11.5 / 10.5 no difference really, my 11.5 is way more accurate than the 7s I shot against. I like the size. Runs well and no issues. Thousands of rounds. None suppressed. Have fun.

 

You just going to slide in here and casually drop a photo with a uspt in 40 like it’s nothing? Nicely staged sir. I’d love to see that in person

 

There are a lot of places with scientific data on how the 11.5 is better but I haven’t noticed any practical difference between my 10.5 Triarc or 11.5 Geissele. If it’s not the only AR, I’d probably go 10.5 to take full advantage of the compact length.

 

I built the 10.5", while I saw the data that the 11" was faster and more accurate, I still did the 10.5. It is a loud sucker when It's not suppressed. I did shoot a 7" once, an ear buster but great for a truck gun.

 

I built the 10.5", while I saw the data that the 11" was faster and more accurate, I still did the 10.5. It is a loud sucker when It's not suppressed. I did shoot a 7" once, an ear buster but great for a truck gun.

Velocity is tied to barrel length yes, accuracy is not so much.

Anything under 10.3" barrel length is pretty useless in 5.56, you're literally just making a flashbang that has a projectile. You have a rapid drop off in velocity under 10".

 

11.5 with K can

But if you want the best of all worlds… 12.5 mid with K can

 

All 10.5” no regrets.

 

My 11.5” with carbine gas is very smooth, but loud AF.

 

I think the answer lies within the purpose. I think my 10.5 Barrett is a great gun out to 200 yards with a dot or 300 yards with a LPVO and it does what I ask of it. It never malfunctions and carries well. Saying that if I had it to do all over again I may push it a little longer just to stretch it's legs out and feel a little better about long term reliability (like 10,000 rounds or so). With the Barrett compensator mine is obnoxiously loud!

 

Love my DD MK18’s (10.3”) with RC2’s. I’d like to try an 11.5 but every time I have one in my cart I ask myself what I’ll gain. From my research, not a lot, or at least not noticeable to me. That being said I still want a DD RISIII 11.5.

 

I probably should have just pulled the trigger on the MK18 upper that was for sale in the classifieds. But, half the fun for me is picking up the parts and building myself. I haven’t decided on a rail yet but the two likely candidates are the RIS II and MK4 Fed

 

A few considerations here: 11.5 versus 10.5 has 40% more dwell time on a carbine length gas system.

This translates to an increase in reliability and less issues as a suppressor host.

Lower wear on parts is an added bonus.

All that said with proper maintenance and care, short of a very high firing schedule, the likelihood of encountering wear issues is pretty low between a 10.5 and 11.5

 

A few considerations here: 11.5 versus 10.5 has 40% more dwell time on a carbine length gas system.

This translates to an increase in reliability and less issues as a suppressor host.

Lower wear on parts is an added bonus.

All that said with proper maintenance and care, short of a very high firing schedule, the likelihood of encountering wear issues is pretty low between a 10.5 and 11.5

The more dwell time the higher the gas flow/pressure. The less dwell time the softer/less pressure. So it’s actually the opposite of what you said in terms of parts wear.

As far reliability, the MK18 with .070” gas port is the most tested/proven short barrel length of modern time. From Crane’s research and development to being fielded in various climates and environments in GWOT, there have been no known widespread failures or reliability issues.

All things being equal, a properly ported 10.3/10.5 will be less gassy with a can, smoother/softer shooting, and have less parts wear. The only foreseeable issue is you want to shoot weak .223/steel cased crap, then yes…go 11.5.

The 40% more dwell time trope is often repeated and because it has a number and a percent , is often assumed to be better. But clearly not everyone has an accurate understanding of what that means or its implications.

 

You get much better velocity and dwell time going with the 11.5”.

 

Define much better. How many fps?

Have you experienced reliability issues related to dwell time with your 10.3 vs 11.5” guns?

 

Deleted

 

I went with a BCM 11.5 based solely on the theoretical benefits. I’m not sophisticated enough to actually tell if there is any difference.

 

Initially My SBR had an 11.5" barrel. By the time I received my suppressor I had decided I wanted to build a similar SBR to the Air Force GAU-5A, which has a 12.5" barrel. Since mine was going to be suppressed and always suppressed, I chose a 10.5". The reasons were that suppressed adds a little bit of back pressure and dwell time and my goal was for it to fit into a 15" laptop case.

When configured with the 11.5" it ran flawlessly, with any good ammo I put in it. With or without a suppressor.

When configured with the 10.5" it runs flawlessly with the suppressor. Without its a little picky about the ammo. It will short stroke sometimes. I generally don't use it without the suppressor so I'm not going to futz around with springs or weights. Which might help.

 

There's always bullpup

For when every inch matters

 

11.5" is better than 10.5"

and 12.5" beats them both by a good margin

nothing wrong with a 10.3-10.5"

you do that if you absolutely want the smallest 5.56 while still getting decent fps, 11.5" goes up quite a bit and same with 12.5"

 

My goal is to set it up similar to the 14.5 just shorter so they would be interchangeable when training.

Can we get more clarification on “training”?
The tool needs to fit the job, and in this case we don’t know what the job is. All the comments are correct, but nobody really knows what the mission specs are.
Backpack gun? Get a 7” with side folder
CQB? Get the 10”-11”
CQB then prone 300 yards? Get the 11”-12”

 

none of the above. 11.75 on a mid length gas system.

 

12.5", when quarter inches count.

 

I’m sure professor zero will be in shortly to school us.

Don’t get mad at me because you were echoing dwell time percentage when in reality it only equates to a 4% difference in chamber pressure. Even though chamber pressure is (marginally higher), the 10.3 pressure drops sooner as there is less dwell time.

 

Don’t get mad at me because you were parroting some marketing claim about longer dwell time percentage when in reality equates to a 4% difference in chamber pressure. Even though chamber pressure is (marginally higher), the 10.3 pressure drops sooner as there is less dwell time.

Dropping knowledge is all good and well. The “aherm well acktually” is another story.

You read the brochure on 10.3, good job.

 

Dropping knowledge is all good and well. The “aherm well acktually” is another story.

No, it just means your thin skinned and/or take offense too easily when I pointed something out.

You read the brochure on 10.3, good job.

Yep. I sure did. Here is the NSWC Crane report/findings for M8551A1 and the MK18 so you anyone can read it as well:

https://static1.squarespace.com/static/597679b68419c2bc1f2f8ef1/t/598390fdb8a79b354102d3fb/1501794563797/CRANE+Test+Data+Mk18.pdf

Interesting to note that even with M855A1 (10% higher pressure) avg. bolt life was almost 10k rounds…compared to 12k rounds in M4A1 with lower pressure M855.

 

I put together a 12.5 with a rainier match barrel and an a5 buffer, and it's smooth (oh, and accurate). I had a hard time finding a stainless match barrel in 11.5 or 12.5, but that one is doing nicely.

 

FCD has a newer offering for that.

 

Interesting. Here's a post on another site by BCM:

BCM pioneered and pushed the 11.5, so to be fair they’re hardly an objective source. They literally came out with the “40% dwell time” (not to mention it’s really only like 33%) nor pointing out its only a 4% reduction in chamber pressure.

I'm not doubting the Mk18s reliability. However, it does have trade offs. Mk18s typically have shown higher wear / parts breakages on bolts as compared to the standard M4 (14.5) platform. Of course we're talking north of 10k rounds, but it matters if you're running high round count and intend on keeping it and replacing parts during its lifecycle.

It’s not that much of a higher rate though.
here it is with M855A1

compared to m4/14.5 with M855 (this is about 55k psi compared to the A1 in mk18 tests that are 61k psi.

Also, on the suppressor front, since it abuses cans more due to the short barrel, Surefire came out with an improved design for the shorter barrels and made the blast baffle thicker due to the abuse, also increased bore size for less backpressure:

SOCOM556-SB2

no-reply@surefire.com

www.surefire.com

Maybe but, was that due to the Mk18 (which afaik is still using RC2) or because they was it a cash grab? Regardless, I’m not saying a 10.3” is infallible, I’m saying there is virtually no real difference between it and the 11.5” based on dwell time (contrary to the “MuH 4o%” claims), and the argument can be made that the longer exposure to pressure before drop off in 11.5 could be detrimental.

 

BCM pioneered and pushed the 11.5, so to be fair they’re hardly an objective source. They literally came out with the “40% dwell time” (not to mention it’s really only like 33%) nor pointing out its only a 4% reduction in chamber pressure.


It’s not that much of a higher rate though.
here it is with M855A1
View attachment 1531514

compared to m4/14.5 with M855 (this is about 55k psi compared to the A1 in mk18 tests that are 61k psi.

View attachment 1531515




Maybe but, was that due to the Mk18 (which afaik is still using RC2) or because they was it a cash grab? Regardless, I’m not saying a 10.3” is infallible, I’m saying there is virtually no real difference between it and the 11.5” based on dwell time (contrary to the “MuH 4o%” claims), and the argument can be made that the longer exposure to pressure before drop off in 11.5 could be detrimental.

It's a consideration is all I'm saying. Plus with those numbers its hardly an apples to apples discussion. Most M4s in circulation in the US Army during the GWOT were M4 Carbines (3 round burst) Mk18s were built on M4A1 lowers (full auto), the M4A1 program to replace Carbine models with A1s didn't come into play until towards the end of GWOT.

Also consider role and placement. Mk18s would've been issued out to more of the specialized or direct action types of units, whereas the M4 has been the US Army standard issue, though as above historically in the M4 Carbine version. There would be more data available in real world use on the M4 but it would certainly be a different use case. Parts wear and breakages aside, with the AR platform its really mission dependent. The common thinking with a vast majority of people who shoot these rifles a lot is the trade off for the Mk18 isn't worth it and the trend has been more toward a longer barrel as its more forgiving.

The US Military is still using the RC2 AFAIK, yes. However, I also wouldn't look to them to procure a variant just to throw on one select rifle that wasn't seeing widespread use. I'm sure in some of the Special Operations units they may have procured some SB2s as well, but its hard to really know. However, my point with it is, they put in the work to create a modified model for usage on rifles that were in the 10" or under range which says something. It's also just not an over bored can to be a faux flow through, the blast baffle at a minimum has been beefed up. Speaking on that front, even if the US military was popping RC2s running them hard on Mk18s, it wouldn't matter because they don't have to pay tax or wait

 

Yeah there is a 14.5 11.5 URGI being fielded now, I think the 14.5 is middy gas but I don't know the specs on the gas system on the 11.5. I do know there is another 11.5-11.75" mid gas URGI that is in R&D/T&D right now.

I had the 10.3 DD MK18 my last spot and they ran well, but that wasn't a DOD position.

I think all development is being geared towards the use with cans, since cans are required in shoot houses now (at least for SF). They found out that the repetitive percussion of muzzle blasts inside the house was causing the same effects as breacher's syndrome over the long haul.

 

I don’t believe they can squeeze anything other than carbine gas in the 11.5.

Some Crane info on testing involving the USASOC 14.5 mid gas rifle is here though: NSWC-Crane Mid-Length Gas System Testing Shows Increased Performance & Service Life For M4 Carbines | Soldier Systems Daily

The link above seems to dive into testing with cans more than previous testing.

 

I have an Anderson build that will shoot the tits off a lark at 300 if I do my part. Would put it up against anything. ☺

 

I have an Anderson build that will shoot the tits off a lark at 300 if I do my part. Would put it up against anything. ☺

 

Can we say that the 10.5 is one inch louder than an 11.5 ??

 

is one suppressed and one not? 🙃

 

My guy, you want to call meetings and parse out stuff that as I stated in my original post really don’t make any significant changes. I’ll say it again, 10.5 vs 11.5 really no big difference.

Re data: the testing occurred in 2013, they signed off in 2015. Check the front page of your study.

10.3 runs fine.

11.5 runs fine.

end of story.

move on with your life.