i was just wondering what the shape of a group means.

i very rarely shoot a group that best resembles a cirlce, usually they run the virtical line " | " , or they run bottom left to top right like a " / "

ill try and find a target and post a picture on here but i think you'll know what im talking about

the rifle is a kimber 8400 300WSM, leupold VX-3 4.5-14x40 LR

all loads are winchester cases
165gr ballistic tip seated to the lands, 67gr of VV N-160 producing 3000fps MV Fed 210
150gr ballistic tip seated to the lands, 70gr of VV N-160 producing 3200fps MV win LR

there are also some berger VLD loads but i cant really remember what they grouped like.

could this be a bedding problem, perhaps the barrel needs to be floated? or am i holding the stock wrong while im shooting. i shoot it with a cold barrel off sand bags

If the barrel is touching the stock on the bottom of the barrel,I've found that it groups in a vertical fashion much of the time. Course the sling swivel studs could be causing that by hitting the sandbags. Lots of possible causes.

The vertical groups are sometimes caused by the shooter's shoulder pressure varying, especially with a "high" recoil factor rifle. The other shapes can also be caused by varying the position of the forearm on the rest (if used) or as mentioned above... bedding issues. When a line shaped group is formed, it is imoprtant to note if the bullets walked the line, or were randomly placed along it. Those which walk the line are sometimes from barrel heat stresses, or once again bedding/shooter issues. Eliminate one variable at a time, and try always to be consistant as possible. Good luck and good shooting.

quote:

Originally posted by Cheaha:
If the barrel is touching the stock on the bottom of the barrel,I've found that it groups in a vertical fashion much of the time. Course the sling swivel studs could be causing that by hitting the sandbags. Lots of possible causes.

I'll have a look and see if the barrel is touching along the bottom, and ill check what the sling swivel stud is going on the sand bags, i guess removing them would be the easiest way to eliminate that problem.

quote:

The vertical groups are sometimes caused by the shooter's shoulder pressure varying, especially with a "high" recoil factor rifle.

the rifle really is "all talk" although i have been guilty of varying my shoulder pressure when i first started shooting this rifle, however now i do my best to keep it consistant.

quote:

When a line shaped group is formed, it is imoprtant to note if the bullets walked the line, or were randomly placed along it. Those which walk the line are sometimes from barrel heat stresses, or once again bedding/shooter issues.

i can only remember what happened with the last couple of groups, the virtical stringing group, started high then dropped a 1/2 of an inch then dropped another 1/2 then the forth shot went through the hole in the middle but just a touch to the right, group size 1"

when i did the group that is bottom left to top right, it walked the line, getting higher and further to the right each time. they were evenly placed along the line.

Hello Paul,

Group shape (bolt action) provides important feedback. Ideally you want a 3-shot triangle which infers the barrel is oscillating uniformly. This triangle group says the rifle is being given the best opportunity to shoot.

A verticle group indicated a pressure point in the stock on the barrel. As the barrel heats up it touches the stock pressure point which pushes the group vertically.

In benchrest a vertical group usually means you need a little more powder if the wind isn't doing that to your group.

quote:

i very rarely shoot a group that best resembles a cirlce,

A study of statistics is really helpful in this.....if you shoot ten shot groups and the group isn't roughly circular then there is a cause (possibly) related to bedding etc.

Even with a five shot group the chances of any pattern is likely to happen.......and don't mean anything except random happenings.....assuming the situation is not effected externally.

i live on a farm in New Zealand and we have our range set up, basically just shooting prone up a gully. whenever im not working and its calm i do some shooting if i have some ammo loaded up.

I am lucky in that regard.

it needs free floating for sure, checked it and you cant put a peice of paper between the barrel and the stock, ive been told you want to be able to fit a peice of paper thats been folded between the barrel and stock all the way along.

the bedding job is also pretty rubish, its a factory done job so what can one expect?
i have had a look for a bedding kit and all i can really find in stores is a Miles Gilbert Bedrock Glass bedding kit.
anyone used one?

Paul, Reloaders Supplies in Auckland sell Brownells Acraglass kits. I havent heard of the other one you mentioned.

Re free floating, in my opinion in NZ bush conditions (read wet) I reckon a good size gap is best. A lot of guys dont like a gap as it doesnt look good but at the end of the day its the results at the target that matter to me.

