1st Gen Sig 556 DMR 21" | SIG Sauer 556 Forum

1st Gen Sig 556 DMR 21"

Discussion in 'Introduce Yourself' started by Yuns, Apr 28, 2020.

  1. Yuns

    Yuns Member

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    After many years of admiring the Swiss 550/551/553 series, I recently became the owner of a used 1st generation Sig 556 DMR with the 21" 1 in 10" twist barrel. It believe it is an early DMR version as it came with the fishgill handguards and a Sig Sauer M4 style stock and not the Magpul PRS stock. I swapped the lower for a steel Swiss 55x lower and Swiss stock and Manticore grip and the fishgills for a Swiss 551 handguard. I put some MFI flip up BUIS on it as well as a scope. I also have a Shooting Sight hammer and sear to install.

    Here is a before and after the first set of changes.
    [​IMG]

    The next project is to test 55gr M193, 63 gr RUAG GP90, 69 gr Federal Gold Medal Match SMK, and 77 gr SMK in the DMR vs my Krieger barreled AR to see how it compares and which ammo is most accurate out of the DMR.
     
  2. CGRBB

    CGRBB Active Member

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    I am eager to hear how this gun performs. Always been curious about them. You ought to get you a bipod spigot and a VersaPod, to complete the sniper package! And a comb riser would round out the look.
     
  3. Yuns

    Yuns Member

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    I do have a climb on comb riser but I didn't put it on for the picture but I'll probably get the versapod adaptor.
     
  4. Yuns

    Yuns Member

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    I've been working on my Sig 556 DMR/551 hybrid and found a few more things.

    The DMR gas regulator valve appears to be drilled correctly. The DMR does not have a regular and adverse condition setting. It has a regular and no gas position for running single shots without running the action. I ordered a Swiss 551 long barrel gas regulator for regular NATO ammo (not Swiss GP90 1.3/1.6) with nominal 1.2mm regular and 1.3mm adverse setting and the DMR gas regular hole size is exactly between the two. For the time being I am running the Swiss valve as I want to use the minimal amount of gas to reliably cycle the action to avoid overgassing and beating up the brass and rifle.

    I took apart both my Swiss fire control group and the DMR one and they are both appear to be different than the standard US 556 FCG. The DMR one is shorter and lighter than the Swiss 551 FCG and probably the standard US 556 one as well.

    Swiss:
    Total travel 0.395"

    Take up slack/pretravel 0.145"
    First stage 0.17"
    Second stage (when second stage plunger is set to the break and minimum necessary overtravel) 0.08"

    Reset is from break to beginning of first stage so about 0.25"
    Total trigger weight is around 8 lbs (4.75 1st stage and 3.25 2nd stage).

    US DMR
    Total travel 0.310"

    Take up slack/pretravel 0.145"
    First stage 0.11"
    Second stage (when second stage plunger is set to the break and minimum necessary overtravel) 0.055"

    Reset is from break to beginning of first stage so about 0.165"
    Total trigger weight is around 7.25 lbs (4.5 1st stage and 2.75 2nd stage).

    The Swiss trigger although heavier and longer is super super super smooth and feels great.

    I tried the Shooting Sight RPS hammer and sear which removes most take up slack and is much shorter total travel but not noticeably lighter. The main advantage of this hammer and sear is the shortened travel through elimination of the pretravel and a sear/hammer interface which promises a true second stage so that you don't need the trigger plunger (pressure point) to create an artificial second stage which means the entire trigger weight remains about the same as the first stage only for the other triggers. While shorter than both US DMR and Swiss trigger and while very smooth, the RPS hammer and sear were not as smooth as the DMR trigger and the Swiss.

    I tested all 3 triggers by eliminating the second stage pressure point spring to see if any of the 3 triggers had a true second stage but all 3 generally acted like single stage rolling break triggers so I could not get rid of the second stage pressure spring even with the RPS. I suspect that the heavy weight of the first stage/TRS prevented me from feeling the wall of the second stage of the RPS trigger.

