I got a note from another shooter who told me that he shot 77 gr SMKs in his 1:9 twist .223 and had good results.
He claimed that the bullet shape overcame the stabilization problem.
I have had great results with 77 grain SMKs and TMKs in my 1:8 .223 but I have always read that a 1:9 twist wouldn't stabilize bullets over 73 gr bullets, so I never tried them in my two 1:9 twist rifles.
Always curious to try something I haven't tried yet, I loaded up 77 gr Sierra SMKs and TMKs with IMR4166 powder at the 12th reflection time (1.360 msec.) at 2540 fps in my 12 FV .223 and gave them a try.
The 10th reflection time (1.134 msec.) pushed the pressure over Pmax.
I was really surprised at the results.
# Grps -------- Load Description -------- --- Bullet --- Wgt. --- --Vel-- -- Avg. -- Median --St Dev-- ---1--- ---2--- ---3--- ---4---
-- 3 --- IMR4166 21.0 gr 2.384 1.758 --- SMK #9377 --77 ----- 2540 -- 0.515 -- 0.524 --- 0.045 -- 0.466 - 0.524 - 0.554
-------- wf 1.360 75/77 deg. F.
-- 4 ---IMR4166 20.9 gr 2.330 1.757 ---- TMK #7430 -- 77 ----- 2436 -- 0.280 -- 0.273 --- 0.053 -- 0.239 - 0.232 - 0.307 - 0.340
-------- wf 1.360 77/80 deg. F.
-- 7 --- Total ------------------------------------------------------------------ 0.380 -- 0.340 --- 0.134
-------- wf 1.360 77/80 deg F.
I have to say I was amazed by the performance of the TMKs compared to the SMKs.
So much for the concerns about stability problems with 77 grain bullets.
The SMKs averaged 0.270 better than the 70 grain Berger bullets that I had tried in earlier sessions but the TMKs shot
0.022 b
etter than any bullets I had tried with the 12 FV .223 so far.
I don't know if the results are atypical but I suspect that the higher ballistic coefficient of the TMKs might have had something to do with aiding in stabilization and achieving these results.
The 77 TMKs also out perform the 77 SMKs in my 1:8 twist.
Actually, TMKs that are similar weights to SMKs in my .308s consistently out perform the SMKs as well as long as the O.A.L. is longer to account for the 0.070 longer tips and get the ogive in the same place wrt the chamber.
I have always been surprised that no one supplies factory ammo with TMKs.
Perhaps it is because the TMKs would have to be seated longer by at least 0.050 and that might cause problems for magazine limits on some rifles.
Factory ammo just can't adapt for individual rifle chamber depths like a reloader can.
They would have to seat back to account for the smallest magazine and, from my experience, that would limit any benefits of the TMK wrt accuracy.
AR type mags limit seating depth on my 1:8 Les Baer Super Varmint and have forced me to use a single round follower with TMKs to seat the TMKs out where they perform best.
Thankfully, Savage mags have plenty of space for seating out the TMKs to take advantage of the TMK's inherent accuracy.
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