Nosler AB and jump nodes.

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Driftertank

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Just wanted to share some observations from a test I did yesterday with some 160gr Nosler Accubonds in my Bergara B-14 Ridge rifle.

The internet has a lot of back and forth with jump info for these rounds. I decided to do a relatively controlled test, using a known combination of case, primer, and powder, and varying only the jump dimension. I used an intermediate load of H1000 in Hornady brass with Fed 215GMM primers. I did not change charge weight throughout the test, so the variation in case free volume may effect pressure and velocity separately from the effects of jump length, but it was my belief that altering the powder charge would introduce more variables and reduce duplicability.

Measured COAL to lands in my rifle was 3.364"

Prior tests with jump dimensions between .020" and .040" were underwhelming at best, so I decided to look into longer COALs.

Ammunition was loaded in pairs (I'm running short of bullets lately) at .020" intervals, between 3.220" and 3.300"

Testing was done at 200 yards. Center bullseye hold was used in every case. Given the small sample sizes, I was only looking for trends.

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Initial conclusions seem to suggest that, for this cartridge/rifle/bullet combination, the 160 AB's are happiest at around .080" or .140" off the lands, with the longer jump possibly being more forgiving, based on the fact that the .120" group shows smaller sizes than the .060" and .100" groups. I didn't go any shorter than 3.220" COAL because the ogive is getting quite close to the case mouth at that OAL.

I have loaded another couple small sample groups worth of ammunition at the 3.220" length and plan to revisit this next time I have a day off to get back to the range.

Sorry for the small sample sizes, I'm trying to get a load put together for my new hunting rifle and still have enough heads to hunt with until more 160 AB's materialize again. Still, I thought my relatively empirical data might be useful to someone trying to get these to shoot.
 
I feel your pain with the small sample size. I’m in the same quandary with pistol rounds. The problem, as you probably suspect, is trying to draw conclusions with limited shots. I wanted to verify my red dot was sighted in at roughly 40 yards, do I chase three round groups or quit when I’m “close enough”?
 
the ogive is getting quite close to the case mouth
Axis 6.5 CM- Seated 1st bullet 123 gr Hornady to deep. So made 4 more to test. First 5 shots out of barrel .312" @ 100 yds. A fluke. Gun is a 1 1/4" average gun, on a good day.

I tried everything else, why not extremely short COL.

Loaded 5 each, 120 MB, 123 Hornady, 123 Nosler & 140 gr MB. All with same 40.5 grs IMR 4350. 5 groups fired, 3 groups under 1" Needs more testing, but very surprising results. The group killing vertical is less.

Or is it because of the 1 other change I made?
After firing, wet patch Break Free CLP.
Run wet patch to where it almost exits the barrel x 5 . Back & forth. Done.

Next outing, before firing, 1 wet patch CLP X 5. Then 1 dry patch x 5. Done, after a quick wipe of the chamber. Go shooting. A lot less cleaning.

The neck splitting Hornady brass that I annealed, have 3 more firings on them, seems to have corrected the factory brass brittle issue. Lost 10 to splits. Annealed remaining 10.
 
My first workup with the bullets gave me about 1" groups at 100yds at 68gr and 71.5gr charges.

Parsing the internet for information reveals a lot of "these bullets like to jump," so I did a methodical jump test.

Seeing the sub 1/2 MOA pair at .140" is sort of promising...and echoes some results from a .30-06 load I made recently with 165 AB's. -.125" was mag length on that rifle, and I did my charge ladder there for some promising results around 1moa, then bumping them back another .020" put them to sleep...1/2 MOA or better, repeatedly.

I have a half dozen of the stumpy little things put together to test, hopefully have a chance on Tuesday. Hoping they prove out; 3/4" groups at 200yd is more than adequate for my purposes. But if it doesn't go how I like, further experimentation will have to wait until I can get more heads...I'm under 2 dozen left on the bench.
 
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