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Posted: 8/17/2004 2:43:17 PM EST
[Last Edit: 9/16/2004 3:10:53 PM EST by Ellery_Holt]
The lower on the left is a Bushmaster, s/n L-280xxx purchased June of '02.

The one on the right is a Bushmaster s/n BFI-428xxx purchased yesterday.

Sorry, the photo's gone. Pictured was a side-by-side shot of two stripped receivers, taken looking down upon them, and showing how I measured mag-well wall thickness at the center of the left side, using dial calipers.


Does anyone know if the new, thin-walled lower is still within specifications? Is there even a published spec for this dimension?

What thicknesses do you find on your lowers, old ones and new ones?

I'm not that old, but is this another case of, 'They don't build 'em like they used to.'

Thanks very much for the replies; I really have a nagging need to know if this new lower is too thin and if it is Bushmaster's common thickness now.

===============================================

Edited to add:

Here's a stem & leaf plot of what we have so far. I'll keep it updated as folks add new data to this thread. I think it would be really interesting to see what kind of shape, center and spread we get from this data. Thanks everyone!

06|
06|5578
07|04
0­7|5555558
08|0001122222334
08|56677899<­BR>09|0001122
09|58
10|03
10|555
­
I think this is enough data -- we've got our (roughly) normal distribution. Interpret as you like as to what is acceptable mag-well wall thickness.
Link Posted: 8/17/2004 2:45:12 PM EST
Eeek! (Omar runs off to check wall thickness of his receivers)
Link Posted: 8/17/2004 2:46:26 PM EST
[Last Edit: 8/17/2004 2:59:04 PM EST by Ellery_Holt]
I know how it is... I remember when somebody posted the distance that the mag catch is supposed to be from the top of the lower -- I had to go measure mine...

OCD I guess.

But living in a mass production era, a person has to watch out for the lemons.
Link Posted: 8/17/2004 3:03:30 PM EST
[Last Edit: 8/17/2004 3:08:37 PM EST by j3_]
There is a drawing for the forging. Says the number is F8448641. Says the forging drawing establishes the AJ line on the machine drawing. You might have to compare its limits to the machining drawing to find out what the thickness left would have to be.
Link Posted: 8/17/2004 3:11:51 PM EST
[Last Edit: 8/17/2004 3:16:02 PM EST by Ellery_Holt]
I have looked all over this...



...but didn't find the relavent dimension. I even wonder about its source. I understand you are talking about a drawing of the forging for compairsons sake. Is there one available somewhere?
Link Posted: 8/17/2004 3:18:46 PM EST
the forging was too thin?

i will be measuring mine
Link Posted: 8/17/2004 3:19:17 PM EST
[Last Edit: 8/17/2004 3:20:11 PM EST by BallisticTip]
I would call and ask Bushmaster this question as they will give you the straight scoop, and make it right.
Link Posted: 8/17/2004 3:42:43 PM EST
[Last Edit: 8/17/2004 3:53:38 PM EST by Ellery_Holt]
True, and I may call Bushmaster, or perhaps ask through their Industry forum here. But I also like the idea of this kind of survey of what's out there among folks here. And I think it makes an interesting thread as a companion to the Qualities of a "good" lower receiver thread.
Link Posted: 8/17/2004 3:46:25 PM EST
correct me if I'm wrong but the sides of the "thin" one look beveled on the insides to me. What do you get if you measure it farther down?
Link Posted: 8/17/2004 3:50:22 PM EST
I've actually a noticed a trend towards this recently. I play a lot with RRA lowers, then my friend got his MEGA lower. Though his lower is otherwise perfectly great in every sense, it does have a cheaper feel to it. I don't know if the thinness will translate to any decrease in durability.
Link Posted: 8/17/2004 3:53:53 PM EST
OK,here's my measurements of four RRA and one Eagle Arms:

.091
.091
.075
.083
.087
Link Posted: 8/17/2004 4:00:44 PM EST
The forging drawing number is listed on the spec prints. It says that the main line listed as AJ that goes the length of the receiver is off the forge drawing so I would guess the forge drawing has the minimum width allowed on the forging from the AJ line. That would give you the least wall thickness when compared to the machine drawing and its limits.
Link Posted: 8/17/2004 4:02:32 PM EST

Originally Posted By jtw2:
correct me if I'm wrong but the sides of the "thin" one look beveled on the insides to me. What do you get if you measure it farther down?



