Which defect is worse?

[justin amateur]

A discussion by a group of old coots, over morning coffee, regarding visible cartridge defects,
and the question that came up was: Which defect caused the most trajectory dispersion?
We agreed the minor scratches and dings on the nose had little effect, but anything that affected
the drive bands was going to cause some serious wobbles. So the discussion moved to where
on the drive bands would the most trouble be produced, the shoulder, where the nose meets the drive band,
or the skirt, where the drive band touches the brass. Made for an interesting topic to argue about,
but no real answer other than "a damaged bullet heel is a bad thing".

So which location produces the worst results? Shoulder or skirt?

I just happen to have a new brick of Eley Action that's been producing decent results,
so I decided to take the time and try it for myself.

3 boxes of Eley Action, lot number 3117-300084.

CZ 455 Lilja, Sinclair bipod, chronograph out front

50 rounds fired as shipped, straight out of the box.

50 rounds fired with the shoulder shaved on one side.

50 rounds fired with a nick cut out at the skirt, just at the crimp.

The results including chronograph numbers.
The damage didn't produce any real difference in the mv's,
but the spread is visibly different from the as shipped results.

Any damage to the drive bands is a bad thing, but damage at the skirt
produces a major difference in trajectories. Explains why hand chambering cartridges
produces better results than magazine fed chambering.
Less chance of scraping the bullet on the lip of the chamber and damaging the drive bands.

 

[straightshooter1]

A discussion by a group of old coots, over morning coffee, regarding visible cartridge defects,
and the question that came up was: Which defect caused the most trajectory dispersion?
We agreed the minor scratches and dings on the nose had little effect, but anything that affected
the drive bands was going to cause some serious wobbles. So the discussion moved to where
on the drive bands would the most trouble be produced, the shoulder, where the nose meets the drive band,
or the skirt, where the drive band touches the brass. Made for an interesting topic to argue about,
but no real answer other than "a damaged bullet heel is a bad thing".

So which location produces the worst results? Shoulder or skirt?

I just happen to have a new brick of Eley Action that's been producing decent results,
so I decided to take the time and try it for myself.

3 boxes of Eley Action, lot number 3117-300084.

CZ 455 Lilja, Sinclair bipod, chronograph out front

50 rounds fired as shipped, straight out of the box.

50 rounds fired with the shoulder shaved on one side.

50 rounds fired with a nick cut out at the skirt, just at the crimp.

The results including chronograph numbers.
The damage didn't produce any real difference in the mv's,
but the spread is visibly different from the as shipped results.

Any damage to the drive bands is a bad thing, but damage at the skirt
produces a major difference in trajectories. Explains why hand chambering cartridges
produces better results than magazine fed chambering.
Less chance of scraping the bullet on the lip of the chamber and damaging the drive bands.

Excellent job there Justin Amateur. When I read your question after that first paragraph, that's the experiment the quickly came to my mind.

It's essentially the very issue I had with my RPRR where feeding from the mag was scuffing the driver bands causing poor results when using good quality ammo (like Lapua Midas, Center-X, RWS R50). Once I solved that feeding problem, good results followed.

 

[JMcQ]

Very cool. Thanks for taking the time to do the experiment it’s great info.

 

[CodeMonkey]

Good info, @justin amateur. I really appreciate what you do and your science adds a lot of knowledge to out sport.

 

[Pondskipper]

Probably a large attribute as to why the V22’s do so well, I tested mine several times to see what if any deformation was caused by mag feeding and I can honestly say I can’t see any actual deformations at all other than slight engraving from the rifling it’s self.

 

[Mr. Wolf]

Excellent job there Justin Amateur. When I read your question after that first paragraph, that's the experiment the quickly came to my mind.

It's essentially the very issue I had with my RPRR where feeding from the mag was scuffing the driver bands causing poor results when using good quality ammo (like Lapua Midas, Center-X, RWS R50). Once I solved that feeding problem, good results followed.

