? .308 Trajectory ?

thatmikeguy

thatmikeguy

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Steinbach, Manitoba
According to my studies, a .308 that shoots about 3 inches high at 100 yards will be about 2 feet low at four hundred. my results have been more rainbow like. mine hits 4 inches high at 100 and about 4 feet low at 450 yards. Is this normal?? I'm using 42 grains of imr 4895 and sierra gameking 165gr spbt. can any one check this combo on quick load? my gun has a 21 inch barrel.
 
You have to chrony your load the BC of sierras is 404 but I used 2575fps you should be
- 22" at 400 if 3.9" high at 100y

Range
yds Path
in ComeUp
clicks Velocity
fps Energy
ft/lbs Momentum
lb ft/s ToF
sec Windage
in Windage
clicks Optimal
Game Wgt
Muzzle -1.5 Infinity 2575 2429 60.70 0.000 0.0 NaN 697
100 3.9 -15 2361 2042 55.65 0.122 0.9 4 537
200 3.1 -6 2158 1705 50.86 0.255 3.8 7 410
300 -5.2 7 1964 1413 46.29 0.401 9.0 11 309
400 -22.5 22 1781 1162 41.99 0.561 16.7 16 231
500 -50.9 39 1611 951 37.98 0.738 27.4 21 171
 
thatmikeguy said:
According to my studies, a .308 that shoots about 3 inches high at 100 yards will be about 2 feet low at four hundred. my results have been more rainbow like. mine hits 4 inches high at 100 and about 4 feet low at 450 yards. Is this normal?? I'm using 42 grains of imr 4895 and sierra gameking 165gr spbt. can any one check this combo on quick load? my gun has a 21 inch barrel.
Click to expand...

What bullet and load are you quoting in your 3 inches high, 24 inches low at 400? A factory load for a fast 150 grain will be vastly different from a low velocity 168 grain handload. Then factor in scope height, and how precise your groups are, will make a lot of difference. Group size will also make a difference (a large 3 shot group will make it hard to determine the exact height of the point of impact, and a single group is no indication of the true point of impact).
Also, bullets will drop a lot between 400 and 450 yards. Check your studies on the difference. It is unlikely to be 24 inches of difference, but it could easily be 8-10 inches.
As others have pointed out, a lot more information is needed if you really want answers.
 
You know, if you read the estimated data provided by Manitou, you would be over 4 feet low at 500 yards. As I have tried to point out above, determining the exact point of impact depends on having a very clear group. Your 'about 4 feet low at 450' is very close to over 4 feet at 500. I don't think there is any mystery in what you are seeing when you shoot. I suspect that you are not getting the 2575 he mentioned, as the IMR page shows about 2500 fps with your load, and you have a shorter barrel. At the ranges you are talking about, slightly slower speed will have a significant effect on the trajectory.
 
Plugging your data into a ballistics calculator (JBM) it appears that your muzzle velocity with the 165 gr Sierra is about 2500 fps. This gives you 4" high at 100 for a 250 yard zero and will result in a drop of 3' at 450 yards. You would be 4' low at 480 yards, so perhaps you made a small error in your range estimation. The fact that the bullet drops a foot only 30 yards beyond shows the importance of accurate range estimation and repeatable sight adjustments when shooting at long range.

IMHO, the velocity is a bit low for that bullet when shot from a .308 unless you have a very short barrel. I also think that your short range zero is a bit high as I prefer that a bullet rises no more than 2"-3" above the line of sight at 100 yards, but if that works for you have at it.
 
for me, 4 inches high at 100 yards is too high for hunting. i've always wanted to try longer shots and this was my first time so i'm still figuring this out including my loads. i don't even have a loading manual. i've been using laod info off the net which can vary quite a bit. sierra's info states 42 grains as a max load where as imr lists 45 grains as max and hogdon lists 43.5 so i'm not sure at all what my velocities are or which one to trust. my sierras have been grouping at best .800 inch up too 1.25 inch at 100 yards. i just bought some hornady sst. they shoot well but don't group quite as good (1.5 inch so far)
 
Go to - 6mmbr.com
In the 308 section there is a link to the Sierea loading maunal for .308.
Print it - now you have aloading manual for .308.
Also good reading on match loads.
 
