[sredish]

I'm looking to build a new rifle. I'm thinking something in the 18" range for a good compromise. I'm trying to decide if I want to do a 5.56 or 6.8. My only 6.8 is an sbr (10.5") and I don't get to shoot it enough due to lack of ammo locally and the price, compared to having plenty of 5.56/.223. Because of this, I'm afraid another 6.8 will sit but I'd really like a good 18" stout rifle.

Rarely would I ever encounter a situation to shoot past 400 yards.... maybe very very rarely to 500. My question is the trajectory of 6.8 compared to 5.56 in the 300 to 500 range. My sbr has a short range zero and I'm anxious to play with it to 400 but have yet to. Is there a good chart showing more accurate trajectories?

 

[JAOwens]

would like to see something along these lines as well. For ammo I am personally looking at 85gr tsx (tactical) and 90gr tnt's. I honestly dont care what loads for 556 but charts and graphs are always good to illustrate (wink wink) just how good the 6.8 really is. The main reason I am interested though is to determine how far off the zero will be if I sight my baby in with the TnT's and use the TSX's come hunting season or whether I will just have to re zero. If I do Art and Nancy will get more money to pay for moving expenses

 

[CaseyJ]

Ill try to get some screen shots of the ballistic program on my iPhone with the data you're looking for.
ETA: these are for the 18" barrel with the velocity figures from Paulo's data.
Corbon DPX 6.8 SPC 110gr TSX (rough numbers)

Sierra 90gr HP

If you have any info you want me to input into the program and make a table for you just let me know. I can change the increments as well as atmosphere, angle, and everything else you see in the table. I can also compare rounds such as 5.56 vs 6.8 vs 7.62. You give me the info and I'll do my best to get you the info.

 

[sredish]

Yea, i was more or less wanting to compare 5.56 to 6.8 to consider my next build. I was kind of wanting to build a 16" or 18" 6.8 for some longer range strong hitting shots, seeing that the 5.56 loses some oomph for game or something other than paper or steel. My sbr is 10.5" is setup with an Aimpoint and I may just set up my 8-14 scope for long range with it and use the aimpoint for the majority of the time. But, I'm not totally sure what my usable distance is on my 10.5" 6.8, I'm assuming in the 300 yard range, which is enough really.

On my 5.56, I can hit 300 to 400 with the aimpoint and a magnifier but it appears the 6.8 drops and may only be reliably usable with an aimpoint / magnifier to 250 or so, which is still fine. I'm struggling to figure out what I want to do with this next build. Rarely do I really take a shot at game (large game/hunting or varmits) longer than 200 yards so the sbr truthfully is suitable for a good all around rifle that's easy to carry. So, I may consider setting the new rifle up as an 18" 5.56 for a nice super flat varmint type rifle. Wonder how many yards out a 5.56 is truthfully usable for something like coyotes or similar sized game? I'm not a paper pusher and don't really go out too much to shoot paper at yardage for fun, but I could see the benefit on my ranch at shooting a coyote at 400 to 500 yards in some cases if I wanted, but not enough to build a dedicated varminter. I have a 16" Colt 5.56 that I thought about using this for but being a Colt, it's not going to be super accurate like a dedicated varminter but probably accurate enough for me. Then I thought about a short 10.5" 5.56 to use for closer distances (0 - 150) and a suppressor a to go with my 6.8 sbr.

Decisions.......

 

[Equalizer_2]

The velocities used on the 6.8 loads in the chart are probably taken using a SAMMI chamber with a 1/10 6 groove twist. Using a barrel with the proper chamber and twist could likely increase velocities a notable bit.

I have SPCII chambered 1/10 6 groove shooting factory 110 gr VMAX and had velocities that were 60-80 fps faster. In my 20 inch DMR chamber 1/12 3 groove I was getting 170-200 fps faster with the same ammo. Of course an 18 inch would be a little slower but definitely faster than the velocities CaseyJ had to work with.

Here is what SSA shows for their 90 gr TNT load - 6.8 SPC 90 grain TNT Practice or Varmint Round, Ammunition, 20 rounds/box
</META></META></META></META>2,900 FPS from a 16" Barrel Excellent accuracy

And the price is about $16 a box if you buy 25 or more boxes. If I hadn't just spent all my money on a new refrigerator for the house and some needed parts on my truck I would be laying in about 30 boxes myself at that price.

 

[CaseyJ]

90gr TNT @ 2900fps as requested

Drop chart