Whats causing these groups?

[Grump]

My son and I have seen that so often, we gave it a name: Two-grouping.

Maybe he got it from someone else.

Two different ARs (one the Grendel upper he sold) and a Remington 700 in .308 have all done it with differing loads. The Grendel would do round groups of 1-1/8 MOA with factory and some reloads, while other reloads would two-group a bit tighter with holes touching but diagonally apart 3/4-inch at 100 yards.

Kinda hard to zero when it does that.

It's not even predicable from which side of the magazine the rounds are fed from!

Both benched and bagged, and off a tripod for two of the three rifles. Two fully free-floated, the other a Colt HBAR as-is from the factory.

Voodoo and witchcraft, I suspect.

 

[Bullet]

Walkalong

5 shots out of a rocking truck with 40+ winds that could almost be covered by a dime?

Wow. You should be giving us tips.

+1

 

[ole farmerbuck]

5 shots out of a rocking truck with 40+ winds that could almost be covered by a dime?

Wow. You should be giving us tips.

I dont think i can give tips to people who reload more than me but i can usually work up pretty good loads. If the wind isnt too bad all i have to do is load a few and step out the door to the bench and try them. Nice to live on a farm! I just cant figure out why these 52gr BTHP's wont group like i thought they should.I have some 69gr Sierra's i can try but i like the lighter faster bullets for what i use them for. Using the mirror for stability out the window isnt too bad really. Thats how i hunt p-dogs. I drive through the pastures looking for them and lots of times all i get is a little head sticking up out of the hole some. Make quite a few long shots doing that so the loads have to be pretty accurate. I'm sure there a lot of people on here that can out shoot me but i do ok. P-dogs sure dont like seeing me.

 

[Bart B.]

Even the most accurate competition rifles will shoot sub 1/4th MOA at 100 yards in a constant 60 mph cross wind. If the wind changes speed by 2 mph and no windage correction is made, the groups will enlarge horizontally by 6 hundredths of an inch.

 

[Walkalong]

Good groups can be shot in the wind. As long as the wind is constant, it's not a big problem, but it usually isn't. Good groups can still be shot, it just gets a mite tougher.

 

[Duce1]

1-9" twist? My 1-9 twist HATES anything lighter than 62gr bullets. If I shoot 55gr or lighter bullets, I get horrible groups. It is a 16" barrrel.

It looks like you have one shot that is keyholed. I would try some 62,69 and 75 gr bullets in your reloads and see if that won't tighten your groups.
madd0c

As advised.

I was having the same problem and a buddy told me to go to a heavier bullet I was using 55 grain Hornady bullets.

He told me not to go below 60 grain bullets and I have not since loading up some and watching my groups come well within my expectations.

 

[Walkalong]

His 40 grain bullets shot well though. Unless of course the wind blew them in to the group, instead of out.

 

[ole farmerbuck]

His 40 grain bullets shot well though. Unless of course the wind blew them in to the group, instead of out.

The 40's shoot great, always have. It's only the 52's and 55's that are giving me fits. I have RL15 W760 and other powder i guess i can try. Not today, the wind is even worse than yesterday.

 

[ole farmerbuck]

Gusts up to 47mph today. I'd better get out there!

 

[JimKirk]

Its blowing 32 mph here in S. GA, time to get my AR out for a shoot!

My problem is... I have two trucks, a Toyota T100 and a Chevy 1500. Which would be the better truck to shoot out of? Both are long wheel base, the T100 has 300,000 miles the chevy 190,000.

Jimmy K

 

[WNTFW]

Ole Farmerbuck,
Is the target moving around on you? I shot Saturday. We had a workday at a range and the wind was dead calm in the morning. When it came time to shoot the wind had picked up. The targets could be seen moving.
I cut a group in half by altering the way the target was weighted down.

I have had it happen at indoor ranges also where the target carrier would just keep swinging.

 

[TimRB]

I couldn't find the range posted anywhere, but it looks to me like those groups are about 1 inch. If shooting at 100 yards, that's about 1MOA, which is pretty good.

It's nearly impossible to get an accurate picture of real group size with only five shots. Also, because invariably there are shots that touch combined with a few that don't, people usually (and often incorrectly) conclude that they have flyers or that there is something wrong. Shoot groups of ten or more. If you do the math, you'll convince yourself that it's almost impossible to shoot five shots that touch unless your rifle really is shooting less than 1/4 MOA.

Also, if you are shooting on a windy day you can still glean useful information by ignoring left-right spread in your groups and only watching the vertical.

Tim

 

[ole farmerbuck]

Ole Farmerbuck,
Is the target moving around on you? I shot Saturday. We had a workday at a range and the wind was dead calm in the morning. When it came time to shoot the wind had picked up. The targets could be seen moving.
I cut a group in half by altering the way the target was weighted down.

I have had it happen at indoor ranges also where the target carrier would just keep swinging.