Could you elaborate on how you fixed the scuffing issue?
I’m trying to work through a similar issue with a different 22 bolt rifle.

MW

 

[straightshooter1]

Could you elaborate on how you fixed the scuffing issue?
I’m trying to work through a similar issue with a different 22 bolt rifle.

MW

In my case, I had one of the early versions of the RPR which had issues with the mag assembly and the mag fit. The mag assembly wad loose, so I took it out and added some thickness with some aluminum tape to the outside so that it fit snugly. But the mag was still too low holding the cartridge at a little too much of an angle forcing the bullet to scuff against the bottom edge of the chamber. So, I did two things: 1. Installed a shim under the mag assembly to raise it up a little, 2. Lightly files the edge of the chamber very slightly so that it wouldn't have a tendency to cut the soft lead bullets as it entered the chamber. All is good now.

 

[barronian]

@justin amateur could you please post some higher res pictures of the damaged rounds ? id like to study the severity/location of the (deliberate) damage and the pictures above are minuscule on my screens...

BTW really nice to see some actual testing rather than the usual AUDIs (Adamant Unfounded Declarations on the Internet)

 

[justin amateur]

B, lucky for you I had a ftf in the door panel.
Easy enough to duplicate the cuts at my desk in the office this morning.
Here's what the cuts looked like close up...

Easy enough to duplicate my results for confirmation.
Grab a box of half decent ammo and send 15 as shipped, 15 with the shoulder nicked,
and the remainder with the heel nicked at 50 or 100 yards.
I sent them at 200 to increase the amount of time for the problem to amplify.

 

[barronian]

B, lucky for you I had a ftf in the door panel.
Easy enough to duplicate the cuts at my desk in the office this morning.
Here's what the cuts looked like close up...

Easy enough to duplicate my results for confirmation.
Grab a box of half decent ammo and send 15 as shipped, 15 with the shoulder nicked,
and the remainder with the heel nicked at 50 or 100 yards.
I sent them at 200 to increase the amount of time for the problem to amplify.

@justin amateur many thanks now I'm trying to work out how I'm going to repeat your experiment but with the nicks orientated A) with a land and B) with an adjacent grove.
My thinking is that a land will squash out the nick while a grove will 'leave it alone'..... alternatively a land might mean that the bullet tail is easier to push towards the land resulting in the bullet sitting at a slight angle in the bore.... as usual more questions than answers !

 

[Cuzz]

Thanks for your time and for sharing, Ive had similar 6.5 mm results, dropping a cartridge on the projectile tip has very little effect on accuracy at 200 yd.

 

[ntrinsik]

Thanks for your time and for sharing, Ive had similar 6.5 mm results, dropping a cartridge on the projectile tip has very little effect on accuracy at 200 yd.

Has a great effect at 1100 yards though! Had a tip that was a little flat and it ended up 30 yards in front of the target.

 

[Cuzz]

wow, thanks, i wondered about long range

 

[justin amateur]

Not finished satisfying my curiosity yet.
Why is as important as what caused the spread.
How much is due to wobble and how much is due to tipping on muzzle exit?
2 more things to attempt. 1) Capture fired bullets without mushrooming.
Should allow for close inspection of the projectiles.
2) Drill small holes in the drive band at the same location/diameter/depth.
Send another 50 at 200 as shipped and as drilled.

Setting up a jig for the drill press and ordered a 10 lb box of polyfil.
Hoping the polyfil will act as a catch without damaging the projectiles.

Don't take much to keep me entertained.

 

[barronian]

@justin amateur have you had a look at the Mass Asymmetries chapter in
Ballistics: Theory and Design of Guns and Ammunition
By Donald E. Carlucci

 

[justin amateur]

I do my reading on line...less expensive that way.

