Home Forums Hunting & Shooting Hunting Rifles Help me diagnose this group?

This one is kind of strange. We have here, ten shots at 132 yds. Actually fired as two groups of three and two groups of two.

The rifle is a Wea MK V with a new 23 inch Pac-Nor #5 w/ flutes and a break. It is bedded into the original stock. I did have the barrel barely free floated, but after a couple of coats of Tru Oil in the barrel channel to seal the raw wood, she makes contact for the full length. It is fitted with a new Viper 6-24x50 PST sight.

I have shot about sixty five rounds through the new tube. It just showed a bit of Copper fouling today after 35 rounds.



The first round after letting the barrel cool goes high, every time. The second, about an inch lower.

Here is the rifle in the sand bags.



I do not think it is the way I am holding the rifle or how it sits in the bags, because the shots are not random. Cold bore always goes high.

This is a better view of the bench. It has six legs made of steel tubing. They are driven into the ground about ten inches. It is quite stable.



So, does anyone have a good guess why she is grouping this way, and a handy cure?

A new stock with a stiffer fore-arm?

float the barrel

Float barrel maybe? Thats what I would do, not saying its right for this case but it would eliminate uneven pressure if there is any.

Does sound like the barrel is contacting the timber.

Odd that the tru-oil would make it swell that much - are you sure that the action is seated properly in the stock?

I'd try an oiled buisness card in front of the front action screw before I bedded the thing and see it that fixed the cold bore shot.

1. Float the barrel
2. if the groups remain similar, seat the bullet out a little, say a 1/4 turn on the die and re-shoot the groups but never fire over 5 in the evaluation groups as more than that doesn't mean much which evaluating.Only wasting ammo. leave the rifle to cool and then re-shoot to determine consistency.

Also, don't expect 200 grain bullets to be the best shooters in .338. The 10 inch twist common to that caliber often likes 225 and 250 grain bullets which is why it is choses as the base level for that caliber.

Float the barrel is the first thing I'd do. After you remove plenty of material for floating, make sure you re-seal the channel with your tru-oil....I'll bet your poi will change after doing that and it will be so consistent you'll be amazed....Another thing, you are shooting virgin brass: My 300 wby was really particular about new brass and I noticed much better accuracy out of it after the brass was fireformed. Another thing, your still breaking that barrel in so it will probably shoot better after you run a few downrange.....I also agree that you should probably be running a little heavier bullet. Just from my own experience, most 338's (340's included) love the 250 gr. sierra gamekings and their BC trumps the 200 gr. bullets you are using......My list would look like this:

1. Freefloat the barrel and re-seal...
2. Use fireformed brass for checking accuracy loads...
3. Use heavier bullets: My suggestion is 250g. sierra GK..
4. Remember the barrel is still breaking in and will get better with time....

It is not a matter of the stock swelling. I went from a Factory magnum sporter weight to a #5 barrel. I sanded out just enough wood to allow a dollar bill to barely pass along the full length of the barrel. Then I added a couple coats of Tru Oil, which sits on top of and raises the surface of the wood.

The fore arm of this stock is so flimsy that it deflects sideways or upwards with the lightest of pressure.



The bullets are seated to absolute maximum (3.713") which will allow a loaded round to be ejected from the action. The mag will accept a slightly longer COAL. But this is primarily an elk rifle, so it must function in the field.

The barrel heats pretty well after two rounds. Very occasionally I will put three into a group to see what the third does. That is why the pictured group was shot as four separate groups.

I have about 100 rounds loaded up with the 225 gr Hornady Interbond for serious applications.

But I have about 100 of these Combined Technology ballistic tips here and would like to make them coyote capable to 500 yds.

On a side note, all of the brass is now fireformed. I shot the last of the virgin cases yesterday.

I have loaded up a few with a lighter charge using IMR4831. I am about to see what they will do. If they do not group any better than yesterday's, then I will have to get back into the stock.

Thanks to all for the thoughts on this subject.

try some accubonds and some retumbo or h1000

Hi you might try a business card near the fore end tip to see if that helps. I have put over 600 rds through my 340, I have not had good luck with H4831. I get better groups with most 250 gr bullets and IMR 7828 and RL-22. Randy

Also try seating shorter. My 300 WBY shot about an inch seated out to max mag length (Rem 700). Shortened OAL to factory and groups shrunk to .5-.75 consistently....seen 257's do the same thing.

I think I am going to call this good enough. Until the good fellow who actually owns the rifle decides to go ahead and invest in that McMillan A5, which he talked about all winter.

I loaded up a few more rounds with the BT 200's and 85 gr of IMR4831. I thought maybe the IMR was wanting to shoot a bit tighter yesterday while I was doing load development over the Chrono. Often two or three would almost touch, and they were all separated by 1 gr in charge weight.