No i dont think my targets are moving. The 40's were good and the heavier were bad. I staple typing paper to boxes filled with enough of BLOW dirt that they wont move. When i shot those in the 1st pic, it wasnt all that windy. Now the last pic is a different story. Windy hiding behind a small tree row.

 

[ole farmerbuck]

I couldn't find the range posted anywhere, but it looks to me like those groups are about 1 inch. If shooting at 100 yards, that's about 1MOA, which is pretty good.

It's nearly impossible to get an accurate picture of real group size with only five shots. Also, because invariably there are shots that touch combined with a few that don't, people usually (and often incorrectly) conclude that they have flyers or that there is something wrong. Shoot groups of ten or more. If you do the math, you'll convince yourself that it's almost impossible to shoot five shots that touch unless your rifle really is shooting less than 1/4 MOA.

Also, if you are shooting on a windy day you can still glean useful information by ignoring left-right spread in your groups and only watching the vertical.

Tim

The target was about 80 yards or so. I have a pile of dirt at that range, then 100, 125 and 150. Like to get them grouping at the closer 1st and then move on.

 

[ole farmerbuck]

Its blowing 32 mph here in S. GA, time to get my AR out for a shoot!

My problem is... I have two trucks, a Toyota T100 and a Chevy 1500. Which would be the better truck to shoot out of? Both are long wheel base, the T100 has 300,000 miles the chevy 190,000.

Jimmy K

If its only 32mph there then you'd better get after it. My old chev only has 170,000. Just gettin broke in! Surely some of you hunt shooting out the window so you know what i'm talking about. Oh yea, p-dogs are the only things i shoot that way.

 

[JimKirk]

Have you ever seen a 1000 acre plot of 100' pine trees with a 32mph wind blowing through it? Dorothy and Toto was in Kansas, right?

Shooting out the truck window? What you mean like uh... deer, possums, aardvarks, stop signs, pole insulators ...stuff that that? You do know that Bubba was born just down the road a ways?

Us ain't got no p-dogs round hare, unlessen you bees talking bout dem hi class house dogs is ya?


Joking aside.
We don't get a lot of wind here, too many trees blocking it from blowing. March is usually our windy month. Not many windmills here.

Jimmy K

 

[eitrheim31]

It's only the 52's and 55's that are giving me fits.

Due to barrel harmonics your gun might just not "like" those bullet weights....

 

[Bart B.]

eitrheim31 suggests:

Due to barrel harmonics your gun might just not "like" those bullet weights....

I don't think so. The barrel and its action whips at a very low frequency which has the muzzle axis changing the most. Most barreled actions whip at less than 100 Hz (cycles per second). And virtually all bullets exit in a narrow range of time of about 1 millisecond. So the barrelled action completes about 1/10th of a whip cycle before the bullet leaves. The difference over a 10% range of muzzle velocities doesn't change that very much.

This whip cycle is the fundamental frequency; harmonics are multiples of it and they have virtually no effect on muzzle axis pointing; maybe one tenth MOA at the most.

When you smack a barrelled action with a hammer and hear that high frequency, that's the sound wave going back and forth from one end to the other at about 18,000 fps. This creates only microscopic dimensional waves and are insignificant to accuracy.

Most barrels will shoot a very wide range of bullet weights quite accurate. Bullets have to be spun at their best right rpm rate by velocity and twist to do so.

Regarding number of shots per group, here's a chart showing the probability different numbers will represent what all bullets fired will produce for accuracy:

One 5-shot group has about a 57% confidence level of being the best accuracy for that load.

 

[lopezni]

just a thought, the 40 v-max is going to have a shorter OAL, maybe you need to seat the other bullets deeper? I know that 40gr definitely shoot better in a 1/12" bolt rifle, but in your rifle that seems odd.

 

[ole farmerbuck]

Yes it does. I'm going to try some 69's since i have them but really, 40's are just fine with me and what i use them for.


And thanks Bart

 

[ole farmerbuck]

Heck Bart, you arent very far from me. I might have to load this thing up and pay ya a visit. I'm 70 miles from our border.

 

[ole farmerbuck]

I got 5 Sierra 69gr BTHP loaded lastnight with Varget. Hopefully late this afternoon i will have a range report. Also loaded 5 more 40gr v-max. The wind is supose to be better today.

 

[ole farmerbuck]

Gee, what a difference a scope makes! I gave up and put on an old Leupold 3x9. It is the first scope i bought many years ago. I noticed the heavier the bullets were, the worse the groups were so i'm thinking the more kick, the worse it jars the scope? Anyway, this is 25.5gr H335 with 55 gr v-max. I know, its only 4 shots but i think i'm on the right path now. Come Monday, its time to order another Nikon Monarch 5x20x44.. I might try 26.0 gr this afternoon and see what happens s should work on the p-dogs.

 

[Walkalong]

Excellent!

 

[Doug b]

26.0 grs. of H335 and a 55gr.bullet puts you over max. by .7grs. according to Hodgdon Data Center.