Gunsmithing .260 Gas Port Dimensions

[19Scout77]

I am starting my research to build a .260 upper for my LWRC REPR. Bolt face, OK, mags, OK-----gas port size?????

As a starting point I am trying to ascertain the the size of both a .308 GP and a .260 GP.

Thanks and Merry Christmas

 

[crumpmd]

Re: .260 Gas Port Dimensions

Kreiger made the barrel for mine chambered in 6.5X47L and the gas port is the same as the .308. Same place and same size. I use an adjustable gas block because it is overgassed and I shoot suppressed.

 

[19Scout77]

Re: .260 Gas Port Dimensions

I do not have the option as I want to use an LWRC 4 postion block that comes on the REPR--only I have to play with the port size.

 

[wnroscoe]

Re: .260 Gas Port Dimensions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 19Scout77</div><div class="ubbcode-body">I do not have the option as I want to use an LWRC 4 postion block that comes on the REPR--only I have to play with the port size. </div></div>

Start on the small end of sizes, <.0931". Test fire using the single feed, empty magazine technique. If the bolt carrier doesn’t lock back after each shot increase the gas port size up to the next largest opening and repeat the test. Once there's enough gas flowing, the bolt carrier group will lock back. At that point you can open one more size up if you like and your there.

LR308 Gas Port

 

[pagana]

Re: .260 Gas Port Dimensions

How far forward is the port? How much barrel past the port (dwell)? Standard rifle length will need less than 3/32". My custom .260 has a 27" Krieger with the port forward 3" from standard and runs with an .085" diameter port and stiff hand loads. If you have a means for adjustment, don't go any larger than 3/32" and throttle it from there as you will likely have plenty of gas to cycle.

 

[19Scout77]

Re: .260 Gas Port Dimensions

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Toolmakr</div><div class="ubbcode-body">How far forward is the port? How much barrel past the port (dwell)? Standard rifle length will need less than 3/32". My custom .260 has a 27" Krieger with the port forward 3" from standard and runs with an .085" diameter port and stiff hand loads. If you have a means for adjustment, don't go any larger than 3/32" and throttle it from there as you will likely have plenty of gas to cycle. </div></div>

Hey A- I sent you an email this morning with the same question. I am waiting to hear back from my contact at LWRC with the various dimensions and port location needed for the piston set-up. The only issue with the adjusting system I will be using is that it is 4 fixed positions, not infinitely adjustable. The positions are wide open, normal, suppressed and closed. I think my plan of attack will be to determine the NORMAL setting via trial and error on the barrel port while using the using wide open setting. After doing so, I will open the barrel port a bit, machine the normal setting on the gas block to the dimension I found for the barrel. At that point I will have 3 of the 4 settings determined, then I need only figure out the restriction needed for suppressed (which will be tough to do in NJ!!).

 

[mountaineerjdm]

Re: .260 Gas Port Dimensions

Should be the same as any AR-10 configuration. The main thing that channels the gas is the size of the gas hole; the theory being that the gasses behind the bullet as it passes by the hole are channeled into the same small area for that brief moment to drive the bolt back. Think of it this way...

A garden hose with one of those pressured heads behind it should release as much PSI as a the same head would being attached to a large industrial hose. The valve (or hose head) regualtes the amount of pressure into that channel. The same should go for the gas port between 308 case-size cartridges. DPMS and Armalite might change them to slightly alter pressures for accuracy reasons based upon field testing, so you might want to call them.

 

[mountaineerjdm]

Re: .260 Gas Port Dimensions

Just read where DPMS advocates the idea I just discussed by using a smaller diameter hole on a larger bore 338 Federal, probably due to low inherent pressures in the barrel. A smaller gas hole would increase pressure of the gasses being forced back toward the bolt. It either for cycling of the 338 Fed or accuracy reasons or both. I'd call them.

 

[Krebaum]

Re: .260 Gas Port Dimensions

.081 port for .260, 20" Barrel, std rifle length gas tube.

 

[19Scout77]

Re: .260 Gas Port Dimensions

Thanks for the info. Looks like the project is a no-go for a while as the manufacturer won't sell the parts needed to build a spare upper in an alternative caliber. Not gonna buy a whole one at $2300+ and scrap the barrel to make a .260. $3k plus to build an upper?? I'll stick to my bolt guns when .308 won't cut it.