Effect of Mass Asymmetry on Ballistic Match of Projectiles | Journal of Spacecraft and Rockets

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space...

arc.aiaa.org

Mass asymmetry and tricyclic wobble motion assessment using automated launch video analysis

This paper describes an approach to identify epicyclic and tricyclic motion during projectile flight caused by mass asymmetries in spin-stabilized pro…

www.sciencedirect.com

Carlucci

 

[barronian]

here you go

Ballistics

Even the earliest weapon developers faced the need to understand how and why guns and ammunition work in order to improve their effectiveness. As weapons became more sophisticated, the field of ballistics naturally divided into three main areas of specialization: interior, exterior, and terminal...

books.google.no

 

[justin amateur]

Turns out, poly-fil can capture a 22lr in flight, without deforming the bullet.
Tried it this morning at about 10 feet from the muzzle. First with a revolver, then a rifle.
Recovered the bullets undamaged.

That's the bullet hanging at the end of the wad of poly-fil.

Here's what it looks like when extracted.

It didn't mushroom, at all.

Tried it with Eley Action as shipped,
nicked shoulder and nicked drive bands.
Recovered all three.

The swaging effect of the bore compressed bullet material down the length of the bullet.
Damage at the shoulder doesn't show up at the heel.
Damage to the drive bands, just above the crimp,
shows up as a flat spot on the edge of the heel.
A damaged bullet heel produces strays.

 

[DrDWD]

Justin - excellent experimental research. The preliminary results are very interesting. Great method to capture the bullets

You mentioned a drill press above and controlled damage. Look forward to those results as well. You should consider publishing an AIAA conference paper on this work. I think you are well on your way to enough data to publish the results.

One question. Looking at the pic of the three targets. Clearly the spread changes between the three. However, it appears that there also is a shift up in the mean poi relative to the target dot, do you think it is just due to the reduced mass of the bullet due to the intentional damage or do you think it is something else?

Thank you for the great work!

 

[justin amateur]

The shift in poi is deliberate.
Sent the first 50 with the scope settings from the previous week.
Had a tailwind to contend with at that time.
After the first 50, adjusted the scope to the center of the group.
Then sent the next two groups of 50.

Research paper? Not me.
Just an amateur on this side of the keyboard
satisfying my own curiosity and trying to understand
why the 22 lr behaves as it does.

For those interested in assembling a poly-fil trap,
it took two 4 foot long 9x9 inch square tubes to hold
the twelve 4 gallon bags (6 ounces of fluff per bag)
to provide the minimal density and cushion to catch, not damage the bullets.
Distance from muzzle to the trap was 10 feet.

I have an assortment of bulk ammo from CCI, Remington and Federal
that all have a tendency to spit strays that are going to be caught
then looked at to see how those heels compare.

 

[justin amateur]

Took some doing but I was able to extract 2 bullets without doing major damage to the seating areas.
Pain in the rear end getting the crimp and brass to let go of the bullet tail.
I'm thinking the deflagration pressure pushing forward explains the irregular skirts.
Look at the top two bullets extracted from the brass, compared to the bottom two from the polyfil trap.
They are longer nose to heel when unfired and shorter after being fired.
Also the heel diameter is compressed outwards to match the rest of the drive band to bore contact area.
So any void in the vicinity of the heel will allow bullet material to move towards it
leaving an irregular shape at the skirt and producing strays as it exits the muzzle.

When the powder ignites it flares the case mouth leaving the crimp seam in the bullet
then as the pressure peaks it expands the bullet heel forward and out to fill the crimp seam.
If there is a void of any sort near the crimp seam the skirt will end up uneven.

If you have an uneven crimp, canted bullet seating, off center seating, dents or dings in the drive bands,
slanted drive bands, irregularly shaped drive bands y'er gonna get strays all due to the deformation/expansion of the heel.
That's why those odd strays show up that most of us blame on ourselves. Maybe.

