Thread: Double grouping .... likely causes ?

Trying to do load dev on rifle with new set up, barrel. Been chasing my tail for a couple of weekends and come to the conclusion it’s not down to me crap shooting or loads/pills but the rifle/action/stock moving between different pressure points. I think I have diagnosed the cause but would like to hear what the experts on here think are possible or likely causes.

In no particular order.
Barrel, stock, bedding, barrel channel contact, shooter, rest, scope, mounts, rings, crown, ammunition, so I need to go on?

Sent from my Mi A1 using Tapatalk

Double grouping is generally a bedding issue

Had my new rifle bedded by a “gun smith” then started hand loading for it, was double grouping and shooting like shit.. after chasing my tail for weeks turned out was the bedding job (last thing I checked I assumed it would have been done properly...) cleaned it up and was a new rifle.

Lockdown whiskey

Perhaps bedding but not always. Sometimes I have had double grouping occur when working up a new load in a rifle that shot well with prior loads. Invariably in this situation the problem went away with reduced or increased pressure, sometimes with only 1/2 grain change, or a slight change in bullet seating depth which alters case capacity ( thus initial pressure).

scope bases loose on rifle......
check ALL screws...do the paper down barrel channel test....put bore sighter/collimeter in place and dial away say 20 clicks in each direction and see that scope coming back to zero....

Bedding.

Different shooting position? E.g. first group wooden stock onto sandbag, the second group barrel against sandbag.

If everything else is good seating depth can sometimes cause it.

Thanks for the comments and suggestions. Been down most or all of these points. I’ve narrowed down the field :
Stock is professionally bedded, including pillar bedding
Actions screws tight, torque checked before and after shooting
Same for scope screws and base. Scope is VX6
Barrel is new and shows suitable clearance with paper down the channel.

Stock is a cf job, but I also have the original bedded wooden stock it came with.
I tried fitting in this but new bbl is slightly bigger diameter so would be binding down the bbl channel.
So removed that and went back to assembling in the cf stock.
While doing so I realised that the mag box was sitting slightly proud. Thought I’d just not fitted it correctly into the action, so pulled apart and checked again. Mag box sitting correctly in action. Fitted stock and bottom metal and took careful note of mag box.
It was binding on the bottom metal and this got worse as the action screws were torqued down. The mag box should be free to move slightly - right ?
So out with the file and Dremel, hour or so later with frequent fitting checks I got a nice slightly loose fit with mag box and no binding when action torqued up.
Tomorrow’s mission run some rounds and keep me fingers crossed.

Hey @chainsaw have you had a look at the bedding to see if there is anything in there that might be caught?
Had this with mine on the recoil lug. Was just a small bit of excess bedding that was sitting on the bottom of the lug. So when the lug came down it contacted this. I shaved it off with some needle files and it was all good to go.
What you need is the front face and bottom clear by a around electrical tape thickness. The back face (toward the trigger should be touching snug fit).
Some times as you take the action in and out of the stock you scrap some bedding back into the bottom of this area.
Might be something like this easy fix and you don't need to re-bed the whole thing.

edit: Just saw your bottom post! Looks like you solved it, nice one

your grouping should be a 2.0m spread for two shots if you are isolating correctly

Chainsaw, the magbox problem you are describing is a very common problem with Howa rifles . The magwell is not properly engaged into the bottom metal. Some how the weatherby vanguard don't seem to have that issue as I supposed it is corrected at the weatherby factory(?)( both actions are coming from same the Howa factory in Japan)

Get your Mum to sight in or sort it out

Sent from my TA-1025 using Tapatalk