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Discussion Starter · #1 ·
I have an old school carry handle A2 upper Colt AR15 Rifle. It’s a law enforcement/ police issue complete with pencil barrel. (Extraordinarily accurate).
It does have large pin connections.
I’d like to try 30 blackout as a caliber. Is there a way of using my lower for this conversion.
What would I need. Best case scenario.
 

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Not sure about the pin issue, but all you really need is a BLK barrel or upper. Everything else is the same.
 

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All you'd need to change is your barrel. Receivers, bolt, colt carrier, magazines, everything else stays the same.
 
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Yes, they make an adapter insert to reduce down to the smaller pin. The smaller pin is a little off center and the insert will also handle that. I have a similar "big pin" colt and shoot a 22LR upper using one of these adapters. I will see if I can find my reciept. I suggest you google search while I look. Or maybe some esle can post a link. These do work..
 

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You will need a new barrel, a new muzzle device (the blackout uses a different threat size and pitch), receiver vise blocks to hold the receiver during barrel removal and installation, a well mounted vise to hold the blocks and an AR15 armorers wrench to remove the delta ring/barrel nut if you intend to use your upper.
It's less expensive to replace the barrel even with the cost of the tools and parts you need than it is to buy a complete upper.
Barrel replacement also lets you retain your A2 sights. Finding an A2 carry handle complete upper isn't impossible but they are few and far between these days as everyone seems to want flat tops.
The one problem you may run into if you change barrels is, some manufacturers locktite the barrel to the receiver. They can be a real bear to get apart depending on what type of locktite that was used. Most are not locktited in though, thankfully.
Also, doing a barrel change instead of a new complete upper eliminates the problem of pin size as you use the upper you have that fits your lower.
HTH
 

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You will need a new barrel, a new muzzle device (the blackout uses a different threat size and pitch), receiver vise blocks to hold the receiver during barrel removal and installation, a well mounted vise to hold the blocks and an AR15 armorers wrench to remove the delta ring/barrel nut if you intend to use your upper.
It's less expensive to replace the barrel even with the cost of the tools and parts you need than it is to buy a complete upper.
Barrel replacement also lets you retain your A2 sights. Finding an A2 carry handle complete upper isn't impossible but they are few and far between these days as everyone seems to want flat tops.
The one problem you may run into if you change barrels is, some manufacturers locktite the barrel to the receiver. They can be a real bear to get apart depending on what type of locktite that was used. Most are not locktited in though, thankfully.
Also, doing a barrel change instead of a new complete upper eliminates the problem of pin size as you use the upper you have that fits your lower.
HTH
He is correct. If it is a well used upper, you may wish to purchase a new bolt for the BCG to use with the 300 blackout, as they do wear differently over time and use in the AR platform, if you are worried about accuracy. Also if you get the correct parts for the barrel you could reuse the same handguards etc. you would just need to purchase the correct diameter size gas block and retaining clip if it is the old style round or triangular handguards. .
 

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Discussion Starter · #11 ·
You will need a new barrel, a new muzzle device (the blackout uses a different threat size and pitch), receiver vise blocks to hold the receiver during barrel removal and installation, a well mounted vise to hold the blocks and an AR15 armorers wrench to remove the delta ring/barrel nut if you intend to use your upper.
It's less expensive to replace the barrel even with the cost of the tools and parts you need than it is to buy a complete upper.
Barrel replacement also lets you retain your A2 sights. Finding an A2 carry handle complete upper isn't impossible but they are few and far between these days as everyone seems to want flat tops.
The one problem you may run into if you change barrels is, some manufacturers locktite the barrel to the receiver. They can be a real bear to get apart depending on what type of locktite that was used. Most are not locktited in though, thankfully.
Also, doing a barrel change instead of a new complete upper eliminates the problem of pin size as you use the upper you have that fits your lower.
HTH
Sounds like a reasonable idea. 👍🏻
 

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You have a relatively valuable ($2500 in certain states) preban and historic genuine, early colt AR15. Final frosting is your gun is very accurate. The reasonable solution is purchase a complete 300 upper and use the adapter pin.
Yes it's a valuable Colt. But a barrel change doesn't change that. The rifle can be easily be put back to its original configuration at any time. That's what is so cool about the AR platform, its ease of assembly and disassembly. I think it's the most modular system of all time and that's what makes it so popular.
If it is a well used upper, you may wish to purchase a new bolt for the BCG to use with the 300 blackout, as they do wear differently over time and use in the AR platform, if you are worried about accuracy.
As far as a new bolt is concerned, unless your trying to make a bench rest or long range rifle you probably won't notice a difference in accuracy with a slightly worn bolt. I think we all know that the barrel you choose has a lot more to do with accuracy than anything else does. Although you should check your bolt for any abnormal wear or cracks. If you find it to be in good shape, you should be good to go with the bolt you have.
JMHO
DaveL
 

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It takes some modicum of skill and tools to build an AR. The factory colt barrel nut can be super tight. It would be a foolish newbie who attempted a barrel swap on this particular gun when a complete upper is easily (and low cost) purchased. If the OP knew what we know, he would not be here asking. I know the AR very well and I would still buy an upper. I try to put myself in the OP's shoes when I answer a question. Then I suggest what I think is best for him.

A new upper also opens up the option to mount a scope or a red dot, maybe deer hunt. Slap the 556 back on in 2 minutes and go to the club shooting his mil configured gun. No tools. That is a sweet system.
 

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Yeah, the main issue I think for most in this case is the Colt upper is probably a fairly high dollar item. What hit it would take in value swapping parts off it would probably more than pay for itself by buying a seperate 300BO lower. Granted, in reality all it takes to swap from 556 to 300BO is a new barrel, although being that the 300 runs best IMO with a pistol length gas system that usually gets changed out as well. But still when talking this case leave the Colt upper alone, it's worth far more as is.
 

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Yeah, the main issue I think for most in this case is the Colt upper is probably a fairly high dollar item. What hit it would take in value swapping parts off it would probably more than pay for itself by buying a seperate 300BO lower. Granted, in reality all it takes to swap from 556 to 300BO is a new barrel, although being that the 300 runs best IMO with a pistol length gas system that usually gets changed out as well. But still when talking this case leave the Colt upper alone, it's worth far more as is.

listen to Mike,


and the thing is, you can just buy and upper and the pin adapter and swap calibers that way, however spare parts (even uppers) tend to turn into complete guns,
 
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