If a rest or bipod causes the stock to bend enough to touch the barrel then the gap isnt big enough.

If shooting off sand bags I remove the front sling swivel. Others have mentioned that too.

quote:

t needs free floating for sure, checked it and you cant put a peice of paper between the barrel and the stock, ive been told you want to be able to fit a peice of paper thats been folded between the barrel and stock all the way along.

This will certainly improve the groups and while you're at it glass bed the recoil lug as well.

I just got done working up loads in a Kimber rifle for a guy named Matthew Fox who some would know as Jack on the show "LOST". His Kimber was a 7mm WSM and the barrel was a fairly thin tapered barrel. It heated up fast and was slow to cool down. A hot barrel will cause vertical stringing also. Those Kimbers are fairly well made rifles and the barrel channel looked good to me with the clearance being even throughout. Without seeing the rifle it is hard to speculate the reason on the vertical groups. I would just caution that the load workup be done with time and patience.

If you have a cluster of 4 and one high, your bedding is low in the tang area

If you have a cluster and one out low then your action is bowed by the front screw or perhaps the center screw if its a M-70.

You can have the above cluster but your first shot will be in the cluster and shot number two will be out and that is caused from a loose tang screw

A circle cluster, usually wide but not necessairly, indicates slight looseness of both the front and rear screws or from very poor bedding. examp: if the rifle will not tighten up.

Group spreading laterally is normally a loose front screw, tighten until a shot comes to center, then shoot a group for effect. If walking laterally 1 to 5 for instance then you have pressure on the side of barrel or the action has been inletted misaligned or you have bent action screws..

This is easier explained with a diagram that shows where each bullet landed..but it pretty well tells the story as is I hope..

The old paper trick is pretty much a trick for folks that cannot inlet. It is sloppy and can collect debris and lots of water, but it works for free floating barrels, A barrel can touch the wood on the top edges and not effect the shooting of a rifle unless there is pressure, if it fits like a glove that is OK and a sign of good stockmaking....

Not written in stone but its darn close. Other problems like a bad barrel etc. can have varing effects.

There are basically three causes for a gun to not shoot.

1. sight system, ie broken scope.
2. mechanical, ie bedding, torque on the action screws, bad chambering job etc.
3. cartridge, ie wrong- bullet, powder or charge, primer or seating depth.

It sounds like a mechanical issue to me since all your loads are vertical stringing. I would reread what Atkinson had to say.

For a load issue, I would tend to increase the powder charge for vertical stringing. So I agree with Pegleg.

A flyer issue, I would change primers.

If the load just plain won't shoot it's a bullet issue, or just a bad combination. I have wasted a lot of time trying to get a certain bullet to shoot in a particular gun.
I now just reach for a different bullet.

Not all rifles shoot better free floated. I've got a couple M77s and a M70 featherweight that do much better with a pressure pad at the forend tip. I would rather be able to free float for a more reliable POI, but these particular guns are particular!

Benchrest is a glued-in action with a massive stiff free floated barrel. Paul has a semi-custom factory rifle.

quote:

Originally posted by Kiwi Vince:
Paul, Reloaders Supplies in Auckland sell Brownells Acraglass kits. I havent heard of the other one you mentioned.

Re free floating, in my opinion in NZ bush conditions (read wet) I reckon a good size gap is best. A lot of guys dont like a gap as it doesnt look good but at the end of the day its the results at the target that matter to me.

If a rest or bipod causes the stock to bend enough to touch the barrel then the gap isnt big enough.

If shooting off sand bags I remove the front sling swivel. Others have mentioned that too.

vince, i was actually looking in the 2007 catalogue and it was the only bedding kit in there. i live down in the wairarapa and sometimes visit the hunting and fishing manawatu for a browse around, however i am a dead eye dicks shooting supplies convert! tracys experience with reloading and the advice he has to offer is superior to the h&f manawatu IMO.

to everyone who mentioned the torque on the action screws, they were deffinately done up tight enough.

i was told to make the front screw a little tighter than the one at the back. i dont have a torque rench but i can get my hands on one.

if i bed the action and float the barrel, then surely the problem could only be me, the load or the scope, but i would be surprised if it was the scope. so it will be either me or the load!

thought id add a pic...
note: those squares are not one inch.


i have re-read a lot of the posts and they all have valuable information. thanks to all those who had a few ideas on what the problem is.