So this is the results: I scrubbed the bore well last night, and fired two this morning to foul the bore. Then I waited thirty minutes to start shooting 10 into the targets. I shot one round from the cold barrel into the target on the left, then one into the target on the right.

Then I waited a minimum of thirty minutes and repeated.



I am going to discount the bottom bullet hole in each target. I left the rifle laying in the sandbags in the noon sun between set two and three. When I went back to the bench after forty five minutes, the barrel was too hot for me to hold in my farm calloused hands.

I believe the sun heated the top of the barrel disproportionately to the bottom and caused the third shot into each target to go low.

An overlay of the two targets looks like this:



It does not show the vertical separation between the cold bore shot and the second shot which was seen yesterday.

Hey, if you and your buddy are happy that's all that matters......

65 rounds through a 340 Wby in one settin' would make most people shoot groups like that.

I'd tie a string to the trigger and hide behind the truck.

I may be reading this wrong...but it seems that the rifle is putting the first shot from a "cold" barrel,pretty consistently to a common point of impact....am I right,or did I misread something?

Under the rather substantial recoil of a 340 Weatherby it would not be unusual for that forend to be flexing just enough to contact the barrel....that with increased barrel heat may be causing the rifle to string vertically, which seems to be what it is doing if you look at the general trend of the groups.

85-90 or so grains of powder in a hunting weight barrel is setting up quite a bit of rumpus in a hunting weight rig,and if everything is not in sync perfectly grouping may suffer.We know it has a new custom barrel....what we don't know is whether the action and bolt face have all been squared up,and other little tweeks performed.Also the rifle may do better in a rigid synthetic stock,and solidly bedded stress free manner.

I have a friend with a 340 Weatherby that we have shot a lot...it has a lighter,factory tube and left hand Mark V action and is very accurate despite its light weight,bedded and free floated in Brown Precision stock.

I have a funny feeling the rifle will do a lot better if the barrel is more fully floated to preclude any contact.

How's that scope holding up?

Isn't that the truth.....I'd be lucky to get them all on a barn door

Yes, Saturday with H4831, the rifle was definitely shooting two groups. Except for an occasional flyer, the first "cold bore shot" was consistently making a fair group. And the second "warm bore shot" was making a decent but lower group.

I noticed the tendency while shooting incremental charge weights with H4831 during load development. Then I shot the ten rounds into the upper most photo to confirm my suspicions.

But Sunday, using IMR4831, that tendency did not show itself.


No! I have not put 65 rounds through it in a session. I shot it around thirty five times on Saturday, and ten on Sunday.

I will admit, a couple of rounds through a 13 lb 22-243AI is a welcome reprieve after shooting a group from the 340.

The tube has a total of about sixty five rounds since it was rebarreled.

Pac-Nor did the rebarrel and it included

Bob, the barrel is not quite "hunting weight" as it is a #5. The scoped rifle weighs 9.5 lbs and it has a brake. Felt recoil is substantially less than my 9.5 lb Ruger #1 in 7mm STW with 160's at 3200 fps. I would not want to hunt with it, (with the brake) but is is quite comfortable for forty rounds or so off the bench.

The PAC-Nor brake is MUY effective.

I had to sand quite a bit of wood from the fore end to make room for the larger barrel, and the fore end was pretty flexible to begin with. As it is now, the slightest pressure moves the fore end all over the place. I am more scared of intermittent and random contact than I am of constant light contact against the barrel.

Do you think I am wrong in this?

One definitely has to be careful in positioning the rifle on the bench. I set the front action screw just behind the sand bag. Allowing the rifle to creep back on the bags does push the bullet up on the target.

I explained to the owner today, that the stock was causing an occasional flyer, despite my best attempts at the bench. Field positions will be even more difficult.

I am pretty sure it will be wearing a #5 McMillan before the year is out. He was all set to have Eddie do that earlier, but he purchased the 6-24 Viper instead.

Oh, yes, the scope.

Doug's price is $750 minus the Campfire 10%. Shooting dollars could not be better spent. This is absolutely the finest optical instrument I have ever looked through. The resolution is simply amazing. I can see things at 12X which I can not resolve at 18X in my Bushnell Trophy.

So far, all indications are.....the tracking is flawless. The EBR m-rad reticule works perfectly. You shoot a round, count mils in the reticle from the bullet hole to point of aim, and click the correction. The next bullet is on target.

I have preordered two of the 6.5-20 Vipers from Doug. If they are half the scope this one is, I will be ecstatic.

You need to have .020 clearance all the way around. If you don't, your simply wasting components.

.020 minimum and a little more doesn't hurt either........