I haven’t popped the FSB to check the exact port size yet…
But if an 11.5 is overgassed somewhat… would a cut down to 10.5 or 10.3 bring it around???
Is there enough difference in the two lengths to tame the beast?
Not sure exactly, but I had ADCO cut a 12.5" to 11.5" and they said there was no need to alter the gas port. I guess your results will depend on the severity of how overgassed it is to begin with. If you’re running a suppressor on it…fuggetaboutit.
I suggest looking into the SYRAC Ordnance Adj. Gas Block. I put one on my 11.5" to tame the gas with the suppressor installed. Works great! Might be cheaper than cutting down the barrel too.
Yeah… no way on the suppressor. I never run cans on my shorties.
I’d hate to lose the FIXED FSB, but that is an interesting option to keep in mind.
Ah, yeah missed the part about it being a FSB. Well if you ever want a longer rail, then that would be an option. Look up port sizes for 10.5" and 11.5" and see what kind of difference there are in spec sizes. There may be a greater difference between 10.5 and 11.5" vs. 11.5" and 12.5".
Also, you could just run a heavier buffer…or A5 (if you’re not already)…or LMT Enhanced Carrier…but like I’ve said before, all these things are really just bandaids for an overgassed system.
I agree on the bandaids analogy. I’ll have to take off the FSB tonight to see if I’m even barking up the right tree.
What about drilling out and threading a set screw in the FSB to function as a dam of sorts.
However big you want the gas port to be, drill that size in the set screw. Tap and screw the set screw into the underside of the FSB.
This would, more or less, function the same as the Syrac w/o the adjustable feature. Well, you could adjust it but it would require the removal of the FSB.
You may have to look at McMaster Carr or the like to find a set screw short enough. In reality, it doesn’t have to be a set screw, just something to restrict the gas flow at the FSB.
Cutting the barrel down a full inch is about the same as changing the GP size from say .060 to .058 IMHO.
C4
Doesn’t sound like much of a gain… (reduction)
Maybe I can get Iraqgunz to stop by the house today when he’s out running his ponzi schemes throughout the city.
I can pull that sucker apart, but really don’t have a good way to measure.
It isn’t, but dwell time does add more pressure for sure.
C4
True… might be worth a cutdown just for the research value.
:laugh:
agreed, doesn’t sound like much return after a pretty drastic change. .02" for 1".
I’d be curious to hear as well. To me, sound like Ironman’s suggestion is the easiest and most practical. Syrac blocks ain’t cheap, but I’d rather do that then send my barrel out. And after shipping/shop fees…you’d probably net out at around the same $…but have more flexibility with the adjustable GB?
Ok, boys.
The Gas port is .082… Talk to me! 
That’s big even for a 10.5"
Did it come that way from the factory? Or is that from erosion?
You may need a heavy buffer and some extra power springs for that puppy! :sarcastic:
LMT 10.5 is .071… You’re screwed.
Sabre?
You’re not screwed.
Taking the LMT 10.5 port size down a hair to compensate for the extra inch would make the port size you’d like the barrel to have around .069".
One of our insertable gas ports would make it right.
Damn. I’d agree…+ a LMT enhanced carrier (not bolt). And never suppress it :laugh:
Please expound.
I’ve never heard of an insertable gas port. I’d like to keep the fixed FSB, but am willing to cut the barrel down to balance the scales.
Have it cut to 10.5" and run a H3 buffer and it should run well with a gas port of .082"
Sure,
Inside the gas block or FSB there is passage that goes between the barrel and gas tube.
Call it the gas transfer port.
The insertable gas port goes inside that passage and reduces gas flow to the desired level.
The effect is similar to an adjustable gas block or switchblock, except it is not adjustable or switchable without removing the FSB and putting a different port in.
This is very much in line with the original intent of the system to not require operator adjustments to the gas system.
IMO, No need to cut down the barrel by 1".
I doubt it will make enough of a difference in gas flow.
You can band-aid it enough to get a healthy 10k rounds out of that barrel without killing your bolt.
Options:
Insertable gas port.
LMT Enhanced Carrier
Heavier buffer in the A5
Stiffer Spring (I like the Springco GREEN M16 spring)
Maybe a stronger extractor would be good too.
The bolt should last 5k. I’m sure of it. I’d also like stronger magazine springs if I was gonna run something like that.
But then again, I’d take these procautions on ANY SBR.