 

[jdemp1]

Interesting data thanks for doing this

 

[justin amateur]

Set up the drill press and jig, then drilled 60 tiny holes.
Little ribbons of lead all over the work bench.
Numbered and weighed each cartridge, before and after.
Waste of time....digital scale copped an attitude and spit out incorrect readings.
Some cartridges gained weight after being drilled, unlikely, eh?

Typical hole from the jig and drill press

What the bullet looks like after running down the bore of the Lilja

The bottom bullet is one extracted from the brass unfired.
The top two are from the drilled and fired cartridges.
Note that the filling of the holes is uneven and mostly from the heel end of the bullet.
Seems to confirm my idea that the deformation of the heel that occurs
does move towards the voids in the bullet and results in an uneven skirt
as well as producing an unbalanced projectile.

The poly-fil trap does the job of catching the fired bullets,
leaving them in good condition to allow close inspection.
Very handy diagnostic tool produced with minimal expense.

 

[*rim-star*]

Good post and interesting , well done JA.

 

[Dirtywork]

interesting read

 

[Near miss]

I have thought of testing 22LR stability by prolonging the bullet by placing something like a small nail into the bullet nose.

This will make the bullet longer, thus significantly reducing stability, without adding almost any mass to the bullet.

The length of the bullet has everything to do with stability so this test should show, upon succeeding (determining at what length the bullet tumbles in flight) how much there is leeway to play with stability and bullet length.

Do you have any ideas how to carry out with this experiment?

 

[justin amateur]

Yep, I do NM.
Cast bullets would be the platform I'd use, not rimfire.

My morning ended with some serious giggles, more on that later.

Eley Action 40 grain 22lr rated 1090 fps

CZ 455 Lilja, Sinclair bipod and chronograph out front

The first 40 were fired as shipped,
10 had been drilled and test fired into the poly-fil for recovery.

The next 25 had holes drilled in the drive bands
and were oriented with the hole at the top of the chamber.

The last 25 had the holes oriented to the bottom of the chamber.

The 40 shots to the left were as-shipped.
The 25 in the middle were hole up.
The 25 to the right were hole down.

Excuse the redneck image editing...inverted the target and mislabeled the results.
Dum-adze.


Now for the punch line.

I had a box of CCI SV in the kit, so I sent it too.
Same conditions, same setup, same distance.

CCI SV as shipped grouped worse than Eley Action,
even though Eley Action had a freakin' hole drilled in the side!.

Oh yeah...CCI SV is for sure some great ammo, eh?

 

[straightshooter1]

Oh yeah...CCI SV is for sure some great ammo, eh?

Yeah . . . like that one box of that lot would tell anyone that, huh?

I know you know better than that.

BTW, the CCI SV's I have have been averaging 1104 fps out of my 18" Shaw SS barrel. I wonder if that extra 50 fps helps reduce the ES's for either velocity or POI's??? My SV's seem to do better than that.

 

[justin amateur]

Yeah, this brick of CCI SV is rather sad.
ES isn't bad, but look at that close up.
Too many of those cartridges have bullet material compressed down past the crimp.
Not CCI's best.

I'm still thinking about the results with the Eley Action drill holes.
If I hadn't oriented the holes in set directions, that group size would have likely doubled.
But as they were set in the same direction, it limited the spread.

 

[straightshooter1]

Yeah, this brick of CCI SV is rather sad.
ES isn't bad, but look at that close up.
Too many of those cartridges have bullet material compressed down past the crimp.
Not CCI's best.

Speaking of CCI's best . . . a while back I bought a brick of Green Tag expecting them to do as well as Wolf, Eley or maybe even RWS or at least like SK. For the price point, I really had somewhat high expectations. As it turned out, they didn't perform as well as any of those brands and not even close to the SV's I have. For that price point, it was very disappointing.

I'm still thinking about the results with the Eley Action drill holes.
If I hadn't oriented the holes in set directions, that group size would have likely doubled.
But as they were set in the same direction, it limited the spread.

Yes, I feel you're absolutely right about the orientation of the holes.

Still . . . good work on your part.