the hammer resting on the firing pin on a closed/locked breech.
If the bolt stop won't move freely in this scenario, that's a sign that the hammer is resting on it.
The solution is to clearance the rear of the bolt stop until it will move freely.
Then, we know the hammer is putting all its energy into the firing pin...
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Old 01-06-2014, 8:20 AM
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Default DPMS LR 308 80% Blueprints? (and hole repair)

Quote:
Originally Posted by kcstott View Post
The thing is i am trying to figure out why. There should be no difference in where the hole patern lands between all the different non AR10 308 lowers.

The fire control pocket and holes need to stay a certain a distance behind the bolt stop.
The bolt stop needs a minimum clearance behind the magwell passage for strength.
Magwell passages vary 0.020" or more in length due to the designers choice of dimensions.
The magwell location from the pivot pin also varies 0.020" from the pivot pin.
That's a bunch of different dependent dimensions that stack up different ways...

When working on a 308 lower where the bolt catch is already located, you can pretty much take the AR-15 print and reverse engineer your fire control pocket and hole locations from the existing location of the bolt catch slot and it usually works out pretty good.
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Last edited by ar15barrels; 01-06-2014 at 8:23 AM..
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Old 01-06-2014, 8:29 AM
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Quote:
Originally Posted by ar15barrels View Post
The advice above about locating the selector hole from a pre-drilled selector detent X axis location and then following AR-15 relative dimensions is solid advice.


Quote:
Originally Posted by kcstott View Post
And different for every Non AR10 out there.
The thing is i am trying to figure out why. There should be no difference in where the hole patern lands between all the different non AR10 308 lowers.
And with all the screw ups in the selector detent location id like something a little better then just line it up and call it good. Now somewhere there is a correct dimension and all these prints need to be corrected.
For the most part I've only seen a few thousandths of an inch difference which is no big deal. But .020" it may not be enough to foul things up but it is enough to make me wonder what else is incorrect. And it's enough to make me question every dimension on the print.
All I can say about that is to buy from a reputable shop. Everything I have seen from Tactical Machining has been grade A. All of the Genesis lowers I have seen also have impeccable machining.

Don't know what you mean about line it up and call it good. I can maintain pretty damn tight tolerances using that hole and the appropriate gauge pin.

I think a big part of the problem was the huge influx of Joe-Schmoes deciding to make 80%ers because of the increased demand this year. A lot of those guys were rushing stuff to market and probably exceeding their skills.

Last edited by Lostsheep; 01-06-2014 at 8:31 AM..
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Old 01-06-2014, 8:42 AM
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Originally Posted by Lostsheep View Post

All of the Genesis lowers I have seen also have impeccable machining.
I have been working with genesis on their KAC clone lower so I have been learning a lot about the feature locations as we compare a bunch of different 100% receivers and see how each different company tackled the tasks of making all the features fit into their design.
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Old 01-06-2014, 9:38 AM
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All I can say about that is to buy from a reputable shop. Everything I have seen from Tactical Machining has been grade A. All of the Genesis lowers I have seen also have impeccable machining.

Don't know what you mean about line it up and call it good. I can maintain pretty damn tight tolerances using that hole and the appropriate gauge pin.

I think a big part of the problem was the huge influx of Joe-Schmoes deciding to make 80%ers because of the increased demand this year. A lot of those guys were rushing stuff to market and probably exceeding their skills.

What I mean by not just "line it up and call it good" is that if the selector detent is not in the correct location your point of reference is useless.

I want to be reasonably sure that my FCG is in the correct location in relationship with the front take down pin.
I can find the location of the detent I just don't trust it to be in the correct location. And I am talking about reputable manufactures. Everyone has made some bad parts at one time or another.
I've fixed JD machine, colfax, & TM lowers, selector detents off, holes missed etc.
what bothers me is I have three or four prints for various manufactures of LR308 lowers and none of the dimensions match. Not to mention I have three sets of FCG dimensions and non of that stuff matches either in position from the front take down pin. Center to center of the holes is correct but how far forward or back is not consistent at all
The biggest difference is with QD. I don't know I guess I'm use to getting a print I can trust and not just hoping for the best.
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Old 01-06-2014, 10:53 AM
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What I mean by not just "line it up and call it good" is that if the selector detent is not in the correct location your point of reference is useless.

I want to be reasonably sure that my FCG is in the correct location in relationship with the front take down pin.
Yes, I understood that.

I understand that even reputable manufacturers make mistakes.

Buying from a reputable manufacturer decreases your chance of getting an out of spec part and I maintain that using the selector detent hole should be GTG.
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Old 01-06-2014, 5:48 PM
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I maintain that using the selector detent hole should be GTG


Right after I check it to a print sure. I'm a tool maker I trust no ones work, not even my own. That's why I have more Micrometers and calipers then guns.
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Old 01-06-2014, 5:51 PM
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Originally Posted by kcstott View Post
Right after I check it to a print sure. I'm a tool maker I trust no ones work, not even my own. That's why I have more Micrometers and calipers then guns.
The X Axis alignment of the selector hole SHOULD be aligned to an existing selector detent hole.
You could easily move the selector forward or rearward 1/10" and not really cause issues with the hammer/trigger.
The fire control pocket and hammer SHOULD be located off of the bolt stop slot/hole, NOT off of the pivot pin.
The trigger pin hole needs to be referenced to the hammer pin hole.

