M14 Forum banner

Assessing Accuracy Quiz!

996 Views 21 Replies 11 Participants Last post by  Ted Brown
Here is an interesting hypothetical question concerning ammunition accuracy.

Your rich Uncle Algernon has decided to support your shooting addiction, and announced that he will give you a life-time supply of ammunition. You can choose any caliber, bullet weight and velocity, and these parameters can be switched at any time as you desire. However, the method of establishing accuracy will be fixed and if you try and change it the whole deal is off. Your three choices for accuracy acceptance are as follows:

Type A - The average horizontal and vertical standard deviation, measured from three 30 round targets, shall be less than 1.6 inches at 200 yards.

Type B - Five 10 round targets fired through two different test barrels at 300 yards shall have an average extreme spread of 3.5 inches, and no individual target shall show an extreme spread greater than 4.5 inches.

Type C - The average mean radii of five ten round targets from two barrels shall not exceed 2.39 inches at 300 yards.

Which type would you pick?
  • Love
Reactions: BlueSun
1 - 20 of 22 Posts

· Premium Member
Joined
·
1,616 Posts
B seems the best, assuming the barrels are both ideal and as similar as can be.
C seems close, though, since it's averaged.

I may have these backwards, 2.39" is a pretty specific value compared to the others.
 

· Registered
Joined
·
740 Posts
Need to do the math to compare apples to apples; use either MOA or AMR, but don't combine the two. I'm too lazy to do the math.

Accurate does not mean precise.

I believe B shoots the smallest overall group size, but C may be more precise.
 

· Registered
Joined
·
740 Posts
Ok- you made me do some math.

With C, approximately 95% of your shots will fall inside about a 10" circle.

With B, your max extreme spread is 4.5", but we have no reference on how far these groups are from center.
 

· Registered
Joined
·
6,373 Posts
Discussion Starter · #8 · (Edited)
A is basically the specification for M855A1.

B is basically the specification for Mk 262 and Mk 319.

C is basically the specification for M80.

With A, 99% of all shots will fall inside a 9.6 inch circle at 200 yards and 68% will fall inside a 3.2 inch circle at the same distance.

With B, 99.99% of all shots will fall inside a 4.5 inch circle at 300 yards, and roughly speaking, 68% will fall inside a 1-1/8 inch circle at 300 yards.

With C, 99% of all shots will fall inside a 11.5 inch circle at 300 yards and 68% will fall inside a 3.8 inch circle at the same distance.
 

· Registered
Joined
·
5,424 Posts
A is basically the specification for M855A1.

B is basically the specification for Mk 262 and Mk 319.
Speaking of those two 5.56 cartridges, here's the down range difference from US Army AMU training. 300 Meters target w/ Rack grade M16 A2 vs a Match grade M16 A2 - but I believe the match ammo made the bigger difference. (These are 10-shot groups).
Font Circle Advertising Parallel Science


There is also difference b/t a rack grade M16A2 and a SDMR (M16A4) with a heavy match barrel, but I suspect the ammo is the even larger variable in their testing (8" vs 26" groups at 600 yards)
Product Writing implement Font Material property Cone


Question for Lysander: Do you have the accuracy spec for M118 LR or Mk 316 Mod 0?
It would be interesting to see how it compares to the M80 spec, thanks.
 

· Registered
Joined
·
6,373 Posts
Discussion Starter · #12 · (Edited)
The demonstrated accuracy of the first lot of T291 (M72) during testing was: Mean radius: 1.0, Extreme Vertical: 2.6, Extreme Horizontal: 2.5, Extreme Spread: 3.3 (EDIT: at 300 yards)

M118 Match - The average Mean Radii at 600 yards, shall not exceed 3.5 inches. 99% of all shots will fall inside a 16.8 inch circle at 600 yards. (Five 10 round targets, in two barrels) If a 300 yard range is used the MR shall be 1.6 inch (99% inside a 7.68" circle).

M118 Special Ball, Long Range - At 1000 yards the average extreme horizontal spread shall not be greater than 10.3 inches, and the average vertical extreme spread shall not be greater than 14.0 inches. -OR- At 200 yards the the average extreme horizontal spread shall not be greater than 1.3 inches, and the average vertical extreme spread shall not be greater than 1.5 inches. (Five 10 round targets, in two barrels) Roughly 68% inside a 3.4 by 4.6, or 0.4 by 0.5 square depending on the range.

Mk 316 - I don't have the production requirements, but the design requirements were that a 10 shot group at 300 yards all fall inside a 3.5 inch circle. The four lots I have data on have an average extreme spread of 1.75 inches at 300 yards.

