BENCHREST SHOOTING OPINIONS

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Last Post 16 September 2021

CBA Member

joeb33050 posted this 21 January 2021

Summary:

Cleaning does not affect group size, and no “lube seasoning” is required.

There is a lot of variation in group size. About 100 groups must be fired, measured, and averaged to make any reliable conclusions.

Some group size variation is caused by the rest.

Wind affects poi little or not at all at lower wind speeds. Shooters cannot offset the poi to precisely correct for the wind at any wind speed.

About cant and bubble levels

Changes in temperature moves the poi.

Frequently, larger groups are caused by several flyers rather than one flyer.

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All data is for 5-shot 50 yard groups unless otherwise noted.

Opinions are based primarily on shooting data for four 22 rimfire rifle after 2/1/2020.

I suspect that some of the findings/opinions here apply to center fire cast bullet shooting.

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Equipment and groups

Since 2/1/2020:

CZ 457 MTR-315 groups

BSA 12/15-150 groups

Winchester M 52, pre A-170 groups

BSA International, MK II-140 groups

Total: 775 groups

Scopes: Weaver T36, two, T36XR, 1

Also, since 2/1/20:

Mossberg 44US-70 groups

Remington 513t-40 groups

Ruger Charger, Kidd barrel and trigger-50 groups

Total: 160 groups

Between 2017 and 2/1/2020

Charger-604 groups

Rem 513t-264 groups

Mossberg 44 US-200 groups

Win 52, pre A-115 groups

Total: 1183 groups

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CBA Member

RicinYakima posted this 21 January 2021

I agree with most of your opinions. However having shot BR-50 for several years, I would say the wind does not affect POI very much at only 50 yards. However, a 10 MPH wind gust from the side, common here in the desert, will move a bullet almost a whole bullet diameter. You are very astute to note that the rest itself can change group size if not use consistently.

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CBA Member

joeb33050 posted this 22 January 2021

Group size is not affected by barrel cleaning, nor are “barrel lube seasoning” shots required.

Some contend that several to many shots are required after cleaning or after changing ammunition before the bore is “seasoned” and accuracy is restored.

I clean every time I shoot a gun because of the very high humidity here in Florida; and my fear of rust.

After 100 record shots, 22LR, cleaning by pulling a .17 caliber brush with a paper towel patch ~ 3/4” X 2”, with CLP, the fourth to fifth patch is clean.

I remove the scope after shooting, put a scope on the gun before shooting. This remove/replace requires checking and/or re-setting the scope settings before going to the record target.

I fire a shot at the center of a blank piece of paper, follow that with five aimed at the first hole. Adjust the scope-to the record target and fire 10 five-shot groups for record.

I have watched these initial 5 shot sight in groups and noted that their group size is representative of the average of the next 10 groups. Recently I have saved and recorded the results:

Starting with a clean barrel, aiming at the center of a blank piece of paper:

11/6/20, CZ457MTR, SHOTS 1-5 IN .5", THEN 10 GROUPS AVG .475"

11/15/20, WIN 52, SHOTS 1-5 IN .8”, THEN 10 GROUPS AVG .485”

11/23/20, WIN 52, SHOTS 1-5 IN .3”, THEN 10 GROUPS AVG .478”

11/25/20, CZ457MTR, SHOTS 2-6 IN .7”, THEN 10 GROUPS AVG .463”

12/14/20, CZ457MTR, SHOTS 2-6 IN .6”, THEN 10 GROUPS AVG .623”

1/1/21, CZ457MTR, SHOTS 2-6 IN .475”, THEN 10 GROUPS AVG .545”

1/15/21, WIN 52, SHOTS 3-7 IN .4”, THEN WENT HOME, TOO WINDY

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CBA President

John Alexander posted this 22 January 2021

Funny how often things we believe about shooting turn out to be doubtful at best and sometimes flat out wrong -- if we shoot lots of groups, and don't disregard ANY of the groups or shots fired, even if we don't like them, except for the occasional shot called bad before looking at it .

I think that's because we forget that groups, even ten shot groups, vary a lot from one group to the next and we usually draw conclusions based on one or a few groups. The technical term for this is "chasing your tail."

The other reason is we have a natural tendency to disregard information that doesn't confirm to our ideas of what a bullet ought to "logically" do.

John

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CBA Regional Director

Tom Acheson posted this 22 January 2021

It is good to see that this subject is clearly identified as a collection of opinions. Here are two other opinions.

I’ve shot at CBA BR matches. Listening to and talking to shooters in the Plain Base Bullet category I’ve heard comments like “I had to aim at the far edge of the target paper to get the bullets to end up near the middle of the target”. This was at 200-yards but to a lesser extent for 100-yards, but still a decent hold-off there. The PBB category does not permit the use of gas checks so the muzzle velocities need to be kept slower than other gun categories. Even so, other gun category shooters experience negative influences of wind. A friend of mine once commented after I told him I was out the day before a match doing some load testing. He said “If you didn’t use your wind flags you were wasting your time and components”. Wind DOES influence bullet point of impact.