Doing it that way solves all the issues of trying to work from the pivot pin hole as your X axis reference.
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  #34  
Old 01-06-2014, 6:11 PM
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Originally Posted by ar15barrels View Post
The X Axis alignment of the selector hole SHOULD be aligned to an existing selector detent hole.
You could easily move the selector forward or rearward 1/10" and not really cause issues with the hammer/trigger.
The fire control pocket and hammer SHOULD be located off of the bolt stop slot/hole, NOT off of the pivot pin.
The trigger pin hole needs to be referenced to the hammer pin hole.

Doing it that way solves all the issues of trying to work from the pivot pin hole as your X axis reference.
And thats what I'm getting at. Not really knowing what the location will affect is my worry. One reason I like the AR15 because there is an Ordinance print for it. There is nothing of the sort so far on the LR308. And to be even more picky thew prints I do have on the LR308 don't list critical dimensions, Basic Dimensions, Datum lines or tolerances. To make matters worse the AR10 and LR 308 are night an day. and the location of the FCG has about a .060" difference.

So let me finally cut to the chase then. so long as the FCG hole pattern is correct the front to back location is not that critical so long as the hammer is not hitting the bolt stop?? and I mean within say .010" .020" because that is the most difference I've seen on the prints.

If thats the case I need to just friggin relax.
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  #35  
Old 01-06-2014, 7:01 PM
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Originally Posted by kcstott View Post
And thats what I'm getting at. Not really knowing what the location will affect is my worry. One reason I like the AR15 because there is an Ordinance print for it. There is nothing of the sort so far on the LR308. And to be even more picky thew prints I do have on the LR308 don't list critical dimensions, Basic Dimensions, Datum lines or tolerances. To make matters worse the AR10 and LR 308 are night an day. and the location of the FCG has about a .060" difference.

So let me finally cut to the chase then. so long as the FCG hole pattern is correct the front to back location is not that critical so long as the hammer is not hitting the bolt stop?? and I mean within say .010" .020" because that is the most difference I've seen on the prints.

If thats the case I need to just friggin relax.
Take the AR-15 print.
Work out the X axis dimension from the bolt stop hole centerline to the hammer pin hole.
Then reference the trigger pin hole from the hammer pin hole.
The selector hole won't matter if it's 1/32" forwards/backwards so just put it over the top of the selector detent hole IF it's already drilled.
Otherwise, reference the selector hole from the trigger pin hole.

The relationship between the hammer and trigger pin hole is most imortant.
Next will be the relationship between the hammer pin and the bolt stop.
Last will be the relationship between the selector and the trigger pin.
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Old 01-06-2014, 7:08 PM
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I haven't seen any dimension on any drawings referencing the distance from bolt stop to hammer pin. Or bolt stop to front take down pin.

Anyone have those measurements?
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Old 01-06-2014, 7:31 PM
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Yeah I come up with .520 from center of bolt stop slot to hammer pin.

Randal I think I found it. Both prints are .520" AR10 and LR308. There is the common dimension I was looking for.
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Old 01-06-2014, 7:46 PM
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Originally Posted by kcstott View Post
Yeah I come up with .520 from center of bolt stop slot to hammer pin.

Randal I think I found it. Both prints are .520" AR10 and LR308. There is the common dimension I was looking for.
I kept saying it different ways as I figured it would sink in eventually...
The differences between most of the different 308's will be in between the pivot pin and the bolt stop.
From the bolt stop back, treat them like an AR-15, except for the takedown pin.
That one has to reference from the pivot pin.
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Glock, XD and M&P pistols, Benelli and Remington shotguns: barrel, sight, trigger and receiver work.
Most work performed while-you-wait, evening and weekend appointments available.
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  #39  
Old 01-07-2014, 5:19 AM
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Originally Posted by ar15barrels View Post
I kept saying it different ways as I figured it would sink in eventually...
The differences between most of the different 308's will be in between the pivot pin and the bolt stop.
From the bolt stop back, treat them like an AR-15, except for the takedown pin.
That one has to reference from the pivot pin.
I'll take the well deserved slap to the back of the head.
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Quote:
Originally Posted by ar15barrels View Post
Dick.
The above statement i consider a term of endearment
Need prints for your build? Need reference materials for Gunsmithing projects, Click Here
I fear that even though as tough as life has been for me I have only begun to pay for my sins.
Don't forget to have your Liberals spayed or neutered !
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  #40  
Old 01-07-2014, 8:05 AM
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Quote:
Originally Posted by kcstott View Post
Right after I check it to a print sure. I'm a tool maker I trust no ones work, not even my own. That's why I have more Micrometers and calipers then guns.
Quote:
Originally Posted by kcstott View Post
And thats what I'm getting at. Not really knowing what the location will affect is my worry. One reason I like the AR15 because there is an Ordinance print for it. There is nothing of the sort so far on the LR308. And to be even more picky thew prints I do have on the LR308 don't list critical dimensions, Basic Dimensions, Datum lines or tolerances. To make matters worse the AR10 and LR 308 are night an day. and the location of the FCG has about a .060" difference.

So let me finally cut to the chase then. so long as the FCG hole pattern is correct the front to back location is not that critical so long as the hammer is not hitting the bolt stop?? and I mean within say .010" .020" because that is the most difference I've seen on the prints.

If thats the case I need to just friggin relax.
Quote:
Originally Posted by kcstott View Post
Yeah I come up with .520 from center of bolt stop slot to hammer pin.

Randal I think I found it. Both prints are .520" AR10 and LR308. There is the common dimension I was looking for.
Quote:
Originally Posted by kcstott View Post
I'll take the well deserved slap to the back of the head.


Well now that you're content, since you're a toolmaker, and since you have been stockpiling prints, I think you should create your drawing and post it here for those that stumble across this thread.
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