I've been handloading for 20+ years but need input. I'm working up loads with a CVA Cascade SB with Suppressor (308 Win) with TAC and 150 SST. In March I used 45g TAC, Sig brass and Fed 210/cci 200 primers. Groups were 1-1.5 moa @ 2700. Last week I swapped primers for WLRM and velocities were 2850! Groups were sub-moa. Thinking my chrony was wacky, I tried again this week and lowered the charge to 44.5 TAC. Verified the pro-chrono was working with other established loads. It shot the groups below at over 2800 again. This is 1.5 grains below max and I'm trying to figure out 1) why the increase in velocity (mag primer and/or 50 temp increase) 2) am I red-lining this load? My initial guess was 2750 would be a good max for an 18 inch 308 but it is "efficient". Thoughts?

In regards to velocity, both probably contributed with the primer maybe your prime suspect.

Accuracy could be either the primer or you've hit a node, you'll find that out when you shoot the reduced load.

Pressure-wise, I think 2700 to 2750 fps is something I'd be more comfortable with, though I'll admit I don't have much experience with TAC.

That group sure causes conflict, doesn't it?

Yup, my head tells me it's too good to be true. Don't need the speed but it sure shoots well.

I’ll have to look when I get home to see what my charge is, but my 18” gets 2800 with 150gr accubonds using published data and CCI 200s.

I think the answer to both questions is Yes.

I shoot a lot of TAC in my 22” 308 Model 700. I get 2,900 fps with 45.1 grains under a 150 Hornady FMJ, which is two full grains below Hodgdon’s max. I also get 2,809 fps with 45.8 grains under a 150 Hornady Interlock. Hodgdon doesn’t have data for the Interlock, but they show 46.6 grains of TAC as max for the similar Sierra SBT, with a velocity of 2,947 fps.

Their loads are in Winchester cases with standard WLR primers. Mine are in Lapua brass with WLRM primers, which may explain the difference.

In an 18” barrel, I’d expect to lose 100 fps (25 fps per inch of barrel). That would give you about 2,800 fps with the first load and 2,700 with the second, so I’d bet that your velocity is high but not necessarily too high.

Hodgdon lists several loads well north of 2,950 fps in a 24” 1:12 barrel, including 46.9 of TAC under a 150-grain Hornady SST for 2,926 fps. Nosler gets over 2,900 fps with three powders including 46 grains of TAC for 2,996 (!) fps in a 24” 1:10 barrel. Subtract 150 fps from any of those and you’d be about where you are now.

So, yeah, I think the primer switch combined with the higher temperature increased your velocity. Fortunately, TAC tends to be most accurate at high pressures, so you might have found a sweet spot. Unfortunately, TAC isn’t known for being temperature insensitive, so you might not want to shoot that load in hotter weather than you already have.


Okie John

Thanks guys.

I agree with Okie John. I get 2900 fps out of my Ruger Hawkeye .308 with a 22 inch barrel using 46.0 grains of TAC, Federal 210 primer and a 150 grain TTSX. So your results don't seem out of line. BTW, I shot my load in hot weather (mid 90's) and didn't see any real difference in velocity.