How many shots in a group to sufficiently demonstrate precision?

[Exitpupil]

Scott is correct about the statistical aspect and pretty well answers the OP question. However, having worked on many PCPs my experience is there are a number of factors to consider. As previously mentioned above barrel fouling. I have seen over choked barrels that would print a tiny group with a clean barrel for 5 shots but by shot number 10 the group was unacceptable due to severe leading. There is the dreaded POI wandering, possibly due to reservoir pressure changing or stock bedding issues. I have seen guns that could put the first five shots in a tantalizing tight group, but each subsequent 5 shot group was "walking" across the target so that by the end of a normal string the POI was 2" off. That matters! Then there is the creepy regulator that yields a significantly faster or slower shot after a pause in shooting. Some guns might manifest this in 15 minutes and others overnight. Some PCPs the exhaust valve seems to "stick" to the seat overnight yielding a useless first shot for pesting or hunting. Or how about the gun that was stored leaned on the barrel in a corner that when shot takes a while for the POI to return to normal while the operator is madly making turret adjustments. Just look at the lengths FT shooters go to in isolating how temp and altitude affect their rig. Many variables affecting the precision of the gun itself can only be determined by lengthy testing, not necessarily by a predetermined number of shots.

Will Piatt

 

[bubblerboy64]

Scott is correct about the statistical aspect and pretty well answers the OP question. However, having worked on many PCPs my experience is there are a number of factors to consider. As previously mentioned above barrel fouling. I have seen over choked barrels that would print a tiny group with a clean barrel for 5 shots but by shot number 10 the group was unacceptable due to severe leading. There is the dreaded POI wandering, possibly due to reservoir pressure changing or stock bedding issues. I have seen guns that could put the first five shots in a tantalizing tight group, but each subsequent 5 shot group was "walking" across the target so that by the end of a normal string the POI was 2" off. That matters! Then there is the creepy regulator that yields a significantly faster or slower shot after a pause in shooting. Some guns might manifest this in 15 minutes and others overnight. Some PCPs the exhaust valve seems to "stick" to the seat overnight yielding a useless first shot for pesting or hunting. Or how about the gun that was stored leaned on the barrel in a corner that when shot takes a while for the POI to return to normal while the operator is madly making turret adjustments. Just look at the lengths FT shooters go to in isolating how temp and altitude affect their rig. Many variables affecting the precision of the gun itself can only be determined by lengthy testing, not necessarily by a predetermined number of shots.

Will Piatt

Boy with all those potential issues (many of which I did not know about or never considered) seems we’re lucky if we can hit anything anytime.

Maybe I shouldn’t know about this stuff I guest figured when I missed or screwed up a group it WAS ME. Now I got all this other stuff to worry about. THANKS A LOT WILL 

 

[Kidpellet]

Well, it's hard to hide imperfections in a 10 shot group or more.

Your only as good as your worst group anyway right?

 

[Guest]

Scott is correct about the statistical aspect and pretty well answers the OP question. However, having worked on many PCPs my experience is there are a number of factors to consider. As previously mentioned above barrel fouling. I have seen over choked barrels that would print a tiny group with a clean barrel for 5 shots but by shot number 10 the group was unacceptable due to severe leading. There is the dreaded POI wandering, possibly due to reservoir pressure changing or stock bedding issues. I have seen guns that could put the first five shots in a tantalizing tight group, but each subsequent 5 shot group was "walking" across the target so that by the end of a normal string the POI was 2" off. That matters! Then there is the creepy regulator that yields a significantly faster or slower shot after a pause in shooting. Some guns might manifest this in 15 minutes and others overnight. Some PCPs the exhaust valve seems to "stick" to the seat overnight yielding a useless first shot for pesting or hunting. Or how about the gun that was stored leaned on the barrel in a corner that when shot takes a while for the POI to return to normal while the operator is madly making turret adjustments. Just look at the lengths FT shooters go to in isolating how temp and altitude affect their rig. Many variables affecting the precision of the gun itself can only be determined by lengthy testing, not necessarily by a predetermined number of shots.

