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Posted: 5/18/2016 2:25:32 PM EDT
| Recently built a 300 Blackout and I'm having cycling issues. Tried a number of buffer/spring combos with no luck. Rifle won't fully cycle. After some conversation with a few guys more knowledgable than me, it was suggested I bore out the gas port and run an adjustable gas block. 16" stainless barrel, carbine length gas tube. My question is how far I should go with the gas port. I'm told to bore it to .120 and go trial and error w/ the gas block. Just wanted to see if this sounds right. Any help would be appreciated. |
| From the reading I have done on this forum, a few other well regarded sources, and in my personal experience, no more than 0.125 opening will fix most if not all cycling issues with the 300 BLK. Usually try 0.108 first. If that does not cure the problem, then going to 0.125 generally nails it. ymmv and I am sure there are/will be some different recommendations along soon. Personally I have never used an adjustable gas port as I have never had a gun that required one to make it work properly. again, ymmv. |
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Before you start drilling the gas port, please answer the following questions first.
What size is the current gas port, and what type of barrel (where is the gas port). Hence is this a 223 gas port type of barrel with the gas port way up front, or is this a ACC 300blk barrel with the gas port way back towards the chamber isntead. Note, with the gas port much closer to the chamber, even on a 16" barrel, it allows the barrel to run both sub sonic and super sonic ammo as well. http://www.flickriver.com/photos/66666941@N02/6857109190/ Next, have you gone through the rig to check for any binding, gas blockages or leakages before you even think about opening the gas port? Also have you scrubbed the chamber clean with a chamber brush and CLP by hand, then check the chamber walls to make sure that are mirror smooth with no reamer marks. Hence if you have any of the above problems, open the gas port and they such solve later, your going to be so over gassed with gas port enlarged (read over cycling with the rifle short stroking), that you going to running the gas port dam near closed instead. Lastly, pretty much ever adjustable gas port out there sucks when it comes to having to adjust it back and forth for subsonic, then sonic ammo, over and over again. Hence in stead of going with a adjustable gas block that can be a PITA, do the above checks to make sure that they are not the problem, then using a light buffer, only open the gas port if needed to cycle your sub sonic factory ammo. When you decide to run super sonic ammo, then it much faster to just drop in a Heaver buffer instead. As for your sub sonic hand loads, work with different types of powders until you find a load that will cycle the rifle like the factory loads. Even with a gas port way out away from the chamber like on a 223 barrel, you can still find powders that have a slower burn rate to have enough residual pressure in the bore with sub sonic loads to still cycle the system. Hence you are dealing with both on a auto loader, over all working pressure of the load, and the gas port pressure, being the residual pressure in the bore once the bullet passes the gas port. |
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What brand of barrel? Have you contacted the manufacturer and made them aware of the issue, and see if they can help? If you haven't contacted the manufacturer, then I highly recommend doing so before you start opening up any gas ports.
CY6 Greg Sullivan "Sully" SLR15 Rifles TheDefensiveEdge.com (763) 712-0123 |
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