ar15 6x45 accuracy puzzle

[427smith]

Usually start a new project with some jackets before I shoot cast. Gives me a good idea of accuracy potential. My new build is a stoner 20" 6x45 barrel with sota arms upper parts and 80% lower. I loaded up 80 rounds. 20 rounds 70 grain hornady SP, 20 rounds 80 grain rem SP and 40 rounds 70 grain sierra HPBT, all with adjusted charges of H335, cci primers and RP cases. Without to many details I'll say all velocities were slightly below published. no pressure signs and extreme spread was 27 with hpbt and up to 60 with the flat base sp. OK, I shot five round groups of one bullet than a different bullet till done. 70 SP's shot a best of 6 3/8"@ 100, 70 BTHP shot a best of 6/10 with the average of .900, finally the 80 SP shot a best of 5". from 6 inches to less than 1. puzzles me. been loading over 40 years never saw that much extreme difference between bullet types If this is boring, moderators can delete no hard feelings.

[lefty o]

how did the barrel fit in the upper? if the barrel fit in the upper reasonably snug, and not loosey goosey, i'd lean towards a bad barrel. that is assuming if you had optics on the rifle, that the optics arent bad.

[country gent]

A friend shot a 6x45 on an ar for several years in the local winter leauge. It was on the finicky side one day a load would shoot great the next same load was all over. This was before the new powders that werent tem sensitive. Barrel twist bullet length and velocity all have to mesh together. Also on a new barrel fouling can raise it nasty head. Another could be brass consistency on reformed brass. Retest with this same brass now that its been fireformed to your chamber it may be better.