The Firing Line Forums

Go Back   The Firing Line Forums > The Hide > The Art of the Rifle: Semi-automatics

Reply
 
Thread Tools
Old October 22, 2012, 03:42 PM   #1
Stressfire
Senior Member
 
Join Date: June 16, 2011
Location: Ohio
Posts: 1,497
AR caliber

Picked up my first AR a couple weeks ago. Private sale, got 6 mags and about 600 rounds of .223 ammo.

It shoots .223 fine. But am curious about 5.56x45

No barrel markings anywhere except "C MP C" stamps the underside between the front sight and the flash suppressor.

I'm 95% sure that the upper is completely Colt (model 602 I think) - but without a marking on the barrel to tell, how to know which caliber?

ETA: no markings under handguard either
__________________
"The best diplomat I know is a fully charged phaser bank" - Montgomery Scott
Stressfire is offline  
Old October 22, 2012, 03:56 PM   #2
Crow Hunter
Senior Member
 
Join Date: January 27, 2012
Posts: 1,078
If it is a Colt, it is most likely a 5.56 chamber.

Even their "target" rifles have 5.56 chambers. (Modern ones anyway)

I wouldn't worry about it.

Worst thing that would happen if you shoot high pressure 5.56 in a tight .223 chamber is you "pop" a primer back into the trigger group and it locks up your trigger.

It won't blow up or anything, there isn't that much pressure difference between them.
__________________
I am no longer participating in gun forums.

Good luck.
Crow Hunter is offline  
Old October 22, 2012, 04:07 PM   #3
pturner67
Senior Member
 
Join Date: February 26, 2006
Location: Fairfax, VA
Posts: 626
found this on another site:

Barrel Marked C MP C. C meaning Colt, M meaning Magnetic particle inspected, P standing for Proofed, and the C marking indicates a chrome chamber

from the other threads out there, your Colt is chambered in 5.56x45mm
pturner67 is offline  
Old October 23, 2012, 08:05 AM   #4
Stressfire
Senior Member
 
Join Date: June 16, 2011
Location: Ohio
Posts: 1,497
Cool, that's what I was hoping for.

<-------AR Newb, does it show?

Thanks!

ETA: Long as I'm at it, anyone happen to know the twist rate offhand, or how I might determine it myself?
__________________
"The best diplomat I know is a fully charged phaser bank" - Montgomery Scott
Stressfire is offline  
Old October 23, 2012, 08:33 AM   #5
pturner67
Senior Member
 
Join Date: February 26, 2006
Location: Fairfax, VA
Posts: 626
doing a google search, everyone out there is saying yours is a 1:7 twist
pturner67 is offline  
Old October 23, 2012, 08:41 AM   #6
Stressfire
Senior Member
 
Join Date: June 16, 2011
Location: Ohio
Posts: 1,497
Ok, so 1 in 7" on a 20" barrel. Considered good? Seems pretty accurate with 55 grain .223. Would that be the optimum bullet weight?
__________________
"The best diplomat I know is a fully charged phaser bank" - Montgomery Scott
Stressfire is offline  
Old October 23, 2012, 10:13 AM   #7
Achilles11B
Senior Member
 
Join Date: November 18, 2010
Posts: 595
Buy a box of several bullet weights from several manufacturers. The rifle will tell you what it likes.
__________________
Good equipment will never be a substitute for good training.
Achilles11B is offline  
Old October 23, 2012, 10:40 AM   #8
plouffedaddy
Senior Member
 
Join Date: May 13, 2011
Location: Carolina
Posts: 3,192
Quote:
Buy a box of several bullet weights from several manufacturers. The rifle will tell you what it likes.
Very true. Likely it'll be 62gr and up but one of my PSA guns (1 in 7) gets just as good groups with 55gr as 75gr. Every barrel really is unique.
__________________
Mrgunsngear's Youtube Channel
Certified Glock Armorer
plouffedaddy is offline  
Old October 24, 2012, 11:06 AM   #9
Stressfire
Senior Member
 
Join Date: June 16, 2011
Location: Ohio
Posts: 1,497
It did pretty well with the 55grain - I was doing a function test more than one for accuracy. Grouped quite well at 50 yards considering I wasn't really trying that hard.

May have to try some 62s and see what happens.

Thanks for the barrel info
__________________
"The best diplomat I know is a fully charged phaser bank" - Montgomery Scott
Stressfire is offline  
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 11:21 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2013 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.07639 seconds with 9 queries