I want only experienced Smiths about gas port size, location and cartridge specific to help out this/these question/s please. Other people with 1st hand knowledge can/could help also IF they know their port size! Some of my barrels I know port size on only due to manufacturer list it and depends on gas system length thereof. While I have many 6.5creeds in AR's, not all function well with standard carbine/rifle buffers and springs. This also translates to other 308 based cartridges of .473 bolts (anything with that bolt face, but not necessarily 308 based). Aero Precision is THE only company I've bought from with 100% reliability in rifle length gas systems with barrels from 20-24" with standard weight buffers and springs. I also have "camgas" systems (+2) in 260rem and 6.5creed that DOESN'T function as well until other mods are done. Is there a good way to find out what the port size is without going to a Smith? The recoil is fine with the AP: barrels and gas length with standard weight recoil components. I have a CBI barrel that shoots bug holes, but is in need on mod work (I haven't had time to do it yet) that has a rifle gas system 22" barrel that's overgassed (for now) as it pops factory ammo's primers (Hornady 123a-max and sst's), but the AP barrels work 100% perfect. I might have the port opened up more or just increase buffer weight (in the works when I have time). I do have several buffers I can change out as not to mess with taking apart buffer in the field. Has anyone used a + gas with a 308win? Port size and location is EXTREMELY important on non-308win's is what I've come to learn the difficult way. Sure, throw in a h3/h2/h4 and call it good, but I'd rather have answers to the questions. This isn't a debate or p i s s i n g match, so keep it calm as some can't help themselves! If you have a factory complete gun or upper and know what specs are as far as port size, location and cartridge goes (non-308 type) feel free to chime in!
gas port size
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Zen Archery
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27" barrel, wildcat caliber w/ +2 gas. Smith started with #42, .0935, knowing it would be under gassed. I was using a super fast powder and we weren't sure if it needed a narrow or wider port to cycle properly.
I worked up to a #38, .1015 to get system to cycle properly without adjustable gas block.
Long story short most +2 systems need a minimal of #39, .0995. Measure yours and if it's .0995 and under gassed, go up to #38. If it's over gassed at .0995 get an adjustable gas block and tune it down.
As you know there is a wide relationship between barrel length, powder selection, buffer, and buffer spring. Fix what you can fix without drilling. If you have to drill yourself it's super easy.
FINALLY BE SURE GAS BLOCK PORT AND GAS TUBE PORT IS PROPER DIAMETER! That's another story for another time.
Included chart for reference.
I worked up to a #38, .1015 to get system to cycle properly without adjustable gas block.
Long story short most +2 systems need a minimal of #39, .0995. Measure yours and if it's .0995 and under gassed, go up to #38. If it's over gassed at .0995 get an adjustable gas block and tune it down.
As you know there is a wide relationship between barrel length, powder selection, buffer, and buffer spring. Fix what you can fix without drilling. If you have to drill yourself it's super easy.
FINALLY BE SURE GAS BLOCK PORT AND GAS TUBE PORT IS PROPER DIAMETER! That's another story for another time.
Included chart for reference.
I've never measured tubes as I've thought all had the same ID and wall thickness? I've been thinking about "why not have different ID tube sizes" per cartridge use? The only thing is that it lets more gas and fouling go towards the bcg. Thanks for the chart!27" barrel, wildcat caliber w/ +2 gas. Smith started with #42, .0935, knowing it would be under gassed. I was using a super fast powder and we weren't sure if it needed a narrow or wider port to cycle properly.
I worked up to a #38, .1015 to get system to cycle properly without adjustable gas block.
Long story short most +2 systems need a minimal of #39, .0995. Measure yours and if it's .0995 and under gassed, go up to #38. If it's over gassed at .0995 get an adjustable gas block and tune it down.
As you know there is a wide relationship between barrel length, powder selection, buffer, and buffer spring. Fix what you can fix without drilling. If you have to drill yourself it's super easy.
FINALLY BE SURE GAS BLOCK PORT AND GAS TUBE PORT IS PROPER DIAMETER! That's another story for another time.
Included chart for reference.
