Discussion in 'Rifle Country' started by South Prairie Jim, Feb 18, 2021.
(ill add this as a window into the madness. Lol)
I’ll share a particular observation I have had which even I feel flies in the face of my generally accepted philosophy....
So I’ve shared frequently my poor experience with a Rock Creek barrel in 6mm Creedmoor from a few years ago. Despite burning out many other barrels, I have NEVER ridden the wave as far with any other individual barrel as I did with that tube, and I observed something I simply cannot yet reconcile. That barrel lost over 250fps over the life I fired from it, using the same load, same powder lot, same primer lot, same bullet lot, same brass (annealed each firing), and same neck tension... however, shooting confirmation ladders every 150rnds or so, the charge weight nodes didn’t move, despite the velocity slipping as much as ~25fps per 100rnds fired. I jumped to a higher node by the end of the competition season to give myself back the speed to keep my DOPE relevant, but despite the fact I was bleeding speed like crazy, my “nodes” were clearly powder charge nodes, not really velocity or barrel time nodes.
OBT, magic velocity goals, velocity nodes, seating depth nodes, etc... none of it reconciles. But the Satterlee velocity curves, modified Newberry OCW targets, and long range Audette ladders all confirmed my charge weight node was holding, even though my velocity was changing a foot per second after every 4th round fired...
Doesn’t make any sense at all, and I don’t intend to ever ride a barrel down that long of slope ever again to retest, so the end result of the observation is largely that about the time I think I have something figured out, something will come along which totally flips the script - but shooting small is easier than understanding WHY it shoots small.
I made it to the range finally setting up at 500 yards with loads at l set at 30.5 gr , my goal is sighting the scope for 500 and see if this rifle is going to print some groups.
Well things didn't quite work out the way I was hoping..wind and mirage added a layer of complexity on top of a what I believe is a slight neck tension issue ...i really don't like these groups shape size or lack of consistency , I also noticed that .0015-.002 neck tension using my components will not hold the +025 depth that came with the rifle data' meaning BTO 1.823 soft seats to 1.806 that will not do at one thousand yards' . I dropped a thousand on the bushing, the depth held so I reloaded a few for another look tomorrow
I will also take a few pictures of the range we have and moving forward ill grab a couple at deep creek.
If I remember .
the view coming back from the 500 y line
Your right about that but the name of the game is consistency so that leaves me another hundred brass to get the same seating force / neck tension followed by fine tuning of the seating depth, in addition to staying on top of the powder charge as the weather warms up however...being in the middle of the node should give me some flexibility.
working with my brass i use a 30/.300 comparator bushing to monitor the brass growth at the base to 300 datum, my chamber is 1.202 then after setting back the shoulder I'm 1.200 on brass #1 however brass #2 is once fired at 1.198.5
One more firing should even them out.
Both sets of brass have necks turned to .0108 -.011 about as close to each other as I can so hopefully the 262 bushing will give me the same OD after sizing followed by very similar seating force, here my tools only go to 5/10,000. Not perfect but not bad. ( why does a 262 bushing size to 261? IDK it just does)
It seems after about 4 foulers this barrel settles down and starts printing very similar to those on post #33. I had my wind flag out giving me an understanding of the slight horizontal I see on paper, I also took my chronoghaph for some speed comparison, ill post that a bit later.
Don't be shy now!
So if im reading things correctly' the chronoghaph numbers reviewing in order of last to first seem to correlate with the point of impact except for shot 4 ( assumed fouler) could just be a crappy shot, nevertheless im gaining confidence in this brass and bushing selection.
Thinking a bit further this may be a great example of what is referred to as positive compensation whereas speeds are varying slightly yet rounds are impacting on the same horizontal plane. (This supports why we look at POI when shooting ladders rather than group size or shape.)
I use a mirage shield on the barrel, what's a mirage board?
at 500 yards then look again on practice day which is Friday before the Saturday Sunday match at 1000 yards or load what I have at +.025 and take my seater and arbor press, shoot a few practice groups for a standard then decide?
166 loaded rounds at full depth ( +.025) going to my event April 9-10-11th
Final seating test will be at 1000 yards.
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