Calguns.net  

Home My iTrader Join the NRA Donate to CGSSA Sponsors CGN Google Search
CA Semiauto Ban(AW)ID Flowchart CA Handgun Ban ID Flowchart CA Shotgun Ban ID Flowchart
Go Back   Calguns.net > INTERESTS AND ACTIVITIES > Gunsmithing & How To
Register FAQ Members List Calendar Mark Forums Read

Gunsmithing & How To Pro, Amateur & WECSOG and Tutorials, Guides & OLL Build Instructions

Reply
 
Thread Tools Display Modes
  #1  
Old 09-22-2007, 4:28 PM
Gunhacker's Avatar
Gunhacker Gunhacker is offline
Member
 
Join Date: Feb 2006
Location: SF East Bay Area
Posts: 266
iTrader: 27 / 100%
Default Changing A2 upper to an A4 Flattop

I have a Colt 7.62x39 A2 upper and I would like to change it into an A4 flattop using all of the existing parts.

Is there any difference between the upper receivers used on the .223 and 7.63x39 guns as far as being reinforced for the larger caliber?

Or is switching a matter of buying an A4 .223 flattop receiver and swapping parts?

Thanks in advance for any help that can be provided.
Reply With Quote
  #2  
Old 09-22-2007, 5:29 PM
Technical Ted's Avatar
Technical Ted Technical Ted is offline
I need a LIFE!!
 
Join Date: Oct 2005
Posts: 12,174
iTrader: 8 / 100%
Default

Quote:
Originally Posted by Gunhacker View Post
I have a Colt 7.62x39 A2 upper and I would like to change it into an A4 flattop using all of the existing parts.

Is there any difference between the upper receivers used on the .223 and 7.63x39 guns as far as being reinforced for the larger caliber?
No difference in receivers construction between calibers.

Quote:
Or is switching a matter of buying an A4 .223 flattop receiver and swapping parts?
Not quite that simple.

More than likely your barrel has an A2 height Front Sight Base which is 0.04" lower than the "F" stamped Front Sight Base used with flat top upper receivers. Using a detachable carry handle, or a properly designed aftermarket rear Back Up Iron Sight (BUIS), may require the front sight post to be raised high enough to expose the threads underneath the flange

Swapping out FSB's is not your typical simple garage work bench chore. You can get by with a taller front sight post, but it will protrude above the FSB's protective ears.

You also want to avoid a flat top upper with extended feed ramps (M4 style). You're barrel more than likely has standard feed ramps. For clarification see this thread about M4 Feed Ramps:
http://www.calguns.net/calgunforum/s...ad.php?t=69729

Otherwise, you should be able to swap out the other parts without issues.
__________________
Quote:
Originally Posted by ChrisTKHarris
That is one of the most idiotic statements I've heard. You are a retard.
Reply With Quote
  #3  
Old 09-22-2007, 6:38 PM
Gunhacker's Avatar
Gunhacker Gunhacker is offline
Member
 
Join Date: Feb 2006
Location: SF East Bay Area
Posts: 266
iTrader: 27 / 100%
Default

Thanks much for the info... the front sight issue won't come into play with me as I'm doing the swap to be able to go to a clamp on open optic sight. My aging eyes are finding it more and more difficult to use the "iron sights".

But I will still try to do this the right way for the next owner of the gun, who may wish to have a carry handle or a BUIS on it. I'm a bit more advanced than "garage work bench" level, so I'll check out by reference books for what swaping out the FSB entails.
Reply With Quote
  #4  
Old 09-22-2007, 9:05 PM
ar15barrels's Avatar
ar15barrels ar15barrels is online now
I need a LIFE!!
 
Join Date: Jan 2006
Location: Van Nuys
Posts: 39,029
iTrader: 88 / 100%
Default

Quote:
Originally Posted by Gunhacker View Post
I'm a bit more advanced than "garage work bench" level, so I'll check out by reference books for what swaping out the FSB entails.
You won't find info about swapping front sight bases because it's just not done.
The barrel and FSB get drilled as a mated pair.

