What causes this -- Grouping inconsistency?

[spencerhenry]

I have a CZ Model 3 in 300WSM. When I first got it, I recall it shooting just under 1 MOA. Lately, I can't seem to get that, I haven't been shooting as much and the first thing I think is that its me. But, in the last couple weeks, it seems to have a pattern. Yesterday I fired the first shot at 200, perfect windage about 1/2 low of point of aim. I let the barrel cool while I shot a couple other rifles. 2nd shot is touching the first, I continue with shooting the other rifles. One is a 270, Model 70 Ranger. The ranger was the first centerfire rifle I ever bought, at age 16 38 years ago. Birch stock, 22" barrel, blind magazine, with a 3-9x50 Leupold in Leupold mounts. Its a no frills, beat up rifle, with probably 3000 rounds through it, but I managed 3 shots right at 1" at 200. I was feeling pretty good about the Model 3, until shot 3 was almost 3" right and about 1" higher than the rest. I was shocked to see the hole in the paper way over there. I figured it was me. Still shooting the 4 rifle roundabout I came back to the Model 3, 4th shot went 2.5" right and 1" lower than the first two. Then I recalled that while shooting at 400 a couple weeks ago the same thing happened, I had two about an inch apart and then the 3rd was about 10" right and higher, then 4 was right and low.
I can't think what would do that. If it were me, how'd I get a 1" group at 200 out of the 270, and how would the 300wsm do the same "group" twice.

 

[K22]

I am not sure I followed everything you posted but I can tell you that in my experience that when you attempt to shoot multiple rifles in the same range session, especially different calibers and different brands of rifles / scopes, dispersion increases.

This can be due to different stock configurations, trigger pulls, pistol grip designs that place the trigger finger at different positions, different cheek welds due to different scope heights, different levels of recoil, different lengths of pull, different scope eye box sizes, etc. to name a few. There is also the issue of shooter fatigue especially in the heavier recoiling calibers.

I normally only shoot one rifle per range session. This gives me the most reliable dispersion data.

 

[Precisionhunter417]

Break out the tourque screwdriver and go over everything. If that doesnt fix the POI shift then im going to the scope to check and see if its toast. 300 WSM has some snort and can be rather abusive to older scopes or even new ones that arent quite up to snuff.

 

[Forum Boss]

I had a Savage that did something similar with the factory .260 Rem barrel. 3 shots in 0.6 at 100, then the 4th or 5th shot opened the group way out -- sometimes to 1.2".

I experimented with a half-dozen powders, multiple bullet types, various seating depths. Nothing cured the issue.

Folks.... it was the factory barrel.

I replaced the factory barrel with a 6mmBR pre-fit PacNor. The gun then consistently shot sub-0.3 MOA groups with NO flyers. The first measured group out of the gun was four shots in 0.168".

Lesson: Don't waste your time, powder, bullets -- get a good barrel. And use Lapua or other premium brass.

Here are nine 3-shot groups with the 6mmBR. Not one non-touching group.



Postcript: Based on the original post there is a possibility of a fault with your scope if you're seeing something like a 3-4" outlier at 200.

 

[joshb]

It sounds like a scope problem.

 

[spencerhenry]

scope is a Leupold VX III 4.5-14x50 long range, side focus, 30mm tube. Its been on the rifle since they were both new, I believe I have about 150 rounds through it. Winchester brass, believe its on its 3rd loading, annealed after 2 uses.

 

[joshb]

Well, the Boss may be right and it’s the barrel. The scope is the cheapest to check. Screws can loosen over time.

 

[jelenko]

About 6 months ago a VX 2 lost holding zero. It was jumping back and forth about 3 moa.
Leupold replaced it.

 

[Knotwild]

I don't have the knowledge you guys have at all. If I owned that gun and it was the barrel, I would then be looking at dumping it (which I could not do without full disclosure) or spending a considerable (to me) amount of money to fix it. So I would check my crown, check the bedding and torque of the action screws, swap in a new firing pin spring, and swap scopes. Then I would clean the barrel to bare metal and let the sight in for the new scope foul the barrel. Then I would shoot a group off a rest (on a calm day) with some well powdered bags and pay attention to my alignment in the rest. All that is pretty cheap. If I didn't find a problem and my group did not go back to normal, then I would address what I was going to do with that rifle.

 

[jelenko]

If it were me, how'd I get a 1" group at 200 out of the 270, and how would the 300wsm do the same "group" twice.

Easy.
As K22 suggested, work on one at a time. And when debugging accuracy start at 100 where there's much less impact from wind.

 

[ronsatspokane]

As the boss says, know when to stop pouring good money down a bad barrel. I've done this a couple of times over the years and I like to think that I can recognize a bad barrel much better than I could years ago. I still end up kicking that dead horse longer than I should though. Hard to give up.

 

[Nvcnvc]

I am in the same situation, I can’t get my new prefit to group. Tried SRP and LRP brass, 4 different bullets, 4 different powders, 2 different primers, checked action screws, and tried 2 different scopes that I know hold POI in my other comp guns. 350 rounds later can’t get it to group. Everyone says to send the barrel back for inspection. Is that the protocol? Do companies replace “bad” barrels? Or do you just eat the cost and move on to another? Thanks and my apologies, I don’t mean to highjack the thread.

 

[spencerhenry]

I have about 150 rounds through the gun, it used to shoot decent groups just under 1 moa. Unless a barrel goes bad from sitting, I don't think that's it. I'm not "debugging" accuracy, I was verifying a zero at 200 yards, and it wasn't just one day. This "group" happened twice a couple weeks apart, puts 2 in tight then throws the 3rd way off to the right.

I bought the rifle in 2011 to replace a Kimber 84 in 300wsm that would never shoot a 5 shot group better than about 1.25". I tried to find a good load for that rifle, powders, primers, bullets, length, everything, it would be 1.25" or worse no matter what I did. I sold it. I had 1 round each of 5 different charge weights leftover from the Kimber. The CZ put those 5 different charges into a better group than the Kimber ever did with one load.

Kimber actually suggest that I wasn't capable of shooting better than 1.25", but then they finally conceded that 1.25" met their quality control.

 

[jelenko]

This "group" happened twice a couple weeks apart,

How many total groups have you fired with this rifle? What size groups do you usually get?

 

[LCazador]

Try removing the scope and base and assure that the base screws are tight per torque specs. Check the base screw that's located over the barrel screw threads and ensure that it is not contacting the barrel threads. If necessary shorten this screw so it does not make contact with the barrel threads. Replace the base and recheck torque with only this screw holding the base. You should not have any wiggle or play in the base if this screw is the correct length. Mark the bottom of the base screws with a sharpie if the mark becomes bright or is removed there is contact of the screw with the metal under the screw. This contact creates vibration that will eventually loosen the base. It's possible you may have a scope that has been damaged by recoil, 150 rounds of 300 WSM is a lot of recoil.