Will Piatt

Would you be willing to elaborate on the steps you've taken for yourself, and others ft rigs to reduce and map poi shifts?

Edit: I'm not calling you out Will. I think a lot of shooters and home tuners can learn from you.

 

[thomasair]

Will makes very good points.

I only build competition guns, so the group sizes and numbers must be representative of what you will encounter in a match situation. Most guns will print a good 5 shot group. Very few will print a good 75 shot group. That’s the difference between an average gun and a competition gun. Competition guns must do what you expect on demand every time.

Most American FT matches are 60 shots. So a FT gun should be able to shoot at least that many shots that go where expected. Like Will said...what good is a great 5 or 10 shot group if you’re going to throw a flier every 15.

Here is a 75 shot group at 25y with a 20fpe FT Carbine. This is a full full.

Mike 

 

[Centercut]

My mind is officially blown...

 

[Swami]

Yup, mine too. That is some insane accuracy and consistency. Know I know what @campfussell is talking about with his Thomas!

 

[Exitpupil]

John, the devil is in the details. I'll touch on a few more. I really got into this 5 years ago when I purchased a very expensive brand new Steyr LG110 transitioning into Open Class. I thought if I buy a top tier gun then all I have to worry about is shooting, right? It averaged .75" for 10- 5 shot groups at 55 yds with no groups smaller than .625". I spent the better part of 2 full weeks sorting that gun and in the end eliminated quite a number of gun issues and variables and determined its preferred pellet, lube or no lube, and cleaning interval. I also learned a few things about shooting BR too. After sorting, the stars finally aligned and it shot back to back 5 shot groups of .2" and .25" in perfect conditions at 55 yds and is the most accurate FT gun I have owned. I refused to disassemble the gun for that entire FT season fearing it might lose the mojo. If a gun is shooting fantastic I don't dare take it apart until absolutely necessary.

Shoot a whole shot string on target in 10 shot groups to see if the groups move around as pressure goes down. Often these walk in a pattern in a particular direction. Sometimes I do this with one group to eliminate the variable of moving the gun position. I am a big believer in free floating the barrel in most cases. Don't rule out technique. I have one FT gun I built for myself (Evanix) that worked very well. The next season I was going to "make it better" so I made several major mods to the stock and barreled action and the gun totally lost its mojo. I chased my tail bad on and off for a year fearing that I had totally ruined a gun before determining that it would never group well again off a bench, but shot good from my FT position!

Double grouping- two distinct but separate groups during a 10 shot group may indicate bedding problems. Due to improper inletting my first RAW was supported in the stock by the optional quick fill instead of the flat action bottom. I have had poor luck with flexible synthetic stocks and avoid them. Switching from syn to wood on a MROD can make a big difference for FT. Always seal your wood against moisture absorption. Sometimes experimenting with stock screw torque can reveal interesting things.

Generally, it is very hard to get a well-tuned gun to shoot as good with an LDC or airstripper as without. Sometimes this is immediately apparent, sometimes it takes a statistically significant sample to judge. Results may change later with a MV change.

Test at different temps. Last winter I purchased BNIB an Ataman M2S FT gun. It dropped MV from 800 fps to 600 fps going from 60* to 35*F. I found the reg packed with grease. I probably could have shot all summer without issues only to discover the problem in October at a nationals competition. (Don't ask how I know this). The interesting thing is my Steyr requires frequent barrel cleaning and this particular Ataman never needs cleaning.

I prefer beefy, rigid scope rails and rings. My preferred rings are Burris Signature Zee. The plastic inserts have multiple benefits for FT.

Does you gun shoot the same for the first 4 shots after being on its side in the FT case vs a session at the bench?

Is your MV consistent first shot to last? How about that first shot after a 15 minute break? Overnight? First shot after a refill?

