Cooper .300 Win Mag not grouping

[kountryboy2]

Shoot it at the same distance they did for the test target

50 yards? Lol

 

[Road_Clam]

I put together an R700 mutt in .300 win mag a few years ago. I have a 26", 1-10" twist heavy stainless fluted Sondero barrel. I was initially very frustrated at the initial lack of precision with handloaded 175+ gr match bullets. I tried 175's, 180's ,190's, 200's with 4350 and R22 and best I was getting was with the 190's and R22 and I was at about 1.75 moa @ 100 yds. Not impressed as I should have a moa capable rifle. I did a lot of research over at Snipers Hide and got some suggestions about trying the 208 Amax and H1000 powder. Long story short I was able to consistently find a MOA load. I run about 75-76 gr of H1000 with a .020" jump and I have a MOA rifle, and if the stars align and i've had no coffee I can shoot as tight as .65 MOA but not cionsistiantly. Per all my data my Sondero barrel is pretty fussy about bullet weight, i'm just relieved that I found a bullet/powder conmbination that worked well. I was ready to throw that Sondero barrel in the trash. Glad I stuck with it. Here's my R700. Used this rifle when I took the Sig Saur "reach for a thousand" long range instructional class:

 

[wapiti25]

I really doubt that it is the scope but it maybe be worth changing, my bet is the barrel or chamber. Bad chambering can screw up the best barrel. I bought a used 6mm Dasher mid range rifle from a friend, three barrels were chambered by top known gunsmith's and I know that two have three groves in the chamber on the cartridge body. It was so bad it would up set the rifle on extraction. I polished out the chamber on the first barrel and now going to do the same on the second. All three barrels came out of two well known gun shops but may not have been fired before shipping out. These are top name barrel's Krieger and Bartlien but it is the chamber's that are bad. I got the reamer with the rifle and now need to send it back and see if anything can be done to fix it.

 

[rbp75503]

Just finished up load development of my son's 300 Win Mag that I put together over the winter. Load development was with only hunting type bullets. Did not have much luck with H4350 powder/bullet combinations. Attached is a summary spread sheet of my load work-ups. Make sure to verify the min and max loadings if you choose to use the data.

 

[SWRichmond]

IMO the .300WM is hard to tune, owing to the short neck, short factory overall cartridge length, and the stupid long throat the freaking lawyers put forward of the chamber to reduce max pressure. I have had a couple of these, and factory .300WM hunting ammo shoots positively awful, 3" at 100 yards not uncommon. I also bought some aftermarket factory stuff from HSM loaded with Berger 210 hunting VLDs but loaded to fit in a factory magazine at 3.340". They were jumping ridiculously far, everyone knows VLDs don't like jumping, and guess what? The HSM ammo shot like crap even at short range. The factory loads are jumping hundreds of thousandths, and that is not conducive to accuracy, less so with VLD style bullets.

I bolted a .300WM into a long action AICS and use the AI .300WM magazines with it, loading Berger's very excellent 230's jumping about 0.005". This puts them at 2.830" to the ogive, 3.532" COL, and obviously you'll never get em in a factory .300WM magazine but I can stack them nicely in the AI magazine which will let me seat them out to 3.600" COL. With a bunch of H-1000 I get 2750 fps and 0.330" at 100 yards. I have done this with a custom rifle as well as with a factory Savage. Find the lands, load close to them, and work up if you want accuracy.

Do yourself a big favor and give up on factory ammo, right away. And by all means don't try to "break in" your .300WM by shooting a couple of hundred rounds through it, as that's about 20% of barrel life.

 

[GrocMax]

Is this a SAAMI 'funnel' chamber or a 'match' long throat?

 

[Prostockstan]

I put together an R700 mutt in .300 win mag a few years ago. I have a 26", 1-10" twist heavy stainless fluted Sondero barrel. I was initially very frustrated at the initial lack of precision with handloaded 175+ gr match bullets. I tried 175's, 180's ,190's, 200's with 4350 and R22 and best I was getting was with the 190's and R22 and I was at about 1.75 moa @ 100 yds. Not impressed as I should have a moa capable rifle. I did a lot of research over at Snipers Hide and got some suggestions about trying the 208 Amax and H1000 powder. Long story short I was able to consistently find a MOA load. I run about 75-76 gr of H1000 with a .020" jump and I have a MOA rifle, and if the stars align and i've had no coffee I can shoot as tight as .65 MOA but not cionsistiantly. Per all my data my Sondero barrel is pretty fussy about bullet weight, i'm just relieved that I found a bullet/powder conmbination that worked well. I was ready to throw that Sondero barrel in the trash. Glad I stuck with it. Here's my R700. Used this rifle when I took the Sig Saur "reach for a thousand" long range instructional class:

