Small cases are not more accurate

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  • Last Post 31 August 2018
joeb33050 posted this 26 August 2018

In the JACKETED BULLET TEST, 223 and 22-250, 3 barrels, 7 powder charges, 3 bullets; 63 combinations each, 223 avg = .945"; 22-250 avg .935".

 

7.12 CARTRIDGE SIZE AND ACCURACY

 

 

 

After finding that the 308Win Savage Striker shot reasonable group sizes with tiny charges of powder and 200 grain bullets at velocities down to under 600 fps, I began to wonder about some of the trends in cast bullet shooting. Specifically, with cast bullets, does the size of the cartridge case affect accuracy, and if so, how much? Are small cartridge cases more accurate than larger cases?

 

            Many years ago John Ardito wrote about his experiments with the 308 Win. case shortened to various lengths. Others wrote about 32/20, 32 S&W and other cartridges as offering great accuracy advantages.

 

             I had three single shot rifles barreled for short small cartridges around this time, but experienced no accuracy tsunami.

 

            In modern benchrest, the 30BR with slow twist has become popular for score shooting.

 

            In Cast Bullet Association, (CBA), shooting, the 30BR / 308 X 1.5” has become the most popular cartridge case in Heavy and Unrestricted classes and the 32 Miller Short, (32 MS), is most often seen in the PBB, (Plain Based Bullet), class.

 

            In the American Single Shot Rifle Association, (ASSRA), matches, the 32 MS is frequently the winner.

 

            These cartridges and their near relatives are small; substantially smaller than the 308 Win or 32/40.

 

            Neither the 30BR/308 X 1.5” nor the 32 MS is available in a factory-built rifle.     ASSRA rifles in 32 MS are often built on the DeHaas/Miller action with custom barrels; and CBA Heavy and Unlimited class rifles are built on Remington 700 or custom actions with custom barrels.

 

            It is difficult to separate the contribution to reduced group size that is made by each variable; the smaller cartridge case, the action, the barrel, the stock, the bullet or the other variables.

 

            Would single shot rifles with DeHaas Miller actions, Smith barrels, and all the other bells and whistles, in 32-40, shoot as well as the same rifles in 32 MS? 

 

            Would Heavy or Unlimited class rifles chambered for 308 Win shoot as accurately as the 30 BR or 308 X 1.5?

 

            Testing would require more effort and expense than I, or probably anyone, would care to expend.  However, there’s a way to look at some data and make at least some statements.

 

            The CBA publishes match results and equipment lists that record groups, some shot with 308 Win in Production class, and 30BR/30X 1.5” in Heavy and Unrestricted classes and 32 MS in PBB class.

 

            The CBA group events are for 5 and 10 shot groups at 100 and 200 yards. There are four 5-shot groups and two ten-shot groups fired at each range.

 

            I took the 2004 through 2009 CBA National Match results, selected the Production class entries shooting 308 Win, Heavy and Unlimited class entries shooting either 30BR or 308 X 1.5”, and PBB class shooting 32 MS, and analyzed the dickens out of the data.

 

            The PBB results should be of some special interest to the ASSRA members.

 

            Since we’re dealing with a lot of possible variables here, and small numbers of data points, we’re not absolutely sure of much if anything. However, the data tell us the following:

 

(Let 1 moa = 1” @ 100 yards.)


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joeb33050 posted this 26 August 2018

 


2004-2009 CBA NATIONAL MATCHES

 

 

 

 

AVERAGE GROUP SIZE, MOA

 

 

 

 

 

 

PRO

HVY

UNR

PBB

HVY/PRO

UNR/PRO

PBB/PRO

5/100

1.253

0.824

0.802

0.715

66%

64%

57%

5/200

1.270

0.918

0.954

0.992

72%

75%

78%

10/100

1.583

1.137

1.128

1.090

72%

71%

69%

10/200

1.702

1.281

1.258

1.308

75%

74%

77%

AVG

1.452

1.040

1.035

1.026

71%

71%

70%

 

           

 

            Heavy, Unrestricted and PBB class rifles shoot, on average, smaller groups than do Production class rifles. (Again, only Production class 308 Win, Heavy and Unrestricted class 30 BR/308 X 1.5, and PBB 32 MS results are included.)

 

            For all years, for all 5 and 10 shot matches:

 

            Heavy and Unrestricted class rifles shot groups 71% as large as Production class rifles. They shot groups 29% smaller than Production class rifles.

