bad grouping. possible worn out barrel???

[me235]

I built a 7mm-300 WIN on a win 70 action and a bartlein 28" rem heavy varmint barrel a little over a year ago. It has been a awesome gun shooting berger 180 VLDs, .3 MOA or better gun. I have been having a really hard time finding the berger 180s, so i decided to try the Matrix 190 grn bullets because i have heard great things about them. I went through close to 150 bullets in load development and couldn't get anything better than .9 MOA at 100 yds. about the time i was ****ed off and angry i found some berger 180s and just decided to go back to my usual load and shoot my group so i could feel a little better about myself. It shot a .8 MOA and bigger group also. I dont know an exact bullet count but i know that im under 800 rounds through it. Visual inspection just looking down my barrel with a light, i cannot see any signs that my barrel is burnt out or eroded anywhere, lands appear to be sharp and not too worn down and the barrel is shinny all the way through. Is it still possible its a barrel thats gone or does it sound like im chasing another problem??

Any input would be awesome, ive been fighting this to wits end and i have a January elk hunt coming up in a couple weeks. Thanks in advance!!

 

[Ingwe]

What is the twist rate on your barrel??

Maybe it is enough to stabilize the 180's but not enough for the 190's......then when you went back to the 180's you just had a bad day because you were stressed?

With the 190's are the holes in target perfectly round?

 

[me235]

its a 1: 8.4. should be more than enough to stabilize the 190s. Also I thought about the bad day, ive tested the 180s again and again over 3 days, and its just not grouping anymore. i even started playing with seating depth trying to chase the lands and give it some more free bore to see if that helped, nothing made it better.

And yep, the 190s are a nice clean hole

 

[FearNoWind]

.,.. lands appear to be sharp and not too worn down and the barrel is shinny all the way through. Is it still possible its a barrel thats gone or does it sound like im chasing another problem??

With 800 rounds I doubt that you've worn out the barrel but, just for clarification, a "shinny" barrel isn't what you're looking for when examining your bore. With a bore scope your barrel should reflect a series of rainbow colors, not a flat shinny surface. Flat shinny surfaces are most probably polished carbon build up. Not a good thing.
That said, I've found Bergers to be exceptionally finicky. I use them almost exclusively but, IMO, they want a very specific powder charge and seating depth combination to work their best. One of my rifles shoost 'em great with ogive just touching the lands. Another likes .010 jump. Same caliber, same type barrel, just different preferences.

 

[Mike 338]

How many times has you fired your brass? As brass is worked, it springs back more increasing grip tension on the bullet. Annealing the brass or seating the bullet a little closer to the lands (if you have the room) can bring the grip tension on the bullet back around to it's preferred state.

 

[nosualc]

Unless you've shot it very hot, I think it unlikely you've worn out your barrel.

More likely is that the throat has eroded to the point where your usual load is no longer in tune like it once was. For example, if you were originally jumping .010", you are now jumping .025". Seat your bullets out further in .005" increments and test. You'll likely find yourself back in tune. VLDs have a reputation for being seating depth sensitive.

The other likely possibility is carbon or copper build-up. Most guys think their barrels are clean when they're really not. Here's where a bore scope is invaluable.

Without that, I'd recommend a deep clean with some J-B cleaning compound. Wrap a patch around a brush, soak it with some kroil, and goop on a bunch of J-B. With a bore guide, stroke the entire bore may 10-12 times, putting a clean patch and J-B on each stroke. Then do another patch with J-B and short stroke the first 6 or so inches of the bore maybe another 10-12 times. Clean the bore thoroughly with clean patches and rubbing alcohol. This will clean out copper and carbon, especially in the throat area, where barrel wear will be the worst.

Good luck,

-nosualc

ps - Buy another barrel and get it ready. Barrels are like tires; they wear every time you use them. Best to have a spare.

 

[MTBULLET]

A BORE SCOPE IS YOUR FRIEND. Find one or pay a qualified gunsmith to ck. bbl and crown

 

[me235]

Brass is all once fired, all annealed, and all trimmed to length. I already went through all of that to eliminate possibilities. I have ran copper cleaners and bore scrubbers my barrel, I will give the jb a try. I have played with seating depth since problem had arose, hasn't seemed to help any. I will try the jb cleaner and see if that has any effect. Thanks for the response guys!