I think the discussion is all academic. If you plan on shootong at game at 350 yards plus, dump the .308 and get a .300 magnum and practice, practice, practice UNDER FIELD CONDITIONS!!
 
sometimes i get a little caught up on the "academic" side. I know there is no replacement for practice. I bought the gun in spring and i've fired over 300 rounds. i find that 200 and 300 yards feels easy now and i want to try farther. I've been thinking of purchasing a 300 win mag. It shoots flatter and farther. I've fired one once and i found the recoil easily tolerable.(for some reason i find the recoil of the 270 much more brutal!!) I really like my .308 but it's starting to feel under powered though i think it is an excellent round.
 
Mike Webb said:
I think the discussion is all academic. If you plan on shootong at game at 350 yards plus, dump the .308 and get a .300 magnum and practice, practice, practice UNDER FIELD CONDITIONS!!
Click to expand...

Pfft. If he wants to shoot further then say 150 yards he should probably just get a .50 BMG. :rolleyes:

Past 200 yards you need a 20mm, and past 350 yards like you say I personally use a mortar. :rolleyes:
 
If the intention is to shoot big game beyond 300 yards I concur, but coyotes and such are good targets for a .308 out as far as you can hit them. Given a 165 Sierra at 2500 (probably chosen for accuracy rather than effectiveness) the bullet has slowed to 1900 fps at 300, and IMHO this is below the velocity where the bullet will function reliably as designed on a big game animal. There is more to the big game bullet than the accuracy required to hit the target. At impact the bullet must have the velocity and the appropriate construction to deliver a lethal blow. It can deliver that blow in a number of ways depending on the design of the bullet, but there must be sufficient velocity to allow that to happen and create a deep and wide wound channel, even when big bones are hit. Bullets that are designed to function with impact velocities up to 3000 fps on big game, tend not to function as reliably one the velocity has dropped below 2000 and almost without exception at velocities below 1700 they will pencil through. In such cases pointed bullets will cause minimal wounding, and almost no blood trail, although flat nosed bullets do better, sometimes much better. Choosing a .300 Winchester significantly extends the range of a 2000+ fps impact compared to the .308.

I can't imagine how you found a .300 Winchester more tolerable to shoot than a .270, but perhaps the .300 fit you just right or perhaps you were feeling sensitive on the day you shot the .270. Anyway, if reach out and touch stuff at long range is your ambition, the .300 Winchester is sort of the entry level to the world or real recoil. It is unlikely that would would be able to shoot as many rounds per sitting with a .300 as you can with your .308, before your trigger control began to slip. Rocky Chandler wrote a very good piece praising the attributes of the 7 Mag for long range work. While some of those advantages don't have significance for a civilian shooter, the combination of long range accuracy and flat trajectory with moderate recoil and blast is hard to ignore.
 
Hey Enigmatic, I wasn't advocating that he join the artillery. I just feel that shooting game at 400 or 500 yards is pushing the envelope for a sporting rifle under real world shooting conditions( e.g., no benchrest ). Any mistakes in range estimation result in big differences in point of impact. Having a .300 Maggie just removes more variables. At that range every little bit helps.
 
so far i have never had the opportunity to shoot at deer beyond 100 yards but i do however want to be able to if the situation confronts me. do i really need something more powerful? most likely not but it would be cool.
i did choose sierra bullets for accuracy however i have not killed anything with them yet so i can not testify to their effectiveness. the majority of my shooting is done at targets hence the necessity of more power is not so great. right now i am experimenting with hornady 165gr sst. they are not quite as acurate but still shoot great. they have a higher bc and seem to shoot flatter. i have not killed anything with those yet either.
 
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