I know the whole mid vs carbine thing has been beaten to death but I was wondering if anyone has ever used an accelerometer to measure the actual difference between the two gas systems.  I have never really wrapped my head around how there can be that big of a difference between these two gas systems if they just open up the gas port in the middies to adjust for the extra length.  I have owned both and really have never been able to tell that much of a difference so i just was wondering if anyone had any hard data.  Thanks

I think you'll be waiting a long time for a real answer with data.

I think it is basically rubbish.

Take a midlength and carbine of EXACTLY the same weight, configuration, stock material and shoot them with the same ammo and I very much doubt anyone will be able to tell the difference.

I can't tell the difference

Can a person tell the difference? Debatable , it also depends on whether both systems are properly ported... but numbers dont lie. There is a big difference in actual pressure not to mention less dwell for mid length gas in equal length barrels.

Shot my 14.5 carbine with a st-t2 buffer next to a 16" mid length Sunday.

Can't tell a difference.

I've owned both and have decided that on a 14.5 I want a carbine gas system and on a 16" a mid length.

Same for me in regards to your final sentence.

I can't say for midlength, but I've shot my 6920 next to my SR-15 (longer than mid) and it's a huge difference.

SR-15 is kinda different... i had one of those and it was definitely different.  Rifle lengths feel noticeably smoother to me as well.

Brutus, thanks for that chart.... kinda interested in recoil impulse.  Chamber pressure doesn't really play a role in recoil from what i understand but i really want to see the acceleration of the impulse.  Not sure that the data exists tho.  Dwell time can be altered with buffers and springs.

The middy had a car buffer.

My mid length with a rifle buffer was noticeably smoother.  I miss it.

I cant tell the difference

I have a PSA 16" mid length and a PSA 16" carbine lengths. Both have te same stocks, buffers and handguarda and have similar optics.

Can't tell one but of difference in recoil, and they chrono the same too.

Indeed

My issue Colt M4A1 has more noticeable recoil than my 16" midlength.... but my 16' middie has an adjustable gas block , semi-auto LMT E-BCG and a Vltor A-5 buffer system.

my 16" carbine with a extra strong buffer spring and a ST-T2 shoots same as my 14.5 middy with a car buffer swap the lowers huge difference the carbine with the car buffer and mil spec spring has more felt recoil and more muzzle flip the 14.5 with the ST-T2 shoots like a bb gun

It's not like comparing 375 H&H and 416 Rigby.  It's a wimpy 223/5.56.

I have both systems in 16" barrel lengths.  I can't tell much of a difference between the two.
Start swapping lowers and optics and a direct comparison is pointless.

YMMV

This is my opinion, worth about what you pay for it.
When I shoot carbines/middys set up the same, the recoil difference is very little- it is there.
For 200-300 rounds the difference matters little, after 400-500+ in a day- I notice the difference more. A middy is slightly softer to me.

I have, and use both, the difference is small in recoil. The question of longevity leans toward the middy, I find reliability equal (in my weapons).
A good gun can be either. There is little reason to start with a carbine gas 14-16"rifle if you have a choice at the get-go.

I still love my carbines in 14.5" or shorter, but I like'em all when setup right.

I can tell the difference.  Middy is softer

A way to maybe quantify test "felt recoil" difference with carbine/middy

Run identical shooting drills with Pro timer. Shoot a multi-shot, multi-target drill with carbine then the same drill again w/ middy. If you can shoot the drill either faster or more accurately with middy, then you can attribute that to better felt recoil, (rifle settling faster/better) between shots allowing more speed, better hits or both.

OP I think you may be missing thr point of the middy entirely, the system will be easier on all components and all things being equal, parts should have a longer life on a middy (and even more so on rifle length)...  The fact middy's can shoot a little softer (lotta variables here, not really black and white) is just an added bonus.

I have never noticed less felt recoiled with a mid length. The mid length just feels different.
May all be in my head......I don't know

Port pressure, not chamber pressure plays a part in felt recoil.  Buffers and springs have nothing to do with dwell time.  Dwell time can be altered by moving the gas port, changing the length of the barrel, or using a faster or slower load.  

I've shot my 16" middy & carbine side by side as well as my 14.5" middy and carbine. I could tell a difference in both, especially with hotter ammo like M193 and 5.56 TAP.

Obviously, neither has much recoil to speak of, but the middy feels smoother and less abrupt.

