I have both a 16 inch and 20 inch AR to put them on and understand the utility of the SPR M4 due to less over all length added but aside from that what else separates them. Is the mounting method of one better than the other?
The dB reduction is listed slightly different but not enough that I could tell the difference I presume.
Bla, bla bla…and so on.
This was a recent topic of conversation on Weapon Evolution as well. Perhaps the most significant difference is that the SPR/M4 offers the M.I.T.E.R. system, while the M4-2000 does not.
What this means in practical terms is that with the M4-2000 you’ll have to zero unsuppressed, and then zero again when the can is mounted, taking note of the shift.
The M.I.T.E.R. system allows you to calibrate the can to the unsuppressed zero, so you get repeatability without the need of making additional sight adjustments. Additionally, the SPR/M4 does a better job of reducing gas blowback through the weapon (and into your face).
AC
And I gather that they do not include the mounts with any of their cans anymore as well right.
Everything I’ve heard is that the SPR is the preferred one for the reasons already listed:
Less gas (also heard that it’s negligible)
Better reduction (ditto)
And a choice of 5 zeros (that’s where it’s at for me)
Hell, you’re probably going to have the thing until you die, why cheap out on the better product for $200? You’re already in it for $1,000 with the stamp…
That is not the issue, I am trying to establish which one it the better product for me. Strangely enough money is not the issue (praying to the keep my job gods) and I already have a Gemtech HALO I am looking to upgrade and am looking for alternatives. I have a SWR Trident in the works for 9mm and this can will likely be my last 5.56 can for a while.
The SPR-M4 is the newer can right. I know I like the mounting system better based on the limited info about it.
I prefer the SPR/M4 on any rifle which it fits. I use the M4-2000 on barrels that are too short for the SPR/M4. The SPR/M4 is quieter though the M4-2000 is still among the most quiet 5.56mm AR cans.
Can the SPR M$ be used on a 10.5 bbl or the LMT 12" Piston Upper?
Not on a 10.5. I am not sure about the LMT 12. It works on direct gas 12 inch rifles.
No question about it, I would go with the M4/SPR. I’m trying to figure out how people are saying they don’t see a difference with blowback between the M4/SPR and the M4-2000, the difference is very evident to me, and to everyone else that has shot them with me.
I just can’t imagine putting either one on a 16" or 20" barrel.
I’ve got an M4-1000 for my 16" carbine.
Installed, it is the same length as my 24" DPMS .204 Ruger upper.
I can’t even imagine hanging a can on a 20" tube.
My M4-2000 on a 10.5" is the same length as that 16" rifle, without the flash hider.
The SPR/M4 is still pending. 
The M4-2000 is for short barrels. The SPR/M4 is for everything else.
Mike did a “Skinny with Mers” on the AAC Blog comparing the two.
FWIW, I chose the barrel length of my upcoming 6.8 build in order to be able to work with the SPR/M4.
Just curious, will a 6.8 SPR/M4 can work on 5.56 guns? Will the 6.8 can fit on a 5.56 flash-hider mount?
Yes.
Yes.
It’s great. I love running my can on a 20" barrel for positional shooting. It’s great for ringing the gongs at long range. It has its limits, but it’s fun.
The M4/SPR is a good bit longer but doesn’t add much length…I assume that’s due to the longer flash hider it uses, right? How much shorter is a M4-2000 equipped rifle compared to a M4/SPR equipped?
From my understand the M4/SPR is like 8" in length and slides back like 4" on the rifle and flash suppressor/mount.
But that would just be the sub 11" barrel offerings, right?
Say if it was an 11.5 you could run the SPR/M4 mount & can… (maybe even perm attach the mount 
)*
*EDIT: Maybe I got it wrong. According to the site, this only adds 1.75" to the length of a barrel…so you’d still need a typical 14.5/7 length barrel to make this legal?