quote:

There are a bunch of other makers I did not mention that I would not select. For one, I think the "Wylde" chamber is a gimmick. If you want a target gun you want a .223 chamber. If you want an AR you want a Colt-dimensioned 5.56 chamber.

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Originally posted by Samuel_Hoggson:
Yeah, the Colts stamped .223 have the usual Colt 5.56 dim chambers. Also, Colt chambers vary according to bbl length - it's not just the gas port diameters that differ.



Sam

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Originally posted by p dog shooter:
Plus a new reamer will cut a chamber a bit differant then one on its last chamber it is going to cut..

A production company sure isn't useing a new reamer for every chamber.

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Originally posted by SmokinJ:
Explain that differ chamber dimension in conjunction with differ barrel lengths.

Also it's not only a difference in gas port size but also where the gas port is placed on the barrel in relation to the chamber.

Milspec only means the rifle was adopted by the military and that there are military specifications for it's parts.

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Originally posted by Samuel_Hoggson:

quote:

Originally posted by SmokinJ:
Explain that differ chamber dimension in conjunction with differ barrel lengths.

Also it's not only a difference in gas port size but also where the gas port is placed on the barrel in relation to the chamber.

Milspec only means the rifle was adopted by the military and that there are military specifications for it's parts.

Dr. Dennis Todd has written about this many times on subguns.com. I spoke to him about it many years ago at the Hiram Maxim shoot at which he had a table. The gist of it is the shortys get a slightly more generous chamber. Anyway, his email info can be found on Subguns.com, recommended dealers list. He is an authorized Colt dealer and would know. I imagine Len Elmore (sawlesales) would likewise be able to describe the differences.

Not sure what you are saying about gas port diameters. Gas port sizes vary between bbls of different lengths that use the exact same gas port to receiver distance. Thus, Colt uses different diameter ports for 10.75", 11.5", and 14.5" bbls using the same carbine gas tubes. Diameters are larger with shorter port to muzzle distance (shorter dwell). I have these specs somewhere on my pc if you need them. I suspect you could also google it.

"Milspec" is a much-misused term too frequently used to promote sales. Nevertheless, Colt's idea of what is milspec is not what obtains from reverse engineering.

Sam

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Originally posted by SmokinJ:
I never heard of different chambers according to different barrel lengths. To me it sounded like BS and I turn out to be correct because here is an email from Dr. Dennis Todd I received this morning:

In theory a .223 chamber is tighter than a 5.56mm NATO chamber. I have been told that shorter AR15/M16s MilSpec barrels have "sloppier" chambers. The pressure curve of the gas is different at different barrel lengths. Shorter barrels don't get the optimal pressure returning to the bolt. The looser chambers allow for easier, more reliable extraction of the fired case. Since the bullet projectile does not sit in the chamber, but in the throat of the barrel, accuracy is not compromised. I do not have access to specific dimensions.

Nowhere in there does it say their are different chamber dimensions for different barrel length. It only discussed a "sloppier" chamber for more reliable operation as I suspected you may have meant. He also talked about different chamber pressures with different barrel lengths which I also knew about.

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Originally posted by Samuel_Hoggson:

quote:

Originally posted by SmokinJ:
I never heard of different chambers according to different barrel lengths. To me it sounded like BS and I turn out to be correct because here is an email from Dr. Dennis Todd I received this morning:

In theory a .223 chamber is tighter than a 5.56mm NATO chamber. I have been told that shorter AR15/M16s MilSpec barrels have "sloppier" chambers. The pressure curve of the gas is different at different barrel lengths. Shorter barrels don't get the optimal pressure returning to the bolt. The looser chambers allow for easier, more reliable extraction of the fired case. Since the bullet projectile does not sit in the chamber, but in the throat of the barrel, accuracy is not compromised. I do not have access to specific dimensions.

Nowhere in there does it say their are different chamber dimensions for different barrel length. It only discussed a "sloppier" chamber for more reliable operation as I suspected you may have meant. He also talked about different chamber pressures with different barrel lengths which I also knew about.

Yes, that's what I meant. I think "BS" is a little over the top, no?

I should have been consistent in my use of "vary". Anyway, he confirms that shorter barrels have "sloppier" chambers, ie., they differ dimensionally from the standard rifle bbls.

In my conversation with him (this was back in the '90s) he indicated this info came directly from Colt.

I did not mean to imply each particular factory bbl length used a different set of chamber specs or tolerances, only that there was a difference between rifle (20") and shorty (10.75" and 11.5") chambers. That is not "BS".

Sorry for the confusion.

