[Botye14]

Hey guys. New to the site. I'm in the beginning stages of building a MK18 inspired pistol/sbr. Decided on an 11.5 barrel. O was deciding between a ballistic advantage and a rosco bloodline when I came accross the faxon heavy gunner barrel. The difference with the faxon is that the gas system is a midlength instead of a carbine like most 11.5 barrels. I know the claimed advantages of a mid vs carbine (less felt recoil, less gas blowback blah blah blah) but the advantage of a 11.5 over a 10.5 is dwell time. So my question is would the mid length gas system counteract the advantage in dwell time on the 11.5? And would that effect on velocity and powder burn be worth the supposed benefits of the mid vs carbine length?

 

[zant]

1."Claimed advantages" are'nt claimed,they're solid technical fact.
2.A 10.5 and an 11.5 will have the same length gas system if both are carbine length...the dwell time is meaningless between the 2...the port pressure will be higher in a 10.5...we used to use "pigtail" tubes to make F/A 10.5s run flawlessly...now we can get barrels with custom gas lengths.
3.I have an 11.5 with mid length that runs great-proper buffer/spring combo.....My 14.5 uses a rifle length gas system and I have a 14.5 with a mid length plus 1"...all shoot soft,parts last longer,etc
Carbine gas systems are used in military because they will run when you don't clean,use crappy ammo and because they just was'nt a lot of research into gas systems when originated.Parts break at lower round counts,which is fine when Uncle Sugar has tons of spare parts.
Barrel length affects velocity....

 

[Botye14]

Thanks for the reply. I was under the assumption that dwell time was the amount of time between the bullet passing the gas port and leaving the barrel, meaning the 11.5 vs 10.5 with a carbine system meant about 40% more dwell time and that this had a significant effect on velocity. Is this wrong?

 

[zant]

Thanks for the reply. I was under the assumption that dwell time was the amount of time between the bullet passing the gas port and leaving the barrel, meaning the 11.5 vs 10.5 with a carbine system meant about 40% more dwell time and that this had a significant effect on velocity. Is this wrong?

It's not that it's "wrong"-it's that "dwell time" is only one variable in a properly operating gas system.Powder has a lot to do with it....buffer weight can make a big difference....and gas port size can really throw everything out the window.You can tune your system perfectly-then load some rounds with the wrong powder and nothing works right....CAR type stocks also screw up the works because of shorter springs/light buffer weight....I prefer my 11.5-16"s with a rifle length stock and buffer-it all seems to operate flawlessly and reliably which is the most important thing.....

 

[Botye14]

It's not that it's "wrong"-it's that "dwell time" is only one variable in a properly operating gas system.Powder has a lot to do with it....buffer weight can make a big difference....and gas port size can really throw everything out the window.You can tune your system perfectly-then load some rounds with the wrong powder and nothing works right....CAR type stocks also screw up the works because of shorter springs/light buffer weight....I prefer my 11.5-16"s with a rifle length stock and buffer-it all seems to operate flawlessly and reliably which is the most important thing.....

Awesome. I'm thinking I could go with the faxon mid length 11.5 barrel and do some tuning with buffer weights and find the right ammo and I should get the results I'm looking for eventually. Like you said reliability is the most important thing. Velocity is useless if you dont hear a bang. Not looking for this thing to perform like a MK12 at 300yds but I want all I can get out of it.

 

[zant]

Faxons are a good quality barrel.yes,get a 3.8oz(M4 weight),an H1 and H2 buffers and test them with different springs and you'll hit the right combo.My son hits steel at 600yds with his MK12.....I can hit at 300,then I can't see the darn steel