Measuring your groups...

flyingfisherman

Well-Known Member
OK,

So im looking for the DEFINITIVE answer on how to measure your group sizes, as per a target shooter for a competition. As i've never shot competitively with a rifle or been anywhere near a rifle club, i don't know if my way is correct.

I look at the holes and figure what the smallest diameter circle all of those shots will fit within, thats what i say my group is.. Reason i ask is because when you get sub MOA, its more tricky and when people say they're getting 1/4'' groups, i don't know how i would measure it accurately. Especially when your bullets are in my case .300'' diameter.. I know that the deer doesn't care, but i do.. Im now getting decent groups which are within my thumbnail at 118yds, but trying to figure out the measurement accurately, i'm not sure how..
 
Simple, measure the extreem spread of the group, outside to outside then deduct the bullet diameter.

My only advice is, be honest with yourself, (and us if you are bragging!) Shoot five shot groups and measure the distance across the furthest apart holes.

It really bugs me when I hear all the old chestnuts about a two shot group, a really good group if you discount the one I pulled four inches left, I never count the first shot as that is always high, the first two went high so I aimed down a bit and fired the rest of the group, need to fire a few fouling shots before she will group properly, there was a 1mph crosswind that pulled that round, etc etc

Trust me, a true half MOA rifle/scope/ammo/firer combination in a sporting rifle is a very rare thing despite what you will read on the internet!

JC
 
It's the measurement from the centers of the two farthest bullet holes. If you're shooting a .30 caliber with .308" bullets, measure to the outside edges of the two farthest spaced holes and subtract .308" that will be the group size. In the old days of target shooting they measured "string length" which was the distance from the center of the target to the center of each bullet hole. These measurements were totaled and that was the measurement of the group.~Muir
 
To save having to do any arythmetic, just measure from the inside edge to the outside edge of the two furthest spaced bullet holes. This has exactly the same effect as subtracting the bullet diameter, giving the "centre to centre" measurement.
 
Cheers guys, JC275, you made me chuckle with the excuses people make! Ive never been a 5 shot group man.. I was always taught 3 shot groups due to barrel heating and you should be able to get a good feeling of the POI from 3 shots.

What do you say regarding barrel warping after 5 shots, does this give a true account of the rifles accuracy?
 
Cheers guys, JC275, you made me chuckle with the excuses people make! Ive never been a 5 shot group man.. I was always taught 3 shot groups due to barrel heating and you should be able to get a good feeling of the POI from 3 shots.

What do you say regarding barrel warping after 5 shots, does this give a true account of the rifles accuracy?[/QUOTE

Although I can't deny that barrel heating can and does have an effect, it is often just another one of those excuses. I have shot service rifle competitions where you fire upto 80 rnds in about six or seven minutes and still turn in winning scores. If barrel heating is having a significant effect on your rifle during a 5 shot group then I would question whether it is too sensitive for the rigours of stalking?

JC
 
ff. Update - My old school ruler knocks spots off both pieces of software. I would be interested to see if anyone can find a worthwhile scanning program. Rgds JCS
 
Cheers JCS.

JC275 - RE barrel warping, lighter hunting barrels heat up quickly and the groups expand too, im sure i dont need to tell you that, but the addage that a stalking barrel will be unlikely to fire 3 shots one after another on a stalking outing so heat dissipation isnt as important with a stalking rifle as it would be with a target machine..

Do 3 shot groups not exist in the competitive world of shooting? I shall start doing more 5 shot groups and see what i come out with.

Also, if i want to work out my group as an MOA, what formula would i use? obviously its easy at 100m/200m/400m etc but at odd ranges such as 118yds (how long the place is where i zero my rifles).. Is it a simple trig formula? would it be T=O/A? or am i over complicating it?

PS: Ive found an MOA calculator and have been lazy. My .308 groups at 0.8 MOA. :)
 
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.... Is it a simple trig formula? would it be T=O/A? or am i over complicating it?
ff
Try 2 x 3.14159 x the range in yds x 36 divided by 360 divided by 60 (2 pi r for circumference, 36 to convert yds to inches divided by 360 degrees divided by 60 minutes)

Therefore 1 MOA measures about 1.24 inches at 118 yds.
Anything, but anything is more interesting than weekly project reports. Rgds JCS
 
Flyingfisherman.

Muir is correct. The competitive shooters measure centre to centre as do the bench rest boys.. Sinclair INt offer a simple device which fits onto a venier gauge.
 
Flyingfisherman.

Comp shooters measure centre to centre. Sinclair Int offer a simple device which fits to a Venier guage. muir suggest however works just as well.

Spiker
 
Yeah im on that.. need to buy a copy of windows to run on it! will be able to run windows based software eventually.. I cant run pointblank software on mac.. Oh, JCS, Steve Kershaw showed me an app for long range shooting stuff.. Ballistic FTE, dont know whether your familiar. Its £12 to get for iPhone but is an awesome bit of kit..
 
Cheers guys, JC275, you made me chuckle with the excuses people make! Ive never been a 5 shot group man.. I was always taught 3 shot groups due to barrel heating and you should be able to get a good feeling of the POI from 3 shots.

What do you say regarding barrel warping after 5 shots, does this give a true account of the rifles accuracy?

Some rifles are 3 shot rifles and I have no problem with that. If you beat 5 and ten shot groups from a three shot rifle you are going to make yourself crazy. I remember working with a master gunsmith named Deward Finley who built sniper rifles for our D.O.E. and local police departments, but also built fine sporters and comp rifles. One fellow wanted light weight packing rifle for Elk so Deward built him one in 30-06 which weighed about 7 pounds. The guy came in a few weeks later wringing his hands and wailing that the 4th and 5th shots opened the group to almost 1.2 inches! The first three however, always cut each other. In answer to the fellows concerns, Deward just asked how many shots he planned to shoot, following by saying that if he needed more then three shots in short order he should just take up golf. That ended the discussion.~Muir
 
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