 

            PBB class rifles shot groups 70% as large as Production class rifles. They shot groups 30% smaller than Production class rifles. The PBB ratios are interesting, in that the PBB rifle ratios are smaller than the Heavy and Unrestricted rifles at 100 yards, but larger at 200 yards. The PBB rifles shot better than both the HVY and UNR rifles at 100 yards, not as accurately at 200 yards. Could this possibly be connected to the flat-nosed bullets some of the single shot guys shoot, that are more affected by the wind at longer range?  

 

            All the Heavy and Unlimited class rifles had custom barrels, with the exception of one Remington barrel on a Rem 40X action.

 

            All the PBB class rifles had custom actions and barrels, there was not one original old-time single shot rifle shot in these matches over the six years.

 

            Of the 34 total PBB entries over the six years;

 

            20 were chambered for the 32 MS cartridge

 

            16 had Miller actions, 7 Peregrine

 

            17 had Smith barrels

 

            These are special rifles with a lot of gunsmithing going into them.

 

            All the special gunsmithing, barrels, stocks, triggers and actions AND the smaller cartridge case in Heavy, Unlimited and PBB class rifles result in a reduction of group size of about 70-71% compared to Production class groups.

 

            I don’t know what part of this accuracy improvement is due to what variable; the gunsmithing, barrels, actions, stocks, triggers smaller cartridge case or other.

 

            This “70-71%” is the only thing I’m pretty sure of that I could find in the data.     

 

            The fascinating data and analysis along with a myriad of colorful charts is in the Excel workbook “CARTRIDGE SIZE AND ACCURACY” in excel workbooks.

 

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RicinYakima posted this 26 August 2018

 "I don’t know what part of this accuracy improvement is due to what variable; the gunsmithing, barrels, actions, stocks, triggers smaller cartridge case or other."

Joe, I don't know either, but I do know smaller cases require or force or allows you to used faster powders to generate required velocities and higher pressures. They are also more uniformly distributed within the small case. Ric

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Ken Campbell Iowa posted this 26 August 2018

ric:: ... if i want to use 4831 can i just make my 308 case smaller and smaller until i get the target 2000 fps in my 6mm rifle ?

etc. ... 

ken

 

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frnkeore posted this 27 August 2018

The PBB ratios are interesting, in that the PBB rifle ratios are smaller than the Heavy and Unrestricted rifles at 100 yards, but larger at 200 yards. The PBB rifles shot better than both the HVY and UNR rifles at 100 yards, not as accurately at 200 yards. Could this possibly be connected to the flat-nosed bullets some of the single shot guys shoot, that are more affected by the wind at longer range?

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To start with, 90% of PB shooters, shoot spitzer bullets, whether it be CBA, ISSA or ASSRA. The BC's usually range from .37 to .44.

The reason that they fall down at 200, is that the velocity range of 1400 to 1500 fps, is the WORSE velocity range for wind drift. Check it out in any ballistic program. I might add that you get approx the same wind drift at 900 fps as you do at 2100 fps. Sounds strang but, true.

We are limited on the high side by the limitation of the PB and on the low side by vertical dispersion in ES. 5 fps ES can make a big difference at 200 yards in the best low velocity range of ~900 fps.

Winning GC loads run from 1900 to 2100 fps and even though they usually have lower BC's, that extra velocity lowers the wind drift in that velocity range.

That last 100 yards is tough on us PBB shooters but, on calm, low mirage days, it can be a toss up.

Another difference, is that PB shooters, shoot through bigger chunk of the Air (vertical) and therefore a larger variation of wind conditions than the GC shooters.

Frank

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RicinYakima posted this 27 August 2018

Ken, yes you can. All is takes is money and a good gunsmith. And a long barrel to reduce pressure at the muzzle! Ric

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RicinYakima posted this 27 August 2018

 I agree with a lot of what Frank wrote. Their bullets are definitely is in the trans-sonic area about 175 yards out. Plus wind drift is determined by the loss of velocity from muzzle to target. While they gain so much from breech seating at 100, they loose at 200.

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frnkeore posted this 27 August 2018

Regarding small cases, I believe that there is a "diminishing return" on case capacity.

First, I have yet to see, in the last 15 years, a Rem 40X, in 308, win a Hvy rifle match, nor any other 308 chambered rifle. Maybe I missed it? The 308 seems to be way overbored for CB match competition.

30 BR and the PPC case seams to be the most efficient case capacity. Mel Harris thinks that the 30 BR is a little larger than need and has stuck with the PPC case. I believe all his records are with that case.

