6br accuracy loss from 150 to 200

[SSE]

I put up a new backstop that gets me to 200 yards recently. I have a load for my 6br 8 twist that shoots bughole groups at 150 yds with 70 gr Speer tnt, but 2"- 2.5" at 200. With Sierra 70 gr, bughole @ 150 and under or at .5" @ 200. I am wondering if anybody might have an idea why that is happening with the Speer.

 

[rkittine]

I am pretty new at this, but I would think that 70 grainers are a little light for 8 twist. I shoot 90s thru 107s in my 1:8 twist 6BR, which are super out to 300 yards.

 

[RegionRat]

Before I went too far, I would ask if that ammo batch is really still performing at 150?

It isn't likely something doing that well at 150 goes to hell in 50 yards, so I am wondering if you had a chance to double check them again at 150?

 

[CharlieNC]

A barrel either likes a bullet or it doesn't. Don't waste too much time and components trying to make it shoot, when you have one that performs well.

 

[snert]

Try a 87 grain vmax

 

[snert]

Oh, and sell the TNT to me...I need some, but that was an afterthought, really.

 

[SSE]

That load clocks 3400fps and will shoot in the high 2's all day long but it goes to heck from 150 to 200 with the tnt's.
I just find that very strange.

 

[expiper]

try a good 65-68 gr Benchrest bullet,,,sometimes I found the factory seconds and cheap bullets will not take the RPM's that a well made competition bullet will,,,,Roger,,,,PS..be smart enuff to listen to your rifle,,,dont waste round count on a worthless bullet or powder combination ,,,,,Roger

 

[snert]

Is there a condition in that last 50 yards you are not seeing?

 

[urbanrifleman]

I shot several of the 70 grain pdog bullets at Tubb's ranch at various ranges. They really slow down because they have such a low BC. And they get blow around at any real distance.

My answer is that shooting at 200 is 5 times harder to shoot small than 100.... not twice as hard. I know that is not a great answer. But, I think it is more about conditions than bullets.

The Berger 80 FB might work a bit better at 200.

 

[Idaho-Lefty]

SORRY,.. but you HAVE the WRONG Twist for, 70 grain, Boolitz !
YES, I have heard of some stories of, People saying that, 60's & 70's are "Good" in a 1-8 TW,.. BUT ???
A 1-12, 1-13, ( Even a 1-10 twist ) etc.,.. would be, better !
GO to, the 87 V-Maxes or,.. 87 HVLD Berger's ( and both, like to "Jump" ! )
Still LOW Recoil, and you will be AMAZED at Distance as, I have shot BOTH to, 650 Yards in, a 1-10 Twist.
1/2 MOA easily at, 200 Yards, in my Tikka with,.. these 2, Bullets !

 

[6ShotsOr5?]

Was there a change in the wind when you were shooting the 200?

 

[urbanrifleman]

SORRY,.. but you HAVE the WRONG Twist for, 70 grain, Boolitz !
YES, I have heard of some stories of, People saying that, 60's & 70's are "Good" in a 1-8 TW,.. BUT ???
A 1-12, 1-13, ( Even a 1-10 twist ) etc.,.. would be, better !
GO to, the 87 V-Maxes or,.. 87 HVLD Berger's ( and both, like to "Jump" ! )
Still LOW Recoil, and you will be AMAZED at Distance as, I have shot BOTH to, 650 Yards in, a 1-10 Twist.
1/2 MOA easily at, 200 Yards, in my Tikka with,.. these 2, Bullets !

My favorite is the Sierra 85 HPBT, and yes it tested WAY better at distance than any of the little varmint bullets.

 

[Evan]

If it is really, honestly shooting 0.5" at 150, then I'd expect no more than 0.75" at 200. Going up to 2" in the last 50yds sounds like the bullets are failing.

3400fps in an 8 twist is 306krpm. Could the bullets be coming apart? Maybe not entirely going poof, but jacket and core are starting to separate and destabilize? Many bullets can go poof at 300krpm and above.

 

[SSE]

I shot both the 70 grainers on 2 different days just to check. Speer and Sierra both shoot great @ 150 and Sierra shoots great @ 200 but TNT sucks. Conditions same both days. If the TNT was coming apart, would it not come apart in the first 150 when vel. is highest?
Anyway, this load is lost to mysteries of the universe.

 

[SSE]

As to the heavier slugs, I have shot everything up to 105 but save them for when I leave home and go to longer ranges.
Thanks guys

 

[Dusty Stevens]

You got flags up? Is there a break in the trees or something past 150? I personally think the core is melting and it finally becomes unstable at about 160yds

 

[ebb]

Butchs bore shine, put the nylon brush away and get a bronze.

 

[SSE]

No wind. I am shooting off my back deck with targets no more than 10 degree change of angle between 150 and 200. The 70 gr. Sierra is shooting less than .5 moa when I do my part @ 200 with same load. Both the Sierra and Speer are shooting WAY under .5 moa at 150. I have repeated this several times on 2 days.

 

[JimPag]

No wind. I am shooting off my back deck with targets no more than 10 degree change of angle between 150 and 200. The 70 gr. Sierra is shooting less than .5 moa when I do my part @ 200 with same load. Both the Sierra and Speer are shooting WAY under .5 moa at 150. I have repeated this several times on 2 days.

There is always wind. I love when people say they shoot when there is no wind. The only way there is no wind is if you shoot in a tunnel or a chicken house. While your shooting those bullets that your shooting they are not the optimum bullet weight for the twist that your using. Also what Dusty said. Get some flags.