View attachment 480060
These are not bad for the price point. I use a different brand, but much more expensive, but the same class.
Precise .061-.250" Plus, Class ZZ Steel Pin Gage Set - 303-503P
Achieve precision in your measurements with the Precise .061-.250" Plus Class ZZ Steel Pin Gage Set. Crafted to exacting standards, this set provides accurate measurements for metalworking and machining tasks, ensuring quality results in your workshop.
www.penntoolco.com
Last edited:
victor3ranger
Well-Known Member
I know I am not a gun smith but I have had trouble like you are talking about on one of mine and helped several others fix theirs.
In the picture the top rifle has a gas tube in the correct location.
Other than that I check the size of the gas hole in the barrel.
My 243 was way under sized and for mine drilling the hole to.0935 fixed the problem
In the picture the top rifle has a gas tube in the correct location.
Other than that I check the size of the gas hole in the barrel.
My 243 was way under sized and for mine drilling the hole to.0935 fixed the problem
Attachments
I appreciate that, but I'm good on tube location and alignment along with gas blocks. How I get mine aligned is have the bcg under recoil pressure and insert gas tube installed on the block, then tighten. This I do without the handguard installed as so easy to inspect/see. I do have the location on the block marked before hand.
Is this considered a good range of pins for gas ports?These are not bad for the price point. I use a different brand, but much more expensive, but the same class.
Precise .061-.250" Plus, Class ZZ Steel Pin Gage Set - 303-503P
Achieve precision in your measurements with the Precise .061-.250" Plus Class ZZ Steel Pin Gage Set. Crafted to exacting standards, this set provides accurate measurements for metalworking and machining tasks, ensuring quality results in your workshop.
Good price as I'll purchase 1 for knowledge!These are not bad for the price point. I use a different brand, but much more expensive, but the same class.
Precise .061-.250" Plus, Class ZZ Steel Pin Gage Set - 303-503P
Achieve precision in your measurements with the Precise .061-.250" Plus Class ZZ Steel Pin Gage Set. Crafted to exacting standards, this set provides accurate measurements for metalworking and machining tasks, ensuring quality results in your workshop.
Another thing is that gas travels slower than bullets down a barrel (on most occasions). So next question will be...................on barrels longer than +2 (appx 14.7" not counting inside the receiver) should a 26" + length barrel meets half the distance of gas port and muzzle? Or does it matter that much? I'm seeing offerings of up to 28" on an AR barrel. I do have a factory rock river 308win w/26" barrel, but haven't checked if it's Armalite length? It might be as the bcg is longer than dpms? No issues with the gun, just questioning?
At 0.001 increment, plenty good for what you intend to use them.
victor3ranger
Well-Known Member
Yes
victor3ranger
Well-Known Member
I reconfigured mine to match a DPMS but used the Armalite gas tube witch I think are probably exactly the same.
I do know that some rifle length gas tubes are shorter than the DPMS and armalite.
I do know also that both of those companies tend to set theirs up to run a little bit on the over gassed side which to me is a good thing.
I do know that some rifle length gas tubes are shorter than the DPMS and armalite.
I do know also that both of those companies tend to set theirs up to run a little bit on the over gassed side which to me is a good thing.
DoneNOut
Well-Known Member
Zen and BamBan got you covered.
I can only add:
Wilson Combat has an intermediate length gas tube that threw me off once.
I'd rather drill the gas port very slightly bigger and harness the pressure with either a restrictive gas block like Aero, or if a suppressor is to be used, a bleed off gas block like Superlative Arms. ( If you drill a hole too big, SA bleed off comes into play as a last ditch fix)
Drilling the port slightly larger, with either gas block lets me really tune the brass ejection.
I can only add:
Wilson Combat has an intermediate length gas tube that threw me off once.
I'd rather drill the gas port very slightly bigger and harness the pressure with either a restrictive gas block like Aero, or if a suppressor is to be used, a bleed off gas block like Superlative Arms. ( If you drill a hole too big, SA bleed off comes into play as a last ditch fix)
Drilling the port slightly larger, with either gas block lets me really tune the brass ejection.