In my sport, the 32/40, isn't as over bore as the 308 is and still does pretty well. The 32/40 is also a straight taper cartridge case allowing the powder to be better place in the line of the flash hole, helping ignition. I started shooting in 1985 with the 32/40 but by 1987 had gone to a smaller capacity 30 cal, called the 32/35 (.400 case head, 1.88 long) Stevens, my last rifle was a 33 cal on a Max case and my current one is a 30 cal on the Max case. For me, all my smaller cases did better than the 32/40.

My feeling about case capacity, is that if your using a case of greater capacity than you need, that case capacity is wasted, as well as the little extra powder needed to fuel it.

I also think that the better internal ballistic's make for better ES's and potential better accuracy on that front.

One other thing, If you have QL, you will see that smaller cases, give less muzzle pressure for the same velocity. QL, shows that but, I can't say the H. P. White Lab or any other source has proven it. Does anyone have any info on that?

Frank

 

 

 

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3Lakes posted this 27 August 2018

If one had the resources to try to make a true apples to apples comparison between a 30 BR and a 308, i.e., using two nearly identical custom barrels (light varmint) and having each chambered with a tight neck reamers to fit one custom action and using the finest cases available for each caliber, Lapua brass with small flash holes, necks turned and cases trimmed to uniform length,  one might be able to discern differences. Keep the barrel length identical so the expansion ratios are nearly identical.

Loren

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RicinYakima posted this 28 August 2018

All it takes is money and a good gunsmith. Heard that somewhere lately.

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Pentz posted this 28 August 2018

Amen brothers....I fought my 32-20 CPA for three years before sending it back to Gail for rechambering to 32-40.  Right off the bat it is hitting 10s at 200 yards with 14.2 of 4227.....what took me so long....angry

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frnkeore posted this 28 August 2018

But, you have to remember that the smallest, witnessed, 10 shot, 200 yard group was shot with that chambering. The group was .512, I believe, shot in Modesto a few years ago.

The biggest problem that most people have with the CPA 32/20 (.321), is the thin, weak brass.

Frank

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John Alexander posted this 28 August 2018

Anecdotes, anecdotes, and talk of once in a lifetime single group records. Do we have any even imperfect test results?

Of course the Miller Short or the 6ppc will win most of the matches if a high enough % of shooters are using them. Several years after the PPC was dominate in JB benchrest 22 calibers were winning a bigger percent of matches PER shooter entered.  But by that time everybody knew you couldn't beat a ppc.

After all these years do we have any evidence at all that smaller if better -- or worse?

The closest thing I have seen is Joe's recent imperfect testing that gave consistently better groups with the 22-250 vs. .223. Even when changing chambers on same barrel. I am not convinced by Joe's work, but do we have anything of even that quality indicating that smaller is better -- for certain situations? for all? never?

Just curious.

John

 

 

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frnkeore posted this 28 August 2018

I don't know, John but, I think that there is a "mountain" of evidence, in the match results.

When I started shooting CBA matches, in ~1988, there were still 308 match barrels on the line but, even then, they didn't do as well as smaller cases. A good friend of mine, "Etz" Johnson, held what was then called, the Silhouette class record, his cartridge of he own doing, was a 1.625 long, 300 Sav case, with a long neck and his throating, another friend, shot a 1.75 long 30/30 case and held a record in the Hvy class, in that time period also. 

The PPC cases came in the mid 90's and they dominated, before the 30 BR became the most seen cartridge on the line. I believe that ONLY came to be, because the 30BR was easier to build, w/o modifying the bolt face and brass was easier to come by.

BUT, even though the 30BR is used much more, the 30PPC still holds many records and is still setting records at this time. Check out Mel Harris's records, his 30 Harris, is based on the 30 PPC and if you talk to him at the next match you attend, he'll tell you that he uses it, because the 30BR has more capacity than he wants or that's needed.

Wouldn't you think that in 30 years of high level BR shooting, that if bigger is better, that would have shown the way at sometime, during those years? Wouldn't someone "accidentally" found that the 308 or '06 would out shoot the smaller cases?

Over and above that, smaller case are more efficient than larger ones, for CB shooting and I believe, that is why we are where we are today. I can only see cases get smaller if, powders are developed that will allow that.

As I pointed out earlier, smaller cases reduce muzzle pressure and with our softer bullets, that can/may deform the bases at exit. Nothing proven there but, reduced MP is advantageous.

