AR Trend or Fad?

[Zak Smith]

Does Noveske's "switchable" gas block change the amount/velocity of the gas coming back down the gas tube? Does he market it for suppressed use?

Yes, I believe it has normal, suppressed, and "off" settings. In FA mode, the S setting reduces the ROF. Note that adjustable gas blocks on DI AR's are nothing new: they've been around for a long time (to cite two examples: the JP adj gas block and the MSTN/PRI gas block).

So what benefits are you referring too?

As a preface, all my AR's are completely reliable and will run 100% when dry. I have run 2000+ round 2-day carbine classes with them without cleaning and no problems.

However, it only takes about one magazine for all the lube to be blown out of the bcg/upper when shooting suppressed. I prefer to have the critical friction points minimally lubed. Thus, if a GP system would retain lube longer when shooting suppressed, that would be a benefit in my eyes.

Some associates and I are testing a 7.5" FA upper for dedicated suppressed use (it is DI). It is very reliable; however, it does put an extreme amount of heat into the whole upper. I would be curious to see how an analogously-set-up GP 7.5" upper would run in comparison.

-z

 

[MCMXI]

However, it only takes about one magazine for all the lube to be blown out of the bcg/upper when shooting suppressed. I prefer to have the critical friction points minimally lubed. Thus, if a GP system would retain lube longer when shooting suppressed, that would be a benefit in my eyes.

This is the US Army's position too. Last year we tested a lubricious coating on M249 internal/external parts that was developed with the objective of reducing friction on bearing surfaces to the point that no lubrication is required. As you know, oil attracts dust, dirt, carbon etc.

Based on your objective and informative articles on long-range shooting, you're one of the few individuals that I'd trust to test and compare (to DGI) the current GP AR offerings. I hope you're able to do that in the near future. I do get the impression that you're open to GP AR technology if only from a theoretical standpoint.

taliv, thanks for the explanation. Since I can't own a suppressor, I generally don't give them much thought so I found your comments very interesting.

 

[Zak Smith]

Thanks. I have not had an opportunity to wring out the best the GP systems can offer. I witnessed one or two POF uppers fail repeatedly at carbine classes in 05-06, but a POF sponsored shooter was on my squad at RM3G this year and his gun worked fine. I am not against GP systems by any means, but much of the rhetoric is bogus based on my personal experience with DI systems.

-z

 

[MCMXI]

I am not against GP systems by any means, but much of the rhetoric is bogus based on my personal experience with DI systems.

I can understand and appreciate that viewpoint which is shared by many. As more GP systems become available, more data will become available too. Those on both sides of this issue will be under pressure to prove that their systems are superior. Hopefully in the midst of the "bogus rhetoric" some real FACTS will emerge. I live in hope.

 

[RP88]

here is what bothers me.

the main gripe about the DI system is not about it being dirty from excessive firing, but...when it comes to the AR...put fine sand in there and you're screwed. Whenever I hear of someone criticizing the DI system, that is always the main point: "I was in Desert Storm, Iraq, etc. and my rifle would not function very well because of the fine sand that gets into every single nook and cranny of your gun, boots, clothes, body cavities, etc."

How exactly does a GP system help against that problem? Are the clearances looser or something?

 

[MCMXI]

How exactly does a GP system help against that problem? Are the clearances looser or something?

Here's a theory for your consideration (you may need a shovel ).

Expanding gases coming down the gas tube have the option to take the path of least resistance when faced with an obstruction. This is why Zak pointed out that with a suppressor, the "majority" of the gas comes back out through the chamber. A piston and op rod that have momentum have fewer options in terms of how they give up their energy. In the GP system, the piston and op rod obviously lose energy due to friction (and heat, minimal I know) but most of their energy is imparted to the bolt carrier when the op rod runs into it. Now the question is, is a piston and op rod carrying 100% of their usual energy more likely to move a sticky/stuck BCG compared to expanding gasses that may be able to find another way out so to speak i.e. seeking a region of lower pressure?

POF touts their GP systems as running without lubrication. In fact, the owner's manual explicitly states NOT to lubricate the piston components. The BCG have a lubricious coating too which reduces the need for lubrication since oil attracts carbon, dust and dirt.

 

[Zak Smith]

On the other hand, the bolt and bolt carrier comprise the "piston" in the DI gun which must expand when gas enters it, pushing the BC back.

In any case, you'd need about 1-2 tablespoons of sand in the bolt lugs, bbl extension lugs, and bolt/bcg interface to figure it out if you had two representative guns.

-z

 

[MCMXI]

On the other hand, the bolt and bolt carrier comprise the "piston" in the DI gun which must expand when gas enters it, pushing the BC back.