I realize this.... you just always hear people saying that middies shoot softer so i was just wondering.  I understand the wear aspect... anyone have any hard data on how much longer parts last on middies tho or is it just theoretical?

Just in the 14.5 length, I have 2 of each that I compared.  I took them all to the range with a pile of ammo.  It is a small sample size for arfcom, but it was good enough for me to get an idea.  I left the 16s. and the SBRs at home.  My goal  was to burn through all of the "other" misc ammo I had left in the bottom of the fort, and tune the 4 rifles once and for all to the ammo I was going to stick with.  I want nothing but M193 and M855 in the stack, and I had accumulated WAY too many others I didn't even know I had over the years, so this was a fun reason to get through it all.

I took carbine springs, Sprinco Blues and Whites, Wolff XP, and carbine through H3 buffers

Ammo consisted of a very mixed bag (hence my description above) of Tula and Wolf steel, PMC bronze, Rem .223, through  AE 5.56 193 & 855. The latter 2 were what I was going to "tune" the rifles to in the end, but wanted to see where the reliability stopped with the others, and heavier buffers.

Barrels were DD carbine, BCM carbine, Rainier Select midlength, and BCM BFH midength.  All 4 rifles are very similar in weight, same barrel profile except for one of the midlengths, set up with red dots, so no weight advantage to soak up any felt recoil.  All my rifles have flash hiders.

While the goal was to get the correct buffers in for 5.56, I also got to pay attention the difference between the 2 gas systems, with equal barrel lengths. I never really cared, or paid attention, they all shot great before.  No hard data that OP wants, just my feelings, unfortunately

Gas port size is unknown, but for the most part I think we all agree that these barrels should be close to proper.

There were interesting results I could ramble on about with the lower powered ammo, but, at the end of the day with H2s
in the carbine rifles, and Hs in the Midlength, I did notice a difference in the feel of the recoil of the 2 gas systems with full power ammo.

The carbines are "snappier", not more recoil, just different, and cycling is faster.  Perhaps this is why it feels snappier, because it is just happening faster.  My midlengths feel less harsh, and I think it is because the cycle is happening over a longer period of time.  They are definitely "smoother".  I don't think they recoil less than my carbines, I think they just spread the cycle out over a longer duration to make it feel that way.  this is not science, I am just telling you how it felt

I did this over a couple of days, and I think my round count was close to 2K.  We loaded close to 70 mags, and tried to keep them segregated and marked by ammo type.  

You really have to compare apples to apples.  I could make my carbines feel like butter with the shit ammo.  I think a lot of the guys are doing this when they state that their DPMS 16 inch carbine is softer than their buddy's BCM midlength.  Putting Tula on the ragged edge of reliability with heavy buffers and power springs makes for a very soft shooting rifle if you compare it to a midlength shooting M855 with carbine buffer and spring.

Everything is subjective, but I have a much better understanding of these 4 rifles of mine.
TL;DR?
THERE IS NO MORE STEEL IN THE AMMO FORT

There is no hard data. Like I said above, just a bunch of dudes with opinions.

 

Firstly, out of all the reasons I prefer the mid length gas system to the carbine, "recoil impulse" is at the bottom of the list.  It's an AR15, not a .308 battle rifle.  

Secondly, there are a lot of factors that come into play here.  Are we comparing a 14.5" carbine to the midlength or a 16" carbine?  I prefer the carbine gas system on a 14.5" barrel.

Gasport sizes, buffer weights, buffer spring strength, bolt carrier weight, etc all play a factor.  The optimum gasport size for a 16" midlength is around .077 and .063 for a carbine, however many have larger ports.

Use whatever you like, just make sure you tune your set up to all the ammo you want it to run with.  

If you're setting up a SHTF gun, make sure it can cycle anything under any condition reliably.  Shoot it heavily fouled, unlubed, in cold climate, etc.  Tune it so it has the least recoil to reliably function the most unreliable / low power ammo under the worst adverse conditions you can muster.

During SHTF, no matter how big your stash, you might find yourself separated from it, and will likely only be able to shoot whatever is available so it's important it can run no matter what.  With the correct sized gasports, this is typically easily achieved with standard power buffer springs and H or carbine buffers.

If you want a gun to be as light in recoil as possible with your pet load under normal range conditions, then tune it for that.  Just have a purpose for what you want your AR to do and be and do your own testing until you're as sure as you can be that you're there.

