Question about groupings

[Doorgunner68]

New to precision shooting and have a grouping question. Went to the range today and shot a 20 round box. I was a little impatient (bad day at work)and shot quicker than I normally do. I guess I was firing about every 30 seconds. Groupings were great and tight until about the 12th round and then the groupings were opening up. I did feel the barrel and it was hot. What is the time interval and number of shots do you usually see the groupings opening up?
Thanks

 

[b6graham]

depend on the rifle and barrel
pencil barrel hunting rifle can be 3 shots
most competition focused guns (PRS, F Class, BR) have barrels that easily handle 10-20 rounds no problem
a medium barrel like a Sendero/Rem Varmint maybe somewhere in the middle

but also depends on cartridge
and barrel mirage can have an impact too

 

[Secant]

Tons of variables here. What does "great and tight" mean and what does "opening up" mean? What distance? What barrel maker, which barrel contour, what cartridge, SS vs carbon fiber wrapped, environmental conditions? It could be anything from shooter fatigue/errors, to mirage from the barrel, to ammo MV speeding up, to the barrel actually 'walking' from the heat, etc.

With a Proof SS competition contour chambered in a 6mm, I don't have issues shooting 12-rounds in 90 -120 seconds. With a Proof carbon fiber wrapped barrel chambered in a L/A magnum, and shooting in cold temperatures, I will see pretty heavy mirage from the barrel by about the 5th or 6th round. If you are shooting out at distance, you could be "cooking" a round in the chamber resulting in higher MV for that round. I've seen some factory match ammo with a temperature variance of about 3 fps/degree. If we are talking 100 yards, this will be less of a factor.

I'd say your first step would be to take yourself out of the equation before looking at your gear. Shoot maybe 4 or 5-rounds, then let the rifle completely cool. I'd step away from the rifle, pick it up and then set-up that prone position between shots. Do that a few times at the same point of aim. It could be as simple as that's the group size that you, your ammo, and your equipment are currently capable of achieving at this point.

 

[Doorgunner68]

depend on the rifle and barrel
pencil barrel hunting rifle can be 3 shots
most competition focused guns (PRS, F Class, BR) have barrels that easily handle 10-20 rounds no problem
a medium barrel like a Sendero/Rem Varmint maybe somewhere in the middle

but also depends on cartridge
and barrel mirage can have an impact too

I have an sig Sauer cross PRS .308 rifle. It has a heavy contour 24” barrel, thanks

 

[b6graham]

So probably mid .8xx which isn't heavy but not a pencil either

 

[Kfive73]

Was your barrel freshly cleaned before shooting?

 

[Doorgunner68]

Was your barrel freshly cleaned before shooting?

Yes it was clean just before shooting

 

[smoothy8500]

New to precision shooting....I was a little impatient...great and tight until about the 12th round and then the groupings were opening up.

Might be something simple as a slight loss of concentration on fundamentals: Breathing, NPA natural point of aim, trigger control, sight focus, cheekweld, pulling into the shoulder, etc.

 

[Mr.BR]

Good friend Rajmond of mine shot this couple of days ago
60rds (+15 or so sighters marked 71-85) at 300m prone ,off hand .sling diopter and with factory ammo (Norma 6BR)

New 300M prone world record for 60rds (6x10)

*circle is 10cm , 1moa is 87.3mm at 300m , so most of the 60+rd group is well under 1moa

Crossed over shots are sighters in the 6x10 course of fire

 

[FredHammer]

Good friend Rajmond of mine shot this couple of days ago
60rds (+15 or so sighters marked 71-85) at 300m prone ,off hand .sling diopter and with factory ammo (Norma 6BR)

New 300M prone world record for 60rds (6x10)

*circle is 10cm , 1moa is 87.3mm at 300m , so most of the 60+rd group is well under 1moa
View attachment 8219312

Crossed over shots are sighters in the 6x10 course of fire
View attachment 8219313

What is the barrel contour? Are these fired in relatively one long 70-80rnd string? What is the translation here to the OP question?

 

[Mr.BR]

What is the barrel contour? Are these fired in relatively one long 70-80rnd string? What is the translation here to the OP question?

these are 6x 10 rd strings shot probably over well north of an hour, at around round per minute for each string , it still had to be a barrel ,ammo shooter combo to hold consistent POI

Relatively skinny, Palma like contour of a 300m free rifle , diopter and sling

 

[FredHammer]

these are 6x 10 rd strings shot over at around round per minute, it still had to be a barrel ,ammo shooter combo to hold consistent POI

Relatively skinny, Palma like contour of a 300m free rifle

I don't disagree. I just want to know the takeaway from your posting of this as it relates to the OP's question. Because I'd like to know too.