View Full Version : How viable is this? (M4 feed ramps)
Magic_Salad0892
06-15-10, 01:05
In Guns & Ammo: Book of the AR-15 2010 I read about why LaRue doesn't use M4 feed rams in their guns (STEALTH, O.B.R., Etc.) this is what was said by the author:
If you put a dummy round into an AR and cycle the bolt by hand, you see that the first part of the round that touches the ramp is the very tip of the bullet. The steeper angle of the ramp found with the M4 feed ramp delivers a much harder blow to the bullet during the loading cycle that further knocks the centerline axis of the bullet out of alignment with the bore. The destruction of this alignment causes the bullets to enter the barrel at varying angles when fired. This degrades accuracy.
Guns & Ammo: Book of the AR-15 2010
Page 128 (Paragraph 5) - 129 (Paragraph 5 of page 128)
Author: Tom Beckstrand
Is this true? If so, by how much?
Also: Does the Mk. 12 use M4 feed ramps or is it rifle?
Although this sounds possible, on paper. I would like to see some real world side to side comparison of the acuracy of both systems to test this myth.
Everything I know about the M4 feed ramps was to improve feeding reliability during FA use and have nothing to due with accuracy.
To me, this makes sense.
M4 feedramps were designed for the full-auto M4, not the M16 or semi-auto AR15's. Since a full-auto weapon's purpose (when fired on full-auto) is to lay suppressive fire, any small loss of accuracy would be a non-issue and therefore acceptable. For us benchrest/precision shooters, it may be slightly detrimental to accuracy, as there's little to gain from auto-capable feeding in a semi-auto weapon.
Since carbines have been the latest craze, it seems that most manufacturers are simply including them to add a check-mark next to their list of features, not because they actually improve the weapon.
That's my speculation and .02.
carbine_kyle
06-15-10, 19:58
Im new to the ARs but i gotta agree with Skyyr.
The only stoppages I've ever had with soft-point ammo was in rifle-ramped carbines. Never had that type of stoppage in an M4-ramped carbine with the same ammo.
The only stoppages I've ever had with soft-point ammo was in rifle-ramped carbines. Never had that type of stoppage in an M4-ramped carbine with the same ammo.
I've had a few failures to feed with M4 feed ramps. Typically it is with Federal soft points, and it ends up raping the bullet nicely. FMJ's haven't let me down yet.
Riley~~~
Everything I know about the M4 feed ramps was to improve feeding reliability during FA use and have nothing to due with accuracy.
If you read the OP again, it talks about the bullet being tilted in the casing from abruptly hitting the M4 feed ramp angle. This would cause the bullet to be off center in the chamber.
Riley~~~
Seems to me like an easy enough test; 1)Pull the charging handle to the back and let go, chambering a round. 2)Pull the charging handle and eject said round. 3) Inspect bullet in round for proper seat.
How hard could that be?
Seems to me like an easy enough test; 1)Pull the charging handle to the back and let go, chambering a round. 2)Pull the charging handle and eject said round. 3) Inspect bullet in round for proper seat.
How hard could that be?
The way I've always looked at it, is in the M4s (or any carbine length gas system), the bolt/BCG speed could basically run fast enough to catch the next round before the nose of the bullet was all the way up, so the nose of the bullet would catch, until the ramps were extended. So, your scenario with simply racking the charging handle wouldn't do it, because it wouldn't be fast enough to "outrun" the mag spring. I think you would need to do a pre-fire check of the second round in a mag, then fire the first round, and extract the second round from the chamber, unfired, using the charging handle, and get an after measurement.
Magic_Salad0892
06-16-10, 03:08
I was thinking about getting a LaRue STEALTH upper receiver anyway, because I am trying to build a parts replacement box, if the M4 feed ramps thing is true it'll replace the stripped LWRCi upper. Internal parts will still be LWRCi.
Not because I need my weapon to be DMR accurate (12.7'') but because
A - I don't want anything I don't need.
B - If it'll further tighten groups, then that will be nice. (The gun shoots better than I do anyway, this will only be a factor in magnified bench-rest shooting.)
C - If I were to one day convert the gun into a 12.7'' Recce build. Then this will make a difference to me.
D - Couldn't hurt giving LaRue more business. :)
Magic_Salad0892
06-16-10, 03:10
The way I've always looked at it, is in the M4s (or any carbine length gas system), the bolt/BCG speed could basically run fast enough to catch the next round before the nose of the bullet was all the way up, so the nose of the bullet would catch, until the ramps were extended. So, your scenario with simply racking the charging handle wouldn't do it, because it wouldn't be fast enough to "outrun" the mag spring. I think you would need to do a pre-fire check of the second round in a mag, then fire the first round, and extract the second round from the chamber, unfired, using the charging handle, and get an after measurement.
The bolt ''outrunning'' the spring was also mentioned in the article.
I don't think this is a factor with a semi-auto gun using good magazines.
