quote:

Even if there is a blowhard present?

Dan,
Will you be present?

Sorry could let a great striaght line like that one pass!

quote:

Posted Dec 13, 5:15 AM
Gentlemen,

As promised, we have taken a brand new BRNO 452 2E 22 rim fire rifle, installed a 6.5-20 X Leupold scope on it, and shot 9 5-shot groups as it came out of the box. The reason for the 9 groups is that we could only fit 9 targets on one piece of paper, and I think this is not going to kake that much of a difference if we had shot 10 groups.

As you can see from the close up photo of the crown, it does not look perfect. There are slight dents that are visible in the photo.

I will post the groups later on.




The following photo shows the damage I have done on the crown, using a carbide case trimmer.

I am hoping to shoot it tomorrow, and the results will be posted then.

After this my plan is to cut the barrel with a hacksaw.

Here are the groups of the rifle as it came out of the box:

0.874
0.594
0.742
0.456
0.372
0.686
0.877
0.693
0.340

Average = 0.621
Smallest = 0.340
Largest = 0.877

I put a piece of paper far to the right of the target, and shot a group of 5 shots after that damage we did to the crown.

We got a group of 17.300 inches.




The ammo we are using for this test



The deburring tool used to clean up the damage.



Crown after it was de-burred. We are going to shoot it again as it si now and see what happens.



THese are the groups we got after deburring the crown.

0.783
0.593
0.623
0.422
0.417
0.531
0.863
0.981
0.578

Average 0.643
Smallest = 0.417
Largest 0.981

Next we are going to hacksaw the barrel, de-burr it by hand with the above tool, and try agin.



We hacksawed the barrel as you can see, and new groups will be shot as it is now. No attempt will be made to deburr the inside of the barrel.

We will deburr it after this lot of groups, and shoot it again.

Here the groups we got after the above hacksaw cut. I fired 7 rounds to get the point of aim back on target - it shot about 2 inches low, and 2 inches to the left after the cut.

0.516
0.830
0.525
0.681
0.632
0.407
0.670
0.875
0.347

Average = 0.609
Smallest = 0.347
Largest = 0.875

So, to get maximum accuracy we should forget about the crown and just hacksaw the end of the barrel off?

quote:

Originally posted by Rusty:

quote:

Even if there is a blowhard present?

Dan,
Will you be present?

Sorry could let a great striaght line like that one pass!

Update on what happens here.

We took the barrel off, and cut the damaged part off. We then made a 90 degree cut on the crown. Our electric supply kept cutting out - Walter was doing some work on the 3 compressors we have, and as he has this incredible knack of screwing things up, the circuit breaker kept tripping.

I took the barrel off the lathe anyway, and chamferred the end of the barrel with a Holland carbide case be-burring tool.

The rifle has been put together again, and hopefully I will be able to shoot it in the next day or two.

The final results will be posted then.

quote:

Originally posted by Saeed:
Gentlemen,

May be some of our more brainy members might enlighten us on statistics.

Let us assume we have 100 rounds we wish to use to test for accuracy.

Which of the following would give us a better answer statically?

1 100 round group
2 50 round groups
4 25 round groups
10 10 round groups
20 5 round groups
100 1 round groups

I think there are more jokes about statisticians than lawyers... that Aside, once the rifle is sighted in I'd prefer to see the stats on 100 single shot groups. You'd have to include azimuth and distance from point of aim, but an "N" of 100 beats any of the other options you've listed... Great test... I for one appreciate the great work.

It would be nice to see the test fully completed by finishing the crown with at least the round head brass screw & mild lapping paste method (consistent with your other economical methods). The factory crown looked horrible, that rifle may very well be capable of .5" groups - mine is with Fed Classic ammo (load #712). The only part of the crown that impacts accuracy is where the lands/grooves end. There is no accuracy difference between a smooth and proper crown produced on a 90 degree or tapered/recessed barrel cut. A recessed or tapered crown serves only to better protect the crown. While hunting, muzzle control is important for safety and to prevent damage to the crown. Bettter to get some scrapes on the stock than damage the crown or get debris in the muzzle. Be careful!!

quote:

Originally posted by Saeed:
Which of the following would give us a better answer statically?

