Colt 6720MP purchased. A couple of questions...

[Odglock]

It's my first colt and my first pencil bbl. What rate of fire will cause stringing to begin? Is the 6720 the same as the 6920, specwise other than the thin bbl (chrome lined, mpt, h buffer, f fsp, ...)?

[Proconsul]

The FSB is not F marked, but it doesn't matter because it has the proper height FSP.

Enjoy your 6720.

[kaiservontexas]

Not what he asked. I know others in the know can answer. I own no Colt AR rifles at this time. But what did you add to his question? He asked about rates of fire. I doubt he can sustain a rate of fire so high that the barrel fudges it. It is a semi-auto, but let somebody answer his question that knows. There are plenty of individuals with pencil barreled rifles on this forum. They know what it can and cannot do much better than others.

[Proconsul]

Not what he asked. I know others in the know can answer. I own no Colt AR rifles at this time. But what did you add to his question? He asked about rates of fire. I doubt he can sustain a rate of fire so high that the barrel fudges it. It is a semi-auto, but let somebody answer his question that knows. There are plenty of individuals with pencil barreled rifles on this forum. They know what it can and cannot do much better than others.

Uhm yeah, that IS what he asked. Check the second sentence of his post. Reading is fundamental.

And for what it's worth, I own 3 6720s, 5 6920s, and 3 6940s. I have plenty of non-Colt lightweights too, including two DD M4 LWs. Each of them performs slightly differently under high volumes of fire, so I'm not about to generalize.

There are plenty of posts by Molon and others about POI shifts and MOA differences between the LW, M4 and HBAR profile barrels that he can search that answer the question of relative barrel performance.

[shootist1970]

May not ever "String" shots, now if your asking about the barrel warming and the groups "Opening up"(getting larger) thats different.

Depends on the gun and stress points created when the barrel was manufactured.

[Odglock]

Thanks for the input everyone.

[robm]

I realize this is non scientific and very anecdotal data but my non free floated Pencil barrel 16 inch BCM can pull 6 consecutive 5 shot groups with about a 2-3 second pause between shots and show no signes of groups opening up.

I've never been able to push it hard enough to open up the groups to the point where it was an issue. Even in a carbine class where the gun got hot.