Link Posted: 8/17/2004 4:22:06 PM EST
[Last Edit: 8/17/2004 4:24:46 PM EST by j3_]
I measured a Mega, LRB, VM Hytek, Stag, Grizzly, Fulton, Century, and an Ammetec .
Measurement in no certain order were:
.070
.067
.090
.082
.065
.082
.075
and a whopping .105 on the Grizzly lower on both sides.
The other sides measurement always made the total of the two sides almost the same on all of the lowers. All measurement were close to the top edge near center.
Link Posted: 8/17/2004 5:43:07 PM EST
[Last Edit: 8/17/2004 7:09:58 PM EST by Ellery_Holt]
.
Link Posted: 8/17/2004 5:51:56 PM EST

Originally Posted By j3_:
The forging drawing number is listed on the spec prints. It says that the main line listed as AJ that goes the length of the receiver is off the forge drawing so I would guess the forge drawing has the minimum width allowed on the forging from the AJ line. That would give you the least wall thickness when compared to the machine drawing and its limits.



I'm afraid that's getting beyond me. I do have the .pdf of the lower machine drawing, but it's just that one page I pictured, and I never did learn how to read blueprints. Took some limited mechanical drawing a long time ago. Sorry.
Link Posted: 8/17/2004 6:11:39 PM EST
pwa 075
eagle 095
bushmaster 080
LRB 065
LRB 080
Link Posted: 8/17/2004 6:18:29 PM EST
[Last Edit: 8/17/2004 6:30:07 PM EST by G35]
I had a similiar parniod question a few months back regarding my new Bushmaster. I posted the question and pics here on ARFCOM, and all I got in response was "go shoot the damn thing and stop worying". So, I am glad to see that people are choosing to help you.

With my situation, I called BM and got a RMA number for them to inspect it. BM DID exchange the lower with another new one !!!!! I am sure they did this to be nice, and the "defective" lower was was probably fine. But, I was very happy that BM volunteered to exchange it.

When you RMA the piece, just be sure to include that first photo that you have that shows the difference. This is what I did - I included the pics that I am showing below.

Edit to add - In defense of Bushmaster, the hole is NOT mislocated. At first sight, you think the hole was drilled too far upward. But, this was NOT the case. The lower fit fine to any upper with no gap between the lower and upper. The problem was that the person doing the smoothing and buffing got too far carried-away, and buffed too much material from the upper section of the ear.



Link Posted: 8/17/2004 6:29:28 PM EST
Anybody got any Colt measurements?
Link Posted: 8/17/2004 6:41:24 PM EST
[Last Edit: 8/17/2004 6:43:46 PM EST by Ellery_Holt]

Originally Posted By G35:
I had a similiar paraniod question...



Hey, I resemble that remark.

Not really. It's not our fault that the anti-gun politicians have us thinking that our firearms might have to last for the rest of our lives. I've got a son due any day now, and I hope he can go out and buy his own AR when he's old enough, but maybe these I have will have to last for him too.


The problem was that the person doing the smoothing and buffing got too far carried-away, and buffed too much material from the upper section of the ear.


I've seen a lot of that too. I think I have figured out how much material needs to surround that hole though.

From the drawing I posted:



0.376
-.251
------
0.125
/2
-----
0.0625"

So maybe a mininum of 0.063 around the hole? BTW, all that stuff in the table below the hole diameter, I have no idea what it means.



Link Posted: 8/17/2004 6:48:10 PM EST
Measured my BM #143XXX. 0.075" just like the one you just bought, cept I got mine in '99.
Link Posted: 8/17/2004 6:53:29 PM EST
Side wall thicknesses of mag wells

Colt Match Target = .088
DPMS (forged) = .080
DPMS (cast) = .102
DPMS (cast) = .101
Link Posted: 8/17/2004 7:01:27 PM EST
I just added your forged receiver measurements to the plot, but am leaving out the cast dimensions since they'd be thicker by design to compensate for the difference in material strength. Thank you.

Hmm... It's still too early to say, but maybe getting one near a tenth of an inch thick is lucky, and that we're gonna see that the most common measurement is near 0.075.
Link Posted: 8/17/2004 7:03:44 PM EST
Are they too thin or is a core shift/mis alignment during machining?
Link Posted: 8/17/2004 7:08:05 PM EST
The receiver isn't thin on that wall because of an off-centeredness. No, it's all centered up -- even at the ears for the trigger guard (though I know that's been a discussion here before too.)
Link Posted: 8/17/2004 7:36:02 PM EST

Originally Posted By Ellery_Holt:

Not really. It's not our fault that the anti-gun politicians have us thinking that our firearms might have to last for the rest of our lives. I've got a son due any day now, and I hope he can go out and buy his own AR when he's old enough, but maybe these I have will have to last for him too.