Sam

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Originally posted by SmokinJ:
Sorry if I offended you or seemed a little over the top. I believe Dr Todd meant, and he did say, milspec rifles have the "sloppier" chambers and I believe he chose "the short barrel ones" because our military is currently using the shorter M4 carbines. I can assure you the M16 has the same sloppier chamber. That brings up what I was trying to convey by "milspec". There IS a dimension to milspec that is followed by the manufacture. That sloppier chamber is one...that is a milspec 5.56 NATO chamber. Nobody except those manufacturers that made/make rifles for our military have access to milspec data. They only get it from the government when they get a contract. Off course they could take a milspec rifle and take it apart and measure everything, but they won't know the min and max dimensions. That's what I've been told about milspec.

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Originally posted by Samuel_Hoggson:

quote:

Originally posted by SmokinJ:
Sorry if I offended you or seemed a little over the top. I believe Dr Todd meant, and he did say, milspec rifles have the "sloppier" chambers and I believe he chose "the short barrel ones" because our military is currently using the shorter M4 carbines. I can assure you the M16 has the same sloppier chamber. That brings up what I was trying to convey by "milspec". There IS a dimension to milspec that is followed by the manufacture. That sloppier chamber is one...that is a milspec 5.56 NATO chamber. Nobody except those manufacturers that made/make rifles for our military have access to milspec data. They only get it from the government when they get a contract. Off course they could take a milspec rifle and take it apart and measure everything, but they won't know the min and max dimensions. That's what I've been told about milspec.

No problem, I have a thick skin that matches my thick head.

The conversation was years ago, but Dennis was comparing Colt 11.5s to Colt 20" bbls. So when he referred to the "shorter" bbls I don't think he meant the 20" A1 pencil or A2 bbls. I didn't ask about 14.5s or 16s.

Again, the gist was a need to facilitate case wall relaxation on the shorter dwell carbine length + short distance to bullet exit system. And this was to help prevent dropped extraction (I...think....this preceded the O-ring Crane M4 upgrade).

Sam

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Originally posted by SmokinJ:
Most AR's I've worked with and seen, including Colts, are over gassed to insure they work under all conditions. What this does to your match accuracy heavy barreled high dollar varmint shooting AR is unnecessarily beat your bolt/carrier group and barrel extension shorting it's life. Notice the new sporter Colt AR15 in certain models have an adjustable gas valve and yes on a DI system. All my AR's I build have them too. The sloppier chambers main function is to insure reliable operation under adverse conditions which the military encounters. It doesn't have anything to do with the dwell time. You can't extract a case until after it has shrunk back from obturating to the chamber wall. In other words until all the pressure is gone.

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Originally posted by Samuel_Hoggson:

quote:

Originally posted by SmokinJ:
Most AR's I've worked with and seen, including Colts, are over gassed to insure they work under all conditions. What this does to your match accuracy heavy barreled high dollar varmint shooting AR is unnecessarily beat your bolt/carrier group and barrel extension shorting it's life. Notice the new sporter Colt AR15 in certain models have an adjustable gas valve and yes on a DI system. All my AR's I build have them too. The sloppier chambers main function is to insure reliable operation under adverse conditions which the military encounters. It doesn't have anything to do with the dwell time. You can't extract a case until after it has shrunk back from obturating to the chamber wall. In other words until all the pressure is gone.

I guess our experiences differ. I've got 3 Colt 11.5s, and the only one I would describe as overgassed is a seriously abused blaster upper that has almost no rifling for the first 3". The gas port is ugly, seriously enlarged. Yet overgassed is a relative term, dependent on ammo. That blaster upper works perfectly with black-box Wolf steel sans any beefed up extraction. It sure needs a D-ring if using M193. My 20" Colt uppers are not particularly overgassed, they do not always act 100% with commercial .223 until broken in. I played with a factory LMG that needed a break-in before it would cycle even M-193 100%.

Whether "DI" (in-line piston) or typical offset piston, no AR unlocks before gas pressure in the chamber is zero. But they can, and do, start to unlock before the case may have sufficiently shrunk from the chamber walls. Difficult extraction caused by incomplete case/hull relaxation - even under non-adverse conditions - can be seen in about any type of firearm, not just automatics. I can, on demand, shuck my Model 42s fast enough to measureably stretch and even bend the plastic hulls. They do not stretch if I hesitate after firing.

Carbine length gas systems pressurize sooner after ignition, and to a higher pressure, vs rifle length systems. This, plus shorter time-under-pressure (dwell), esp. with 10.75 and 11.5s, tends to make extraction more violent and more problematic. This phenomenon is extremely well-documented. A full explanation involves a discussion of balancing extractor and button ejector forces. Bottom line: carbine length gas systems are more difficult to make reliable vs standard rifle-length gas systems. The reason is not because short bbl uppers get dirtier vs rifles.

