I’ll start out by saying I’m completely new to this, but I recently purchased a browning Xbolt Speed SR in .308. I’m trying to get it dialed in for hunting season and am unfamiliar with the .308 caliber and it’s ballistics since I grew up hunting with a .270. I do not have a suppressor on my gun at the time but might look into it in the future. I went to the bench and shot my gun today and had it shooting about 2” high at 100 so I backed out to 200 yards and shot a couple of times. I was surprised to see that the bullet drop was about 4” low at 200. Is this common for a shorter barrel .308? I’m using factory Winchester XP 150gr bullets and the ballistics on the box showed that 2” high at 100 would be zeroed at 200. I apologize for my ignorance with this whole situation but would like to learn more about my new riffle and my situation.
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18” .308 help
- Thread starter DW308
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- .308 18" browning x bolt
- Nov 3, 2010
- 9,697
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Factory ammo speed on box is more than likely from a 24 inch barrel. Your not going that fast more than likely.
I figured I was going to be a far bit slower than the barrel the ammunition was tested with. I’ve done some searching to try and get a rough estimate on speeds out of an 18” barrel. From what I’ve seen it still seems shocking to me that it there is that much bullet drop for me when I shot today.
- Nov 3, 2010
- 9,697
- 20,383
Depends on what number you believe, but ranges from 25-50 fps loss per inch of barrel. I’m your case that could mean anywhere from 150-300fps or better depending on all the variables combined.
JBM - Calculations - Trajectory
www.jbmballistics.com
A Win .308 150gr Power Point at standard temperature and pressure shows a 6" drop from the 100 yard zero to 200 yards at 2465 fps.
I'm willing to bet you are cruising 2700fps with an 18" 308 bolt barrel. Hornady calculator with generic but common numbers:
The box trajectory is actually pretty spot on for a 2” high 100 and zero 200. You would have to run an incredibly low velocity or BC for this round to be that bad of a drop at 200yds. 4” is absurd.
The box trajectory is actually pretty spot on for a 2” high 100 and zero 200. You would have to run an incredibly low velocity or BC for this round to be that bad of a drop at 200yds. 4” is absurd.
Would that factory ammo be that daggum slow?JBM - Calculations - Trajectory
A Win .308 150gr Power Point at standard temperature and pressure shows a 6" drop from the 100 yard zero to 200 yards at 2465 fps.
I have a couple different boxes of ammo (I know the ballistics on the box are for a longer barrel), but the Winchester deer season XP 150gr show 2820 muzzle velocity 1.9” high at 100 is dead on at 200 and 8.1 low at 300. My Barnes vortx TTSX 168gr show 2” high at 100 dead on at 200 and 8.4” low at 300 with a 2700 muzzle velocity. I know I’m shooting slower than this but I’m just putting that out as a reference for a couple of different brands.
I’ve got a Vortex viper 6.5-20x44. I never really had the chance to shoot longer ranges growing up hunting where I did, but the last few years those places are changing and having potential longer shots now. Shooting the slightly longer ranges (for me anyways) is still something new to me.
If he didn't offset his 100yd zero....he'd be basically 6" low at 200yds. That's 3 MOA low....which is roughly .8 mils.
Beings .5 mils low for 200yds is common as fuck for 308WIN with a traditional barrel length.
So being a short barrel and only being .3 mils more isn't extreme at all. Especially when the OP uses words like, "shooting about 2" high at 100yds". Which means we don't even really know if it even amounts to that much. He could in fact only need .7 mils and we wouldn't know and it would be even more rational.
That said, he could go shoot the actual distances and write down what was actually needed and we would have actual info to work with.
Beings .5 mils low for 200yds is common as fuck for 308WIN with a traditional barrel length.
So being a short barrel and only being .3 mils more isn't extreme at all. Especially when the OP uses words like, "shooting about 2" high at 100yds". Which means we don't even really know if it even amounts to that much. He could in fact only need .7 mils and we wouldn't know and it would be even more rational.
That said, he could go shoot the actual distances and write down what was actually needed and we would have actual info to work with.
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I took this as he had actually shot at 200yds. I suppose you could also infer that he just read what his dope chart said.
"I went to the bench and shot my gun today and had it shooting about 2” high at 100, so I backed out to 200 yards and shot a couple of times. I was surprised to see that the bullet drop was about 4” low at 200."
The "about 2" is not confidence inspiring, but he clearly stated what he did, the results he got, and referenced the ballistics chart on the box. I don't understand the confusion as to what he did or said, only to the results he got in comparison to what physics calls for. There is bad data being imputed into the equation, or the dude can't shoot for shit. Hard to tell from a chair and computer!
