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.
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?
Based on my experience, that would increase the amount of gas.
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.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 pretty sure that I tried that, but the diameter of the 751 gas valve was larger.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?
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.
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?
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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