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View Full Version : Scratch or Crack (Microscopic) in lower


Gator Monroe
09-30-2009, 8:42 PM
My CMMG lower has this 1 and a half in. long line/scuff/scratch that mimics a tiny hairline crack (But I have not fired weapon yet and only pressed bolt catch release sending bolt home with a nice loud clank a few times (like 5 tops) with at least 3 of those times having the BCG & bolt nice & oiled. I have not looked at scuff/scratch with Jewlers goggle but it does not appear to be a crack or go over top of lower & down inside , but i'm unfamilure with the potential types of metal failure on AR lowers (there is no metal showing or seperation of annodizing or finish looking with readinhg glasses and what I'm asking is "Are most Cracks in lowers blatant and fingernail feelable?"

SCMA-1
09-30-2009, 8:44 PM
Can you post some pics?

God Bless The Mauser
09-30-2009, 8:48 PM
Try a dental pick and see if it catches.

Gator Monroe
09-30-2009, 8:51 PM
Can you post some pics?

Rifle is in Tony Soprano hidden Lazy Susan Rifle rack (Unavailable) and am not bringing her out anytime soon. but scuff is an 8th of an inch behind pin that is nearest the magwell (trigger pin?) and goes up (Kinda straight) to almost top of lower (It could be a scuff from removing takedown pin & opening up rifle with sling on it and one of the sling metal parts was pulled/ dragged against a moving section of rifle, but Finish is intact without bare metal, only a Scuff ?

Gator Monroe
09-30-2009, 8:55 PM
Try a dental pick and see if it catches.

Scuff is no more than 3 to 8 thousandths (less than half of the depth of the finnish/outer coating ? and about a 50th of an inch wide

sevensix2x51
09-30-2009, 8:55 PM
dont expect an accurate answer to your query without pictures, but i doubt theres anywhere near enough strain in that part of the rifle to crack the lower receiver... or really, in any part of the lower, unless you dropped it out of a helicopter...

Gator Monroe
09-30-2009, 8:59 PM
Try a dental pick and see if it catches.

Tried polishing it off with a Dremil (Little buffer wheel) but it was not powerfull enough, and I think I can remove it with a Trick from one of you AR guys (Toothpaste perhaps) ?

Gator Monroe
09-30-2009, 9:02 PM
dont expect an accurate answer to your query without pictures, but i doubt theres anywhere near enough strain in that part of the rifle to crack the lower receiver... or really, in any part of the lower, unless you dropped it out of a helicopter...

Ditto , It appears to be a scuff (Not from building process) and I'mnot sending it back unless it's a crack. But anyone know of tricks to overcoat or buff out not so deep scuffs with lotsa finish to work with before bare metal is exposed.

sevensix2x51
09-30-2009, 9:04 PM
ive never worried about scuffs on rifles, but ive been able to get cd's to work with some automotive buffing compound and a microfiber towel....
i have also used those dremel buffing wheels on high current electrical connections... but thats on bare, uncoated copper....

EOD3
09-30-2009, 9:45 PM
Hold the lower so the whatever is vertical and put a drop (Q-tip works) of alcohol on the BOTTOM of the crack. "IF" it's a crack, the alcohol should wick into it. .02

Gator Monroe
09-30-2009, 9:47 PM
Hold the lower so the whatever is vertical and put a drop (Q-tip works) of alcohol on the BOTTOM of the crack. "IF" it's a crack, the alcohol should wick into it. .02

Genius ! :)

mydogsmonkey
09-30-2009, 9:47 PM
also a good idea that i've heard is to not let go of bolt release and send the bolt home empty because it can be a bit too rough on the gun. from what i hear, the bullet actually cushions the slam so it won't be harmful, just a tip

Gator Monroe
09-30-2009, 9:49 PM
also a good idea that i've heard is to not let go of bolt release and send the bolt home empty because it can be a bit too rough on the gun. from what i hear, the bullet actually cushions the slam so it won't be harmful, just a tip

I gathered this (After around the 4th time doing it ) but I'm sure there are AR guys who would poo poo this .

