308 Ammo vs Twist Rate

[ROK]

So, a little help with right bullet. 1:10 20" Barrel.

I have access to a 100 yard range but have some time investment to get to longer ranges. New AR chambered in 762x51. I am told by maker that gun can handle and feed properly 308w.

At 100 yds the following were over 3 different days and 60 rounds of each.
1. tried 168 HSM 762X51 AMAX and my groups were loose about 2"
2. had some 168 W HSM HPBT for another rifle and shot 1" or better with a few groups shamrocked below 1/2".
3. M118 175 HPBT 3" was a good group? HSM was not in stock so I tried this (http://usarmorment.com/m118lr-762-175-gr-long-range-sniper-ammunition-p-1.html) and I thought 175 would do me justice?

1. Can anyone explain the difference between the 168 NATO vs 168 Win? Maybe too much caffine? In thought I wounder if there is a difference between the bullet lenght of the HPBT vs the AMAX? I do not see it on the site I will have to reseach that.

2. With the 175? Could it just be the difference of needing longer range... but really 3" groups at 100yds? I thought this round would do me justice.

- Barrel was boken in properly by the following procedure (http://www.snipercountry.com/articles/barrel_breakin_II.asp)

I appreciate the feedback.

 

[LoneWolfUSMC]

Re: 308 Ammo vs Twist Rate

First....what rifle.

Second....what chamber (is it 7.62NATO or .308WIN) there IS a difference, although not one that would explain a 3" group from a precision AR.

168 is not going to be optimal for a 1:10, but it shouldn't be bad. My 1:10 Noveske shoots 168gr Federal Match under 1" at 100 yards. I will be getting the heavy stuff out tomorrow (175SMK and 178 AMAX).

Break in: http://www.youtube.com/watch?v=f_LvPjreNjg

And ya, I am going to keep linking to that until it gets through.

 

[ROK]

Re: 308 Ammo vs Twist Rate

1. POF

2. nato

3. I realized that 168 would not be optimal and expected a better result with the 175.

4. Nice link... I have always followed Mike Rock's recommendations since I have several of his barrels.

 

[ORD]

Re: 308 Ammo vs Twist Rate

Generally speaking, you can shoot 308Win out of a 7.62x51 chambered rifle and it will perform very well, but not so much a good idea shooting 7.62x51 out of a 308Win chambered rifle because of variations in brass specs/dimensions (particularly in foreign military ammo) and other known issues.

That said, I have had excellent results with 168gr FGMM and my own reloads in my POF P-308 with a 20" tube. The rifle is easily sub-MOA and actually shoots right around 0.75" when the driver isn't asleep at the wheel. I think it is capable of better, but I have not done much load development on this rifle yet. I have also shot some BH 175gr SMK loads out of mine with very similar results...all sub-MOA. I will be getting to the 175gr SMK reloads soon enough as those are my preferred bullet for the 308 (along with the 155gr Scenars)!

As for your ammo choices...I am not a big fan of HSM ammo as I have found it to be somewhat inconsistent and not as accurate as it should be (decent enough for range ammo). Your results with the 168gr HPBT loads are about average for what the ammo should do. The 168gr A-MAX and 175gr SMK loads are waaay off the mark of where you should be. The USA/Amer. Ballistics stuff is usually pretty consistent and accurate out of the bolt action rifles I have shot it from...no experience with it in any of my gas guns, but it should perform much better than what you experienced.

If you are experiencing poor accuracy (yes...3" with 175gr Match ammo from that rifle is pretty piss poor), I would look to your scope, rings, mounts first...then your shooting position, bipod (are you properly loading it before shooting), trigger control, etc. second. Since you are able to get decent groups with one type of ammo and you know the rifle is capable of MOA or better accuracy, I would tend to go with operator error (!!caffeine!!) as the cause just seeing what you've posted so far.

Try to find some FGMM and/or BH 175gr ammo and try it out on a decaf day at the range (or if you reload...start developing a load for your rifle).

 

[ROK]

Re: 308 Ammo vs Twist Rate

I agree with everything you said. It is odd that the 168 win shot so well...

It is not the scope... S&B PM II 3-12 locked down tight,

Shooter... possibly although I do consistenly get results. I could say I was having a really bad day with the 175; however, I asked a buddy at the range to try a 5 round group and he had similar results -- his was consistent with most of my groups at about 2.5"

I think you confirmed for me that I need to try some differnt 175 and 168, leave the caffine at home, and enjoy myself.

 

[samnev]

Re: 308 Ammo vs Twist Rate

One of the top shooters at my club shoots 175 grain Sierra Match Kings in his TRG (1 in 11) twist and consistantly shoots .5" 5 shot groups (or less) @ 100 yards out of his 308 TRG. I shoot 168 grain match kings out of my TRG and usually shoot beween .5 .and .7 inch groups. The same load in my Devine, TX M1A usually shoots just under an inch @ 100 yards.