    In disassembling the FCGs I noticed that they were different that the standard US 556 trigger groups. The Swiss has 2 different sears with a baffle plate between with a single sear spring on the left sear. The US DMR has a one piece sear that looked like 2 identical pieces fused together with 2 side by side sear springs and a different hammer shape at the sear interface. I believe the standard US 556 has a sear and a plastic spacer where the second sear would go and a single sear spring.

    I'm happy with the Swiss and DMR triggers although a bit long and heavy as they are very smooth. I'm going to use the RPS hammer and sear when I get a third lower in order to experiment more. I am also working on a trigger return spring to reduce the first stage pull weight and a pressure point spring to reduce the second stage weight. My goal is 2 lb first stage from the TRS and 1-1.5 lbs from the second stage spring for 3-3.5 lbs.
     
  5. CGRBB

    CGRBB Active Member

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    Great write-up! Cool note on the gas valves. I like the idea of only one position on the DMR, with the ability to shut gas off.

    You lost me after that. Only because I have never been a trigger person. I am the guy who is totally fine with “mil-spec” triggers. I don’t have any aftermarket trigger components in any of my guns. I do take advantage of the adjustability of the plunger, but feel no need for further modification. I totally understand why you’re tinkering with it though, considering the DMR role.
     
  6. Yuns

    Yuns Member

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    Thanks. I come from a bullseye pistol shooting background hence the obsession with triggers but I agree that the standard 551/556 is actually good enough without tinkering. The main reason I wrote this all up was to document all the differences and varieties of 55x series rifles for reference since there is so little information available since Sig dropped support for the 556. Even with the 556 DMR series, it's hard to know the types. Most people know the Gen 1 21" barrel 1 in 10 twist, quad rail and PRS stock and the Gen 2 18" 1 in 8" quad rail and CTR stock. But because mine is different, I went back to the old advertising to see how many variants there actually were. So far I have identified:

    Prototype 556 DMR - advertised in 2008 Sig Sauer catalog as 24" 1:9 twist CHF barrel, fishgill handguard with bipod and, PRS stock and flip up BUIS in written material but not in photos, enhanced single stage trigger

    1st Gen 556 DMR as advertised in 2009 Sig Sauer catalog as 21" 1:9 twist CHF barrel, fishgill handguard with bipod and, PRS stock "factory tuned trigger" The description notes that the DMR is based on a ":heritage of a rare variant used by Swiss security forces" This is clearly a 550 Sniper reference. This 1:9 twist might be incorrect since 1:10 was the 550 sniper twist and all known early non-prototype DMRs are believed to be 1:10.

    My early 556 DMR - 21" CHF barrel probable 1:10 twist (I haven't tested true twist rate yet), fishgill handguard, metal commercial carbine extension (with open ends) and Sig labelled M4 style stock (probably a FAB defense M4 style stock with battery compartment) and an enhanced trigger (feels like single stage)

    1st Gen 556 DMR as advertised in 2010 - 21" 1:10 twist CHF barrel (6 groove), text still refers to polymer fishgill handguard and Harris bipod but photos show quad rail with bipod, PRS stock and a "Two-stage match trigger with over travel stop" of 5.5 lbs.

    2nd Gen 556 DMR as advertised in 2011 - 18" 1:8 "hammer forged" heavy barrel threaded (1/2x28 TPI) and A2 flash suppressor, quad rail and Harris bipod, Magpul CTR stock and riser

    2nd Gen DMR as advertised in the 2012 international Global Defense version of the Sig Sauer catalog - 2 barrel choices LB - 21" 1:10 twist, SB - 18" 1:8 twist. Both are advertised as CHF, quad rail and Harris bipod, Magpul MOE stock and riser, 5.6 lb "two-stage match trigger with over travel stop"

    2nd Gen 556 DMR as advertised in 2013 - 18" 1:8 heavy barrel threaded (1/2x28 TPI) and capped, quad rail and Harris bipod, Magpul MOE stock and riser

    By 2014 only the 556xi and the 522 are advertised and no other 556 models appear.