Bench technique is too often overlooked. Inconsistency here will negatively influence your results. This includes alignment of the rests with the target area down range, positioning of the rifle in the two rests being the same for each shot, the rifle moving across both bag rests the same for each shot, the shooter’s body contacting the rifle during the shot the same for each shot, trigger management, consistent follow through at the end of each shot, shooter awareness of the ever changing environmental conditions while shooting is taking place and adjusting to those variables, etc. Shooter health, mindset and mental attention to details also enter the picture. A shooter is not exactly the “same” person every shot.

FWIW

Tom

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CBA Member

4and1 posted this 23 January 2021

Good post Tom. Wind does indeed effect bullet impact. When I started shooting benchrest, I would attend the cast bullet matches, pay the fee, and shoot for the practice. I would set out my flags. There was not a single cast shooter at that time using flags. I would watch shooters run their targets in switchy wind, complete reversals, and their bullet holes were scattered from one side of the bull to the opposite side. Slowly some shooters started putting out flags.

Bench technique is real, we call it table manners. That's why guns built for bench shooting are made the way they are, 3" forearm, adjustable front rest, rear bag, and 2 ounce triggers. Free recoil. A stock that tracks straight. Cast bullets are slower, barrel time is longer. I can tell the difference between shooting a 13.5 pound gun and a 10.5 pound gun. Small things make a difference.

Temperature makes a difference. Perhaps not in the gun itself per se, but the load. Mornings are cooler the air is denser, by noon things are different. Same is true with the light. There is a difference between shooting in full sun, and then a big cloud comes by.....And then there is mirage.

I personally clean my gun after every target. When I shoot a target, I want to know my barrel is as close to the same condition each time, not an accumulation.

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CBA Member

joeb33050 posted this 23 January 2021

here is a lot of variation in group size.

There is a lot of variation in group size. About 100 groups must be fired, measured, and averaged to make any reliable conclusions. These groups should be fired at ~ 10 groups per day, on ~ 10 different days. The following tables/graphs show the results, each “dot” on a graph is a 10 group average.

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Standard Member

TRKakaCatWhisperer posted this 23 January 2021

You mention powder temperature. Good. In the artillery, powder temperature is MEASURED. It is one of the factors in calculating the azimuth and elevation to get the rounds to the right place.

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CBA Member

Squid Boy posted this 23 January 2021

Interesting data and there seems to be a trend in the group size opening up as the shooting continues. It also seems to hold across all the different guns tested. Any idea as to the factors that might be causing this? Where the barrels cleaned between sessions? Changes in weather conditions? Anything? Thanks, Squid Boy

"Squid Pro Quo"

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CBA President

John Alexander posted this 23 January 2021

What does the horizontal axis represent?

I nothing, are these are just ten different days that you have arranged in order of group size?

Thanks.

John

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CBA Member

joeb33050 posted this 23 January 2021

The 10 group averages are sorted, numbered, and graphed. I have not been able to ascribe a reason to the variation in group size. All guns are cleaned as described at the range after shooting. There is no trend I can find in time, and time between 10 group sets varies from minutes to months. 7550 record groups in < 1 year.

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CBA Member

Squid Boy posted this 23 January 2021

That's a lot of shooting and there is certainly something going on. Interesting that the biggest jump in group size for the CZ and the two BSA's seems to occur at the 9th group. I don't know if you shot all those rifles on the same day but if you did certainly something must have happened. My math isn't the best but I tried to run a standard deviation for the 15 groups out of the Rem 513T and came up with .044". I was trying to test various brands of 22's in my own Martini but C19 and the run on ammo put an end to that. Thanks for sharing your work, Squid Boy

"Squid Pro Quo"

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CBA Member

Ross Smith posted this 24 January 2021

Looks like maybe possibly could be shooter fatigue?????

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CBA Member

joeb33050 posted this 24 January 2021

Some variation is caused by the rest.

Accuracy is affected, decreased, by the rest, by the bags. The gun recoil is affected by pressure of the bags on the gun during recoil.

The gun must recoil straight back, it cannot curve or feel any pressure sideways from either front or back rests. If the gun feels any pressure, right or left, from the rests; then the shot will be off.

If the front rest/gun are free to rotate; then the front rest is not contributing to inaccuracy. There will be no pressure on the gun by the rest.

If the rear rest is free to rotate on ABOUT the pivot point under the front rest; there will be no pressure on the gun by the rest.

I have been working on rests for years, attempting to meet the above conditions.

A sled and a flat top rest works, but not well enough so far.

If there is no front bag, it can't exert pressure on the barrel.

The latest contraption. The front rest top is free to rotate, the forward two screws fit in the crack between 2 table boards, the rear screw adjusts elevation.

The rear rest board has a screw through to fit in a crack between 2 boards, and pivots on that , adjusting windage,

I had a problem in the past with poi changing as the point of aim changed, moving from target to target.

This problem went away as the rests were improved.

