Upper conversion advice

[DocCasualty]

I have a Colt Sporter 6551 pre-ban in 5.56mm. What caliber options do I have when it comes to upper conversions and what is actually involved in doing this? I'm sure this has been discussed ad nauseum, but the search function hasn't really directed me to any useful threads, except for .22LR drop-ins. Is it a matter of a short time involved in switching out uppers, bolt, etc. and you're good to go or is it more involved than that? What is a typical cost? I've taken a look at some different retailers and for some reason I'm not getting the big picture here. Any thoughts or links would be appreciated.

[cyrsequipment]

Most rifle calibers switches are drop ons, just switch the upper and the magazine (7.62x39... 5.45x39, 6.8)

Pistol caliber switches usually involve going to a blowback system so buffers springs and hammers need to be changed in some cases....

[DocCasualty]

Wow. So I could pick up a rifle caliber upper and corresponding AR mags and I'd be good to go? Well, this certainly sounds simpler than I thought and might be worth looking into. I was guessing this would require changing out bolt carrier groups and possibly springs or some kind of gas adjustment. I'm not sure I need more calibers in my life but have had some thoughts about exploring 5.45. I have an SKS but a 7.62X39 AR would open up a lot more possibilities. I'm not that familiar with the 6.5 and 6.8 cals I've seen mentioned but am intrigued about this idea. Guess I need to do some more research. Thanks for the reply.

[cyrsequipment]

Wow. So I could pick up a rifle caliber upper and corresponding AR mags and I'd be good to go? Well, this certainly sounds simpler than I thought and might be worth looking into. I was guessing this would require changing out bolt carrier groups and possibly springs or some kind of gas adjustment. I'm not sure I need more calibers in my life but have had some thoughts about exploring 5.45. I have an SKS but a 7.62X39 AR would open up a lot more possibilities. I'm not that familiar with the 6.5 and 6.8 cals I've seen mentioned but am intrigued about this idea. Guess I need to do some more research. Thanks for the reply.

I'm sorry, you WOULD have to have at least a new bolt (I was thinking a complete upper including BCG, my bad)...

Most of the rifle conversions do use the same bolt carrier though and are ok to use with the standard springs...

[KalashniKEV]

Need to know what buffer weight and hammer type.

"GI Style" or DPMS pattern hammer will run with everything (not notched)

H2 is probably your best bet buffer for working with Carbine length uppers and 9mm uppers, .22 as you know doesn't use the receiver extension.

M&P Factory guns in 5.45 use a stronger hammer spring for hard primers, but most have reported this is not an issue with stock springs.

[vafish]

Your older Colt Sporter probably has the larger diameter pins between the upper and lower receiver.

You will need an adapter pin to fit a milspec upper to it.

As for calibers, there are lots of them out there now.

.204 Ruger
5.45x39
7.62x39
6mm/.223
6.5 Grenedel
6.8 SPC
.300 RAR
.450 Bushmaster
.458 Socom
.500 Beowulf

And Olympic is supposedly coming out with some based on the Winchester Super Short Magnum's like the .243 WSSM and .25 WSSM.


And I'm sure there are some that I've missed. For almost all of them except the 6mm/.223 you will need a new bolt if not the whole bolt carrier group. Usually if needed they come with the upper. You may also need a different spring or buffer. The upper manufacture should tell you this and often will include the necessary items. Any gas regulation would be done through the size and location of the barrel port and you should not have to mess with that.

If you want to know more about the various AR15 calibers try here:

http://www.ar15.com/forums/forum.html?b=3&f=121

[rjrivero]

Need to know what buffer weight and hammer type.

"GI Style" or DPMS pattern hammer will run with everything (not notched)

H2 is probably your best bet buffer for working with Carbine length uppers and 9mm uppers, .22 as you know doesn't use the receiver extension.

M&P Factory guns in 5.45 use a stronger hammer spring for hard primers, but most have reported this is not an issue with stock springs.
I would recommend a heavier buffer for the blowback 9mm. You'll also want a spacer to limit the travel of the buffer to prevent the possibility of breaking bolt catches. If going with a 9mm conversion, consider using the Spikes Tactical 9mm buffer or the ST-T2 with the 9mm Spacer.

I like to use a DPMS lower for all my builds, just in case I decide to go with a .22 conversion, or Pistol Caliber conversion down the road. The smooth hammer makes it easier to make the swap.

[cyrsequipment]

I like to use a DPMS lower for all my builds, just in case I decide to go with a .22 conversion, or Pistol Caliber conversion down the road. The smooth hammer makes it easier to make the swap.

Can the DPMS hammer be used for 9mm?

[KalashniKEV]

I would recommend a heavier buffer for the blowback 9mm.

See my post in the GD 9mm Carbine/ Subgun thread. H3 is within an ounce of a standard 9mm buffer, and is ideal. I run H3.

I'm only saying that for all around use on a 16" gun and a 9mm H2 would be a better choice.


You'll also want a spacer to limit the travel of the buffer to prevent the possibility of breaking bolt catches.

That would depend on what block you're using. No last round BHO = no broken bolt catch.

[KalashniKEV]

Can the DPMS hammer be used for 9mm?

You must use a DPMS pattern hammer for 9mm.

[cyrsequipment]

You must use a DPMS pattern hammer for 9mm.

I knew it had to be a different hammer, but didn't realize that it was a standard DPMS hammer.

What is the difference?

[KalashniKEV]

I knew it had to be a different hammer, but didn't realize that it was a standard DPMS hammer.

What is the difference?

DPMS = "GI Style" = Standard pattern

The notched hammers are said to produce "bolt drag" in the 9mm... and to be honest I have no idea why a hammer would be notched anyway, except that I understand it was part of the whole "let's make an AR as different from an M16 series rifle as possible."

[DocCasualty]

Your older Colt Sporter probably has the larger diameter pins between the upper and lower receiver.

You will need an adapter pin to fit a milspec upper to it. . .

And I'm sure there are some that I've missed. For almost all of them except the 6mm/.223 you will need a new bolt if not the whole bolt carrier group. Usually if needed they come with the upper. You may also need a different spring or buffer. The upper manufacture should tell you this and often will include the necessary items. Any gas regulation would be done through the size and location of the barrel port and you should not have to mess with that.

If you want to know more about the various AR15 calibers try here:

http://www.ar15.com/forums/forum.html?b=3&f=121


Thanks for the helpful post and link. Are there any mfgrs of uppers that have a better rep or conversely, ones to avoid?

[vafish]

Thanks for the helpful post and link. Are there any mfgrs of uppers that have a better rep or conversely, ones to avoid?


That's opening a whole can of worms and really depends upon who you talk to. But there are some AR parts manufactures that have worse reputations then others.