Personally, I think the rule of thumb for gas systems holds true.  Stick with carbine for 14.5" barrels, mid for 16" and rifle for 18" - 20".

Never cared to.

The 14.5 barrel / carbine gas system has been proven reliable under combat conditions.

So if my carbine got sand or muck in it or is dry from lack of lube . I will take the extra force.

SBR 10.5 - 14.7  with car gas system.

BTW I have no use for 16-18 inch rifles and prefer a 20inch rifle

Recoil in a gas-driven rifle is all about pressure development and bleed-off.  Pressures are generated, obviously, by the powder charge exploding and the bullet being the path of lowest resistence.  Because the bullet travels further to access the gas port the longer the gas system is, it makes sense that the impulse would be less sharp with longer gas systems.  Boyles Gas Law shows us that pressure and volume are inversely proportional; that is, the same amount of gas trapped in a vessel of known volume (the barrel to the bullet, in this case) if the volume is doubled the pressure is cut in half.  We see this well illustrated using a syringe.  If you close off the end, and you are using a 5cc syringe, as you push the plunger it gets progressively harder to do so because pressure doubles at 2.5cc, then 1.25, then .625 etc.  Do the opposite, and measure pressure at around 4" of a pistol system compared to a rifle at 12" and the volume is tripled, and thus the pressure is a third for the rifle when compared to the pistol.  The difference, however, is not that great from a carbine (7") to a middy (9").  the volumetric change is only a 23% increase and thus a 23% decrease in pressure.  While this will create a lower pressure when the gas charge hits the respective ports, the bullet is travelling at well over 2000 fps, or 24000 in/sec, the dwell time difference for the bullet to travel 2 extra inches makes the perceived difference a mental exercise at best.  Where recoil really matters in this comparison is in reciprocating weight, recoil spring strength, bullet weight, and powder charge of the ammo itself.  

Ultimately if you can feel the difference between 2 indentical guns with only the port being moved from carbine to middy you are way too sensitive to be shooting anything larger than a sling shot.

This is curious to me.  I agree, I have no use for a 16", but if you research the bullet velocities at 18" vs 20" there is almost nothing to be gained.  While you lose 200fps from 18 to 16", you only gain 30ish fps going from 18 to 20".  This is the reason the SPR is the compromise weapon that it is.  It does most things well without doing any one thing exceptionally (even though it is exceptionally accurate).  That's why my shtf piece is an 18" piston driven stick inspired by the SPR.  I don't have to keep my BCG wet because it never heats up to burn lube off.  I realize that spare parts aren't on every AR out there, but wait, they are!  It's a 10-minute affair to retrofit my rifle back to DI if it were ever necessary, but the benefits of running grease in my lower are how I get around the need to test running it dry.

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This is curious to me.  I agree, I have no use for a 16", but if you research the bullet velocities at 18" vs 20" there is almost nothing to be gained.  While you lose 200fps from 18 to 16", you only gain 30ish fps going from 18 to 20".  This is the reason the SPR is the compromise weapon that it is.  It does most things well without doing any one thing exceptionally (even though it is exceptionally accurate).  That's why my shtf piece is an 18" piston driven stick inspired by the SPR.  I don't have to keep my BCG wet because it never heats up to burn lube off.  I realize that spare parts aren't on every AR out there, but wait, they are!  It's a 10-minute affair to retrofit my rifle back to DI if it were ever necessary, but the benefits of running grease in my lower are how I get around the need to test running it dry.

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Never cared to.

The 14.5 barrel / carbine gas system has been proven reliable under combat conditions.

So if my carbine got sand or muck in it or is dry from lack of lube . I will take the extra force.

SBR 10.5 - 14.7  with car gas system.

BTW I have no use for 16-18 inch rifles and prefer a 20inch rifle

This is curious to me.  I agree, I have no use for a 16", but if you research the bullet velocities at 18" vs 20" there is almost nothing to be gained.  While you lose 200fps from 18 to 16", you only gain 30ish fps going from 18 to 20".  This is the reason the SPR is the compromise weapon that it is.  It does most things well without doing any one thing exceptionally (even though it is exceptionally accurate).  That's why my shtf piece is an 18" piston driven stick inspired by the SPR.  I don't have to keep my BCG wet because it never heats up to burn lube off.  I realize that spare parts aren't on every AR out there, but wait, they are!  It's a 10-minute affair to retrofit my rifle back to DI if it were ever necessary, but the benefits of running grease in my lower are how I get around the need to test running it dry.

