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I am interested in doing a SBR project with the MR762 when they are available and cutting the barrel to 12 inches.My question is will the gasblock ,and in particular the gas dump hole on the front have to be covered/welded? I am hoping somebody went to Shotshow and got a look at the gasblock of a 12 inch HK417 gasblock.Thanks!
 

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My guess would be that if anything, the gas port might need to be enlarged a little bit.

Reduce the dwell time (time that the bullet is in the barrel after passing the gas port and before it exits the barrel) so the system has less time to get gas into the piston chamber before the bullet exits the barrel and the system depressurizes and evens out, and the rifle will be under-gassed and won't function so well. Enlarge the gas port in the barrel to allow more gas to get into the system during that reduced dwell time and let the system work.

After having the gas block off of an SL-8 and an MR556, i've seen that the gas ports are relitivly small for this type of operating system, so there's plenty of wiggle room.

That being said, I really wouldn't want to be messing with the vent hole on the gas block and take the chance of screwing with the timing of the system. The nipple and vent are there for a reason.
 

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I don't really think we can look at this as we would a 5.56 DI gun as it sounds from Grumpy's explanation. The 7.62 requires much less barrel length past the gas port than its 5.56 counterpart to function reliably. Consider the KAC EMC and its gas block placement in relation to the muzzle. Also realize that certain piston systems don't need as much pressure/dwell time to generate the force require to operate a mechanical pusher rod as you aren't sending pressurized gas all the way back to the receiver.

I can't say for certain, but you might be fine with the standard gas block.
 
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