1 100 round group
2 50 round groups
4 25 round groups
10 10 round groups
20 5 round groups
100 1 round groups

None of the above, really. The best yardstick for accuracy, if you have a way to measure it, is the distance each shot lands from the center of the group. Then you can figure the average distance from the center and the standard deviation. The advantage is that every single shot provides a data point, whereas in group shooting, you only get one data point per group. The disadvantage is that it's not practical to do this fancy form of measuring by hand, unless you have a lot of time on your hands. Seems like the Oehler gadget that measures POI should have the ability to calculate it automatically, but I don't remember for sure.

So for the average guy, the best method is to measure groups. To calculate statistical significance, you are going to need at least 5 groups for each experiment and 10 groups is much, much better. 10 groups is not overkill, by any means.

As for how many shots per group, that's hard to say. Personally, I follow the common practice of 3 shot groups for featherweight hunting rifles, 5 shot groups for standard weight rifles, and 10 shot groups for heavy bull barrels.

Once you get collect your data, use something called the student's t-test to see if there is a significant difference between the control load and any one experimental load. There are other, more sophisticated ways to test for statistical significance, but I suggest the t-test because it is the simplest and most popular.

Some googling should turn up a few online t-testers. Some spreadsheets have these test functions built in, if you can figure out how to use the functions. Or PM me and I'll run the numbers for you, and post the results.

Without even crunching the numbers, I can assure you that your muzzle crown data shows no significant difference except for the badly mangled crown that threw the bullets way off.

It's challenging to prove statistical significance for accuracy because there is commonly a lot of variation from one group to the next, due to human error if nothing else. For example, the largest group in your last string (0.608") is over twice as big as your smallest group (0.290"), and the % standard deviation for that string is 35%. You will see that magnitude of % standard deviation even with a world class benchrest gun. Mathematically speaking, that's a lot of variation, and it makes it difficult to detect statistical significance.

Compare that to chronograph data, where the % standard deviation is typically a mere 1%, and each shot gives a data point. This enables us to prove statistical significance for chronograph data with as little as 10 shots (again, using the t-test).

Wouldn't it be nice if accuracy testing were that simple?

No credible muzzle damage test is complete without first plugging the muzzle with mud or snow and firing the gun. A majority of guns that come through this shop with a complaint of sudden loss in accuracy while hunting is a result of an accident where the muzzle was jamed into the mud or snow.

Of course it would be a stroke of luck for both the gun and shooter to survive such a test fully intact!

popenmann -
You might find an interesting read at http://www.public.iastate.edu/~jessie/PPB/Stats/Testing%20loads.htm

Brent

quote:

Originally posted by malm:
No credible muzzle damage test is complete without first plugging the muzzle with mud or snow and firing the gun. A majority of guns that come through this shop with a complaint of sudden loss in accuracy while hunting is a result of an accident where the muzzle was jamed into the mud or snow.

You're more than welcome to conduct such a test. You don't expect Saeed to do everything here do you?

quote:

Originally posted by malm:
No credible muzzle damage test is complete without first plugging the muzzle with mud or snow and firing the gun. A majority of guns that come through this shop with a complaint of sudden loss in accuracy while hunting is a result of an accident where the muzzle was jamed into the mud or snow.

We tried malm, we tried.

But we were unable to find any mud of snow in our fully airconditioned under ground shooting tunnel.

My take on this particular test is if one is out hunting, and somehow get the muzzle damaged, even scrapping the end with a hunting knife seems enough to at least get hunting accur5acy back.

We have found a 308 rifle for our next test. I am in the process of gathering enough ammo of one type so we can start it.

quote:

Originally posted by johnu:
Of course it would be a stroke of luck for both the gun and shooter to survive such a test fully intact!

Guns and shooters survive such things all the time. I'm not talking about plugging the barrel full of snow or mud, just a little in the very end.

quote:

Originally posted by Saeed:

quote:

Originally posted by malm:
No credible muzzle damage test is complete without first plugging the muzzle with mud or snow and firing the gun. A majority of guns that come through this shop with a complaint of sudden loss in accuracy while hunting is a result of an accident where the muzzle was jamed into the mud or snow.

We tried malm, we tried.

But we were unable to find any mud of snow in our fully airconditioned under ground shooting tunnel.

My take on this particular test is if one is out hunting, and somehow get the muzzle damaged, even scrapping the end with a hunting knife seems enough to at least get hunting accur5acy back.

We have found a 308 rifle for our next test. I am in the process of gathering enough ammo of one type so we can start it.

