Mike1476 Posted March 8, 2022 Report Share Posted March 8, 2022 Is there a formula used to calculate the correct size of the gas port that can be shared...or perhaps just let me know if I'm on the right path. I've got a 260 that has not cycled properly since I assembled it. At best, it ejects the fired casing, but will not pick up a round from the magazine, and does not lock back on an empty magazine. Here's the specs on what I have: JP Supermatch .260 22" with XL gas length (end of gas tube is centered in the cam pin cutout); .936" journal at the gas block; 7" from gas port to muzzle; gas port diameter 0.0655.; SLR Sentry adjustable gas block. Fulton Armory upper and lower; buffer tube has 7" internal depth; buffer is 2.5" and 5.4oz; have tried Armalite EA1095 spring as well as Tubb flat wire. BCG is JP full mass weighing 18.9oz and has been well lubed during use; bolt is from JP and headspaced to this barrel. I've tried factory ammo of several weights from several manufacturers (Black Hills, Hornady, Federal) all with the same results. Am I correct in thinking that the gas port diameter is undersized? I have emailed JP Enterprises to see if this is within their specs, but I have yet to hear back from them (only been a few days). Any input is greatly appreciated! Thanks, Mike Quote Link to comment Share on other sites More sharing options...
98Z5V Posted March 8, 2022 Report Share Posted March 8, 2022 41 minutes ago, Mike1476 said: Is there a formula used to calculate the correct size of the gas port that can be shared There is - in my head. I've written about it as much as I can, every single time I can, and I spill details as often as I can - on why gas ports work. And when recoil systems must be matched. And why both systems MUST be balanced, in order to reliable function your rifle. Gas systems and recoil systems are the heart of your reliability. I've delved into this as much as I can here, on why what works, WHAT works... Different journal diameters just came up the other day, and I got into that. And why. It really just sucks to keep going over it, time and time again, it really does. The info is already all here. Hate to be a dick about it, but the info is already here. I've even made posts on how to calculate it. With diagrams, because some of the guys here need the crayon-method to comprehend shiit. I'm talking about the old-timers, too - not newbies. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted March 8, 2022 Report Share Posted March 8, 2022 (edited) 58 minutes ago, Mike1476 said: JP Supermatch .260 22" with XL gas length Define that gas system length, exactly. How long is your gas sytem - it's not rifle-length gas - and how long is that gas tube, end to end, exactly... Details. Not names. Numbers, matter. That gas port size is fucked for a .260 Rem, with your barrel dimensions that have been stated. Thanks, JP, for sending us another customer. Let's see what JP says about this - so make SURE you post what they reply to you... You're dealing with Race Gun Parts - and not trying to make a Race Gun. That's the first problem... Edited March 8, 2022 by 98Z5V Quote Link to comment Share on other sites More sharing options...
98Z5V Posted March 8, 2022 Report Share Posted March 8, 2022 Rule #1 with adjustable gas blocks. You run adjustable gas blocks WIDE OPEN, like you'd savage a 2-stroke MX bike on a motocross track. You ALWAYS start an adjustable gas block WIDE OPEN. If you don't, you're wasting ammo, and wasting time. If it's not wide open, you'll never, ever know if your gas port is large enough - which your's isn't. Rule #2. Dwell time. Distance between the gas port and the end of the barrel. Exactly why I asked you to specifically define your "XL Gas System" that you got from JP. Rule #3. Gas block journal diameter. You never stated it, and I'm not looking it up on JP's website, for your barrel. What's the journal diameter? You answered alot, with the details you provided - but there's alot more that you left out. I'll fix your .260 - I have 2 that run like Swiss watches. Until I get these details, I'm wearing a blindfold, and throwing darts at the dartboard... Quote Link to comment Share on other sites More sharing options...
Matt.Cross Posted March 8, 2022 Report Share Posted March 8, 2022 On 3/7/2022 at 11:40 PM, 98Z5V said: Rule #3. Gas block journal diameter. You never stated it, and I'm not looking it up on JP's website, for your barrel. What's the journal diameter? On 3/7/2022 at 10:32 PM, Mike1476 said: 936" journal at the gas block; Quote Link to comment Share on other sites More sharing options...
98Z5V Posted March 8, 2022 Report Share Posted March 8, 2022 Alright already... I missed it... Quote Link to comment Share on other sites More sharing options...
Matt.Cross Posted March 8, 2022 Report Share Posted March 8, 2022 On 3/8/2022 at 12:04 AM, 98Z5V said: Alright already... I missed it... Quote Link to comment Share on other sites More sharing options...
Mike1476 Posted March 8, 2022 Author Report Share Posted March 8, 2022 The gas tube is 17.25" overall, and 16.56" from the receiver end of the tube to the center of the hole at the gas block. Gas block journal is .936". I actually did start with the gas block wide open, and only backed it down initially to see if it was overgas causing the issues. I do appreciate the replies, and very much appreciate the help! Quote Link to comment Share on other sites More sharing options...