While rare in expensive guns, I have found transfer port burrs in most brands including RAW and Daystate. Bad crowns can happen too, no brand is totally immune. I inspect with a jewelers' loupe.

An interesting test duplicating FT conditions- summertime in the early morning I took my gun out of the 60* basement into outdoors ambient in the mid 60's and shot a group. I left the gun outside and shot a group every hour as the day warmed up into mid 80's. I did this twice. Once keeping the gun in the shade, the second day leaving the gun in the sun. Do this again in the winter to see what lower temps do.

While not totally inclusive I hope this helps some folks.

Will

 

[Motorhead]

Interesting note ... That the top 3 contributors in this thread are all TUNERS and also AAFTA Field Target National Champions. The premise of accuracy is multi faceted being Gun, Pellet, Shooter working in harmony. ALL must be at 100% on any given day to find that ever elusive sweet spot where ultimate accuracy become repeatable.



Scott S

 

[thomasair]

Here are some groups on 12fpe 15” FT Carbine rifle leaving my shop today. This rifle has a titanium shroud/brake combo on it that is new for me. The 25y group is 125 shots at 25y indoors. The 55y group is 75 shots in 3-5mph wind. I did not attempt to hold for the wind. Just held on the bull to the right. The 55y target was standing up sideways.

This is what I expect when everything is working harmoniously.

Mike 

 

[Centercut]

I’ve seen so many people post a five or a ten shot group and call a couple fliers their fault. If you are going to do that what’s the point. Just shoot the three and put your gun away. 

I think the number of shots is based on competition. How many shots in a match.

What we are looking for is consistency. I feel after 40 years of shooting I don’t need to shoot all that many shots to have a real good idea of the how the gun and ammo is going to do., now if I was buying a gun to compete with then I’d want to see how it would do in match conditions so a couple ten shoot groups a good idea. 

Short answer. All depends

Probably the answer that makes the most sense - it depends. For hunting, I'm of the opinion that a five shot group, shot in the same conditions but at different tube/bottle pressures will tell you what you need to know. I'll do a five shot group at 250 bar, shoot the gun for a while, shoot another group at 200 bar, shoot some more and then another at 150 bar. If your gun is a top performer, it shouldn't make a difference - and doesn't when tuned properly... I tend to use 75 yards when testing for hunting since most of my ground squirrel shots are in the 40 to 90 yard range. Sometimes more, sometimes less...

To add to the "it depends", it also depends on the distance you will be shooting. For 25M BR, 25M is "good enough" as long as the barrel doesn't foul in less than 40 or 50 shots. Same for 50 Y BR, or the longer events like 100+ yards. For distance limited shooters like FT, then 50 or 55 yard testing is appropriate. The gun needs to group well at the intended distance for the intended purpose in calm weather.

The skill factor comes into play in real world conditions when the wind starts to blow... When I started shooting 25M BR, one of the better shooters at my club told me he loves when it gets windy, the windier the better. He said under calm conditions, I might get close to his score, but the windier it gets the more he'd beat me like a red headed step child... .

 

[thomasair]

Looks like pics didn’t show up..Sorry.

.sorry.

 

[Davec107]

Nice shooting Mike, i like the new shroud set up. Wish it was headed to my house..

Dave..

 

[thomasair]

Thanks, Dave. I can always make more. ;-)

 

[elh0102]

There is a lot of good information in this thread. As others have said, when it comes to testing for accuracy, there are so many variable involved, trying to establish rules is challenging. The one thing of which I have become convinced though, the more shots fired (within reason) the better the indication of accuracy potential. The big challenge is controlling external variables which can influence results. I have to do my shooting outdoors, so wind, temperature variation, mirage, etc., can occur. Rifle variables also have to be considered, bore condition (is it leading up), air cycle (where are you in the sweet spot), and of course, the pellets themselves. It is indeed complicated, easy to weed out losers, maybe difficult to rate the winners. 