I always thought I would hate 16" rifles too.... I owned one a long time ago before i even knew how to clean an AR (literally would shoot it and put it up... Colt 6920.  And actually i did own a 16" SR15 but that is kinda a different breed of AR) but other than that, I have owned nothing but 14.5s and 20s.  I recently picked up another 16"... i did not feel like making this an NFA item and that perm attached muzzle device 1. just pisses me off in my own mind and 2. fucks things up when I want to add a suppressor because I have thread ons and am waiting on an AAC.  I can't tell the damn difference between my 14.5s and the 16.  I don't know if I am just too dumb to notice or what but the length didn't bother me like i thought it would and the operation of the rifle has been as good as I would hope for.  If I run across an accelerometer I will take some data but i don't see that happening soon.  They are like $300 and i don't feel like buying one now... might be able to borrow one from our physics lab.

You wouldn't notice a real difference because the OAL difference is less than the 1.5" difference in barrel length since the 14.5" must be pinned to 16" anyway.  It ends up being around an inch length difference.  That's it!  

Also, that 1" length difference translates to around 100 FPS for M193 and M855, which translates to around 50 yards reliable fragmentation range.  All of that for an inch....

Dwell time cannot be altered with buffers or springs, only by barrel length between gas port and muzzle. A carbine will propel the BCG backwards with more force than a Middie and a middie with more force than a rifle. this contributes to felt recoil. Can anybody feel the difference? That is debatable but it doesn't mean the difference isn't there

The OP created the thread about "recoil impulse differences", ala felt recoil, which is a tangible thing to experience and is effected by all those aforementioned variables.

Are you sure about this?

This is from windham weaponry sight in regards to the H buffer

I cant tell in the recoil amount but I can tell in the cycle action it is smoother and less harsh

That's not dwell time.  Dwell time is the time from the bullet passing the gas port to exiting the muzzle.  Basically it's the amount of time that the gas system is pressurized.

That's what I thought it was as well... i think that dwell time and the time it takes for the bolt to unlock kinda gets confused.  I can't say that I am a huge Windham fan but those guys have been making ARs a long time (whether thru bushy or widham) so it kinda baffles me that they would say something on there website that is blatantly wrong.  IDK

ETA:  this is where that came from

http://www.windhamweaponry.com/shopexd.asp?id=275#axzz38tSbV2VD

"Dwell time" is of course commonly applied to the length of time a bullet spends in the barrel AFTER passing the gas port, as has been said, but there is nothing that prevents the use of the term to describe what the Windham guys are describing.  

It is like the word "clip".

Not trying to pick a fight but why guys flip out over the use of that term is beyond me.  The whole English-speaking world has used the slang term "clip" to describe a magazine since time immemorial.  That it more accurately describes a charger notwithstanding.

I think most of those that get wound up on use of such terms are noobies trying to sound knowledgable.  The rest of us really don't care.

It's more than theoretical, 20" rifle length AR bolts have a significant longer life span than a 16" carbine.... Just as a 16" middy will pretty clearly  have a longer part life than an 10.5" carbine length.

I've seen an app where you can use a smartphone to measure vibration in a high speed rotating system for the purpose of balancing.  Basically the smartphone is attached to a housing and acts as an accelerometer.  I wonder if it could measure an AR's rearward acceleration?

Wrong is wrong whether its coming from a manufacturer or an individual  . When a person is trying to reduce recoil by thinking he is altering "dwell time" with buffers and springs, he is wasting his time and money.  Not only that, he is also learning wrong info about how his weapon operates, this will only make things more difficult to figure out in the future.  Getting out correct information about AR's on an internet site dedicated to AR's.... it is worth the risk of coming off as pedantic to some,  otherwise this site is a waste.

I've done this.

This is how I talked myself into buying my first middy

This nails it.


Beer to you Sir.

That method might help quantify muzzle rise, but not felt recoil. Measuring duration and magnitude of rearward movement during the firing cycle is a better method.

 

I agree

Not the most scientific test, "felt recoil" could be different depending on the shooter and if you shave off time during the drill even its its just a second or even less and granted it could be that you are warmed up, its all in your head or it could be that running a middy helped then I would lean towards the platform that I think helped me shoot better as a shooter.

Without a comp on a rifle just a flash hider I think there is a difference, I like middy system, With a Comp on a rifle I can't tell the difference at all, hence my main 3gun rifle is a carbine length system.