Trust me on this.

Go with the extended post if required.
__________________
Randall Rausch

AR work: www.ar15barrels.com
Bolt actions: www.700barrels.com
Foreign Semi Autos: www.akbarrels.com
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.
Founding member of the CAPRC
Reply With Quote
  #5  
Old 09-22-2007, 9:34 PM
Santa Cruz Armory's Avatar
Santa Cruz Armory Santa Cruz Armory is offline
Veteran Member
 
Join Date: Feb 2006
Location: Santa Cruz, CA
Posts: 4,330
iTrader: 76 / 100%
Default

You could just sell the 7.62 upper and buy another .223... just a thought?

How much for the 7.62 upper?
__________________
FFL07 offering special order firearms sales and transfers in the Santa Cruz Area. Custom Gun-smithing also availabe. $35 dealer transfers

Check out or web page for current *Web Specials* WWW.SANTACRUZARMORY.COM
Reply With Quote
  #6  
Old 09-22-2007, 9:36 PM
Technical Ted's Avatar
Technical Ted Technical Ted is offline
I need a LIFE!!
 
Join Date: Oct 2005
Posts: 12,174
iTrader: 8 / 100%
Default

Quote:
Originally Posted by blfd1 View Post
You could just sell the 7.62 upper and buy another .223... just a thought?

How much for the 7.62 upper?
I believe he wants to keep the 7.62X39 barrel and just change it from a fixed carry handle A2 receiver to a flat top, railed receiver.
__________________
Quote:
Originally Posted by ChrisTKHarris
That is one of the most idiotic statements I've heard. You are a retard.
Reply With Quote
  #7  
Old 09-22-2007, 10:24 PM
TonyM's Avatar
TonyM TonyM is offline
Veteran Member
 
Join Date: Oct 2005
Location: SF Bay Area
Posts: 3,059
iTrader: 85 / 100%
Default

If you need to, you could replace the FSB with a gasblock that has a rail, and mount a front sight on it. Or you could use a PRI type flip up/gasblock. If the one you have won't work for the new config.
Reply With Quote
  #8  
Old 09-23-2007, 3:40 AM
Gunhacker's Avatar
Gunhacker Gunhacker is offline
Member
 
Join Date: Feb 2006
Location: SF East Bay Area
Posts: 266
iTrader: 27 / 100%
Default

Quote:
Originally Posted by ar15barrels View Post
You won't find info about swapping front sight bases because it's just not done.
The barrel and FSB get drilled as a mated pair.

Trust me on this.

Go with the extended post if required.
Thanks much for that info, I appreciate it greatly!!
Reply With Quote
  #9  
Old 09-23-2007, 3:54 AM
Gunhacker's Avatar
Gunhacker Gunhacker is offline
Member
 
Join Date: Feb 2006
Location: SF East Bay Area
Posts: 266
iTrader: 27 / 100%
Default

Quote:
Originally Posted by Technical Ted View Post
I believe he wants to keep the 7.62X39 barrel and just change it from a fixed carry handle A2 receiver to a flat top, railed receiver.
Yep... that's exactly what I was planning to do in order to go with an open "red dot" style optic sight, as I'm having problems using the stock apeture sights with my aging eyes.

But my wife has come up with an alternative and says leave the rifle along and go have my eyes altered... Lasik.

Damn , she may have something there, it would solve a multitude of sins considering all of the different guns I go shooting with.
Reply With Quote
  #10  
Old 09-28-2007, 10:30 AM
supersonic's Avatar
supersonic supersonic is offline
Calguns Addict
 
Join Date: May 2007
Location: Sactown, Sacramento, Sac, Etc....
Posts: 5,612
iTrader: 160 / 100%
Default

Quote:
Originally Posted by ar15barrels View Post
You won't find info about swapping front sight bases because it's just not done.
The barrel and FSB get drilled as a mated pair.

