7mm Rem Mag Accuracy Issues?

[bdpayne2000]

So here is the deal Pacnor barrel, 180 VLD's, has shot lights out for about 250 rounds. Always less than MOA and when I was doing my part truly 1/2. Last time out it was not good from 600 yards. First group 9". Second group a little worse and the POI even shifted. Checked scope, base and action and everything is/was to spec. No wind as dispersion was verticle not horizontal. Weather was 50 degrees and have shot it in much warmer weather with much better results. My cleaning regime is BBS and then wipeout for copper. Barrel cleans super easy and is leaving virtually no copper. Could it be a carbon ring in the throat? I have Isso paste and brush but have not used it yet.

Thanks Brian.

 

[FearNoWind]

With that history I assume your barrel free float is verfied and action screw torque is within specs. How are you setting up the bench? How many firings on your brass betwen annealing cycles? What, if anything, has changed in your reload regimine? When did you last check overall case length? Are you full length resizing or simply using a body/shoulder bump die? Have you scoped the bore?

 

[bdpayne2000]

Barrel is floated all screws are in spec. Shooting prone and bipod is tight, brass is still all virgin as I have 300 pieces. Has not been sized but all has been prepped exactly to the same specs. The only thing different is a new box of bullets. No bore scope so that's a negative.

 

[FearNoWind]

.... Shooting prone and bipod is tight,... The only thing different is a new box of bullets. .

Without a scope image of the bore you're working essentially blind. But we have to work with the elements we currently have available.
Vertical dispersion is fairly common shooting prone off a bipod when:
1. The rear bag (if used) is not properly adjusted or placement of the hand under alongside the butt.
2. The butt isn't properly positioned at the shoulder or two much/too little shoulder pressure is applied
3. The bipod is not preloaded or is too heavily preloaded.
I find that I have to manage the bipod quite differently on firmly packed dirt than I do on lose dirt or gravel. Grass demands yet other considerations.
Powder sensitivity to temperature change could also be a factor.

 

[SansSouci]

Hi Brian,

I own a 7MM Rem Mag. It is an extremely accurate rifle.

Since your rifle shot accurately at 250 yards and opened up substantially beyond that distance, my first though is bullet stability. Is your rate-of-twist correct for a long bullet?

I have no knowledge of VLD bullets. I use Sierra and Nosler bullets exclusively.

Maybe this might help: buy a box of Sierra MatchKing bullets and see how they shoot at 600 yards. Sierra MatchKing bullets are extremely accurate. Or you could try 150 grain Nosler Ballistic Tips. They will shoot on top of each other out of my 7MM Rem Mag.

I honestly don't think that there is anything wrong with your rifle. But I might be wrong. If your rifle is sideways, it wouldn't be accurate at 250 yards. Something is happening between 250 yards and 600 yards. And I think that that thing is external ballistics.

I hope that you're able to resolve your problem. And I hope that it turns out to be a very minor one at that.

 

[dkhunt14]

MOA at 600 yards is 6 inches. Could be carbon. When you put your boreguide in and run a patch through. You can feel carbon. After a wet patch or two to get rid of fouling. Run a wet patch through and if it is hard at the beginning and gets easy you have carbon. What twist is your barrel? Are the new bullets a different lot? Matt

 

[deadidarren]

gday i have a rem sendero in 7mm and i use the 180vldh as finding 168g

is hard here in au .

now if the temp gets below 65*f they shoot like crap but at around 20* +

they hold 1/2 to 3/4 waaaaaay out yonder rifle has a twist of 1:925

and velocity is 2960fps load is H1000 69g .015" in to lands.....


hope this helps




cheers D

 

[dkhunt14]

With those kind of groups I would say a mechanical problem. Scope or bedding but I have seen carbon destroy accuracy. I wrap a patch around a worn out bronze brush. It has to fit tight. I then put on a little Iosso and short stroke the throat about 50 times back and forth and then finish by short stroking out the rest of barrel. I do this about every 40 rounds in my Match rifles. It is a lot easier to maintain carbon then to let it build up where it takes 3 days of cleaning with Iosso or JB and soaking to get it out. Matt

 

[bdpayne2000]

Barrel is 1-9 twist specifically for this bullet so stability is good. So shooting prone with rear bag. I have a shot process I follow which I got from a previous thread that Broz had a lot of input in. It's certainly possible I screwed up but I was unhurried and deliberate with both strings of shots. I am hopefully going to go out and reshoot again this week and will check the bore with the wet patch.

 

[bdpayne2000]

Shot gun last night at 300 it was awful 7" vertical and 4" horizontal. I will be mounting a known good scope to determine if the scope has failed. I am pretty sure it wasn't me because I was also doing load development on a 338L and all were sub MOA with the best at just over 1" at 300. Wind was almost non existent.

 

[birddog67]

Tagging in ?

 

[bdpayne2000]

Update: shot at 300 with known good scope and it was not good 6" group with 5 1/2" vertical and 4" horizontal group. Friend just got a bore scope but won't be able to get my hands on it for about a month. What do folks use for removing carbon?

 

[bdpayne2000]

Much to my surprise the problem was carbon in throat. Got some wipeout carbon cleaner and patch showed carbon in throat only. Came out very easily with this cleaner. Didn't seem like a lot so I was not terribly optimistic going out today to shoot it. Ran about 10 rounds down it and shot 3/4 MOA at 300 yards. Seemed to tighten up even better near the end. Never would have thought that was it except I have read about it. Interestingly accuracy was good and then went away very rapidly. Thanks for the help and advice.