Bolt Life?

[everready73]

Do civilian Colt's have the same size gas port as the Army?

From my understanding they do. Ammo difference civilians use would be the biggest difference for bolt life if using a Colt bcg. I am not sure if rate of fire would matter., Most civilians don't have a fun switch on theirs

[GrumpyM4]

From my understanding they do. Ammo difference civilians use would be the biggest difference for bolt life if using a Colt bcg. I am not sure if rate of fire would matter., Most civilians don't have a fun switch on theirs

FA and ROF do play a significant part.

[WS6]

Colt, DD, Bushmaster, and a number of other manufacturers supply 16 inch carbine gas barrels with 0.0625" - 0.0630" gas ports and these work, which indicates that anything bigger might be an over kill. Some claim 0.058" is all that is required.

Your going the opposite direction (shortening) and going twice as far 3 vs 1.5 inches). We know from empirical evidence that 11.5 in a carbine gas system needs a bigger gas port to operate. Colt uses 0.074", BCM uses 0.073" or 0.076" depending on who you ask, etc. But, if someone offers you a 11.5 carbine with a 0.086", you may what to think about it for a minute or two. For one thing, the port pressure is the same, as the port is in the same place, the port is bigger, so the pressure to the carrier is greater, the force is bigger, and the accelerations are higher. Even if the impulse is shorter, to keep the final carrier velocity the same, the accelerations are still higher.

In contrast, the longer 16 inch barrel might have a tiny bit longer of a push, but that would only increase the velocity by a tiny bit, and the extra gas arrives very near the vent phase of the piston stroke. So, the extra push is, in my opinion negligible, especially if the barrel has an oversized port.

Why is a 0.074-0.076" port used on a barrel with 1.2" longer dwell time vs. the Crane spec 10.3 using a 0.070" port? Especially when made by the same company (Colt)?

[lysander]

Why is a 0.074-0.076" port used on a barrel with 1.2" longer dwell time vs. the Crane spec 10.3 using a 0.070" port? Especially when made by the same company (Colt)?

Ammunition.

Crane can expect a port pressure within a relatively narrow range and tailor the gas port to that ammunition.

Stuff sold to civilians has to work with good ammunition as well as under powered crap like Tula. If they don't they get angry letters and internet posts about how unreliable their guns are. As I recall back when the mid-length first came out, BCM or one of the well respected companies made 16 inch mid-lengths with relatively small gas ports that worked quite nicely with American ammunition, but short stroked with some weak foreign ammo, which required the company to enlarge the gas port. People today, 10 or more years later, still bitch about how unreliable mid-lengths are because of this.

[Clint]

The Colt FBI HRT 11.5" barrel uses an 069 port, much more consistent with Crane spec.

Why is a 0.074-0.076" port used on a barrel with 1.2" longer dwell time vs. the Crane spec 10.3 using a 0.070" port? Especially when made by the same company (Colt)?

[opngrnd]

Ammunition.

Crane can expect a port pressure within a relatively narrow range and tailor the gas port to that ammunition.

Stuff sold to civilians has to work with good ammunition as well as under powered crap like Tula. If they don't they get angry letters and internet posts about how unreliable their guns are. As I recall back when the mid-length first came out, BCM or one of the well respected companies made 16 inch mid-lengths with relatively small gas ports that worked quite nicely with American ammunition, but short stroked with some weak foreign ammo, which required the company to enlarge the gas port. People today, 10 or more years later, still bitch about how unreliable mid-lengths are because of this.

This. I know people who would cry if their rifle wouldn't run on TULA because the "AR is inherently unreliable. " I also think that shooting quality ammo through massively overgassed carbines is harder on the bolt, esp since many of the said bolts are lower quality.

[ABNAK]

In danger of sounding arrogant here, BUT.....buy shit guns to shoot your shitty ammo out of. Steel-cased, weak-ass Tula/Wolf/Brown Bear/whatever has never desecrated my AR's. Hell, unless it's the Gold Dot 64gr'ers that I have I don't even shoot .223 fodder. It's all 5.56 NATO pressure stuff. That steel-cased foreign crap is for AK's, not AR's. Don't care if this is a popular opinion or not; why should quality weapon makers cater to the lowest common denominator ammunition? If you're too broke-dick to buy 5.56 stuff buy a crappy AR with a window-sized gas port and have a ball.

[RetroRevolver77]

Delete

[opngrnd]

In danger of sounding arrogant here, BUT.....buy shit guns to shoot your shitty ammo out of. Steel-cased, weak-ass Tula/Wolf/Brown Bear/whatever has never desecrated my AR's. Hell, unless it's the Gold Dot 64gr'ers that I have I don't even shoot .223 fodder. It's all 5.56 NATO pressure stuff. That steel-cased foreign crap is for AK's, not AR's. Don't care if this is a popular opinion or not; why should quality weapon makers cater to the lowest common denominator ammunition? If you're too broke-dick to buy 5.56 stuff buy a crappy AR with a window-sized gas port and have a ball.

I'm not in disagreement with your SOP, but let's not pretend large commercial manufacturers don't get the lion's share of their money from consumers who don't see it that way. I started out with a S&W M&P15 that I largely shot PMC Bronze through. Eventually put a BRT gas port in and switched to higher quality ammo, then higher quality rifles as I learned a thing or two. Most consumers vote with their dollar, and stay where they voted the first time.

[ABNAK]

The lowest common denominator ammo decides which rifles are reliable.

"Reliable" to who? Mine all function quite well with full-power 5.56 ammunition. Now I do have steel-cased stuff, but it ain't for an AR!

As Taekwondopreacher said "....I also think that shooting quality ammo through massively overgassed carbines is harder on the bolt". This is a true statement. Overgassed guns made for shit ammo will accelerate wear on parts when used with mil-spec fodder.

I guess my point is that quality AR manufacturers like Colt, BCM, LMT, etc. should keep the proper gas port sizes for mil-spec pressure ammo in civvie guns, not alter the size because of cheap-asses wanting to use crap ammo. They can buy a PSA or such and go to town. Hell, given the price of PSA stuff and the price of crap ammo you could legitimately get some good training in while keeping your 6920 and some 5.56 set aside for a "rainy day".