Surely a gas piston system is more effecient in terms of energy transfer since all (most) of the available energy is directed on a small face on one end of the piston. There's a fundamental difference with the DGI system since the gas expands in the gas tube (giving up heat). Then it changes direction again, and again, before it fills another substantially larger chamber giving up more heat. Finally it gets to drive the bolt forward (to unlock) and the BCG backwards. It would be interesting to see some numbers showing the energy overhead in terms of energy delivered compared to energy required for the two systems.

 

[gunnie]

..."when it comes to the AR...put fine sand in there and you're screwed."...

that is a function of the close fitting bolt carrier clearances that make the 15/16 systems so accurate. the AR 180 uses a nearly identical bolt/bbl locking system, and is much less sensitive to contamination. the 180 bolt carrier rides on twin recoil springs over guide rods, as in M3, "grease gun". only the rods are horizontal instead of vertical. as such, there is plenty of room for crud to get outta the way upon cycling.

gunnie

 

[gunnie]

..."Surely a gas piston system is more effecient in terms of energy transfer since all (most) of the available energy is directed on a small face on one end of the piston."...

the DI gas tube is a very small I.D., also. there is some mechanical advantage from the larger O.D. piston, like a larger bore on a hydraulic cylinder.

the biggest heat advantage is the unused gasses venting outside of the reciever.

gunnie

 

[mp5a3]

I know some of the stuff being discussed is probably a little off from the OP, but this is very educational. Good posts.

 

[dispatch55126]

Are the tight tolerances designed for accuracy only or is it needed to add reliability in a DI system? Could a GP system still utilize the rotating bolt pattern in the current BCG and keep accuracy while loosening the tolerances the the BCG? If this were the case, the GP may not be more reliable but the secondary benefits could be.

 

[CoRoMo]

I think it's in response to gun writers...

When Magpul developed the Masada/ACR, and FN the SCAR, they were trying to build the most versatile/adaptive weapon with serious reliability in mind. They had military contracts in mind, not a gold star from G&A or American Rifleman magazines.

 

[Zak Smith]

I would point at the bolt lug vs. bbl extension design and possibly the cam pin area as two places particularly susceptible to sand. Note that there are other contemporary rifles that have virtually the same bolt head design.

On the other hand, I haven't really ever had my AR-15 rifles malfunction due to grit, sand, fouling, etc. When I ran the JP low-mass aluminum bolt carrier in my race gun (with a low-mass buffer), the blowing dust from the ITRC did start to slow things down; but that system has a lot less reciprocating mass than a standard AR.

 

[MCMXI]

I would point at the bolt lug vs. bbl extension design and possibly the cam pin area as two places particularly susceptible to sand.

I noticed that POF is about to release a roller cam pin ... I'll be ordering some of those once they're available. I don't know if other companies offer them already but they might improve reliability in dusty, sandy conditions ... assuming that is a problem. I just spoke with a Marine last week who was back from Afghanistan/Iraq and his M4 malfunctioned while on foot patrol due to sand/dust so it does happen. Maybe it doesn't happen often, but when your life is on the line, once may be all it takes. That's not to say that a GP wouldn't have had the same problem.

I know some of the stuff being discussed is probably a little off from the OP, but this is very educational. Good posts.

I agree that there's lots of good information here but it amazes me how hostile some members are here when it comes to GP ARs. I really don't understand that attitude. It shouldn't be such a big deal. I have two GP ARs because I do like them but I'm learning as I go. Intelligent, well-thought out posts (such as Zak's and many others) go a long way to helping me gain a better understanding and appreciation of BOTH systems. In fact, many of the comments and experiences here have increased my confidence in both systems. I shoot at least one a week and sometimes twice a week so I have my own experience for reference as well, but the shared knowledge here is a big deal.

 

[gunnie]

..."Are the tight tolerances designed for accuracy only or is it needed to add reliability in a DI system?"...

not sure of eugene stoner's design parameters. can only state that the close fit reciever I.D.-to O.D. of BCG -to bolt -to bbl is the main reason(s) for the platform's superb accuracy for an autoloader.

not being a firearms designer, i can only reverse engineer the qualities that lend themselves to accuracy in existing weapons. please note the agonizing depth of tolerances on surgeon brand rifles. their actions AND bolts are entirely electro discharge machined from billet, a very slow process. also note in below spec sheet that their bolt to reciever clearances actually reduce upon closing, this is from a matching taper on bolt O.D. and reciever I.D. also note 100 thousandths of an inch tolerances, this is the stuff accuracy is made from, starting the bullet/casing as exactly concentric/square/headspaced as is practical to insert and remove after heat expansion.

