270 Win BT's vs CTBST, WLR vs WLRM

NYDAN

Handloader
Sep 17, 2013
1,165
91
To satisfy my own curiosity I shot two comparisons yesterday, one to compare 150 gr. BT's to CTBST and one to compare WLR to WLRM primers.

In the first test I loaded two sets of cartridges from 55.5 grs of IMR 7828ssc to 57.5 gr. In one set I had 150 gr. BT's and in the other set I had 150 gr. CTBST's. The two sets of cartridges were identical except for the bullets.

I found that for every load pairing that the BT's ran from 33 fps to 61 fps higher than the CTBST's. On average the CTBST required about 1/2 gr. more of powder to achieve the same velocity as the BT's. The POI's were nearly identical. The BT's may have printed about 1/4" higher. Both group were vertical strings with the higher charges printing higher than the lower charges. It appears that if I make up loads with either bullet I could acieve 0.5 MOA.

In the second test I loaded two sets of cartridges from 55.5 grs. of IMR 7828ssc to 57.5 gr. Both sets had the 150 gr. CTBST bullets. In one set I used WLR primers and in the other set I used WLRM primers. To my great surprise the cartridges with the WLRM primers averaged lower velocities than the cartridges with the WLR primers. Also, the velocities were less consistent and the group was much larger. I have Rol_P as my witness.

Can anyone make sense of why the cartridges with the WLRM primers would have achieved less velocity than the cartridges with the WLR primers? I tried the magnum primers because some reloading manuals listed using the magnum primer with the IMR 7828ssc powder. I am not inclined to try them again!
 
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