anyone care to explain this to me?

[40calfragout]

so i was looking around a picture thread somewhere or another and i came upon this image. now while im not the be all end all AR knowledge god it kinda goes against what i have learned here and elsewhere about gas port size and location. i didn't think one could have what appears to have a rifle length gas system on a barrel so short cause there wouldn't be enough dwell time or back pressure to cycle the action. but the owner of the rifle stated that it shoots great in the thread. just curious as to how it was done, over sized gas port? low mass carrier (if they exist)? magic? i cant figure it out or if there is any benefit to setting up ones rifle in such a manner but it does look kinda cool. if your the owner of this rifle im kinda envious.

*this thread is not meant to stir up any debate or shit storm.

thanks for your time

[Jaysop]

With DPMS parts I wonder how long it will run :sarcastic:

[40calfragout]

With DPMS parts I wonder how long it will run :sarcastic:


ya i saw that on the lower too but it looks like the guy had a DD rail system and a noveske barrel so maybe it is only the lower that was made by "Dont Purchase My Shit" i dont know though i saw the pic was curious so i asked.

[TehLlama]

17" barrel, it'll run with a stock gas port and decent pressure ammunition, no lightweight parts gimmickry. No worse dwell time ratio than a 10.3".

That looks like a 3-gun system (lite rail tells me it's probably not rubbish grade, probably just built on a stripped DPMS lower) that is only going to be fired on one operating system - hell, it might even be in .300BLK to meet a major power factor through that system.

[40calfragout]

17" barrel, it'll run with a stock gas port and decent pressure ammunition, no lightweight parts gimmickry. No worse dwell time ratio than a 10.3".



thanks for the explanation. is there a chart editorial or something i could read that can better explain dwell time ratio and all that to me somewhere?

[rob_s]

People have been chopping 20" barrels down to 16" and fiddling with the gas port to get them to run for years. If the gun in question is a 17" it may be even easier to make it run.

I *personally* wouldn't want one as I don't really see the point (especially in the configuration posted where the end-goal appears to be to run a free-float over top of it, but it can be made to run, and they have been made to run.

Just because you can do something doesn't mean it's a good idea.

[az doug]

I know an agency that received hundreds of M-16A1s from the government on the lease program. They cut several of the 20 inch barrels down to 16 and keep the rifle gas system.

[Tweak]

Chuck Taylor wrote about this mod back into the '70's. It works better with the 0.625" sight base seats than with the 0.750" ones. Generally, it requires opening up the gas port, depending on the manufacturer.

EDIT: Hmmm, when I replied the thread only showed three replies, multiple attempts at submittal earned me "Database Error" windows each time. When it finally did submit I see a whole host of earlier responses.

[zb39]

With enough time and effort, anything will run. But is it really worth it. Only the user can decide that.

[mtdawg169]

I have a 17" Noveske with a rifle length gas system. It is set up as a precision rig, so it hasn't seen hard use. However, it runs very reliably with weak .223 centurion ammo, h buffer & standard GI recoil spring. I have no idea what the gas port size is, but it shoots extremely soft and would be a great 3-gun or competition set up. The one pictured above looks a little shorter, but it could be the extra long gas block playing tricks on my eyes.

[ST911]

I had some M16 barrels chopped by Kurt at KKF during a phase I was going through. I saw many more done by KKF and others. It was popular with LESO guns for a time, and against the rules. Kurt cut and recrowned them without ill effect, but there was little (or no?) shoulder for a new flash hider to seat on. The gas ports were opened up, unknown dim. Kurt's guns ran with good ammo and ammo that could be problematic at the time.

I recall guns done by others, and/or in odd configurations, that had weird functional thresholds. I think the chopped barrels had fewer issues overall when left on rifle lowers. I didn't keep as many notes or pics back then.

When I see the mod now, I'm left a little perplexed as to why.

[Todd.K]

We make them for a dealer, and they spec the port size. I don't know if they recommend a lightened operating system with them.

[40calfragout]

thanks for all the replies guys i really appreciate it. ive assembled many AR's over the past few years but im looking to build a few. not before i do a lot of research, am reasonably sure i know what im doing and back in the states. cant do anything over here for obvious reasons even though our 45B is quite literally developmentally disabled.

[MudPuppy]

I thought DPMS and Bushmaster were owned by the same company, so should be of equal quality.

They also own Chrysler and GMAC

[Iraqgunz]

It wasn't always the case. Yes they are both of the same equally crappy quality.


I thought DPMS and Bushmaster were owned by the same company, so should be of equal quality.

They also own Chrysler and GMAC

[Unicorn]

I thought DPMS and Bushmaster were owned by the same company, so should be of equal quality.

They also own Chrysler and GMAC

DPMS is large enough that they still run themselves. The Freedom Group reps don't handle DPMS accounts, those are still solely done by DPMS itself.

[wetidlerjr]

I thought DPMS and Bushmaster were owned by the same company, so should be of equal quality.
They also own Chrysler and GMAC

They don't own Chrysler. :cool:


DPMS is large enough that they still run themselves. The Freedom Group reps don't handle DPMS accounts, those are still solely done by DPMS itself.

That makes it all better. :rolleyes:

[MudPuppy]

Cerberus Owns Chrysler, GMAC, Bushmaster, and DPMS

http://en.wikipedia.org/wiki/Cerberus_Capital_Management

[wetidlerjr]

Cerberus Owns Chrysler, GMAC, Bushmaster, and DPMS
http://en.wikipedia.org/wiki/Cerberus_Capital_Management

This is more OT but they don't anymore. It's FIAT controlling Chrysler, now.
http://blogs.wsj.com/autoshow/2009/03/30/718/
Read under the "Chrysler" heading on the page you linked above.
That's the end of the OT info from me. You need to do some reading. :cool: