Building an AR is harder then I thoguht... Help with 300m build please?

I'll throw out an appetizer before Kevin answers. The 16" barrel produces 94%(I believe, its in the 90% range) of the velocity as achieved from a 20" barrel. Near identical ballistics with 4 fewer inches is always a plus for both length and weight. The Mid-length gas system significantly reduces the pressure in the system allowing for a more consistent impulse and one that more closely mimics the rifle length gas system as the AR platform was designed around.

TDC
 
Not exactly - but depending upon round the 1.5" increase from 14.5" to 16" can equate the same increases from 16" to 20"

M855C77.jpg


RUAGGP-90.jpg
 
So fella's,
250-300 fps about from 14.5 to 20 and about 100 from 14.5 to 16. Hmmm...Is that substancial? I guess beyond a certain range eh? So within, say 300 or so metres probably insignificant but 300-500m or so I guess it might make more of a difference? So by making the M4, is it safe to assume that the typical engagement scenario's in mind were within about 300m? Is M855 ammo 55gr.? Is the Ruag 63gr? Just curious, thanks Kevin for any further insight.
 
Most engagements(according to stats from several military's) indicate the average engagement range is around 100 yards and almost never exceed 300. Think about Iraq. Mostly urban work which doesn't lend itself well to long range engagements. Shorter and lighter rifles excel over the alternatives, but come at a cost during greater distance engagements.

TDC
 
Thanks for the number's info ^ kevinB/TDC. So recommended is the 16in. for a "general purpose do it all" type of AR. Anything shorter (ie 14.5 and <) is more and more geared to CQB? Right? I guess I can't really go wrong eh?!! Grrrr...still can't decide, and I better real soon or I may not get the chance in the future. Cheers.
 
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The length you choose is really your choice. For punching paper it isn't really an issue. The benefits of any length are really dependent on your intended use. Shorter barrels and their ease of handling for CQB really isn't an advantage for the average shooter. Weight savings and a particular "look" would be the greatest advantage to a short barrel. The longer barrel uppers naturally produce higher velocities but come at the addition of length and weight. Personally I would go for the 16" mid-length. I feel it offers the best of both worlds. Great ballistics and reduced length while offering a lower pressure more consistent operation. I sold my 14.5 and won't buy anything shorter than 16' with a mid-length gas system. The difference in recoil or "feel" between a carbine gas system and the mid-length is noticeable.

When I first got my mid-length(my second one, I sold the first as it was a heavy barrel contour) I was on my way to a carbine class. I fired 200 rounds to establish my zeros then proceeded to fire another 1000 rounds over the next two days. I never had one failure and still haven't after close to 2000 rounds. Whether or not that has to do with the gas system, the make, or just plain luck I can't say for sure. I can tell you I had issues with my 14.5" carbine top.

TDC
 
here are some more stats

m855

Velocity

20" 3100
16" 2989
14.5" 2970
11.5" 2738

Fragmentation

20" 125-190
16" 90-155
14.5" 85-150
11.5" 10-75

m193

Velocity

20" 3259
16" 3132
14.5" 3064
11.5" 2872

Fragmentation

20" 135-190
16" 105-160
14.5" 90-145
11.5" 45-95

Fragmentation happen's in milspec 5.56mm between velocities of 2700fps and 2500fps

pulled from somewhere on the internet so I wouldn't bet on these stats being 100%
 
Is the M4 done?

I want to do the 10.5 - versus 10.4 Hk416
11.5, 12.5, 14.5 (and 14.5 Hk416) 16" and 16" middy, 18" SPR, and 20"

I have limited amounts of M193, M855, GP90, and Mk262
 
Well it was cold - so we did only RUAG GP90 ammo - I have some real questions about the QC of this lot - as we had some RTFO velocities

8" Noveske 2370fps
10.4 Hk416 2550fps
11.5 Noveske 2688fps
14.5 Hk416 2820fps
16" Colt 2881 fps
18" Noveske 2952fps

All 1:7 barrels.

I am hoping kako, RobAk, Reaper and myself can find a noce day in the next few weeks - and get some M193 and M855 done as well as a few more barrels and lengths into the mix.
 
The swiss spec called for something under 3000 fps out of a SG550. This is not fast ammo by design. THe number you guys got look about right.
 
I chono'd some a couple of years back out of a Colt 20" 1:7"
2980 - 2971 - 2998 - 2998 - 3016 - 3020 - 2999 - 3023 - 3001 - 3018 fp/s
 
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