300 Win Mag custom rifle charlie foxtrot

[mountainman56]

I hate to admit this but I am running out of ideas. I've been working on a friends custom 300 Win mag for some time now. We had a lot of grief with this rifle from the day he received it but I thought we had most all the accuracy issues sorted out. I have been doing this off and on for 40 years and I'm pretty sure I've gone through all the mandatory accuracy steps. I settled on a load with 175 barnes lrx that was shooting sub moa out to 500 no problem. At that point my friend indicated an interest in heavier bullets, no problem, we have a load that works, we can always go back to it.........right? I tried 180 ttsx, 190 ablr and 200 lrx. Most shot well with the 200 lrx shooting less than 1/2 moa............. BUT every so often this rifle would throw a lousy group way the hell off....usually low and right but not always. Now this is getting more frequent. Saturday I went several times to our range.........2nd trip I shot one group at 200 that simply ate the 3/4 inch bullseye up. 3rd trip out, same identical load, shot a 2" group, 2" right and 1 1/2" low. All things being equal, first thought is the scope. This rifle has a new 3.5 - 18 Swarovski on it so I replaced it with another new 4 - 12 Swarovski. Sunday morning shot 3 groups at 100 yards. First group with identical load was a cloverleaf you could cover up with a dime. Next two groups with marginally different loads still were very very good.

Naturally I thought I had the problem solved, unlikely as it seems the new Swarovski has an issue. Loaded up half a box of rounds and gave them to my amigo. Today he sends me pictures of these horrible nasty groups all over the place. On top of that the original load with 175 barnes lrx shoots poorly also! FYI Jeff shoots my rifles better than I shoot them myself most of the time so I know he ain't the problem.

Sorry for the long post. Kinda hoping for some ideas I ain't thought of yet. This rifle has to go on a marco polo sheep hunt very soon. I don't want to let my buddy down.

Thanks in advance for your advice.
Pappy

 

[Lefty7mmstw]

Sounds like the powder you are using may not be burning uniformly at all temperatures and conditions.
I had a 7rem a couple of years ago doing just that with 7828 and 140 sierra's. 1/2 moa at times (usually hot out) and not only would the velocity fall off but the accuracy would fall to 2 moa when it was even a bit cooler out. I'd switch powders first and give her plenty of ignition (if you aren't already) with a mag primer to see if she sorts out. With my 7rem I switched to rl22 for full throttle loads and went up to 4064 for mild plinking stuff and she sorted out.

 

[roninflag]

Mountain- what rifle? the scope you named are AWEsome. the 300 win mags i have loaded for were very forgiving. after the .222 and 308 i rate the 300 win mag. as easy to find a good load for.

 

[shortgrass]

Is the front scope mount screw too long and bearing on the barrel tenon?

 

[quigley257]

Does the rifle have a muzzle brake?

 

[mountainman56]

Thanks guys, Ronin, I should have been more specific, rifle is a custom with a Stiller Predator action and I'm pretty sure a Hart 3 groove barrel in a Bell and Carlson stock with PTG bottom metal. I also like loading for the 300 win........usually. Actually when it shoots well it shoots very well, for a lightweight rifle. I want to think it's a bedding issue cuz it sure points that way but I can't seem to locate any problems.

Could be powder I suppose although nearly identical conditions the last 2 times out.

Screws are not bottoming out although I do not care for his choice of rings/bases. Talley one piece lightweight, which are fine but they don't fit the Stiller action correctly. I originally bedded them but may possibly have had some issues there. I have since lapped them to the action.

It does have a brake. The guy that built the rifle installed a mini magnum muscle brake although he did a rather poor job installing it......not timed correctly and held in place with loctite. I now have the means to correct that.

 

[quigley257]

I recently came across a guy displaying the same syptoms as you describe. It turned out to be the muzzle brake. For starters, the brake was installed incorrectly(not aligned properly). Next, the entire brake was bored too small. After measuring, I believe it was only .005" over bore diameter. There were times when the bullets were actually touching the brake and others when just the fouling buildup was enough to affect groups. Once that was fixed,(barrel cut off/rethreaded and brake reamed), all problems went away and the groups got nice and small. Good luck!

 

[roninflag]

Mountain- i mainly load for remington senderos. I loaded and shot a Bat action/krieger 6.5-284 in competition. i also have hart barreled .243. Both are just amazingly accurate. when you mention the stiler/swaro/hart combo i want say the groups should get smaller as you fire ( in jest). i shot federal factory 180 tsx the group was .171. maybe try some factory ammo?? It sounds like a great hunt to go on. Good luck to you in solving the mystery. roninflag

 

[shortgrass]

I've been doing business with Hart for a long time. I think they only make 6 groove, but I've ben wrong before.

 

[mountainman56]

I've been doing business with Hart for a long time. I think they only make 6 groove, but I've ben wrong before.

Ha! You would be in good company! I don't know for certain it is a Hart, just did some quick research and out of the 3 or 4 barrels this guy uses I thought Hart was the only one did a 3 groove. Most likely me that's wrong.

It also turns out you may have been right about the front base screw. I thought I had lots of room but it's very, very close (or was). Thank you for making me double check this! If this turns out to be the problem I owe you many beers!

 

[dkhunt14]

If its a 3 groove it could be Lilja. Do you clean the barrel good? Barnes bullets are known to copper up a barrel. If a barrel coppers bad they can shoot erratic. Is the action bedded? Matt

 

[Lefty7mmstw]

I recently came across a guy displaying the same syptoms as you describe. It turned out to be the muzzle brake. For starters, the brake was installed incorrectly(not aligned properly). Next, the entire brake was bored too small. After measuring, I believe it was only .005" over bore diameter. There were times when the bullets were actually touching the brake and others when just the fouling buildup was enough to affect groups. Once that was fixed,(barrel cut off/rethreaded and brake reamed), all problems went away and the groups got nice and small. Good luck!

that issue also happened a bit to me with my 300win... I've shot it so much I was getting enough metal flow inside it's boss that the bullets were starting to brush the fouling in the brake. A bit of metal removal later and all is well. It's for sure worth checking out.

 

[mountainman56]

Thanks again for your input guys. The action has been bedded, I usually do that before I ever shoot them. I have checked the brake clearance and it's fine. I found an issue with the bedding on the bottom metal but unlikely that's my problem. Right now I'm hoping by shortening the front base screw as well as lapping the bases to the action I have it sorted. Going shooting in a couple hours, I guess I'll know then.

 

[mountainman56]

Cautiously optimistic. Poor quality phone pictures....four groups, four different loads and three different bullets. The 175 lrx did rather poorly, the 180 ttsx stuck 2 in the same hole and one just high. The 200 lrx seems very consistent and is the bullet we were leanin towards. The good thing is (so far) it hasn't been throwing any OUT there.