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Thread: Sig 551s are inbound.

  1. #231
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    Quote Originally Posted by Bret View Post
    Based on shooting my 553R, 551LB and 751 SAPR, I think that each setting allows too much gas through. I'd much rather be able to fine tune it myself. I understand that they want to make sure the valves work for everyone and pretty much all ammunition, so I'm not saying they're made wrong. It would just be nice to be able to do it right for the ammunition I'm using.
    Why not just weld up the entire thing and then re-drill it? Truth is, this is why I got back into FAL's. You can fine tune the gas system with a wrench.

  2. #232
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    Quote Originally Posted by 7n6 View Post
    Why not just weld up the entire thing and then re-drill it?
    I have several extras from Sig USA. That's exactly what I'd like to have done to them. I have no welding skills myself, not to mention pinpointing the exact location to drill. Most importantly, the valve has to be milled on the opposite side so that the detent can keep it in place.

  3. #233
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    Quote Originally Posted by Bret View Post
    Based on shooting my 553R, 551LB and 751 SAPR, I think that each setting allows too much gas through. I'd much rather be able to fine tune it myself. I understand that they want to make sure the valves work for everyone and pretty much all ammunition, so I'm not saying they're made wrong. It would just be nice to be able to do it right for the ammunition I'm using.
    I agree. My 751LB with the 20" bbl seems over gassed, throwing cases 30' forward to 1 o'clock and severely denting the case neck and body. It came with a 1.4 valve opening which is spec'ed for the 17.8 bbl. The 17.8 bbl measurement also includes the built in flash hider, so the actual rifled length is closer to 16" I was told. The 20" bbl has a removable flash hider and the actual rifled length is 20".

    I'm wondering if the extra 4 inches of rifled length in the 20" bbl is enough to cause it to be over gassed when using the gas valve designed for the 17.8 bbl with only 16" of rifled length.

    Also, if you got your 551LB 17.8" from JDI, did you get a replacement gas valve? It seems that some of them may have been shipped with the incorrect valve. Mine initially came with a 1.5/1.6 valve, but I was sent a 1.2/1.3 as a correct replacement.

    I'm actually thinking of trying the valve from the 551LB in the 751 on the 1.3 setting. Does anyone know if 551 and 751 gas valves are interchangable?

  4. #234
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    Quote Originally Posted by plnkr1234 View Post
    I'm wondering if the extra 4 inches of rifled length in the 20" bbl is enough to cause it to be over gassed when using the gas valve designed for the 17.8 bbl with only 16" of rifled length.
    Based on my experience, that would increase the amount of gas.

    Also, if you got your 551LB 17.8" from JDI, did you get a replacement gas valve? It seems that some of them may have been shipped with the incorrect valve. Mine initially came with a 1.5/1.6 valve, but I was sent a 1.2/1.3 as a correct replacement.
    Yes, I received the replacement valve. I noticed the overgassing immediately when I shot it. When I checked the gas valve chart, I found that it had the wrong one and notified Dave.

    I'm actually thinking of trying the valve from the 551LB in the 751 on the 1.3 setting. Does anyone know if 551 and 751 gas valves are interchangable?
    I'm pretty sure that I tried that, but the diameter of the 751 gas valve was larger.

  5. #235
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    Quote Originally Posted by Bret View Post
    Yes, I received the replacement valve. I noticed the overgassing immediately when I shot it. When I checked the gas valve chart, I found that it had the wrong one and notified Dave.


    I'm pretty sure that I tried that, but the diameter of the 751 gas valve was larger.
    So you're the one who got us the new valves. Thanks.

    I did try fitting the 551 valve in the 751 and it seems to fit, but Dave is checking into it for me.

  6. #236
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    Quote Originally Posted by plnkr1234 View Post
    So you're the one who got us the new valves. Thanks.
    Well I don't know if I'm the only one that figured it out, but Dave was unaware when I initially contacted him. I'm guessing that he got back with San Swiss Arms and they confirmed it. I'm glad they followed through and made it right.

  7. #237
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    Quote Originally Posted by Bret View Post
    Well I don't know if I'm the only one that figured it out, but Dave was unaware when I initially contacted him. I'm guessing that he got back with San Swiss Arms and they confirmed it. I'm glad they followed through and made it right.
    Yes, Dave and SAN seem great.

    Is your 751LB a 20"? What are the openings on your valve. As I mentioned, mine seems over gassed. It has the 1.4/1.6 valve with 1.0/x for suppressor.
    Last edited by plnkr1234; 01-13-19 at 17:55.

  8. #238
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    No, I got one of the 5 17.8" 751's. I'm very happy about that. I shot '85 Radaway Green 150gr FMJ, '03 GGG FMJ M80 and Saltech (Swiss) 150gr FMJ through it. All ran 100% at the 1.2 setting.

  9. #239
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    I just checked the fit of the 551 and 751 gas valves. The 551 gas valve will fit in the 751. However, I have no idea if there would be any negative consequence. The 751 gas valve will not fit in to the 551. This is because the 751 gas valve has a portion that's a bit wider than the same area on the 551 gas valve. The 751 gas tube is cut to relieve this area, but the 551 gas tube is not. Perhaps they did it this way to make sure that nobody uses 751 gas valves in 55X series rifles?

  10. #240
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    Yes, I see that, too. Can you tell me what the other settings are on your 751 valve? Are they 1.4/1.6/x?

    Good move on the 17.8". I'm beginning to think I should have gotten that one instead. It also looks like my 20" has a thicker profile than the 17.8.

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