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joeb33050 posted this 24 January 2021

Notes:

Fatigue: For a while I shot two sets of ten 50 yard 5-shot groups per trip to the range. This shooting required a lot of concentration- it is hard work. I found myself wanting the last few groups to be over. I never found an increase in the second ten group size, but went to one set of ten groups per range trip. This gets me done shooting before the advice starts.

Statistics: For the 775 groups so far, 1/24/21, the average 5-shot 50 yard group size = .491”; this with four lot numbers of GECO SEMI AUTO; one lot of which is less accurate than the others. The standard deviation is .148”, thus the standard deviation/average, the CV, is .30. This compares with the Normal model CV of .27. This may be boring, but substantiates all the other boring stuff I have written about group size statistics.

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CBA Member

Squid Boy posted this 24 January 2021

JoeB, not boring at all to me. I have been considering problems in my rest system for some time now but have not acted on it. This has motivated me to look more closely at the parts and how they might affect the shot. waiting for some warmer days. Great stuff, Squid Boy

"Squid Pro Quo"

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CBA President

John Alexander posted this 24 January 2021

Keep the "boring" stuff coming Joe. Some of us are very interested. I takes all kinds of interests in different aspects of shooting to make up the CBA, or a good forum.

We don't have to read the posts we're not interested but that doesn't mean that we shouldn't respect each others interests.

By the way have you taken a look at what the 22rf shooters are using for rests to shoot groups in the 0.5 moa range with the fancy ammo that costs more per shot than a dozen CB loads? I know we have at least a couple of that type lurking here.

John

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joeb33050 posted this 25 January 2021

Wind affects poi little or not at all at lower wind speeds. Shooters cannot offset the poa to precisely correct for the wind at any wind speed.

Wind blows bullets around. Poi offset varies with wind speed and direction. We know, or think we know, that.

My wind rule is: If wind gusts blow stuff around on the bench, I quit shooting.

For 30 years or more, I have, when the opportunity presents itself, fired a shot while aiming center as the wind blows. The overwhelming majority of the shots, rimfire or center fire, hit within the group. There has been no connection between wind speed or direction and poi.

I conclude that: In reasonable wind conditions, wind effect on group size is indistinguishable from other effects.

I do not believe, nor have I found any evidence or reports to support the notion that, shooters have the ability to observe wind flags/conditions and calculate the effect of the wind on the bullet.

Some shooters put up wind flags, get information from those flags, and act on that information.

Some of these shooters wait for “no wind”, then fire at the same point of aim. This may increase accuracy.

Some shooters wait for “the same wind conditions”, adjust the sights to those conditions if shooting a score match, then fire at the same point of aim.

Some shooters get wind information, compute the offset required, then fire at that offset point of aim.

I have yet to find a practical method of comparing wind-corrected and not-wind-corrected groups, or the ability of shooters to correct for wind. They say the do it, but offer no proof. I do not do it, and bullets hit within the group, most times.

If a wind correcting shooter and a machine rest were set up with two accurate rifles, on a windy day, and both guns fired at the same time; then we could measure the effect of wind correcting. The practicalities are daunting. Yet we believe that wind correcting works, without evidence. There is a lot of that going on.

I have CBA NM data with graphs from 1995 to 2019, and have noted that group size has not fallen much if at all over those years. There is a lot of variation in group size from year to year. I suspect that a lot of this variation is caused by wind. 1998/2002/2007/2012 much wind? 1996/2000/2003/2008/2010 little wind?

If so, shooters do not correct for wind very well?

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CBA Member

joeb33050 posted this 25 January 2021

I forgot this picture of screw adjustable windage adjustment on the rear bench rest.

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joeb33050 posted this 26 January 2021

Temperature change moves poi.

I found that my rimfire groups got higher on the target as I shot, quite noticeably. In the Florid heat I keep guns and ammunition inside the house, in the A/C, fearful of rust and degradation.

Figuring that the group rise was caused by the colder guns and ammunition getting warmer at the range, I kept the next gun and ammunition in the garage overnight, no A/C. This worked, the height increase went away.

Fall happened, the next gun and ammunition were kept back indoors. The first cool morning, warmer guns, and ammunition, to the range. The groups marched upward again, yes upward, as gun and ammunition warmed up. And repeated.

Groups rise as temperature changes up or down.

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joeb33050 posted this 27 January 2021

About cant and bubble levels

“Cant” is the rotation of the gun about a/the long axis, cant is when the horizontal crosshair is not level.

Cant right moves the poi a teeny bit down and a lot right.

Canting a gun does NOT cause inaccuracy, some offhand shooters cant the rifle a lot. As long as the cant is the same for each shot, accuracy does not suffer.

Some shooters mount bubble levels on the gun or scope; I have several. Centering the bubble adds another task to the multiple tasks required to shoot from the bench, and is not necessary.

My testing showed that people have the ability to see cant of less than 1 degree, most of the time; and that this ability is enhanced with a horizontal reference, such as a horizontal crosshair on a scope.

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