AA 6.5 upper in lwt18

[swift6six]

Anyone have experience with this upper on their site? I was debating between 18" and 20", but my lower recoil spring and buffer will run smoothest with midlength gas tube and I'm not sure how the rifle length on the 20" will run. Only concern on the 18" is the 1:7.5. Thoughts?

Oh yeah first post, long lurker...waited for 3 months before account was squared away to post. Thanks whichever admin fixed that.

[Spurrious]

I'm curious about that as well. AA barrels generally have significantly slower twist rates for 20" barrels. 8.75 to 9 are typical of their offerings. On the other hand the .264LBC has been offered typically in a 1:8 twist.

AA going from a 1:9 twist in 20" barrels to a 1:7.5 twist in an 18" seems extreme given the modest drop in velocity.

On the other hand if Les Baer and CSS had the twist rate right all along at 1:8 for a 20" then 1:7.5 for shorter barrels makes way more sense.

[swift6six]

So anyone have comments on the AA lightweight 18" upper in a 1:7.5 twist?

[bwaites]

Guys, this has been addressed at length in old threads by Bill Alexander. All the other people building barrels went off the research he did when he finalized the design and recommendations for barrel twist.

Search posts by Bill Alexander and you'll find the info.

[swift6six]

Sorry bwaites, I had spent countless hours reading every thread I could, but I was looking for updated information - if Bill deems that length and twist acceptable, then I who am I to question I suppose. I'll do more reading.

[Drifter]

From the man himself:

It is our conclusion that the 9 twist offers the best solution for the Grendel for barrels of 20" and longer while the 18" and shorter barrels thrive on 7.5 twist.

Link to source (and with additional insight): http://www.65grendel.com/forum/showt...est-twist-rate

[bwaites]

From the man himself:



Link to source (and with additional insight): http://www.65grendel.com/forum/showt...est-twist-rate

Thanks Drifter, I didn't have time this AM to run that down!

[swift6six]

Thanks to you both.