Heavy_Grinder
09-30-2009, 9:50 PM
Don't worry about it. It is normal. It's neither a scratch or a crack. Just a mark

Most of the MOD4SA lowers if not all have that Machine mark on the right side of the reciever. This has been discussed before years ago here.

it's all good. Now go out and shoot the damm thing:D

Here's my CMMG lower. Does the mark look like this??? (Center Of the Pic)
http://i97.photobucket.com/albums/l232/Arch_Royal/DSC00609.jpg
http://i97.photobucket.com/albums/l232/Arch_Royal/DSC00611.jpg

Gator Monroe
09-30-2009, 9:52 PM
Don't worry about it. It is normal.

Most of the MOD4SA lowers if not all have that Machine mark on the right side of the reciever. This has been discussed before years ago here.

it's all good. Now go out and shoot the damm thing:D

I built the lower and this imperfection was not there befor if my memory serves me (I looked it over pretty well too)

sspen003
09-30-2009, 10:38 PM
also a good idea that i've heard is to not let go of bolt release and send the bolt home empty because it can be a bit too rough on the gun. from what i hear, the bullet actually cushions the slam so it won't be harmful, just a tip

I slam mine all the time.. you sure about this? Gun works fine

Gator Monroe
09-30-2009, 10:43 PM
Don't worry about it. It is normal. It's neither a scratch or a crack. Just a mark

Most of the MOD4SA lowers if not all have that Machine mark on the right side of the reciever. This has been discussed before years ago here.

it's all good. Now go out and shoot the damm thing:D

Here's my CMMG lower. Does the mark look like this??? (Center Of the Pic)
http://i97.photobucket.com/albums/l232/Arch_Royal/DSC00609.jpg
http://i97.photobucket.com/albums/l232/Arch_Royal/DSC00611.jpg

Why yes , but a little more pronounced & a little longer !:eek:

Gator Monroe
09-30-2009, 10:47 PM
Why yes , but a little more pronounced & a little longer !:eek:

Why does my lower not have the Safe & Fire on other side like yours ???

Satex
09-30-2009, 10:51 PM
But anyone know of tricks to overcoat or buff out not so deep scuffs with lotsa finish to work with before bare metal is exposed.

The easiest trick is to crawl in the back yard for an hour or so pretending to be Rambo. When you return, all the new scratches, scuffs, etc will make this one disappear. Real men don't care about scuffs on guns.
;)

Gator Monroe
09-30-2009, 10:59 PM
The easiest trick is to crawl in the back yard for an hour or so pretending to be Rambo. When you return, all the new scratches, scuffs, etc will make this one disappear. Real men don't care about scuffs on guns.
;)

Uh, it's prolly not going to be fired (Even after I get the correct NDS Retro 603 Lower & various other M16A1 tidbits) and build a beater truck gun with this CMMG lower to shoot .

ar15barrels
09-30-2009, 11:20 PM
What's with all these completely coherent gator posts?
Did you get banned from OT?

mds2004
09-30-2009, 11:23 PM
I miss OT if its the same thing Im thinking of :(

ar15barrels
09-30-2009, 11:26 PM
I miss OT if its the same thing Im thinking of :(

Off
Topic

reidnez
09-30-2009, 11:52 PM
I gathered this (After around the 4th time doing it ) but I'm sure there are AR guys who would poo poo this .

Yep, I'll poo poo it! Servicemen are taught to close the bolt this way as part of manual-of-arms, and when routinely clearing the weapon as well. I didn't even realize people practiced the "slingshot" method until I got around more civilan shooters. A typical M16A2 probably has its bolt "slammed" home with the catch 500,000 times by the time it is retired. It doesn't seem to hurt anything on the service rifles, which are in general neglected to a degree that our pampered civvie AR-15's only have nightmares about, so I wouldn't worry. :)

EOD3
10-02-2009, 10:44 PM
Yep, I'll poo poo it! Servicemen are taught to close the bolt this way as part of manual-of-arms, and when routinely clearing the weapon as well. I didn't even realize people practiced the "slingshot" method until I got around more civilan shooters. A typical M16A2 probably has its bolt "slammed" home with the catch 500,000 times by the time it is retired. It doesn't seem to hurt anything on the service rifles, which are in general neglected to a degree that our pampered civvie AR-15's only have nightmares about, so I wouldn't worry. :)

Maybe that's why they have a BIG honking release button... :)