Mack Gwynn told me that even with 20" rifle systems, the M16 extractor starts to disengage the rim during extraction. But this only manifests as a dropped extraction problem with shortys. He (MGI) developed the D-ring specifically to deal with the more rigorous demands shortys place on extraction force. Dotgov went with the less expensive Crane O-ring.

(Parenthetically, a slotted bolt and fixed blade ejector would probably have solved the problem. But that's a Daewoo K2, not a M-16, and that is another story.)

I think we are looking at dirt and dwell from different directions. By definition, MGs (including assault rifles) operate under adverse conditions. Therefore, IMO, dirt is a constant. MG design engineers all seem to understand this, thus MG chambers all have generous specs. The chamber gets dirty very quickly, no need to add environmental dirt, and we don't stop after five rounds to clean them. Anything that compromises extraction - and short dwell is most definitely one of those variables - only makes having a generous chamber dimension that much more desirable.

Sam

quote:

Originally posted by SmokinJ:
There is a problem, whether you want to address it differently then me, that I'm also speaking of that shows up as a very flat primer demonstrating too high of a pressure which is is not and it has to do with bolt opening timing. David Tubbs addressed this with his carrier weight to delay the timing a little and in not only my opinion but some top builders the now heavier bolt/carrier group batters the rifle even more. The better way is to control the gas.

quote:

Originally posted by Samuel_Hoggson:

quote:

Originally posted by SmokinJ:
There is a problem, whether you want to address it differently then me, that I'm also speaking of that shows up as a very flat primer demonstrating too high of a pressure which is is not and it has to do with bolt opening timing. David Tubbs addressed this with his carrier weight to delay the timing a little and in not only my opinion but some top builders the now heavier bolt/carrier group batters the rifle even more. The better way is to control the gas.

OK. Yes, we must be coming at this from different directions. M193 and M855 can be pretty hot stuff. My SA '86 still chronos over 3400 fps from a 20" A1. I cannot safely duplicate it at the bench. But I don't try b/c I will not shoot reloads in my 16s - for several reasons.

I have never had the primer-flattening you describe with any factory load in any unmodified Colt AR or M16. Not ever. With a shorty buttstock I prefer the MGI buffer to the various H series. But, here, I'm worried about bolt bounce, not overgassing, in full auto.

That said, I'm interested in understanding the problem you describe. Is this happening with reloaded ammo? Do you have a link to Tubbs comments? Sam

quote:

Originally posted by lee440:
One thing that never gets mentioned here is that Colt does magnetic particle testing on the bolt, bolt carrier and also the barrel after it has been high pressure proof tested. Every one, whether military contract or civilian. Virtually every high volume manufacturer like Bushmaster, S&W, DPMS etc, do random inspection. Colts used to be a lot more expensive than Armalites and Bushies, but now I see them at gunshows all the time for less than $200 more and the resale value alone makes that a deal, the MPI is icing on the cake. There are a lot of high quality "boutique" manufacturers that probably do this, but you are not going to get one for $1100. If I were in the market, I would grab up a Colt or two real quick and don't forget to load up on mags while they are still fairly cheap, its gonna get crazy quick!

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Originally posted by BISCUT:
Colt is an exceptional AR. So is LMT and Noveske. One should always be aware that there are differences in Colt's LE and civillian versions. 6929 is NOT the same as buying a Civ version.

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Originally posted by SmokinJ:
I just checked out Tubb's website and he changed his tune a little bit on the carrier weight now claiming he designed so you could shoot the heavier bullets (he mentioned 80 grain) with a hotter powder load. Says it slows down the unlocking of the bolt which helps extend the life of the brass and reduces the speed of the bolt/carrier which is easier on the rifle. You can't find his original ad showing the primer difference. He doesn't tell you the bolt/carrier group has more mass with his device and beats both the carrier and barrel extension more because of more mass. Like others and myself think the adjustable gas valve is a better way.

quote:

Originally posted by SmokinJ:
Sam I just noticed something interesting reading the new issue of Rifle. They were testing the new Colt 223 Elite HBAR rifle. Interesting is that the receiver is marked 223 but the barrel is stamped 5.56 NATO MP 1/9. I remember you said that some manufacturers are making all the chambers to 5.56 NATO specs no matter if they are intended for the 223. I was wondering, and it's been answered by at least one manufacturer now..Colt, if they would mark the barrel 223 or not even if it had the NATO chamber. Well now see how Colt is doing it. I didn't think that it would be like Ford selling you car that is a Chevy and embelling it as a Ford. Colt is actually telling you what the chamber is.