Agree completely. This was my primary motivation to "get it right." Well said E.H.
Link Posted: 8/17/2004 7:46:54 PM EST
[Last Edit: 8/17/2004 7:50:34 PM EST by G35]
Here are mine -

Bushmaster BFI series = 0.092
Bushmaster L series = 0.098

Both are approx 1 yr old.
Link Posted: 8/18/2004 5:20:25 AM EST
My OLY measures .089. Great lower. No problems
Link Posted: 8/18/2004 9:11:29 PM EST
Now that you guys have my attention. Is there anything that needs to be worried about with these thinner receivers? Has anyone tried measuring a Rocky Mountain Arms Patriot pistols milled lower receiver or even an LMT/LCW lower receiver?

Thanx.
Sammy
Link Posted: 8/18/2004 9:31:07 PM EST
[Last Edit: 8/18/2004 9:31:23 PM EST by Not_A_Llama]
Given the location of the abnormalities, even if a large portion were gone, your rifle would still be perfectly functional. Your magazine is retained vertically by the mag catch, and to a lesser extent by the wall in question..
Link Posted: 8/19/2004 10:20:22 AM EST
Anyone in SoPRK that can let me borrow a caliper? This will be interesting to see everyone's results, although I don't understand stem leaf plots. A plain list would be easier I think.
Link Posted: 8/19/2004 10:56:21 AM EST
Please allow me to put in my "two cents worth"

IMHO......

I think you have to allow for the difference between the overall thinknesses of the two
recievers being measured. Are they both the same dimension across that area of the forging?

(Across the outside...?)

The difference between the one that is .105" and .075" divided by two is only
.015"

That is the .105" may be .015" higher than the "mean" dimension and the .075" could be
.015" lower than the mean.

So...each forging might have been machined to the extreme side of the tolerance.

IF that's true, then there is only .015" (four sheets of paper) between center the two castings.

Do you know what I mean?

Link Posted: 8/19/2004 3:12:19 PM EST
[Last Edit: 8/19/2004 3:35:53 PM EST by gs430]
Here's some more data to add to the Stem and Leaf plot ...

Bushmaster Model XM15-E2S - Serial L166xxx - 0.089" wall thickness, 0.929" magwell opening (measured from the top)

Colt Sporter Target Model - Serial ST020xxx - 0.086" wall thicknetss, 0.929" magwell opening (measured from the top)

All measurements were done with a EDMT Digital Electronic Caliper


Kisara, you're more than welcome to use my Caliper but I'll be out of town until the 28th...as for the stem and leaf, it's REALLY easy...but I SUCK at explaining things simply so here's a try...

Say we have the following numbers ... 0.080, 0.083, 0.085, 0.085, 0.087. 0.089, 0.092 and 0.093 and you want to show it in a quick and dirty graph...

For these set of numbers let's "throw out" the "0.0" since it's understood that all the measurements are in 0.0XX range.

So we have 80, 83, 85, 85, 87, 89, 92 and 93...the stem and leaf would be..

8|035579
9|23

So measurements that are in the 0.08X range shows six entries (0,3,5,5,7,9) and the measurements in the 0.09X range show two entries (2 and 3) So you can see that we just made a "sideways" graph AND it shows the number data to boot.

Now you can break our graph down a little more by splitting up numbers that are 0 to 4 and then 5 to 9...this is what Ellery_Holt did in the first post....that stem and leaf would look like this...

8|03
8|5579
9|23

There isn't a second set of "9" data because all the input numbers we used, that were in the 0.09X range, didn't go 5 and above (there was no 0.095 through 0.099)...

It would probably make more sense to more people if the stem and leaf looked more like this...

8|0,3,5,5,7,9
9|2,3

So you can see the seperation in the data numbers but of course, this is completely unnecessary as each number *IS* a seperate entry.

Hope that made sense! :)


<edit - apparently, I also suck at typing... >
Link Posted: 8/20/2004 7:03:47 AM EST
Thanks for the explanation, Lexus man. I learned something new today.

...and to think, I minored in math.

I'll try to get my numbers in this weekend.
Link Posted: 8/22/2004 7:18:22 PM EST
I will get back to update this thread soon. Wife and I just had our first baby on Friday and I'm, well... distracted (and staying at the hospital (c-section)).

Thanks again everone.
Link Posted: 8/23/2004 11:40:50 AM EST
Congrats on the new child! Good health to all of you!
Link Posted: 8/23/2004 5:13:15 PM EST
Ameetec Arms = .084"
Link Posted: 8/24/2004 2:39:06 AM EST
Bushmaster:

L0691xx .090"
L0737xx .082"
L0737xx .081"
L3035xx .083"

Rock River

CM06820 .068"!!

MN
Link Posted: 8/24/2004 1:51:28 PM EST
Does anyone want to measure an LMT/LCW?