 

[nomojo65]

This just confirms my lust for a Thomas!, sigh... someday!

 

[Dairyboy]

Some great reads in here!! I agree with the majority though. 5-10 shots explains a whole lot more than just 3 period. Shooting my Evanix Airspeed the other day shooting 10 shot groups at 35yds, if I stopped at 3 shots that gun shot everything awesome! After that flyers. And no they weren't from me. The gun was in a vise and held dead steady and no wind. And I'm a hunter not really a target shooter except for testing accuracy. Unless you want to do a ton of 3 shot groups and then line them up to see if they all hit in the same spot on target that's what matters to me.

 

[bubblerboy64]

I very much appreciate the time and effort taken by several to share and hopefully educate . 

i also admire the dedication it would have to take to sort out a gun to achieve those resolutes. My mind is officially blown too ( but it was before so no worries ) 

I don’t have the knowledge equipment or skills and like I would guess the majority at a certain point shooting groups is like wondering in the wilderness. If you are going to shoot groups to make improvements then you hopefully know and have an organized approach as to what to correct. 

The following I say somewhat in jest but there is truth too. I’m so glad that there are experts out there who can do this work so I can buy a gun or have it tuned so I can shoot my three shot group and be happy with it.

Much respect to the members of the air gun tuning community and all those professionals (and dedicated amateurs ) who advance our hobby.

Perfection is a goal we should all strive for in our professions

I’m a retired dentist and dentistry has its own challenges. The problem with dentistry and surgery of any kind is we have a very limited time to achieve acceptable results. Maybe my life’s work has bled over into my hobby? I have always admired those who can fix the small. Have you ever taken a mechanical watch movement apart? I admire the watchmakers as well. Thanks for doing what you do all of you.

My goal is to improve my shooting skills without tipping the scales into frustration. I guess that is the most important point I am trying to make. If watched guys at the range shoot a box of 20 trying to sight a deer rifle in at 100 yards Just to hit a pie plate target no clue. Applying that to myself I have to consider my limited abilities and so there is a point for each of us And how many times have we all wished we had stopped while we were ahead



Great thread centercut. John Heckman

 

[bandg]

Some great reads in here!! I agree with the majority though. 5-10 shots explains a whole lot more than just 3 period. Shooting my Evanix Airspeed the other day shooting 10 shot groups at 35yds, if I stopped at 3 shots that gun shot everything awesome! After that flyers. And no they weren't from me. The gun was in a vise and held dead steady and no wind. And I'm a hunter not really a target shooter except for testing accuracy. Unless you want to do a ton of 3 shot groups and then line them up to see if they all hit in the same spot on target that's what matters to me.

How does that gun know to fire 3 "good" shots before throwing a flyer? Why could the flyer not be the first, second, or third shot? Cannot grasp that concept myself.

 

[Dairyboy]

Some great reads in here!! I agree with the majority though. 5-10 shots explains a whole lot more than just 3 period. Shooting my Evanix Airspeed the other day shooting 10 shot groups at 35yds, if I stopped at 3 shots that gun shot everything awesome! After that flyers. And no they weren't from me. The gun was in a vise and held dead steady and no wind. And I'm a hunter not really a target shooter except for testing accuracy. Unless you want to do a ton of 3 shot groups and then line them up to see if they all hit in the same spot on target that's what matters to me.

How does that gun know to fire 3 "good" shots before throwing a flyer? Why could the flyer not be the first, second, or third shot? Cannot grasp that concept myself.

Ok wasn't always 3 "good" shots but the majority were yes. Then a flyer here another good then another flyer maybe 2 more good then 2 flyers. My point being if I would have stopped at 3 shots during my testing I would have thought it was pretty darn accurate until I shot it alittle more and showed it's true colors. Believe me I don't understand it 100% on the gun and has actually been quite the head ache that I plan on selling it as a parts gun or tossing it all together.