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#6926895 - 10/20/17 10:03 AM 7mm08 build not shooting well
ccoker Offline
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Registered: 09/17/09
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Have a rifle project I am working on and initial results at the range are very disappointing.
It started as Savage lightweight hunter action that I had a McGowen 17" lightweight profile threaded barrel made for it.
It's in a McMillan stock that has not been bedded (yet)...

Several different brands of 139 and 140g bullets are grouping right at 2" at 100 yards!
I checked the paperwork that came with the barrel and it is 1 in 10, we didn't discuss twist rate and I am starting to wonder if it's just not fast enough to stabilize the 140s. I am going to try some 120g loads next.

I don't think it's the scope, mount, etc..
With regards to bedding, according to McMillan it's not "needed" and the advice is to try it first without. The stock action seems to fit tight with no play. My first thought was to bed it first of course but thought I would try it without first. I typically think bedding should tighten up a group a bit. Plenty of factory rifles that should 1/2" groups just bolted into cheap plastic stocks.

I am really thinking that with the shorter barrel and slower twist the 140s just aren't stabilizing.

Thoughts?
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#6926908 - 10/20/17 10:10 AM Re: 7mm08 build not shooting well [Re: ccoker]
redchevy Offline
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Pretty sure a 1:10 will easily stabilize a 140 grain.
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#6926919 - 10/20/17 10:16 AM Re: 7mm08 build not shooting well [Re: ccoker]
ccoker Offline
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I would think so too, but it is a shorter than normal barrel..


Edited by ccoker (10/20/17 10:16 AM)
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#6926994 - 10/20/17 11:16 AM Re: 7mm08 build not shooting well [Re: ccoker]
TackDriver Online   content
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What powders are you using? Or are you using factory ammo?

If I am not mistaken, the 1-10 twist is ideal for up to 140 grain bullets and the 1-9 twist for over 140 grains. Especially with your 17 inch barrel. I would say to try the 120 grain bullets and give it a shot.


Edited by TackDriver (10/20/17 11:18 AM)

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#6927002 - 10/20/17 11:24 AM Re: 7mm08 build not shooting well [Re: ccoker]
ccoker Offline
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factory loads, good stuff
Just got off the phone with McGowen and he said drop down in bullet weight.
A little torqued because they made the 1-10 recommendation and 140s have way more options.
I don't have time to handload these days..

Contacted Barnes and Federal for some 120 samples

THanks
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#6927008 - 10/20/17 11:30 AM Re: 7mm08 build not shooting well [Re: ccoker]
ChadTRG42 Offline
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I can tell you in 100% confidence, it is not a lack of bullet stability causing your problem. A 1:10" twist is adequate twist for the 140 grain bullets.

Tell me what the groups look like on paper; as in, are they open and random, are they stringing up and down or diagonal? Is there a pattern in the groups with each shot (like shots 3 and 4 shift)?

I would bet it's going to be a bedding or a stock to action mating issue. Knowing what the groups are doing would help with this.
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#6927034 - 10/20/17 11:57 AM Re: 7mm08 build not shooting well [Re: ChadTRG42]
FiremanJG Online   content
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Originally Posted By: ChadTRG42
I can tell you in 100% confidence, it is not a lack of bullet stability causing your problem. A 1:10" twist is adequate twist for the 140 grain bullets.


^^That's for sure.

Charles, I use a 1:9 and shoot 162's. You've got plenty of twist rate.
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#6927068 - 10/20/17 12:37 PM Re: 7mm08 build not shooting well [Re: ccoker]
ccoker Offline
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no pattern, just a random 2" group

I started this project last year and shelved it.. I swapped optic mounts from Talley Lightweights to a rail and rings to be able to twst different optics easier.

I get that a in 10 should be fine, I was just thinking that with the shorter barrel I might not be getting enough velocity to spin then fast enough..

Will go ahead and bed it.
thanks


Edited by ccoker (10/20/17 02:13 PM)
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#6927296 - 10/20/17 05:13 PM Re: 7mm08 build not shooting well [Re: ccoker]
603Country Offline
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Just to eliminate one possibility for inaccuracy, i’d swap out the scope. I had a similar problem with a new rifle and new scope. I told myself that it couldn’t be the scope, but it was.

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#6927348 - 10/20/17 06:03 PM Re: 7mm08 build not shooting well [Re: ccoker]
RiverRider Online   content
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One thing always in the back of my mind when I change a stock is the length of the action screws. And I'd not expect a brand new McGowen barrel to have a dinged crown, but you just can't say "that's impossible." Well, you COULD say it but you could be wrong, too. I've owned a couple of Savages, but never rebarreled one. I understand that when you swap barrels the headspace needs to be set up. There's something to double check. Now I'm all outa ideas.
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#6927369 - 10/20/17 06:21 PM Re: 7mm08 build not shooting well [Re: ccoker]
Buzzsaw Offline
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McGowan screwed it up, send it back
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#6927452 - 10/20/17 07:31 PM Re: 7mm08 build not shooting well [Re: ccoker]
blackcoal Offline
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Could it be a scope issue?
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#6927531 - 10/20/17 08:49 PM Re: 7mm08 build not shooting well [Re: ccoker]
kmon1 Online   content
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I would rule out scope issue before bedding but have not seen many rifles that cannot be improved with a good bedding job.

I also have a 7mm-08 that just hates one factory load I have tried in it. Superformance from Hornady if it shooting inside 3 moa it is a fluke, 4 to 5 inches is more likely. This rifle will shoot inside 1/2 most of the time with reloads and did the same with Hornady lite Mags. Most consistently accurate load I have worked up for it is 46.5gr IMR 4350 with a 140gr ballistic tip which is now over max listed load these days but was 1.5gr less than the max load listed at the time I worked that load up.
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#6927852 - 10/21/17 10:58 AM Re: 7mm08 build not shooting well [Re: ccoker]
ccoker Offline
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I will definitely check optics..
it is a new LHRS 3-12..

The Syperperformance 139 sst was one of the loads. Fusion 140s,Federal Nosler Partition 140 and another Hornady 140 load. Headspace was set by a local smith.
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#6927881 - 10/21/17 11:36 AM Re: 7mm08 build not shooting well [Re: Buzzsaw]
ccoker Offline
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Registered: 09/17/09
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Originally Posted By: Buzzsaw
McGowan screwed it up, send it back


bow do you figure?
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