GUN Suppressor POI shift with 75 gr PPU factory ammo+reloads

Discussion in 'On Topic' started by ChipOnShoulder, Nov 20, 2009.

  1. ChipOnShoulder

    ChipOnShoulder New Member

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    About a week ago I was down in the Portland area shooting. Ended up spending a lot of time on the range, so I got to experiment with suppressor shift.

    Here's the rifle and I as phogographed by Titlest1 on other boards.

    [​IMG]

    I experimented with 75 gr factory loads and 75 gr reloads, as well as with 77 gr SMK reloads. I didn't expect to be spending time shooting from a bench, so i had brought only my 14.5" N4 with an Aimpoint T-1, and was shooting at targets that were not really ideal for shooting groups. No sandbags, just rested the rifle on some PMAGS and started shooting. I was able to document interesting results.

    Here's a bunch of rounds onto the bullseye. Consistent performance with what to expect from my batch of 75 gr PPU (Jan '09)

    [​IMG]

    And here is a similiar target but suppressed.

    [​IMG]

    Later, firing reloads I saw a similiar, but slightly more dramatic shift.

    Unsupressed

    [​IMG]

    Suppressed

    [​IMG]

    I later shot 10 rounds of 77 gr SMKs suppressed, and 10 rounds unsuppressed at the same target, thinking I could makes out the difference. However, the two groups were so closely spaced together there was no distinct space between the groups! The combined group of the suppressed and unsuppressed 77 SMKs would have fit inside the groups the 75 gr factory loads produced :rofl: I'll upload those pics tonight.

    It definitely seems that 77 gr SMKs seem to resist suppressor shift better in my particular set up. Any idea why?
     
  2. Crossett

    Crossett New Member

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    Do you know the muzzle velocity difference between the 75 and 77? That would be my only guess.
     
  3. ChipOnShoulder

    ChipOnShoulder New Member

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    Probably shouldn't be much. Haven't seen a chronograph in more than a year now :wtc:

    The 75 GR privi has a rounded base, whereas the 77 gr SMK's base is perfectly flat. That might have something to do with the 77 gr's superior accuracy: more consistent base for the expanding gases to push on.

    It was funny to see how one loading would create 10 shot groups to the left, and .5 grains more of the same powder would push 10 shot groups to the right.

    I found a "sweet spot" zero that was practical for all my main loads of 55 gr FMJ-BT, 75gr PPU, and 77gr SMKs though.

    It kind of a pain in the ass... but I was waiting nearly 2 hours for everyone else to zero their guns, lol.
     
  4. thegooch

    thegooch OT Supporter

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    M42000's are notorious for POI shift, or so I've read.
     
  5. ChipOnShoulder

    ChipOnShoulder New Member

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    I don't understand why there aren't more range reports about POI shift. They are kind of hard to find.

    I heard that Gemtech HALO is really bad with POI shift, but i've never seen a shared report. I've also heard that the Surefire suppressors have less POI shift... but once again, no pics.

    The only thing that seems to be documented meticulously with suppressors is dBs, which the M4-2K seems to win.
     
  6. Razardica

    Razardica Active Member

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    I have the exact shift you do in the first target - about 3 MOA to 5 o'clock
     
  7. I think his is more a 4:30 shift.
     
  8. Razardica

    Razardica Active Member

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    oh thanks ever since I got my Blackberry 9700 I just rely on that for time so I've basically forgotten what a clock looks like

    no just SPR/M4
     
  9. I was making a joke. :hs:
     
  10. thegooch

    thegooch OT Supporter

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    SPR/M4 does, M4-2k does not have it
     
  11. phrozenlikwid

    phrozenlikwid New Member

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    You are looking in wrong places for this info. Check SnipersHide, and some of the other LR precision orientated sites. Suppressor shift is very real, very well documented, and definitely some makes do better with it than others. I've seen guys run two completely different sets of dope for their rifles, based on whether or not the can was attached.

    It used to be no one with a LR rifle would TOUCH a quick-change can setup. Single cut threads ONLY. A lot of this had to do with guys putting hinky adapters on their rifles, creating odd pressure points unto the barrels, and throwing shots. It also had the side benefit of helping minimize POI discrepancies. You will likely never eliminate the shift, especially on something like an AR barrel. You are hanging a weight at the very end of the tube, which certainly puts pressure on the barrel itself proper (notice the downward shift), and using a QD setup which likely wasn't created/installed with complete uniformity and precision in mind. Just how it goes.
     
  12. ChipOnShoulder

    ChipOnShoulder New Member

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    :rofl:
     
  13. Razardica

    Razardica Active Member

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    nh wp

    the guy in the picture in the 'what handguard is this' thread is grant timberlake who is one of the most vocal advocates of the k-can, him and jeff carpenter both

    they both say it has a <1 MOA shift which I think is cool

    I suppose if I bought another 5.56 can it would be a k-can

    what I've seen and heard especially from 5, 7 SFG is that the k-can is the best for like, fighting...I'm just a 'lifestyle' customer so I got the M4-2000 because it has maximum suppression

    and before, when I was in the market, the k-can had shit mounts
     
  14. ChipOnShoulder

    ChipOnShoulder New Member

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    Oh yeah, i know it's real.

    It's just that people don't seem to bother documenting it on the AR oriented sites. Not really interested in seeing how a M4-2K affects a Remington 700, but that was one of the few detailed reports i was able to find.

    I would really like it if someone could show the supposed zero-shift of the Surefire cans.

    IIRC, the 12th model from OPS is one of the few cans people have agreed that there is very litte suppressor shift

    http://www.silencertalk.com/forum/viewtopic.php?t=13648
     
  15. Razardica

    Razardica Active Member

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    grant timberlake posts a lot on m4c about them
     
  16. phrozenlikwid

    phrozenlikwid New Member

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    I'm not completely following you... what is a "K-Can"?
     
  17. Razardica

    Razardica Active Member

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    my friend has a 12th and a 15th and would suck Ron from OPS' cock if he asked (even if he asked in a gruff, demanding and impolite way) and the 12th is pretty rockin in terms of being without a POI shift

    the only problem is that you have to profile a barrel for it, it has to be at least a 16" barrel and the can itself is like, the size of a D-cell maglite

    the suppression was also not as good as even say an M4-1000 08

    OPS and SF cans have a lot in common - Barry Dueck (dick) learned almost everything he knows about cans from Ron Allen...if you look at the x-rays of SF cans and the x-rays of OPS cans they are very similar
     
  18. Razardica

    Razardica Active Member

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    Surefire FA-556K suppressor (the 'k can')
     
  19. ChipOnShoulder

    ChipOnShoulder New Member

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    Surefire 556K?

    K as in Kurtz/Short
     
  20. ChipOnShoulder

    ChipOnShoulder New Member

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  21. Razardica

    Razardica Active Member

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    jinx wtf? i'll cum on your face
     
  22. ChipOnShoulder

    ChipOnShoulder New Member

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    Very gross, the usual suspects of Hoss/Pixel will gladly help you in this regard though. :ugh2:

    :mamoru:
     
  23. Paul Revere

    Paul Revere OT Supporter

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    surefire cans FTMFW. no POI/POA shift
     
  24. Crossett

    Crossett New Member

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    :bowrofl:
     
  25. ChipOnShoulder

    ChipOnShoulder New Member

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    20 rounds of 77 gr SMK

    10 rounds suppressed, 10 rounds unsuppressed.

    Can't make a distinction between the suppressed and unsuppressed group

    [​IMG]
     

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