hi, I have a Noveske diplomat  - 7.5" barreled pistol, its great ,accurate, it runs great etc....but after about 250 rounds or so the thing gets filled with carbon muck that interferes with the action and will cause a failure of some sort. What typically happens is there will be a very great amount of drag between the bolt carrier and hammer after firing 250 rounds as opposed to when clean.

studying this I have learned that tapping the gas @ about 4.5" from the chamber results in   pressures that are about double that of a midlength gas system which would tap gas at about 9.8".

this has become clearer after shooting about 250 rounds out of a midlength gas system upper with a 16" barrel the action remained smooth and about a third as dirty as the Diplomat would have been.

Now there are different ways to address this :

1.fail zero bolt carrier / hammer combo to reduce the drag or a similar subtitute { although fz seems to be the best option in this area there are alternatives like young manf chrome nm bcg / jp enterprises qpq bcg etc}

2. more sophisticated lubricants than clp like - mobil 1 synthetic 20w50 v twin motor oil?
lithium grease? i have no real experience with any of thwese only what i've read so anybody who knows please share.

there may  also be other ways to reduce the effects of the excessive fouling  that results from tappping the gas so early ...like lube on the go ? anybody


If the aforementioned measures cannot consistently  increase the  reliability envelope of the pistol then alternatives may include:

1. a piston system -
been looking at them ...LWRC seems the most sophisticated to me / but the gas block takes impact and in the end it may be just trading one set of problems for another . also the DI variables are known to a greater extent than the new piston systems which are still evolving . That being said I still believe that LWRC definitely will realize the best piston if they have not already.

2.a longer DI gas system-
there are many 10.5 + barreled uppers with carbine length gas systems which still have alot of pressure but would be a substantial improvement over the shorter pistol systems as the carbine systems taps at 7.5"- this seems to be the safest bet while including fail zero components and the right lube like mobil 1. a midlength setup would be ideal ...tapping gas at 9.8" but I dont know of any pistol length uppers using a midlength system...all the midlengths are barrelled 14.5 and up due to dwell time issues ...but I am not sure that a 12.5" upper with a mid length gas system is not workable.
if it is it would answer the problem very nicely with a reliable pistol.

  http://www.ar15barrels.com/prod/operation.shtml

heres some data taken from the web page cited above:

pressure at the 4.7" gas port of a pistol= 48,311

pressure at the 7.8" carbine gas port = 32,900

pressure at the 9.8" midlength gas port =  26,507







So these are my thoughts I hope to hear what you guys think .........
thanks

Run it wetter.

Piggy back gas tube will give you a longer tube but everything I read says they are bullshit.

I hear that hi temp lithium grease will work better than clp ...I must try it.

the problem is tapping the gas too close to the chamber, to fix that the gas needs to be tapped further down the barrel ...the longer tube is irrelevant it's about where you take the gas from that regulates how high the pressure is ...and how hot/dirty etc  the action will get

So have you contacted Noveske about your problem?  Surely they would like to hear about one of their products not working.

Please understand there is absolutely NOTHING wrong with the Noveske Diplomat it is top notch tuned perfectly and really top of the line !

my musings are solely upon the nature of a pistol length gas system period.

the only way the Noveske product may be improved would be by using fail Zero coating which is a new process relatively.

thankfully I can easily upgrade with a FZ bcg and use Mobil 1 oil and see how it goes when the round count gets kinda high.

if I had a midlength gas system I wouldnt notice this problem- which is double pressure at the gas port  of the pistol as compared to the midlength system which means double the heat and fouling. this is the nature of the DI system and a short barrel ....Noveske  is not responsible for the laws of physics.

Yep tough to beat physics.  And as we seem to always hear that you shouldn't go below 10.5 for sakes of reliability yada yada and mine is relatively problem free being at that length.  But plenty of internet shooters seem to seemingly reliable shortys too.  Still anything can/will hic-up as there are so many things going on at once that any combination of factors will Murphy law you.

DO you have a 7.5"  - how many rounds have you shot at one range session no cleaning/lube?

and I gotta be honest the range session I am talking about I was using an rra pistol tube which did not have the hole in the back ... I have since opened the hole but havent had time for another 250 round range session.

I will soon post a range report after I use a fz bcg and mobil1....

Mine is a 10.5 WOA, with a RRA fluted tube.  The only hic-up is using crappy Wolf it on occasion will not lock back after the last round.  But I also run with a slightly heavy buffer which may be part to blame.  Short of that particular malfunction it runs and runs with decent ammo and is flipping accurate to boot.  Mine RRA tube has a hole in the back, but it may not go all the way through, i'd have to check.

What is the hole in the back of the tube for?

Sorry I was replying to the piggyback answer and forgot to hit "quote".   I was wondering about the gas tube that coils around the barrel, if the tube is the length of say a middy on a carbine just coiled around and the tube is the same length from gas port to end of the barrel, then why would it not act like that particular kind?  The gas still has to travel the same length?

Nice ...thats what I want now a 10.5!
the carbine gas system has 2/3 the pressure @ the gas port compared to my 7.5". and it will have better terminal ballistics due to higher velocity.

RRA makes a great ret but in the back the hole does not go clear through it is only countersunk.

it really makes a difference letting it breath back there. it's also necessary if it gets submerged to clear water out.

a pigtail gas tube does nothing to change the facts concerning the pressure at the gas port which is solely determined by how close the gas port is to the chamber.

go here:  www.ar15barrels.com/prod/operation.shtml  

tword the bottom of the  page he explains about pressure and gas block placement

I don't see how you can change that distance on a 7.5". I would think you have to have a couple inches of barrel left after the gas port or the timing would be thrown completely off.

I know I need a 10.5 cqb upper

ok this is what I think I am going to do .

crown a noveske afghan barrel at 14" - it has a midlegth gas system so it will run cooler and cleaner = reliability after many rounds without cleaning. I'll have at least 4" of barrel in front of the gas port so dwell time should be fine.


a 10.5 cqb needs the kx3 which brings it to 13.5" with a carbine length gas system.

a 12.5 and a carbine gas system with a muzzle brake would be 14" with a carbine gas system
...now  I could probably crown this at 12" and it would work but... for 2 more inches I can get the midlength gas system and more velocity.

I am thinking a fail zero upper and bolt carrier group  / larue 13" handguard
+ leupold prismatic dcd

brownells sells the muzzle crown chamfer tool  and probably a guide to keep the cut straight ...I might buy a dremel any advice?

So what say you?

I havent seen anybody go this way but my research has led to this as an answer to the need for a very high reliability and accurate  pistol with better ballistics due to the higher velocity.

I know it'll be long but really not that much - the 10.5 is only a half inch shorter .
for the 14" i am getting cooler / cleaner operation and significantly  higher velocity.