    So what was actually delivered? Did anyone actually receive a Harris bipod? I haven't seen any that came with a DMR of any generation.

    The 1st Gen DMR were all 21" CHF. The 24" appears to have been the prototype based on the 550 Sniper barrel length. Though 1st Gen DMR are all believed to be 1:10, early advertising says a 1:9 twist. Was this a mistake or were some early ones 1:9?

    Early 1st Gen came with fishgills and some came with M4 stocks and some PRS. The later and most common 1st Gen is quad rail with a PRS stock.

    2nd Gen were all 18" threaded barrels, some advertising says hammer forged and some doesn't. Not clear if the barrels were hammer forged. Most people assume they are not. All advertising says 2nd Gen is 1:8 twist unlike the other 1:7 twist 556s.

    The 2nd Gen came with quad rail and Magoul CTR stock.
     
    Last edited: May 3, 2020
  7. Yuns

    Yuns Member

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    Also my 556 DMR is quite front heavy with the 21" heavy barrel and the gas system so the balance point with the Swiss furniture is just ahead of the mag well.
     
  8. CGRBB

    CGRBB Active Member

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    That is an astonishing amount of possible variants. I had no idea. It is quite frustrating to me that not enough people realized the potential of the 55x for Sig Sauer to give a damn about it in the long-term. That and the fact that no one in Sig Sauer really cares about the heritage of the company enough to keep the model alive in some capacity. The American market was never really ready to take on a gun that costs as much as a properly manufactured 55x though, I guess.

    I have been contemplating a “sniper” build using a barrel blank. It probably won’t come to fruition anytime soon, but I enjoy brainstorming. Knowing what you know about the US DMR series, would it be an idea worth pursuing, or is there a factory DMR variant that is better than anything someone could build?

    Is this the first 55x you have owned? I imagine yours is rather front heavy, due to the barrel. The series is not known for being light-weight in general though. Especially not when compared to modern ARs.
     
  9. Yuns

    Yuns Member

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    This is my first 556.

    Yes, all Sig Sauer USA had to do is bring out a perfect clone of the 550/551/553 series with good QC and they would have done well. They could then follow up with a modernized modular xi style version with swappable mag wells for Swiss, STANAG and AK mags and switch bolt/barrel system to switch calibers if it was accurate and relaible with good QC. But by starting with an Americanized version that strayed from the Swiss 55x series and having serious QC issues, they doomed the rifle and the later Series 2, 551A1, 556R and 556xi were too late to save the rifle. In some ways the troubles with the 556 mirror Colt's return of the Python. Looks like a Python but with new modern lockwork and far less craftsmanship and QC problems.

    I know that most testers found the normal 556 series to be 1.5-3 MOA guns and the DMRs maybe 1.5-2 MOA, but I don't see why they should not be capable to shooting well. I don't know where the barrels were made but aside from maybe a handful of Swiss barrels finished in the U.S. for the very very early ones, there are rumors that the U.S. made CHF barrels were contracted to FN Herstal in the U.S. FN is a solid company and there is no reason why their barrels should be inaccurate. So long as everything is consistent, I don't see why every 556 shouldn't be as accurate as most ARs.

    If I can't find ammo for the DMR that works well, then I'll look at a rebarrel or maybe even just do a rebarrel for the experience. I've been contemplating getting a Bartlein or Krieger barrel blank and getting someone to finish it for the 556 but don't know where to even start since no one seems to do 556 custom barrels. If I rebarrel it'd be similar to my precision AR. A heavy barrel cut rifling 1:7.7 blank of about 20". Hopefully I can get to the bottom of how accurate my DMR is and what is the minimum I need to do to accurize it if necessary.

    If I do get some barrels made I'll probably get a few different barrels of different profiles made and have a few spares for other 556 rebarreling.
     