Okay, thanks.

quote:

Originally posted by Brent:
popenmann -
You might find an interesting read at http://www.public.iastate.edu/~jessie/PPB/Stats/Testing%20loads.htm

Brent

Thanks for the link, Brent. I'll give it a look-see this evening.

And thanks again, Saeed, for the excellent data. I'd like to see more experiments and copious data like that on the AR forums.

Malm,
You did say plug the barrel with mud or snow and then fire it. That did happen to me once with a shotgun and snow when I was very young. It split the end of the barrel for about 6" and peeled back the rib for about 12". Ever since I'm very careful to use tape on the end, or check muzzle often

So, Saeed, what are your conclusions? you shot the gun and did the damage. From this side of the pond it looks like only gross damage will have an effect, and this crown tool and lapping kit I just bought from Brownell's was a waste of Dirhams...

quote:

Originally posted by johnu:
Malm,
You did say plug the barrel with mud or snow and then fire it. That did happen to me once with a shotgun and snow when I was very young. It split the end of the barrel for about 6" and peeled back the rib for about 12". Ever since I'm very careful to use tape on the end, or check muzzle often

Shotguns peel like bananas. Rifle barrels, having a little more beef, will usually just bulge. Unless of course it's packed with mud or snow. If Saeed hammered a little ice from his soft drink in the end barrel and pulled the trigger he would be fine. A slight bulge at the muzzle is considered severe damage and the groups would scatter.

You can tape the end of your barrel, just don't plug it. The air trapped ahead of the bullet will move the tape long before the bullet gets there. Or, go to an electronics supply store and buy yourself some finger cots. They come in different sizes. Roll one of these over the muzzle. Just don't let your friends catch you with any of them in your wallet.

Brent, I enjoyed reading the article you referred to at http://www.public.iastate.edu/%7Ejessie/PPB/Stats/Testing%20loads.htm

The author's answer to Saeed's question is 50 each 2-shot groups. His theory is that 2-shots give you more data with less shots.

Sounds logical, but .......

Here's an observation on his example data. He mentions testing Wolf Match Extra against another brand of 22 ammo and then testing Wolf Match Extra against a third brand of 22 ammo. Apparently, these were different range sessions and he ends up with 2 sets of data for Wolf Match Extra. All with his 2-shot groups, of course.

So what happens when we compare these two sets of data for his Wolf ammo? Here's the spreadsheet results. Sorry, the format is going to be lost when I paste it here.

Wolf #1 Wolf #2
1 0.6300 0.9400
2 0.7480 0.8100
3 0.6325 1.0000
4 0.8275 0.9400
5 0.0910 0.8800
6 1.0395 1.0600
7 1.1335 0.9400
8 0.3825 1.6900
9 0.7990 1.8800
10 0.6135 1.3100


Average 0.6897 1.1450
Std dev 0.3017 0.3653
% std dev 43.7 % 31.9 %
T value 0.0036
T probability 99.6 % Probability of statistical difference

The t-test says that we can be 99.6% sure that there is a real difference between these two sets of data for Wolf Match Extra. Yet as far as we know, this is the same lot of Wolf Match Extra. That doesn't make sense, does it? Either something was different -- maybe the wind was blowing during one of the tests, maybe he was tired, maybe the temperature was different (some people claim that Wolf is prone to lose accuracy in cold weather), etc., etc. Or then again, maybe his 2-shot method is inadequate.

Also note the high % standard deviations, 31.9% and 43.7%. This is oh-so-common for group shooting, and it's the root cause of our difficulty.

I'll have to experiment with the 2-shot group method and see what happens. In the mean time, I can only repeat what I said earlier: it's always challenging to detect a difference in accuracy because there is so much inherent variation in group shooting.

Popenmann,
Yes, the ammo lot was the same. Conditions change, and that is why the old ammunition has to be tested each time a new ammo is selected for comparison. This would be true regardless of the methodology chosen.

Were I to have used the mean radius method you allude to, the same results would have occurred. and the two sessions with Wolf ammo would still have been significantly different. Imagine all those 2-shot groups laid on top of each other and you will quickly see the same result.

A good discussion by of accuracy testing using the mean radius method is to be found at http://www.ar15.com/forums/topic.html?b=3&f=118&t=279218&page=1 It is a good way to start, though very very tedious. And that particular discussion stops short of statistical testing.

Multivariate analyses of variance are more or less the creme' de la creme of analyses for this sort of thing. But few folks can stand to learn the methodology involved.

Brent