I have a S&W upper in 5.45x39 with 16" barrel, and contemplating to reduce its barrel to 10.5" or 11.5" for SBR/Pistol. However, I don’t know if the gas system will function properly with the short length.
I found a few have done this conversion. Please share your experiences on how to make it work. Do I need any mod besides the barrel reduced and recrowned ?
I have one cut down to 11.5. Works fine.
Actually, I’d love to have it cut to the same length of my 10.5" LMT upper in 5.56.
Will the 10.5" length works well, too ?
RustedAce,
Can you post a pic? That sounds like a sweet package.
rustedace,
Thanks much. I like the 2nd one. Can you provide more details? Buffer type, etc… etc…
The S&W MP15R is supposed to be an overgassed barrel to begin with (and considering the gas blowback on my 16", I can’t dispute that :p) so I don’t think you’d have to tinker with the gas port much.
The 5.45 round doesn’t lose as much velocity with shorter barrels as 5.56, so it’s a good SBR candidate…2950 fps in 16", 2755 fps in 12" AK-105 barrels, and 2411 fps in Krink barrels according to the info I can find.
2nd one is just a regular old 5.56
Colt 614 lower
H3 buffer, H2 and H were not tripping the sear.
LMT bolt/carrier
ADCO EXT 11.5 barrel
Giessele SSF trigger
For the 5.45x39 upper, do you have standard Carbine configuration ? Anything has to be changed to make it work ?
Standard carbine buffer/ spring that came with that RRA entry stock, nothing changed to make it work.
Pretty cool, dude. How is the felt recoil?
Gotcha. I thought they were two separate ones. Both are nice I just liked that UBR stock a little better.
I cant notice a difference between this and when it was full length.
I’d like a UBR for it, but I dont feel like I could justify the cost for a gun I just consider a toy, I dont have the 5.45 for any serious use, just money saving without having to go all the way down to .22.
That’s a winner !! $.15/round and as flat as the 5.56. 
i have the standard 16" and also the 10.5"
both run perfect
did put h-buffers in the 16 per grant as i had major back surgery and smith sent me the gun last June/08.
so i put the h-buffer in the 10.5" smith as well. both run fine. shot the shorties at adcos black swamp thing 2 weeks ago w/o a hitch after i jammed a slpit case winchest w/b 556 rd in my h&k 10.5" 416 upper switched uppers and kept on ginnin’‘’’
will do fine if its smith barrel any others i would not trust it but i also know of no failures. we all run factory stuff.
i cant load a pic but can send 1 to someone and they can post if if u wish
ask i am around
Sonicbuff,
Did you ever do this? What length did you decide on? Does it run reliably? Do you have any pics?