    Last edited: May 4, 2020
  10. fachries

    fachries Member

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    +1
    [​IMG]
     
  11. Yuns

    Yuns Member

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    I'm a big fan of Swiss firearms in general

    My Swiss P210-5, German P210 Legend Supertarget and American P210 Target
    [​IMG]

    My Sphinx Grand Master
    [​IMG]
     
  12. CGRBB

    CGRBB Active Member

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    No Swiss or German duty 210? I have been pining for one with the black plastic grips and heel mag catch.
     
  13. Yuns

    Yuns Member

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    I prefer the target models though I am on the lookout for a pristine example of a duty model P210-1 or -4.
     
  14. Yuns

    Yuns Member

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    Current configuration: steel Swiss semi lower, Swiss gas valve, green stock and handguards, cheek riser was black but Kryloned it ODG, Manticore grip, added MFI BUIS and Versapod bipod adaptor, Leica glass in a LaRue QD mount, B&T sling, Also removed green fiber optic rod and switched to an orange TruGlo fiber.

    I have a Versapod 50 series bipod on the way.

    Is it worth swapping any of the gas system (tube, piston, spring, gas block) for the Swiss versions? Or worth swapping the U.S. bolt head for a Swiss one?

    Obviously the inspiration for my build and the inspiration for making the Sig Sauer 556 DMR was the Sig/SAN 550-1 Sniper.

    [​IMG]

    [​IMG]
     
    Last edited: May 9, 2020
  15. CGRBB

    CGRBB Active Member

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    Looks pretty damn slick! I would say the gas components aren’t worth swapping. And the bolt won’t necessarily be any value-added either. Heck, it could actually hurt, if it alters your headspace in the wrong direction.
     
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  16. Yuns

    Yuns Member

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    My 556 Sniper project continues now that I have the Versa Pod and adaptor. There are unlikely to be any external changes until I can get a sniper stock and grip, but I'll continue to make some internal changes.

    [​IMG]
     
    Last edited: May 13, 2020
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  17. Yuns

    Yuns Member

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    I'm glad that I did not order a Swiss gas tube. The DMR uses a gas tube that is a shorter 551 length version of the 550 Sniper gas tube that has a relief cut in the front to allow it to clear the heavy barrel. A standard 551/556 gas tube does not appear to be able to fit.
     
  18. CGRBB

    CGRBB Active Member

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    Looks friggen awesome. How do you like the versa-pod so far? I like the purpose-built aspect of it. A bit more deliberate-feeling than merely clamping something on a 1913 rail.

    It never dawned on me that the gas tube would be different, but makes absolute sense. The 751 is the same way.
     
  19. Yuns

    Yuns Member

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    I like the Versapod a lot but you have to get the Series 50 or 300 or later all of which allow you to lock down pan/tilt etc. The Gen 1 didn't have the lock out and are too floppy as a result (although you can buy a Series 50 head to allow you to lock it out.) I got the Series 50 150-050. The mount itself feels a little wobbly but that disappears once you load up the bipod. The bipod is super quick to deploy and fold and loads backwards and forwards very easily. I normally run a Harris on my bolt guns and also shoot with Atlas as well on my friends guns as well and I do like the Versapod a lot so far.

    I love the Versapod spigot mount and I might try to buy a Versapod head with no bipod and use it to mount other accessories like lights by home building some adaptors. The mount is too wobbly to use for something like a laser but a light would be perfect.

    Also I got a bunch of ammo to test:

    PPU M193 55gr
    Federal MK 318 Mod 0 SOST 62 gr
    RUAG GP90 63gr
    Federal GMM SMK 69gr
    Lapua Scenar-L 69 gr
    Remington Premier Match SMK 77 gr
    Black Hills MK 262 Mod 1 (civilian version) 77 gr

    Notably absent is the M855 as my testing ranges don't allow M855 due to the steel penetrators.

    I also weighed the DMR as it currently is with the scope and mount and bipod. It's a hefty 12 pounds and 10 oz with no magazine and no ammo.

    EDIT:

    Turns out the SOST I got is the newer MK 318 Mod 1 62 gr lead free

    [​IMG]
     
    Last edited: May 21, 2020 at 7:12 PM

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