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7mm08 build not shooting well #6926895 10/20/17 03:03 PM
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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?

Re: 7mm08 build not shooting well [Re: ccoker] #6926908 10/20/17 03:10 PM
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Pretty sure a 1:10 will easily stabilize a 140 grain.


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Re: 7mm08 build not shooting well [Re: ccoker] #6926919 10/20/17 03:16 PM
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I would think so too, but it is a shorter than normal barrel..

Last edited by ccoker; 10/20/17 03:16 PM.
Re: 7mm08 build not shooting well [Re: ccoker] #6926994 10/20/17 04:16 PM
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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.

Last edited by TackDriver; 10/20/17 04:18 PM.
Re: 7mm08 build not shooting well [Re: ccoker] #6927002 10/20/17 04:24 PM
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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

Re: 7mm08 build not shooting well [Re: ccoker] #6927008 10/20/17 04:30 PM
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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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Re: 7mm08 build not shooting well [Re: ChadTRG42] #6927034 10/20/17 04:57 PM
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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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Re: 7mm08 build not shooting well [Re: ccoker] #6927068 10/20/17 05:37 PM
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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

Last edited by ccoker; 10/20/17 07:13 PM.
Re: 7mm08 build not shooting well [Re: ccoker] #6927296 10/20/17 10:13 PM
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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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Re: 7mm08 build not shooting well [Re: ccoker] #6927348 10/20/17 11:03 PM
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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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Re: 7mm08 build not shooting well [Re: ccoker] #6927369 10/20/17 11:21 PM
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McGowan screwed it up, send it back


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Re: 7mm08 build not shooting well [Re: ccoker] #6927452 10/21/17 12:31 AM
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Could it be a scope issue?


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it is the illusion of knowledge.--Stephen Hawking
Re: 7mm08 build not shooting well [Re: ccoker] #6927531 10/21/17 01:49 AM
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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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Re: 7mm08 build not shooting well [Re: ccoker] #6927852 10/21/17 03:58 PM
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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.

Re: 7mm08 build not shooting well [Re: Buzzsaw] #6927881 10/21/17 04:36 PM
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Originally Posted By: Buzzsaw
McGowan screwed it up, send it back


bow do you figure?

Re: 7mm08 build not shooting well [Re: ccoker] #6927883 10/21/17 04:38 PM
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2 of those are the least accurate factory loads I have tried in the old 7mm08 788. The first 2 on your list are those two. The Superformance load I was talking Hornady about something else and ask the guy about Superformance accuracy. He said I could send the rest of it in and they would tryit but it most likely would fall in accuracy spec. Then said hiw 7mm-08 hated the stuff as in 4 inch or more groups like I experienced. How words were some rifles love it and those that don't hate it.

But with 4 it does sound like the gun.


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Re: 7mm08 build not shooting well [Re: ccoker] #6927890 10/21/17 04:51 PM
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Without handloads I wouldn't be sure how good the accuracy of the rifle is. If you don't handload, have Chad make you up some and try them.


Re: 7mm08 build not shooting well [Re: ccoker] #6927918 10/21/17 05:16 PM
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Originally Posted By: ccoker
Originally Posted By: Buzzsaw
McGowan screwed it up, send it back


bow do you figure?



you have done everything you can, the ammo you are shooting is fine, scope is good, everything (all screws tight), something is wrong with barrel. "local gunsmith" scares the he77 out of me. especially on the savage action floating bolt, collar screw in, short barrel, light barrel, all adds up to trouble to me.

There are some Savage experts here but my bet is on the barrel and smith


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Re: 7mm08 build not shooting well [Re: ccoker] #6928094 10/21/17 09:15 PM
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I need to rule everything out before saying it is a barrel problem. I do handload but I dont eant to have to..
And I sure dont want to start working up loads if therr is an issue somewhere. Need to eliminate all the variables first.

Last edited by ccoker; 10/21/17 09:18 PM.
Re: 7mm08 build not shooting well [Re: ccoker] #6928145 10/21/17 10:24 PM
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Listen to Chad. . .

Re: 7mm08 build not shooting well [Re: ccoker] #6928469 10/22/17 03:15 AM
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I tried Remington Corelokt 140, Fusion 140, and one other 140gr factory load in Ruger American 7-08. None shot very well. 1-9.5 twist. 120gr Fusion? Yep, .75" 3-shot group. Try the 120s if everything else checks out.


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Re: 7mm08 build not shooting well [Re: ChadTRG42] #6929187 10/22/17 11:32 PM
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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.

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.


Agree 100%

Re: 7mm08 build not shooting well [Re: ccoker] #6929294 10/23/17 12:50 AM
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thanks for the feedback guys..
will be bedding tomorrow (as initially planned)
Really would like to run this gun next week hunting.. plenty of other rifles are dialed in but want to run this one for the opener. we are on an MLD and can start going after a "trophy" on Nov 1 (land owner rules)

Re: 7mm08 build not shooting well [Re: ccoker] #6929354 10/23/17 01:26 AM
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You didn't say if you are running a can, if so and after seeing your discloser statement , I assume you are, ......problem could be there?


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Re: 7mm08 build not shooting well [Re: ccoker] #6929605 10/23/17 04:23 AM
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Have you chronographed any of the ammo?

I also set targets , Manila folder type stock , at 25' , 50' , and / or 100' to verify bullet stability.

Had a custom silhouette gun in 7mm TCU that keyholed on me. Dropped bullet weight , increased velocity to solve problem.


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