http://www.surgeonrifles.com/about-us/rifle-accuracy-facts/

another way of reverse engineering accuracy traits is to study the workings of wartoys that are known for worst case scenario reliability. the COMBLOC issued AK is a good example. generous bullet to chamber clearance specs. proportionately loose headspace clearance specs, a bolt carrier that is centered by the bolt in battery and recoil spring guide rod and forward gas piston. it can be SEEN to move from side to side with force applied by hand when the dust cover is removed, bolt closed. plenty of room inside the reciever for sloughing off contaminants from BCG upon cycling. known for accuracy?

my favorite in the reliabilty VS accuracy equation is the above mentioned M3 grease gun. riding on two recoil springs, that are around 2 guide rods, the bolt makes no contact with the reciever. it doesn't even have the centering qualities of the bolt in battery like the AK. an open bolt fully doesn't require the bolt to lock to, or into the bbl. same eliminates most headspace "issues" as they usually fire before the bolt has even stopped moving forward, and a complete insertion of the round into the chamber is strictly optional. one of the least accurate subguns ever made, it was also the ~ONLY~ one the US ever fielded to pass the aberdeen arsenal proving ground "mud, blood and crud test".

gunnie

 

[MCMXI]

Talking of dust ...

http://www.defensetech.org/archives/003908.html

... results of the US Army dust test in 2007

XM8: 127 Class I, II and III stoppages.
Mk16 (5.56 SCAR): 226 Class I, II and III stoppages.
HK 416: 233 Class I, II, and III stoppages.
M4: 882 Class I, II and III stoppages.

This test is extreme without a doubt, and most likely doesn't apply to most of us, but it's still interesting nonetheless.

Here's another perspective of the sand/dust test ...

http://www.defensetech.org/archives/003932.html

... and LOTS of details here ...

http://elementsofpower.blogspot.com/2008/01/extreme-dust-test-m4-and-others.html

 

[Zak Smith]

Something wrong with scientific method here..

 

[MCMXI]

Zak, I'm still reading but there's some funny stuff here ... like the source quoted as saying:

Here ya’ go, direct from one of our U.S. military contacts—and we're quoting:

"1. Because the HK416 and M4 were the only production weapons, the ten HK416 and M4 carbines were all borrowed 'sight unseen' and the manufacturers had no idea that they were for a test. The 10 SCARs and 10 XM-8s were all 'handmade' and delivered to Aberdeen with pretty much full knowledge of a test. (The SCAR even got some addition help with 'extra' lubrication)

2. With the HK416, 117 of the 233 malfunctions were from just one of the 10 weapons."

 

[MCMXI]

I think what comes out of this test is just how good the M4/DGI system is in a sandy/dusty environment. Even if the numbers (and test methods) are valid, 882 failures out of 60,000 rounds fired (6,000 per M4) under unrealistic conditions is still less than 1.5%. These rifles were exposed to a severe dust "bath" every 120 rounds, wiped down and lubricated every 600 rounds and received a detailed cleaning every 1200 rounds!! I need to seriously reconsider my cleaning regimen.

Maybe there'll be a market for DGI conversion kits in the future ... so that people can "upgrade" their gas piston ARs to DGI!!

 

[Grantman]

Of interesting note is that the m4s in the above dust test adhered to the findings in an earlier lubrication test that recommended heavy lubrication to increase reliability. Without this heavy lubrication there were a tremendous amount of stoppages.

http://www.armytimes.com/news/2007/07/army_carbine_lubrication_070716/

So to recap, with the dust test the m4 fell well behind the competition with 882 stoppages in 60,000 rounds. The earlier lubrication test utilised the standard practise of light lubrication on the M4 yielded a whopping 9,836 stoppages in 60,000 rounds which was then reduced to 678 with heavy lubrication.

If the army had not conducted their earlier lubrication testing and applied their findings in the later dust test the results would have been a sight to see indeed.

 

[gunnie]

slide #10-the M4 had only one ruptured case for the entire test. the SCAR came in at 7, and the XM8 topped the list at 10. this suggests to me that the M4 started the test with a closer to "match grade" fitting chamber. and that the SCAR and XM8 had generous chamber clearances from the get-go.

the XM8-slide #11..."The only thing I found really interesting in this slide was that while all the weapons had pretty much the same dispersal pattern at the end of the test, the XM8 was quite a bit ‘looser’ at the start".... this suggests to me that the chamber and bolt carrier had a "looser" fit at the start of the test. the reason it finished out grouping with the rest of the competition is that it had been abused much less from the massive contamination that they had force-fed the test weapons.

..."From the XM8s dispersion performance, my ‘inner engineer’ wonders if perhaps there were some ‘tolerance management’ or other novel aspects to the XM8 design that contributed to its reliability performance?"...

note that the overall stats in slide #8 favor the XM and SCAR in that order.

gunnie

PS-but if the rumor about lube differences are true, "it don't mean squat"!!!

 

[Zak Smith]

Alternatively it could mean they are more likely to fire out of [full] battery,