The bolt ''outrunning'' the spring was also mentioned in the article.
I don't think this is a factor with a semi-auto gun using good magazines.
I have not read the article, so I can't specifically comment on what they said. I don't think it is "outrunning" the mag spring in the traditional sense people think of, where the bolt runs over the next round causing other sorts of misfeeds, but just not giving the mag enough time for the round to settle in against the feed lips of the mag fully, ie, staying a bit nose down for too long.
Why wouldn't a semi-auto gun (even with good magazines) be affected? Bolt/BCG speed (effectively cyclic rate) isn't controlled by the trigger group. Relavent to this discussion, it is controlled by the position of the gas port in the barrel. Closer gas port = higher pressures = faster moving bolt. Personally, I would always run the M4 ramps on anything with a Carbine length gas system or shorter, unless I had done something else to slow the rate down, like a significantly heavier buffer or BCG,
don't p-mags kind of take care of the bullet nose problem as well?
What we are discussing here is Runout.
When shooting Benchrest I use to worry greatly about Bullet Runout...and so I used a dial indicator setup on a case block to spin each casing for concentricity. In these rifles I was seeking sub 1/4 MOA accuracy out to a known distance of 300 yards. And most importantly...I was shooting only paper targets with these guns.
Lets face it....an M4 was never intended to be a sub MOA weapon...Yes we should hold to a certain reasonable expectation of accuracy with our carbines. But that accuracy should be Minute of Man and any better groups should not be pursued at the expense of reliability.
Pumpkinheaver
06-16-10, 10:44
This would be east to test. Any body on here have a gauge to test bullet runout? Test one before chambering and one after and see if there is a change. I wonder if some ammo might be more apt to be damaged than others?
https://www.m4carbine.net/showthread.php?t=24003&highlight=feedramps
C4
I've owned two different uppers that would drive 68 gr reloads back into the case - both were 90's era purchases with rifle cut feed ramps. I replaced the 20" Colt upper with a 20" BM upper only to find the same problem. (No problems with 55gr bullets, btw.)
I recently duplicated this problem with the BM using 75 gr OTM dummy loads when I started reloading again. I absolutely do not have this problem with my two (new era) rifles with M4 feed ramps, despite multiple attempts to force it with dummy rounds.
I won't own another rifle-cut upper regardless of who makes it.
CarlosDJackal
06-16-10, 14:08
My priorities of selecting a firearm that I would stake my life on:
(1) Comfort - you can't make the hit if you flinch at every shot. I don't care how big the caliber, fast the muzzle velocity or great the muzzle energy is; if you are uncomfortable using it you're probably going to miss a lot.
(2) Reliability - this is what the M4 feed ramps were made to address. Accuracy can only be achieved with a firearm that actually works.
(3) Accuracy - Combat Accuracy is all I really need. Unless I plan on making a hostage rescue shot at 100-yards; I'm content to use a firearm that has the capability to place rounds within a 4-inch circle at any distance.
My F/A converted SP1 came with a carbine upper (Colt) that did not have the M4 feed ramps. The most I can run through it was 2 or 3 shots - even in S/A. I haven't had an issue with it since I topped it with a BCM 11.5" upper. YMMV.
(1) Comfort - you can't make the hit if you flinch at every shot. I don't care how big the caliber, fast the muzzle velocity or great the muzzle energy is; if you are uncomfortable using it you're probably going to miss a lot.
How many people actually find the AR-15/M-4gery uncomfortable to shoot that a little training won't cure?
(2) Reliability - this is what the M4 feed ramps were made to address. Accuracy can only be achieved with a firearm that actually works.
How many people have had problems that could actually be attributed to the lack of M4 feedramps om semi-auto M-4s?
How many people have had problems that could actually be attributed to the lack of M4 feedramps om semi-auto M-4s?
At least one. See my comments about three posts above this one.
At least one. See my comments about three posts above this one.
I saw that....
that would drive 68 gr reloads back into the case
So let's rephrase that to how many have had problems with factory ammo.
I saw that....
So let's rephrase that to how many have had problems with factory ammo.
That would be a different question than the one I responded to.
CarlosDJackal
06-16-10, 15:32
How many people actually find the AR-15/M-4gery uncomfortable to shoot that a little training won't cure?...
Notice I said "firearm" because I wasn't implying that the AR platform cannot be modified to fit the user. Not all firearms is as flexible as the AR.
...How many people have had problems that could actually be attributed to the lack of M4 feedramps om semi-auto M-4s?
I have with my pre-ban ARs. Which is why I now only buy ARs with feed ramps.
Since I tend to shoot about 12k rounds a year through my ARs, what I experience the regular plinker/hobbyist may never experience. But as I said, YMMV.
ADDED: I only shoot factory ammo in my ARs.
I saw that....
So let's rephrase that to how many have had problems with factory ammo.
I have and have seen it in testing (which I posted a link to).
C4
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