98Z5V Posted March 8, 2022 Report Share Posted March 8, 2022 2 minutes ago, Mike1476 said: The gas tube is 17.25" overall, and 16.56" from the receiver end of the tube to the center of the hole at the gas block. Gas block journal is .936". I actually did start with the gas block wide open, and only backed it down initially to see if it was overgas causing the issues. I do appreciate the replies, and very much appreciate the help! That's 2" over AR15 Rifle Length gas, right there. Every gas tube is 0.600" from the center of it's end gas port to the end of the tube (capped end), so that number can come in handy when ordering spare custom-length gas tubes. Dwell time on your 22" with Rifle +2 Gas will be the same as my 20" Rifle gas .260 barrel. It needed 0.080" gas port diameter to run right, with a 0.750" journal. You have the same dwell time, but up two sizes on the journal diameter. General rule is 0.005" port diameter per journal size, but that's a range, not a spec. Your 0.655" port diameter needs to be at leasy 0.070" diameter, but could run up to around 0.073" diameter. Drill the gas port up. The gun will run. Keep the gas block wide open for all the testing - maxed, wide open. Quote Link to comment Share on other sites More sharing options...
Mike1476 Posted March 8, 2022 Author Report Share Posted March 8, 2022 Thank you very much! I’ll work up from 0.070 and post the results. I’ll also be sure to post any reply I get from JP. Thanks again! Quote Link to comment Share on other sites More sharing options...
Mike1476 Posted March 14, 2022 Author Report Share Posted March 14, 2022 Drill bits were finally delivered. Drilled to 0.0700, and it wouldn't lock back on an empty mag, but it would pick up the next round. Went to 0.730, and first round locked back on the empty mag, but the next three wouldn't. Brass is landing at around 4 o'clock about 8 feet away. Any issues going up to 0.760? Still haven't heard anything from JP. Thanks! Quote Link to comment Share on other sites More sharing options...
98Z5V Posted March 15, 2022 Report Share Posted March 15, 2022 (edited) 57 minutes ago, Mike1476 said: Any issues going up to 0.760? No issues at all, to 0.076" - take it up, and let us know. Make sure you're getting those decimal points in the right place, otherwise, you're putting more than a 3/4" hole in your barrel... Edited March 15, 2022 by 98Z5V Quote Link to comment Share on other sites More sharing options...
98Z5V Posted March 15, 2022 Report Share Posted March 15, 2022 Max you can ever make a gas port is 0.125", because that's the I.D. of a gas tube. If you need bigger than that, we'd have to braze in a turbo encabulator into the middle of the gas tube, to bump up gas pressure when you fire. Quote Link to comment Share on other sites More sharing options...
dpete Posted March 15, 2022 Report Share Posted March 15, 2022 44 minutes ago, 98Z5V said: If you need bigger than that, we'd have to braze in a turbo encabulator into the middle of the gas tube, to bump up gas pressure when you fire. Is that like splicing in a flux capacitor? Quote Link to comment Share on other sites More sharing options...
98Z5V Posted March 15, 2022 Report Share Posted March 15, 2022 3 minutes ago, dpete said: Is that like splicing in a flux capacitor? Same principle, but for gas pressure instead of electricity. Quote Link to comment Share on other sites More sharing options...
Mike1476 Posted March 15, 2022 Author Report Share Posted March 15, 2022 So not this one then? Quote Link to comment Share on other sites More sharing options...
Matt.Cross Posted March 15, 2022 Report Share Posted March 15, 2022 On 3/14/2022 at 9:01 PM, Mike1476 said: So not this one then? I won't wander as much as a drill bit will, but you'll still end up oversized... Quote Link to comment Share on other sites More sharing options...
dpete Posted March 15, 2022 Report Share Posted March 15, 2022 3 hours ago, 98Z5V said: Same principle, but for gas pressure instead of electricity. Sounds good! As long as the turbo encabulator doesn't overcharge the tubular gas re-energizer enough to blow up and become a gonadal emasculator. That would be BAD, VERY BAD! Quote Link to comment Share on other sites More sharing options...
98Z5V Posted March 15, 2022 Report Share Posted March 15, 2022 3 hours ago, Mike1476 said: So not this one then? We can work with that, and get it running. Have no fear. 2 hours ago, Matt.Cross said: I won't wander as much as a drill bit will, but you'll still end up oversized... I need to teach you the definition of "oversized..." I mean, I can SHOW you was oversized is... but sometimes, that still doesn't stick... Quote Link to comment Share on other sites More sharing options...
Mike1476 Posted March 15, 2022 Author Report Share Posted March 15, 2022 We have success! Had to go up to 0.0785, but now it runs as it should. Thanks again for all of the help! Quote Link to comment Share on other sites More sharing options...
DNP Posted March 16, 2022 Report Share Posted March 16, 2022 Damn good looking rifle. Glad you got her up and running! Quote Link to comment Share on other sites More sharing options...
Armed Eye Doc Posted March 16, 2022 Report Share Posted March 16, 2022 I'm glad you got it running right. Quote Link to comment Share on other sites More sharing options...
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