Interesting article on barrel length as it applies to velocity, pressure and sound

[24Pink14Stink]

Found this gem this am that talks about the impacts of the trend toward a shorter barrel on the M4/AR15 and thought I'd share.

http://www.sadefensejournal.com/wp/?p=1093

[thughes]

Good stuff, thanks for posting.

[Meketrefe]

Thanks for sharing. One more study that clearly demonstrates what we already knew.

A) 16 carbines with carbine porting is really a bad idea and should have never existed. A mid length porting is a better way to go both w. and w.o suppressor. It would have more sense
to redesign the granade laucher around the MBR and avoid the carbine porting and those stupid M4 profile cuts.

B) 14.5 inch barrels can be tuned to work but they loose too much energy and also become even more problematic when suppression is needed defeating the original purpose
of getting things a lot shorter.

C) Perhaps an ideal compromise would be 18 inches for the cartridge but that might be too long in the AR for many uses but IMO it would be a better rifle. That is why the Israelis, Chinese and other armys went bullpup and kept their 18" barrels for maximum performance.

D) Anything shorter than that is a stupid idea. One can tune with special purpose ammo with lighter bullets and much faster powders but still a waste.

E) The 5.56 is an amazing round but the army could have easily adopted the 6x45 that is a lot more efficient and powerful out of the same case and w/o the need for new magazines, bolts or anything else. Only a simple barrel change and then the new ammo.

BTW another thing that should have never existed are the 1/2x28 threads on 5.56 barrels. They are just to thin and barrels loose accuracy faster over time due to crown swelling. Another senseless design courtesy of the thinking heads in the armies.

[Cory]

Question Mek, My AR has a 16.1 inch barrel with a midlength gas system. When I bought it, my understanding was I am getting only slightly less velocity than the full length M16, and only slightly more length than my M4 from the service but with increased reliability because it doesn't have the carbine length gas system.

Is that understanding far off? I can shoot it pretty well, and can field strip plus BCG blindfolded... but I have never built one myself and am not familiar with all of the intricate details of the rifle.

[Meketrefe]

Question Mek, My AR has a 16.1 inch barrel with a midlength gas system. When I bought it, my understanding was I am getting only slightly less velocity than the full length M16, and only slightly more length than my M4 from the service but with increased reliability because it doesn't have the carbine length gas system.

Is that understanding far off? I can shoot it pretty well, and can field strip plus BCG blindfolded... but I have never built one myself and am not familiar with all of the intricate details of the rifle.

I think you will get virtually the same speeds as the M4 but one thing is you will have is a potentially more reliable function by design w/o so many potential fluctuations in back pressure and less risk for overgassing, early extraction and such. As I said the carbine system porting should have never existed. It didn't have to exist but the Army got involved. lol. .. But if one has one then it can be improved by a piston system or by using and adjustable gas block assuming the initial porting is well done that is not the case with many budget / kits builds. There is a huge difference in pressure between lets say a PMC bronce round and a M855 lake city round. And a better porting design like the mid length will give you more versatility and reliability when dealing with the spreads in ammo depending on manufacturers and actual loads.

[Cory]

You used a lot of big words there... Virtually... Potentially... Assuming...Reliability... Fluctuations... Porting... Depending...

hahaha, Good to know that the midlength was a good choice. And from BCM I'm going to assume that the porting is done properly because everything I do understand has been top notch quality.

[Meketrefe]

You see I am cautious because many barrel makers screw up the porting in mid lenght too but if you have a good quality one vs el cheapo parts kit then you should be fine and it will run better and cooler than a carbine one. The speed will br the same. The rifling type, the twist, the material and the finishing has more impact on speed changes in barrels of the same length than mid vs carbine porting with both well tuned.

[Meketrefe]

In fact if one was to run hp loads all the time the best option would be a rigle length on a carbine barrel like it is for r he 18" one. This could be tuned to run a lot smoother and cooler. But mid length seems to be a great compromise for 16". Never buy carbine ported barrels and alsi avoid 1/2 inch theads specially in barrels intended for accuracy. There is no point in getting something that has to run at higher pressures and hotter and harder on everything only to later having to find meassures to slow it down and reduce pressure. It is like having a ferrari to go nuts from one red light to another only to accelerate and then burn brakes at the next light when the prius next to you will only use a small fraction of that energy and meet you at the red light and arrive home at the same time. In other words, avoid a total waste and run smoother and smarter.

[Cory]

I'm fairly certain that you have forgotten more about the weapon I carried downrange then I will ever know. You're awesome. Thanks Mek. Meke? Meket? lol

[24Pink14Stink]

I'm fairly certain that you have forgotten more about the weapon I carried downrange then I will ever know. You're awesome. Thanks Mek. Meke? Meket? lol

I think we should just call him the English translation, but that wouldn't be very nice, nor would it be accurate.

[Meketrefe]

I can explain it for you in four different languages if you like. no problem. LOL

[Meketrefe]

I'm fairly certain that you have forgotten more about the weapon I carried downrange then I will ever know. You're awesome. Thanks Mek. Meke? Meket? lol

Thanks but there are many smarter and even faster than I will ever be. I do watch things closely though and when it comes to some platforms like the AR I got to know them pretty well.
An AR can run much better with softer springs and less gas. even a carbine spring in a rifle tube with a rifle buffer will run fine but then the rifle must be tuned and one needs
to make sure the thing runs smooth as butter. One simple trick is to precharge the carrier with a bit of taper at the end of the buffer (small cut on a lathe). This allows the upper to open and close no problems but will also avoid the jump of the carrier and hitting the buffer and spring that creates a momentum reaction. So when you stick the buffer with a minute amount of pressure to the carrier even a lighter buffer and spring then the feeling of the action is a lot smoother. But this will not make a difference if there are huge frictions with stiff hammers and rough finished carriers or friction on the magazine lips etc...I have seen broken bolts and extractors due to excessive pressure and early extraction. All with carbine porting, never with mids or rifle.
So once you review all these points the rifle can run a lot slower, smoother and better. I do this with my match systems where I use an adjustable gas block to give the optimal
amount of gas. You can actually tell and this paired with a good smooth trigger also contributes to accuracy if you are going with a match / precision setup.
Everything has an explanation in the end.

[24Pink14Stink]

Softer springs where? I just read an article yesterday suggesting stiffer buffer spring and heavier buffer and stiffer extractor spring. I think the article was a couple years old. Lemme check...

[24Pink14Stink]

http://www.defensereview.com/m4m4a1-...yre-our-fault/

http://www.defensereview.com/the-big...m4-unreliable/

[Meketrefe]

They use harder springs to overcome pressure. Those carbines should have never existed in the first place. The armorers do preventive maintrnance all the time and true soldiers know very well how their firearms work so not sure where the writer is getting this info from, maybe the army cooks and engineers.