Mk262 - 18” vs 20”

[longshot2000]

I don’t believe Douglas uses any formula for steel different than other manufacturers. Wasn’t the MK262 round designed for the MK12 specifically?

Yes, the Mk262 was designed for the SPR (Mk12). Yes, the Mk262 performs great in many rifles, including 10.3" Mk18.

I am not privy to their steel, but I know enough about barrel construction to say that the actual steel is not the same barrel maker to barrel maker. I have seen the barrel damage, one barrel blank manufacturer to another, inside the bore at the gas port, and the Douglas barrel has just worn less and lasted longer. This has been documented. I assume it is the steel. I am not sure what else it could be.

[markm]

There was a guy on another forum who ran tests on barrels/finishes years back. He noted that certain powder (burn rates) and bullet combos made drastic differences in port erosion.

I've never found port erosion was anything to worry about for the average shooter. Perhaps if you do a LOT of training and high volume shooting, it might be a concern.

[redpillregret]

Yes, the Mk262 was designed for the SPR (Mk12). Yes, the Mk262 performs great in many rifles, including 10.3" Mk18.

I am not privy to their steel, but I know enough about barrel construction to say that the actual steel is not the same barrel maker to barrel maker. I have seen the barrel damage, one barrel blank manufacturer to another, inside the bore at the gas port, and the Douglas barrel has just worn less and lasted longer. This has been documented. I assume it is the steel. I am not sure what else it could be.

As I understand it, Douglas, as well as the other major barrel manufacturers purchase cylindrical rods of a given formula from an outside source, no matter if it’s Bartlein, Douglas, Kreiger, etc. Barrels are chosen based on the desired formula of 4140, 4150, 416, 416R, etc.

In most instances, a 4140 blank from Douglas will be of the same 4140 from the next maker. The steel follows a given formula or isn’t given the label.


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[JediGuy]

Is the gas port on the Douglas initially sized a little differently, as an alternative explanation for the difference in wear?
I find this very interesting and would love to see a clear reason, especially if we’re seeing differences from manufacturer to manufacturer, when using the same steel.

[Tx_Aggie]

The gas port thing seems like much ado about nothing for an 18-20 inch barrel.

I'm not seeing how, all things being equal, an 18" rifle gassed barrel should wear faster at the gas port than a 20". The 18" barrel will have a slightly shorter duration of gas impulse because of the shorter distance from the port to the muzzle. In either case the port is far enough from the chamber that port pressures and the associated wear are relatively low (and nearly the same for 18" & 20").

Short barrels with their shorter gas systems are really where gas port erosion becomes an issue and can greatly reduce barrel life.

Barrel material and surface treatment should have an effect, but as far as I know Douglas uses 416 Stainless for their AR15 (SPR, Recce, Service Rifle, etc) barrels, or at least that's what I remember from eyeballing them on Compass Lake Engineering's website. 416 is widely used by barrel makers and isn't something specific to Douglas.

[redpillregret]

Tx you are correct on 416 in the Douglas. Believe it or not, it’s a bit of an outdated choice these days. 416R or 410 may have better wear properties.


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[docsherm]

Yes, the Mk262 was designed for the SPR (Mk12). Yes, the Mk262 performs great in many rifles, including 10.3" Mk18.

I am not privy to their steel, but I know enough about barrel construction to say that the actual steel is not the same barrel maker to barrel maker. I have seen the barrel damage, one barrel blank manufacturer to another, inside the bore at the gas port, and the Douglas barrel has just worn less and lasted longer. This has been documented. I assume it is the steel. I am not sure what else it could be.

The MK262 does not work well in 10.3" set ups. I have seen it break more Bolts than you can think of. I do not use it in anything shorter than 12.5". That is one of the main reasons John Noveske was working on the 12.5" barrel.


OP- Nothing really gained from 18" to 20" with the MK262. It was designed to be used in the MK12, 18" rifle gas system.

[556BlackRifle]

As far as velocity with 18 vs 20 inch barrels, in my experience, the difference is negligible.

[HelloLarry]

Rule of thumb is 25fps per inch.
However, barrels of the same length can vary by 100fps.

YMMV, not valid with other offers, void where prohibited.

[longshot2000]

As I understand it, Douglas, as well as the other major barrel manufacturers purchase cylindrical rods of a given formula from an outside source, no matter if it’s Bartlein, Douglas, Kreiger, etc. Barrels are chosen based on the desired formula of 4140, 4150, 416, 416R, etc.

In most instances, a 4140 blank from Douglas will be of the same 4140 from the next maker. The steel follows a given formula or isn’t given the label.


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That is really not the case. There is a great deal of variability in the steel quality, and the making of a great barrel begins with the steel supplier, then continues to the barrel driller or blank manufacturer and then to reamer (chamberer) and lathe shop. Each step has its degree of variability and differences. Douglas is not typically known as the best of the best, but they are darn good, and it just so happens, that empirical evidences suggests that 18" stainless barrels do better from Douglas than other shops. I am not smart enough to know what is different, but many hypothesize that it is the underlying steel alloy. It is possible that it is something else, but I cannot imagine what if might be, if not the metal itself.

Either way, this is after 2,000 to 6,000 rounds of firing, so it could very well be a discussion of how many angels can dance on the head of a pin, for most recreational shooters.