Thanx.
Sammy
Link Posted: 8/24/2004 2:11:44 PM EST
tag
Link Posted: 8/24/2004 2:14:00 PM EST
Damn, this sucks, now I have to messure mine.
Link Posted: 8/24/2004 4:20:42 PM EST
Thanks for all the new measurements. The new family is back at home and I'll enter the new data this PM.

Link Posted: 8/24/2004 4:59:54 PM EST
I have 3 Stag Arms:

.081
.082
.090


.082 & .090 are consecutive serial numbers, .081 is a few serial numbers lower.

Cool Thread!
Link Posted: 8/24/2004 5:10:36 PM EST
Have you gotten any info from Bushy on this?
Link Posted: 8/24/2004 6:19:12 PM EST
[Last Edit: 8/25/2004 12:11:21 PM EST by Ellery_Holt]

Originally Posted By sjauch:
Have you gotten any info from Bushy on this?



No, haven't contacted them. I have decided not to -- the data collected here will provide us with a better picture of the common dimension for this particular measurement than Bushmaster probably would.

The stem and leaf plot is now updated to include observations up to this point. I added in a 0.103 that I got with a Bushmaster stripped lower I found at Northwest Armory in Portland. It is S/N L-288xxx, which makes it kind of old. They had it overpriced and burried in the back of the safe, which explains why they still had it. I talked them down a bit, but not to Internet sale levels. But hey, I wanted it, so I was happy to pay a bit more for it. As the graph shows, receivers with mag well walls 0.1" thick are relatively rare.

06|
06|5578
07|0
07|55555508|0001122222334
08|67899
09|00011209|58
10|3
10|555

Edited to add TN-MadDog's measurements.
Link Posted: 8/25/2004 3:49:40 AM EST
Here are two more.

Armalite US447XX .105

Colt MH067XX .082
Link Posted: 8/25/2004 5:33:04 AM EST
[Last Edit: 8/25/2004 5:39:45 AM EST by mo4040]
Ok.....

I do not have digital calipers, but, I have well calibrated Infantry eyes. This is what I observed:

I have four lowers....

1) Pre-ban bushy

2) Pre-ban Colt

3) "Older" Post-ban Bushy (purchased back in 1998 or 1999)

4) New Post-ban Bushy (purchased earlier this year)

The Pre-ban Bushy, Pre-ban Colt, and the older Post-ban Bushy all had definitively thicker sidewalls than the newer Post-ban Bushmaster. Again, I do not have calipers, but the three older lowers looked to be about the same......

Here are some questions to ponder:

Are the forging manufacturers making thinner lowers because of advances in metalurgy that allow thinner materials of the same strength?

Is it a money saving measure (if you take just a little off a whole bunch of lowers, that is a lot of aluminum that is not being used)?
........Years ago, the airlines saved a shit-load of money by removing just one olive from the salads they served.

Has the "spec" changed? (I would think this is not the case)

As for me, I am somewhat irked by the prospect of a possibly weaker lower, but...in the grand scheme of things, I am not going to lose sleep over it......

EDITED to add one more comment:

Perhaps the thinner walls are a moot issue due to the thick band of material around the bottom of the magwell? Just a thought......
Link Posted: 8/25/2004 11:05:47 AM EST
Thank you mo4040,

I think if I was smart, I would have purchased a SOCOM lower receiver or a Rocky Mountain Arms Patriot pistol lower receiver when I had the chance and turned that into a DIAS host. I would assume those would be the most durable lower receivers. However, the next question would be, do KNS pins fit in?

No one has an LMT/LCW receiver? Geez. I those those were all so famous now

Thanx.
Sammy
Link Posted: 8/26/2004 12:58:41 AM EST
[Last Edit: 8/26/2004 4:36:01 PM EST by gs430]
Edit - Revisting data....
Link Posted: 8/26/2004 2:30:35 PM EST
[Last Edit: 8/26/2004 2:35:34 PM EST by j3_]
I read the C-C measurement of .10 as being how far the radius has to curve before it can begin to go flat at the bottom of the lower. Not as a wall thickness measurement. I took one of them Interpreting Engineering Drawings classes too. Where is a real engineer or a very good machinist when you need one.
Link Posted: 8/26/2004 4:38:54 PM EST
[Last Edit: 8/26/2004 5:27:48 PM EST by gs430]
You might very well be correct. I'm going to look over the blueprint again to see if I can extrapolate the right measurement.

Another thought might be that the "exterior" measurements are up to the company that forges the lowers so therefore it might be on a separate blueprint as I can't seem to find any exterior magwell dimension...

Edit - I know others have already brought it up but after really studing the blueprints, it seems that the wall thickness isn't that critical of a measurement....another thing that makes me believe this is that if it was a critical measurement, I'm sure there would be a clear measurement on the blueprints...which there isn't...
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