Rifle - Tikka T3x Lite 6.5CM 24" barrel
Load - Hornady brass, Fed 210, 42.4 H4350, 140 SGK
Chronograph shows average right around 2680 pretty consistently. I shot to 800 yesterday - reversing the trajectory shows closer to 2580. 200 yard zero, 4.1 Mil at 600, 6.9 Mil at 800. Crazy accurate - way sub-MOA out to 800. I won't do anything until after the season, but should I step on the throttle and see what happens? Velocity seemed awfully low for the load and barrel length. Thoughts?

It could be that the chronograph is accurate but the published BC of the SGK is a little overstated.

Tikka are pretty well known for there slow barrels so you may not get a whole lot more before pressure.

43.0 gr under a 140 gr bullet is usually all they will handle.

Ckat, you'll pick up some more speed if you're currently on virgin brass, and you headspace the fired brass .001" to .002" back from the fired length.

good info above
, 2680fps is good, I think you would need to change powder. I'm using RL-16, 143ELDX, 20" Proof Carbon barrel, getting 2734 if i remember correctly

Is it the velocity that is off or the BC?

If I were looking for more horsepower I'd try RL16, as Buzz mentioned. It's great stuff.

Typically you true velocity inside of 700 and adjust bc out at farther distances. This is if you are already in the ballpark velocity and bc wise.

Didn't think about that. This is using JBM. They don't have a Litz verified option for that bullet - and verifying the BC of a hunting bullet is probably low on the priority list.

Thanks for the info. I know you all have a lot of experience with this chambering.

This is twice fired brass, just bumping shoulders back a bit.

I have no issues with leaving it as is. This combo is INCREDIBLY accurate. Pretty neat to get down and shoot 3-4" groups at 600-800 yards with a lightweight hunting rifle. Sub-1/2MOA 3-shot groups at 100 yards are the rule, not the exception. 1/2-3/4" 3-shot groups at 200 is also common. Hard not to love a setup that is that easy...

Pretty good speeds, Buzz. I'll take accuracy over speed any day... I just didn't want to be leaving a bunch of FPS on the table.

I'd personally leave it. I'll take 100fps slow but boringly consistent any day over max speed.

If you're using Sierra bc they are fairly close in my experience with a few extreme exceptions.

What chrono were you using?

I may need to try it. I tried some RL26 in it one time as suggested on another forum, but was unimpressed. I use a good bit of RL15 in other chamberings. I think I still have around 15 lbs of H4350, though.

If you (or someone else) get a chance, can you expand/explain this? Thanks!

ProChrono. Not a top-tier, but has been very consistent (not sure about accurate) for me.

Consistent shooting is more important than velocity. Yes, we want them going as fast as possible, but I'll take a tight shooting slow load over a big shooting fast load, every time. Your current powder charge is right in line with where it should be, you just might have a slower barrel. Just the way it is sometimes.

BC can be input incorrectly but velocity can be input correctly and the calculator data and true DOPE will match to 700-800 yards. You have to shoot father to see if your BC is input correctly. So, if there was a BC error, you wouldn't know it inside 800 yards, but you'll see it farther out.

Similar to BC and weight being off my 100 fps at the muzzle, and your corrections at 200, 300, and sometimes 400 yards are still matching the calculator. 500+ yards is where you'll really see if your MV is right or wrong. So if you need more elevation correction up for 500 yards, you need to lower your MV in your calculator. If you are hitting, or missing high at 500+, you need to go back in the calculator and raise your MV.

I've got access to really good chronographs, but I often use the DOPE vs calculator method anyway to find MV, but I've got 800 yards to work with every week of the year, and I'm there every week of the year.

I'm sure it is nice to have an 800 yard range in your front yard.

Some might say I'm spoiled. I say, I worked my azz off for it, so not spoiled, very blessed though.

JG covered it well. Something to keep in mind when verifying bc is that your high bc fast rounds will typically need a little bit more distance to give you a clear answer. I prefer large targets to verify both speed and bc. I will paint a horizontal line across the middle of the plate for a watermark line for aiming that way I have wiggle room for wind allowing me to hold center of the plate all the time. All I'm concerned about is if I hit the line not left or right.

Thanks for the feedback. I think I'll just roll with it for a while...

Dee, good idea on the large target with a "watermark."

If you are not using a G7 then Sierra does give 3 different G1 accounting for loss of velocity over distance and related BC changes. If you are using the highest velocity BC only that may be part of it.
The most common error I run into is the 100 yard zero is a half inch low or high or more and not accounted for.

I was going to bring up the G1 vs G7 argument. I struggled getting good consistent results with the "Shooter" app with my 6.5CM and 140 ELDM, so I downloaded Hornady's calculator and it's always dead nuts on. Not sure what the issue was before, but I didn't change any of my inputs - the results are just more accurate. I agree if you're getting bad results at 800 with a slow-moving round, it could be due to BC or MV. If we had this same conversation at 400-500, it would almost have to be MV.

He also uses a beer can to show group size at distance

Dee has several tricks up his sleeve.

Every farmer has empty beer cans laying around right.........