Frank

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Scearcy posted this 29 August 2018

What is you guys opinion of the 300 Blackout? It certainly is a smaller case. I see there was one in the Nationals last year. I shot one for two years but in an 8 1/2 lb rifle so there was little to learn other than it could be used safely.  I still believe if smaller is better, there is more work to be done there. That case would push an 160 gr bullet about 2000 fps with a full power load.

Jim

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RicinYakima posted this 29 August 2018

IMHO, the 300 Blackout is an excellent design to shoot the Hornady 220 grain round nose at 300 meters and hit a 9 inch target from a suppressed AR15.

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Ken Campbell Iowa posted this 29 August 2018

.... only one thing to do ::

take johna's winning killer tikka barrel in 223 and rechamber it in 22-250 ....  and see if it shoots better/worse .

*******

although sometimes things just don't seem right ... ( g ) 

*************

speaking of smaller cases i have an extra (used ) 7BR 1/10 short in a shilen ss varmint barrel that needs a good home ... now that i am into 6mm .... $200 shipped .  remington 700 threaded .  pm me if  .

ken

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frnkeore posted this 29 August 2018

What is you guys opinion of the 300 Blackout? It certainly is a smaller case. I see there was one in the Nationals last year. I shot one for two years but in an 8 1/2 lb rifle so there was little to learn other than it could be used safely.  I still believe if smaller is better, there is more work to be done there. That case would push an 160 gr bullet about 2000 fps with a full power load.

Jim

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It would also be a excellent cartridge for a bolt action PBB class rifle.

Frank

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John Alexander posted this 29 August 2018

Frank,

I don't really doubt that smaller cases probably confer some small advantage under certain conditions probably for some of the reasons claimed.  I just think we make too much of it. On the other hand when someone finds the opposite of the conventional wisdom we ignore the unwanted evidence.

There is also the herd instinct that seems to infect a large share of our shooters. Shooting in the order cast is a good example that was the official word for decades.  A few years back in JB benchrest there was a lot of fuss about the uniform thickness of case body walls (not necks) -- special instruments to measure etc. much hand wringing.  Anybody with any concept of the pressures inside a cartridge case should have said WHAT BS but everybody seemed to have their knickers in a twist about it for awhile.

If Tony Boyer won some matches with a 22 Swift and a Mossberg barrel, there would be a bunch of them on the line before the season was over.

It just seems we might do a LITTLE serious experimenting once in a while instead approaching questions by navel gazing.

John

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Brodie posted this 29 August 2018

John A said:"I don't really doubt that smaller cases probably confer some small advantage under certain conditions probably for some of the reasons claimed.  I just think we make too much of it. On the other hand when someone finds the opposite of the conventional wisdom we ignore the unwanted evidence."

The above proves what I have already said:L "Feathers;  American shooters spend too much time worrying about little differences in their equipment while trying to 'get an edge on the competition' instead of facing up to facts and working on their shooting".   A loose nut holding the trigger will always shoot worse than a tight one.

B.E.Brickey

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frnkeore posted this 30 August 2018

It just seems we might do a LITTLE serious experimenting once in a while instead approaching questions by navel gazing.

John

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That is a excellent idea, John and one that I would promote also.

BUT, individuals aren't likely to do it themselves. What I would suggest is that CBA, take it on and either sponsor it  or conduct it. Use a UNR rifle as the platform.

Use 50% CBA money and ask for donations to fund the rest and use the same gunsmith and barrel testing scientifically.

I would donate to that!

In the NRA's early days, they did things like that. That was when The American Rifleman, was worth reading.

Frank

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John Alexander posted this 30 August 2018

Frank,

That is a good idea. I suspect others would also donate.  The fly in the ointment is (as always) someone would have to organize and do the work.  We have a lot of good ideas, not so many volunteers.  The CBA usually has a position open at any given time and no flood of competitors for it. 

I will see what the competitors and the Board of directors at the nationals think of it a week from Friday.  But I don't expect to be overrun with volunteers rushing to the front of the room.

If anybody on the forum woiuld like to look into organizing such an effort go to the thread I am going to start "Sponsored Research" and give us your thoughts.

John

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John Alexander posted this 30 August 2018

Sorry about that I did start a "Sponsored Research" thread and at the moment I tried to post the forum went out of business. Been out of the house all day.  Will try later.

John

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OU812 posted this 31 August 2018

Bullet fit and design is WAY more important than case size (30BR vs 308 Win). Thoughts based on my limited experience lately anywaycool

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