blue109 Posted February 23, 2012 Report Share Posted February 23, 2012 mikes dumb question for the week. probably been discussed but i searched around a bit and didnt see it in here. thinking of having my DPMS 24" bull chopped down to 18" or 20". would like to go with 18" since i honestly dont do any precision or serious bench shooting. if i did this there wouldnt be much barrel left past the gas block. ive seen people on other forums saying theres no issue but its usually regarding 5.56 guns and i trust the info on here a little more than most sites.in a perfect world id just order up a fulton titan upper and call it a day but thats not gonna happen any time soon with a kid on the way so i have to work with what i got. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted February 24, 2012 Report Share Posted February 24, 2012 Can it work? Yep, sure can. Fulton offers two different 18"-ish barrels with rifle gas. The stainless Criterion barrel is 18.5", and I'm pretty sure the cromoly is 18.5" also. Both rifle gas. You might need to play with the gas port diameter a little, but it wouldn't be much, just going from 24" to 18". Hell, it might even run fine like it is. It's do-able, man. <thumbsup> Quote Link to comment Share on other sites More sharing options...
robtmc Posted February 27, 2012 Report Share Posted February 27, 2012 You might need to play with the gas port diameter a little, but it wouldn't be much, just going from 24" to 18". <thumbsup>I just measured a Criterion 18.5" chrome lined barrel gas port diameter. Much to my surprise, it is .093". Was in the middle of trying to find out why my AP4 build will not feed or lock back on an empty magazine. AP4 gas port was .063, which is why I was curious why the rifle gas port on the 18.5" would be so much larger. Quote Link to comment Share on other sites More sharing options...
pdc Posted February 28, 2012 Report Share Posted February 28, 2012 I've asked around about cutting down an existing barrel and usually get negative responses. Things about barrel "concentricity" or something. I didn't see what the problem was but I'm not a gunsmith yet.... Quote Link to comment Share on other sites More sharing options...
blue109 Posted February 29, 2012 Author Report Share Posted February 29, 2012 thanks for the replies guys! like i said, im not worried about groups at 1000yds with this, or any, rifle. at this point in my life im just happy i have a few cool toys and a little time now and then to play with them :) i think the rifle would be more fun for me with a little less weight and a little more maneuverability. i can get it chopped by one of a few reputable AZ guys relatively cheap.i just dont want to give myself headaches getting it to run well afterward. Quote Link to comment Share on other sites More sharing options...
robtmc Posted February 29, 2012 Report Share Posted February 29, 2012 The only thing concentric to anything else on a barrel is bore to outer barrel. Cutting it shorter ha nothing to do with that. Getting the contour cut down to save weight would be the issue, though I suspect good machinists know how to do that right. After all, the barrel blank is chucked up in a lathe to bore it in the beginning. No personal experience with them, but heard good things about an outfit called ADCO for barrel re-profiling.I've asked around about cutting down an existing barrel and usually get negative responses. Things about barrel "concentricity" or something. I didn't see what the problem was but I'm not a gunsmith yet.... Quote Link to comment Share on other sites More sharing options...
98Z5V Posted February 29, 2012 Report Share Posted February 29, 2012 I just measured a Criterion 18.5" chrome lined barrel gas port diameter. Much to my surprise, it is .093". Was in the middle of trying to find out why my AP4 build will not feed or lock back on an empty magazine. AP4 gas port was .063, which is why I was curious why the rifle gas port on the 18.5" would be so much larger.Material, construction, barrel diameter, wall thickness, barrel profile, gas port location - all play into gas port diameter. I'd have to guess that "experimentation" must play a role in it, too, since there are so many "ranges" in diameters on like barrels.I just worked on a DPMS 7.5" 5.56 barrel tonight. Wouldn't cycle more than 2 or 3 rounds at a time. Took everything apart, and the gas port diameter was 0.052". Drilled it up to a 0.064" diameter, so we'll see how it runs tomorrow. <dontknow> Went through alot of different tests prior to taking it apart, so don't just jump to drilling gas ports - I tried everything else that I could think of first. Quote Link to comment Share on other sites More sharing options...
survivalshop Posted February 29, 2012 Report Share Posted February 29, 2012 Gas port size is directly related to where it is on the barrel & of course what some manufacturers may want it .Gas pressure decreases proportionally to barrel length, further out toward the end of the barrel , the port needs to be larger to keep gas pressure up to properly cycle action . Further out , longer gas tube, more expansion & less pressure , so ya need more gas pressure & volume to work the action, = larger port size .Bore dia. has a lot to do with it also.I had a M16 ( XM 177 )that I installed a new 10 1/2 barrel on & like 98 , I had to increase the port size to make it function properly in full auto .That doesn't mean it was the first think I tried or checked out , it was the last . There are far too many other things in an AR to check , before open holes larger . Quote Link to comment Share on other sites More sharing options...
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