WEIGHT VS. RIM THICKNESS - part 2, 100 yards

Discussion in 'Rimfire and Airguns' started by top predator, May 23, 2010.

  1. top predator

    top predator Well-Known Member

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    Nov 17, 2008
    I started off at 50 yards, see: http://www.longrangehunting.com/forums/f33/weight-vs-rim-thickness-part-1-50-yards-55942/ Unfortuanately we've been plagued with enough wind that would not do a 100 yard test justice, and today was the first chance I had to hit the range in a calmer setting.

    Just as in the 50 yard test, three different ammos were shot from a Savage MKII BV 20" heavy barrel, bipod and rear bag, 1 lb trigger, 18x on the scope. 65 deg., high humidity (80%), cloudy to partly sunny, 3-5 mph but managable wind (may have opened up groups slightly).

    I seperated the ammo like in the 50 yard test - several different 5 round same weight lots, several 5 round rim thickness lots (making sure that every round weighed differently to ensure results were based on rim thickness, not weight). This time I brought the chronograph to measure what is any differences / simularities there were between the diffeerent weight and rim thickness lots of the three different ammos, placed 5 feet from muzzle. Groups were measured on the outside edges of the group.

    Group #1 excluded obvious flyers (main body of the group), group #2 included obvious flyers (ranging .25" to 1.25" away from the main group). Anything further away I considered a pulled shot and took another round to replace it. Any shot that I knew I pulled was refired also.

    AGUILA MATCH RIFLE

    (weight sort):

    Weight - avg. fps - dev. - grp. 1 - grp. 2 - # flyers

    50.6 gr --- 1001 --- 42 ---- 2.5" ----- 3" ------- 1
    50.8 gr --- 1010 --- 20 ----- 1" ------ 1" ------- 0
    51.0 gr --- 1017 --- 7 ----- 1.5" ----- 2" ------- 1

    (rim thickness sort)

    Rim t. - avg. fps - dev. - grp. 1 - grp. 2 - # flyers

    .0355 ---- 1008 --- 25 ---- 1.5" ---- 2.25" ----- 1
    .0360 ---- 1010 --- 14 ---- 1" ----- -2.75" ------ 2
    .0365 ---- 1020 --- 13 ---- 1.75" --- 2.5" ------ 2
    .0370 ---- 1011 --- 31 ---- 1.25" --- 2.25" ----- 1
    .0375 ---- 1014 --- 30 ---- 1.5" --- -2.25" ----- 1

    FEDERAL BULK PACK

    (weight sort)

    Weight - avg. fps - dev. - grp. 1 - grp. 2 - # flyers

    49.1 gr --- 1143 ---- 61 ----- 2" ----- 3.25" ---- 1
    49.2 gr --- 1163 ---- 49 ----- 2" ------- 3" ------ 2
    49.3 gr --- 1165 ---- 57 ----- +2" ----- 2.5" ---- 1
    49.4 gr --- 1199 ---- 42 ----- too large to mention / measure accurately

    (rim thickness sort)

    Rim t. - avg. fps - dev. - grp. 1 - grp. 2 - # flyers

    .0350 ----- 1193 --- 56 --- 3.25" --- 3.25" ---- 0
    .0355 ----- 1157 --- 68 ---- 1.5" ---- 3.5" ----- 2
    .0360 ----- 1177 --- 40 ----- 2" ----- 3.5" ----- 2
    .0370 ----- 1175 --- 51 --- 3.25" ---- 3.5" ---- 0

    CCI BLAZER

    (weight sort)

    Weight - avg. fps - dev. - grp. 1 - grp. 2 - # flyers

    50.5 gr --- 1230 ---- 50 ---- 1.25" --- 2" ----- 2
    50.7 gr --- 1237 ---- 35 ----- 1.5" -- 1.75" --- 1
    50.9 gr --- 1238 ---- 38 ----- +2" --- 3.25" --- 1
    51.2 gr --- 1246 ---- 19 ----- 1.5" -- 1.5" ---- 0

    (rim thickness sort)

    Rim t. - avg. fps - dev. - grp. 1 - grp. 2 - # flyers

    .0380 ----- 1239 --- 12 --- +1.25" --- 2" ------ 1
    .0385 ----- 1233 --- 30 ----- 2" ---- 2.25" ---- 1
    .0390 ----- 1243 --- 35 ----- 1" ---- +1" ------ 0
    .0395 ----- 1238 --- 22 ---- 1.5" --- 2.25" ---- 1

    The one trend I did notice with all three ammos (in general) is that with the weight sort the FPS increased and deviation between the highest and lowest FPS decreased as the lots used heavier ammo. No such trend was evident with the rim thickness sort.

    Both weight sorting and rim thickness sorting improved on the baseline groups shot by .25" to 1" - the baseline groups were 5 shots each of different weights and rim thicknesses to guage what or if any improvement was made. I also felt this simulated an absolute randomly picked "out of the box" 5 shot group.

    CONCLUSIONS:

    weight sorting -

    1. Tighter groups, however flyers were further away from the main group.
    2. The heavier the weight the higher the FPS.
    3. The heavier the weight the lower the deviation.
    4. More predictable the group and velocity.


    rim thickness -

    1. Larger groups, most flyers were not so far away from the main group.
    2. No real trend or correlation between rim thickness and change in FPS or deviation.

    Weight sorting produces more "lots" than rim thickness, perhaps telling me that it singles out more differences than rim thickness sorting. Although neither completely weeded out flyers, both did work to reduce them drastically and shrunk group size. Most of what I call "flyers" were only .25" away from the main group. If you feel that a .25" or even a .5" impact away from the main body of the group isn't really a flyer, you can make adjustments to the above measurements and eliminating many "flyers".

    Both weight and rim thickness sorting produced a "magic lot" or two in all three ammos that the rifle really liked and produced a better group than the other lots. By looking at the group's size and shape, it appears that the rim thickness sorting was less "finicky" when switching from one lot to another, perhaps due to the larger group size as compared to weight sorting at 100 yards.

    Strangely enough, the group results of 100 yards almost completely contridicts the 50 yard results. At 50 yards rim thickness seemed to have and advantage, while at 100 yards weight sorting performed better. The only thing i could ASSUME is that at longer distances, whatever it is about weight sorting superceeds rim thickness sorting and takes priority at those longer distances. If I didn't shoot it myself, I probably wouldn't believe it either. Yet another rimfire mystery.

    For me, it appears that at shorter distances, rim thickness wins for group size, and for longer distances weight sorting. Of course different ammos, rifles, etc. may have different results. However, the use of the chronograph revealed the better consistancy of the weight sorting over the rim thickness sorting and the groups at 100 yards backed it up on average. This consistancy with the weight sorting in the end equates to accuraccy, at least at further distances, and isn't that what it's all about?