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Mark Christian, Judge Colt--9mm SP1 Upper ?

bama55
Can an early Colt SP1 9mm upper receiver be used with a .223 barrel,
bolt and carrier, etc.? I have a chance to get one, only saw a pic.
It has the full bolt cover slot, no shell deflector, etc. It looks like a standard .223 SP1 upper. I may be wrong, but I believe the difference, with the 9mm, was the bolt, and you used a magazine block. Is this correct?

"Don't send flowers when I die. Send money now so I can buy more guns and ammo."
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Comments

7 comments

Date Votes
  • mark christian
    This is one that had never crossed my mind before. I own Two AR-15 9mm Carbines- and several .223 rifles and carbines- but both 9mm's are purpose built and not conversions. These carbines use an A1 upper without FA, have a deflector, and a shortened cover. A standard .223 bolt assembly will fit into the 9mm upper, at least up until the point where the bolt head meets the breech. By way of my MK-1 eye ball, the interior of the receiver looks to be identical between the two calibers and it would appear that a .223 barrel could screwed into the 9mm upper- although I am not prepared to break out the wrench and tear one down for you! My own opinion is that this sort of barrel/caliber swap would work...but I'd prefer to get a second opinion. Perhaps you should just hold out and purchase an upper already chambered for .223.

    Mark T. Christian
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  • bama55
    Oh, come on Mark, tear one down and check it out.[:D] LOL.

    I already have a barrel, and just need a SP1 upper. BTW, can a
    GI A1 upper be drilled for the large pin holes? (to fit a SP1 lower)

    "Don't send flowers when I die. Send money now so I can buy more guns and ammo."
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  • mark christian
    Before you start drilling I seem to recall that there was an "off-set pin" or a "reverse off-set pin" (I forget which one you'll need) which will function as an adapter and allow you to mount your upper to the lower. You might want to ask around at one of the local gunshows.

    Mark T. Christian
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  • bama55
    Yes, there is an off-set pin. When you use it, you get it set and tighten it up. You have to remove the pin to breakdown the upper from the lower, not like the standard where you push out the rear pin and the upper hinges from the lower.
    Thanks for the info.

    "Don't send flowers when I die. Send money now so I can buy more guns and ammo."
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  • JudgeColt
    I do not know either, although I agree with Mr. Christian's logic. The 9x19 is a blow-back and the bolt does not lock into the barrel as with the .223. I ASSUME .223 parts could be installed in the 9x19 upper, but you know what they say about assuming: It makes an ass out of you and me.
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  • bama55
    Thanks JudgeColt for your input. If I get this 9mm upper and try it,
    I will post my findings.

    "Don't send flowers when I die. Send money now so I can buy more guns and ammo."
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  • bama55
    I didn't get it, so, guess I will use the GI A1 upper I have.

    "Don't send flowers when I die. Send money now so I can buy more guns and ammo."
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