One string of fire, two separate groups?

[mattri]

At the range today trying a new load at 200 yards, had a strange thing happen, fired 7 rounds and they formed two separate groups, about an inch apart.

Don't have a pic but imagine you fire a round, then another that lands almost on top of the first, then a 3rd that is within 1/4", then the 4th that is about an inch high and left, then the 5th is on top of the original group, then 6 and 7 are clustered with the 4th.

Both groups were very nice and tight, they were just separate from each other.

Barrel is well floated, no contact anywhere even when barrel is warm (which it wasn't) and action is pillar bedded.

Rifle is a 7mm-08 built on a Savage PTA with a 30" Criterion in a Stockade Prairie Dog/Tactical, Scope is a Weaver T36. Everything is tight, action screws are torqued.

This was not the first group shot today, but barrel was plenty cool when I started, and again it was only 7 shots and the odd group was not the first few or last, it was a mix.

Load was 44gr of R17 in virgin but full length sized, trimmed and chamfered WW brass, CCI200s and 175gr SMKs seated with a slight jump. Vel was 2775 with an es of 28 and a sd of 9.

Thoughts?

 

[jonbearman]

Are you sure the front base screws are not bottomed out on the barrel threads.It is a common problem with savage's especially.It may look tight but in many instance's it is screw against threads allowing the scope to move ever so slightly.I realize you said everything is tight but it happens to the best of us.Have you tried any other powders to be sure the r-17 isnt causing the problem.I personally have had better accuracy with rel15.JMHO One other note is to change the scope out just as a test.

 

[pdog2062]

possibly a paralax issue,I have had the same thing happen when the knob gets bumped by accident

 

[mattri]

Thanks for the replies.

Good point regarding the front screw, I've had that happen as well. I just removed the scope to re-check everything and it all looks good, scope is back on and loc-tite is drying.

The paralax is a possibility for sure, but wouldn't that cause all shots after the move to be shifted?

What I can't figure out is that the two groups were not consecutive, there was a shift, a shift back, and then a 3rd shift to the same point as the first shift.

 

[K22]

Ruling out parallax which you should do first, you may want to try a different load combo. I had the same thing happen to a new 243 I purchased. I was totally puzzled since the load I was using was a proven load in several of my other 243's. I changed powder and the groups settled into a nice 3/4" cluster. Still not sure why my old standby 243 load didn't work but I managed to resolve it with another load combo.

PS- Since you mentioned that you checked bedding I didn't mention it but this is always another first place to look for these kinds of problems. My rifle was glass bedded so I didn't suspect it.

 

[mattri]

Thanks, at this point I'm just going to load that load, and a few on either side and see what it does next time out.

The irony is that both groups were about 1/4 MOA @ 200, would have been very happy with either.

 

[chevytruck_83]

what type of shooting are you doing? I shoot mostly prone and fought with similar issues. messed with the load and gun forever. problem would go away if I shot all my shots in a string without moving my cheek off the stock. naturally meaning my cheek wield was causing my issue.

 

[foxhunter223]

I had this same problem and eventually traced it to my Leupold scope. Sent it back for repair and now shoots well. I was told what caused it at the time but cannot remember what it was now as all I was interested in was getting the scope back on. But same problem two small groups about an inch apart.
Pete

 

[North Fork]

If it was me i would let some one else shoot the gun and see if they do the same thing

 

[mattri]

Thats a good idea too. The gun's never done it before, neither have any of my other rifles. Hopefully I'll get to run back to the range before too long and see if it repeats itself.

 

[lpreddick]

had this happen on several occasions and i think i discovered what was happening. neck tension variation! when loading i would note some bullets seated harder than others and often measured longer and there would be a slight ring on tip of bullet from pressure of the seating stem( often with new brass). i segregated these tight seating cases and noted where they printed and they invariably were off to the side while looser seating cases were slightly elsewhere. i'v done this on purpose by necking fireformed brass .001 tighter with a bushing and they group differently from ones .001 looser. this is about what one would expect since tighter neck tension requires more pressure to move the bullet and more pressure equals more velocity and reduced barrel time affecting barrel harmonics, etc. when working up loads with 5 rounds if one or two are tighter i'll note on case neck and note where they print and almost always...a separate group. there is a gauge i'v seen on a k&m bullet seater that records the pressure differences required to seat a bullet to the desired depth. i try to cull these tight neck cases and suspect if i anneal more often, i would see less difference in neck tightness.

 

[fredhorace77]

Just some more food for thought. I had same thing happen with my savage .243. Ended up being me flinching. I dropped the. 243 for a 22lr. for a couple months and when I went back to the. 243 the problem was gone. Shotgun shooters deal with this same thing all the time. some switch between standard triggers and release triggers to trick their mind. I discovered this two ways...I first let my buddy shoot my gun and the groups were great. I shot it and it printed two different groups. He also slipped in a dummy round on me when I wasn't suspecting it...and low and behold I jerked the daylights out of that trigger.

 

[mattri]

Certainly a possibility, it would have been a flinch on non sequential shots.

The neck tension is definitely a possiblity as well. This was virgin brass that had been fl sized, trimmed to length, chamfered and weight sorted but never actually fired. Bullets are seated to within .003 to the ogive, each round measured.

Hope to be able to hit the range Fri, will be interested to see how it goes.