M118LR is slightly inferior to Mk 316 in accuracy potential.
 

· Registered
Joined
·
189 Posts
A very thought provoking topic! I have often wondered what to consider for a personal acceptance standard.

A is basically the specification for M855A1.

B is basically the specification for Mk 262 and Mk 319.

C is basically the specification for M80.



With B, 99.99% of all shots will fall inside a 4.5 inch circle at 300 yards, and roughly speaking, 68% will fall inside a 1-1/8 inch circle at 300 yards.

Two questions for my edification:

1) What is a good source for these specifications? I am used to looking up ASME, NAS, and etc specs, but admittedly have never looked up the standards for ammunition acceptance.

2) The 68% makes decent sense - a 1-sigma value. How do you get to 99.99% for the full population? I am by no means a stats guy (ask me what my least favorite undergrad math class was 😄) and always poke my much smarter reliability group for a number when I’m figuring out what cases I need to analyze or test, but to me it seems if you had one round out of fifty (1/50) giving you a 10 rd group extreme spread of 4.5” (I may be doing apples and oranges here with the 5x 10 rd groups vs 50 rd), that would be 2% of your population… yielding between a 2 and 3-sigma confidence of 98%.

Just mathematically curious and hoping to pick up some new knowledge. Again, I continually ponder how to “accept” and quantify the differences in reloaded ammunition for myself.

Thanks for the great discussion!
 

· Registered
Joined
·
189 Posts
Personal ammo addendum: I could get comfortable personally whenever I had 2x 10 rd prone slow fire strings off a sandbag at 300 yds that would each hold 4.5” extreme spread. I’d know the combo of rifle and ammo lot worked well together, and know that it was only ever me that prevented a clean target.

I figured 95% confidence, assuming 1 of 20 rd would be the furthest out, was good enough for me.

And I don’t have DoD’s test budget 😄.
 

· Registered
Joined
·
6,373 Posts
Discussion Starter · #15 · (Edited)
A very thought provoking topic! I have often wondered what to consider for a personal acceptance standard.



Two questions for my edification:

1) What is a good source for these specifications? I am used to looking up ASME, NAS, and etc specs, but admittedly have never looked up the standards for ammunition acceptance.

2) The 68% makes decent sense - a 1-sigma value. How do you get to 99.99% for the full population? I am by no means a stats guy (ask me what my least favorite undergrad math class was 😄) and always poke my much smarter reliability group for a number when I’m figuring out what cases I need to analyze or test, but to me it seems if you had one round out of fifty (1/50) giving you a 10 rd group extreme spread of 4.5” (I may be doing apples and oranges here with the 5x 10 rd groups vs 50 rd), that would be 2% of your population… yielding between a 2 and 3-sigma confidence of 98%.

Just mathematically curious and hoping to pick up some new knowledge. Again, I continually ponder how to “accept” and quantify the differences in reloaded ammunition for myself.

Thanks for the great discussion!
MIL-DTL-32338B with Amendment 3
Accuracy Measurement Methodologies, Chuck Marsh, NSWC Crane IN.
MIL-DTL-46931W with Amendment 3

Five groups of 10 rounds with two barrels (100 rounds total), with no group exceeding 4.5 inches, extreme spread, and the average of those ten groups extreme spreads are less than or equal to 3.5 inches. What are the odds you will get a group larger than 4.5 inches? It is going to be higher than 3 sigma, because your average extreme spread is (on average) close to 3 times sigma, or 99.7% of the population, the additional inch gives you an extra 0.1% at each end, or 99.9%.

EDIT: it appears I hit the "9" button one too many times.
 

· Registered
Joined
·
189 Posts
Ahhh! I was not thinking of the barrels together, and it makes sense when you talk about the likelihood of anything past your extreme as beyond 3-sigma.
 

· Registered
Joined
·
740 Posts

· Registered
Joined
·
6,373 Posts
Discussion Starter · #20 · (Edited)
Type A would be my choice if it were imperative to chose one.
Uncle Algernon appreciates your choice; that ammunition will be cheaper to make than "B".

"B" will yield the most accurate ammunition of the three specifications.

With "B" 68% of all shots will fall inside a 3/8 MOA circle and better than 99% will fall inside a 1.5 MOA
With "A" 68% of all shots will fall inside a 1.06 MOA circle, an 99% inside a 3.2 MOA circle.

"B" is basically match grade ammunition, you would be hard pressed to volume manufacture better.
 
1 - 20 of 22 Posts
Top