11.5 midlength barrel pros and cons

[The Triple strand]

So in the quest to build an incredibly flat SBR I have been toying with the idea of using a midlength gas system on an 11.5 barrel. The internet is completely on fire when this gets google searched. Any of you guys smarter than me explain why or why not it’s a good idea. Rifle will be unsupressed, have an adjustable gas block and a jp silent capture system

 

[8RoundPing]

I just assembled an upper with 11.5" DD barrel with carbine length gas. I thought for sure that it would be overgassed so I planned on using a superlative arms adjustable block. Those were backorderd every place I looked so I put on a standard low pro to get by for awhile. Only 100 so rounds through it now but it seems to be just right without the adjustable.

 

[Anderhammer52]

I was in the same boat as you not to long ago. From the research I did, people were generally advising against it due to the decrease in dwell time. In a recent SOLGW Instagram post, some one brought up a similar question with a 12.5 midlength. The response from SOLGW was that it was almost as bad of an idea as a 16in rifle length due to dwell time. Then stating that for a dedicated suppressed set up it would be "fine" because the can would "force" the gun to work. For my own anecdotal experience, I purchased a larue ultimate upper kit in 12in, they don't list there specs for the barrel on the website, but I purchased a 12in barrel it appears to be a carbine length and it shoots just as soft as my 14.5 pws midlength. 500 rounds later no hiccups yet but I will let you know if any problems do arise.

 

[PartyHardyMarty]

A shorter dwell time means more pressure required to cycle the rifle, and therefore more violent? Are dissipators more violent then? I thought their whole point was to be slower cycling?

 

[The Monk]

If unsuppressed its a bad idea. You have to make the gas port very large to get it to run and even with a large gas port your dwell time is less than that of a 10.3" (MK18). On a 12.5 its viable but you would better off restricting gas in a carbine configuration like Hodge is doing. There are better ways to achieve what you are after that are reliable. A standard 11.5 with a adjustable gas block and a A5 buffer system with be very soft shooting. You may also want to look into Sionics Reduced gas port barrels.

 

[Sunshine_Shooter]

A shorter dwell time means more pressure required to cycle the rifle, and therefore more violent? Are dissipators more violent then? I thought their whole point was to be slower cycling?

Not quite. The low dwell time means there is very little time for the gas to act upon the carrier. So little that (unsuppressed) it might not even get the chance to cycle it properly. Think 'not violent enough'. You need to upsize the gas port or add a suppressor or something else to make it 'violent enough' to even cycle the action.