Trust me on this.

Go with the extended post if required.
What about REMOVING A2 FSB to get off Delta ring/handguard cap/BBL nut/etc., then REINSTALLING FSB (needs to be done if you want to install BBL assy to MGI upper?
SS
__________________
"HAMMER OF JUSTICE CRUSHES YEE!"



*FACTORY-CERTIFIED ARMORER IN SACRAMENTO*http://www.calguns.net/calgunforum/s...d.php?t=393331 GUNS 4 SALE: http://www.calguns.net/calgunforum/s...d.php?t=923745 WILSON COMBAT MAGS------ http://www.calguns.net/calgunforum/s...d.php?t=928518
Reply With Quote
  #11  
Old 09-28-2007, 1:20 PM
ar15barrels's Avatar
ar15barrels ar15barrels is online now
I need a LIFE!!
 
Join Date: Jan 2006
Location: Van Nuys
Posts: 39,029
iTrader: 88 / 100%
Default

Quote:
Originally Posted by supersonic View Post
What about REMOVING A2 FSB to get off Delta ring/handguard cap/BBL nut/etc., then REINSTALLING FSB (needs to be done if you want to install BBL assy to MGI upper?
No problem.
You can remove the taper pins, slide off the FSB, handguard cap and delta ring and then re-install the FSB and taper pins.

You just can't swap out the FSB from one barrel to another, or easily install a new FSB on a barrel that's been previously drilled.
__________________
Randall Rausch

AR work: www.ar15barrels.com
Bolt actions: www.700barrels.com
Foreign Semi Autos: www.akbarrels.com
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.
Founding member of the CAPRC
Reply With Quote
  #12  
Old 09-29-2007, 8:50 AM
supersonic's Avatar
supersonic supersonic is offline
Calguns Addict
 
Join Date: May 2007
Location: Sactown, Sacramento, Sac, Etc....
Posts: 5,612
iTrader: 160 / 100%
Default

Quote:
Originally Posted by ar15barrels View Post
No problem.
You can remove the taper pins, slide off the FSB, handguard cap and delta ring and then re-install the FSB and taper pins.

You just can't swap out the FSB from one barrel to another, or easily install a new FSB on a barrel that's been previously drilled.
Aaaahhhh.....okay. Thanks for the clarification, as I have a "clamp-on" FSB coming from Armalite to replace my 4-rail GB. Maybe the two aren't even related, I don't know.
SS
__________________
"HAMMER OF JUSTICE CRUSHES YEE!"



*FACTORY-CERTIFIED ARMORER IN SACRAMENTO*http://www.calguns.net/calgunforum/s...d.php?t=393331 GUNS 4 SALE: http://www.calguns.net/calgunforum/s...d.php?t=923745 WILSON COMBAT MAGS------ http://www.calguns.net/calgunforum/s...d.php?t=928518
Reply With Quote
  #13  
Old 09-29-2007, 2:14 PM
ar15barrels's Avatar
ar15barrels ar15barrels is online now
I need a LIFE!!
 
Join Date: Jan 2006
Location: Van Nuys
Posts: 39,029
iTrader: 88 / 100%
Default

Quote:
Originally Posted by supersonic View Post
I have a "clamp-on" FSB coming from Armalite
A clamp-on FSB can go on ANY barrel of the proper diameter.
It does not matter if there are taper pin holes or not.
__________________
Randall Rausch

AR work: www.ar15barrels.com
Bolt actions: www.700barrels.com
Foreign Semi Autos: www.akbarrels.com
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.
Founding member of the CAPRC
Reply With Quote
Reply

Thread Tools
Display Modes

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 -8. The time now is 2:25 PM.




Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Proudly hosted by GeoVario the Premier 2A host.
Calguns.net, the 'Calguns' name and all associated variants and logos are ® Trademark and © Copyright 2002-2016, Calguns.net an Incorporated Company All Rights Reserved.