 

[Prostockstan]

IMO the .300WM is hard to tune, owing to the short neck, short factory overall cartridge length, and the stupid long throat the freaking lawyers put forward of the chamber to reduce max pressure. I have had a couple of these, and factory .300WM hunting ammo shoots positively awful, 3" at 100 yards not uncommon. I also bought some aftermarket factory stuff from HSM loaded with Berger 210 hunting VLDs but loaded to fit in a factory magazine at 3.340". They were jumping ridiculously far, everyone knows VLDs don't like jumping, and guess what? The HSM ammo shot like crap even at short range. The factory loads are jumping hundreds of thousandths, and that is not conducive to accuracy, less so with VLD style bullets.

I bolted a .300WM into a long action AICS and use the AI .300WM magazines with it, loading Berger's very excellent 230's jumping about 0.005". This puts them at 2.830" to the ogive, 3.532" COL, and obviously you'll never get em in a factory .300WM magazine but I can stack them nicely in the AI magazine which will let me seat them out to 3.600" COL. With a bunch of H-1000 I get 2750 fps and 0.330" at 100 yards. I have done this with a custom rifle as well as with a factory Savage. Find the lands, load close to them, and work up if you want accuracy.

Do yourself a big favor and give up on factory ammo, right away. And by all means don't try to "break in" your .300WM by shooting a couple of hundred rounds through it, as that's about 20% of barrel life.

I have a new build that shoots .525 at 300 yds. Bartlein MTU 11.25 twist 27" barrel, Surgeon 1086 action, Manners T4A stock, Fat Bastard muzzle break, SWFA 5-20x50 HD scope, badger mid rings, Shot this group with Factory GM300WM Gold Medal Match Ammo. Use this Ammo as your baseline and work loads from this. I chambered this with a PTG Tactical match Reamer and the jump was excessive and still shot this group. I'm in the process of loading some formed brass and set the oal at 3.570 with 208 ELDs 72.4g relaoder 22 This is with a .010 jump to the lands. This is a proven load for my other win mags and my go to load for comparing apples. I will never use anything but Gold Medal Match on the first day with a new gun.

Stan

 

[Changeling]

You seem to know enough about guns to know how to shoot, and you have shot this rifle quite a bit, so I'll assume you can shoot.
If you are getting 4 inch groups it's not the reloads, something is definitely wrong. It would also be advisable to have some one else shoot a few rounds.
Check ALL screws, locking lugs (as was said), definitely the clearance under the barrel (as was said) fire a group of 3 a couple times. Still the same, try a different proven scope off one of your other rifles (Definitely do this). Still the same, call Cooper for a return of Merchandise number, anything else you do not going to fix.

Buying factory ammo is just going to empty your wallet and could have paid for the trip back to Cooper.

OH, please tell us what you find and how things work out, lots of people don't.

 

[davecb]

Sorry guys I didn't get back on here sooner. The gun was sent back to Cooper. My buddy had his LGS call them a while back to check progress. They said they had shot the gun then added "Tell those guys they weren't lying, it sure won't shoot"! They pretty much checked everything on the gun trying to eliminate a barrel problem but still couldn't get it to group. He talked to them a week or so ago and they had put a new barrel on it and said it seemed to be shooting very well. He asked if they would mind shooting it a few more times to be sure and they agreed to do so. I haven't heard anything more since then. Looks like they have it taken care of though. Hopefully he will have it back soon and we can continue on.
Thanks for all the help here. I'll check back and let everyone know how it works out.

Dave

 

[Lone Hunter]

Sorry guys I didn't get back on here sooner. The gun was sent back to Cooper. My buddy had his LGS call them a while back to check progress. They said they had shot the gun then added "Tell those guys they weren't lying, it sure won't shoot"! They pretty much checked everything on the gun trying to eliminate a barrel problem but still couldn't get it to group. He talked to them a week or so ago and they had put a new barrel on it and said it seemed to be shooting very well. He asked if they would mind shooting it a few more times to be sure and they agreed to do so. I haven't heard anything more since then. Looks like they have it taken care of though. Hopefully he will have it back soon and we can continue on.
Thanks for all the help here. I'll check back and let everyone know how it works out.

Dave

Had a buddy that did the same as Dave. Bought a new cooper,don't know the model, was around 1,800 + . Never could get the rifle to shoot after trying factory and reloads. Sent the rifle back to cooper and they said the same as to Daves friend. Put a new barrel on it and honestly was not impressed with accuracy when it came back. Used factory, hunting reloads, match reloads and never got great accuracy out of it. He ended up selling the rifle. Rifle was a very good looking weapon also, just wouldn't shoot worth a darn. I think I would rather have someone build me a custom than go that route.