The First Thousand Shots

Does barrel polishing occur shooting rimfire ammunition,
does it improve accuracy over time, if polishing does occur
how many shots does it take to show that improvement?

X-Act? Steve, really?

Not much difference in price currently, between hi end Lapua and bulk CCI.

I plan on using SK Biathlon Sport from the brick that did the best at 200 yards.
First box, fifth, tenth, fifteenth and twenty-first will be shot for accuracy at 50 yards off heavy bags.
This is an eight year old rifle, been used with a variety of barrels.
CZ 455 Varmint, single set trigger, pillared, bedded, barrel is free floated,
Mueller 8-32X44 target reticle, set trigger breaks at 10 ounces.
All targets shot will be posted including pics of setup and ammo.
Barrel wear and results with the SKBS are the important parts.
The rest is just letting cheap ammo drag powder/primer residue down the bore.

CZ 455 Varmint, Mueller 8-32X44 Target retical, heavy bags, new factory barrel, 50 yards
SK Polar Biathlon from a tested brick, first 50 shots





ten 5 shot groups



Note the change in pattern at shots 35 to 40.
First 35 shots 1.5 to 2 moa, then submoa.
Something changed. Wasn't me or conditions.
This is a well used rifle, I understand it's quirks.


Possible answer seen after running the bore following the first 100 shots.
Before image of the crown, see the cotton fibers hung up on the burr at the crown?




Where's the burr at the same location after 100 shots?
No cotton fibers hung up at the crown after cleaning.




Note also the circumferential pattern has been worn away
and replaced with a linear abrasion pattern.
Looks like 400 grit sandpaper was run down the barrel.


Next 50 shots with a low quality batch of CCI SV.
This stuff is not CCI's best. Dents, dings, chips, bullet material over the crimp on to the brass.
Throws strays even from my Lilja and Shilen barrels.





Yeah, that's as expected, crap ammo, crap results.
All it has to do is go bang and clear the barrel.
Each bullet is dragging primer/powder residue through the rifling and polishing the surfaces.


After cleaning with Hoppes 9, patches and nylon brush,
the next 96 images of the bore after 100 shots downrange.
Bore shows a linear abrasion pattern, the deposits are gone,
tool marks still visible at the leade, still a few rough edges on the rifling.

Hoppes 9, patches and a nylon brush look to be doing a decent job on this new barrel.
Every 100 shots, clean until patches show no discoloration, then capture images with the borescope.

Second 100 rounds sent using bulk Winchester.





200 rounds through the bore, still visible rough spots.
Still a few burred edges on the lands showing up.
Crown now looks very sharp and clean.

Other portions look very smooth, almost looks honed.



Link to view bore images after 200 shots...https://photos.app.goo.gl/zFvkL37McxW95tBF6

How do you know if there's an abrasive in the residue?
Any way to find out?

Probably

Okay....easy enough.

Pull apart some cartridges,
primer in one foil tray, powder in another



Liberate my inner pyromaniac and ignite the primer, then the powder
and by chance, or luck, there was no flare up, just a puff of smoke in each foil tray.



Piece of marine stainless from my store of boat parts,
marked into 3 zones. One for bullet rub only,
one for bullet coated with primer residue,
one for bullet coated with powder residue.



Rubbed each bullet in it's sector for 25 passes back and forth.
Not much pressure applied using two finger tips to hold the bullets.



Top sector, bullet only, some lead and bullet lube deposited, but no scratches.
Middle sector, primer residue coated bullet shows visible scratch patterns.
Bottom sector, bullet with powder residue shows a few scratches.

Looks like the primer residue is responsible for the majority of the polishing.

Good thing I'm easily entertained.
Kept me busy for 30 minutes in the garage.
Wife came out and asked: Is something burning? I can smell it in the kitchen.

Some cheap Aguila Super Extra, 3 cartridges
Dumped the powder, then used a paper clip to scrape loose the primer....gently....very gently.

Most of the rimfire I've read about uses lead styphanate as a primer.
Contains silica/glass powder as the igniting agent.
The silica can be up to 20% of the primer by volume.
That's a hefty bit of abrasive.

Abrasive problem?

Read an article that Eley changed their primer mix due to excess wear just forward of the leade.
That was a while back, no further information available.

Still reading Hoyt.

Be aware, that particular priming methodology is pretty old school and not largely practiced with higher end ammo,
which is a big reason it’s higher end, ELEY in particular. ELEY eps ammo, for instance, is for ELEY priming system.
the older method with liquid mixture being spun was found to yield fairly uneven primer distribution.
Now they take a wet matrix in pellet form, drop it in and press it to swage it evenly throughout rim.
A few years back Shooting Times did a comprehensive writeup all about ELEY and still should be available online....pretty good read.

I'll find it and read it Tim, thanks for the heads up.

The Best of The Best Gets Better

You don't have to be an Olympic shooter to appreciate Eley's excellent rimfire ammunition.

www.shootingtimes.com

From the linked article...

the goal of the TenEx improvement project was to increase the percentage of reference groups (less than 15mm diameter at 50 meters) from 8 to 10 percent to 30 percent. Current Eley TenEx Ultimate EPS ammo averages 50 percent.

Click to expand...

So only half of the Tenex Ultimate is capable of sub 15 mm groups at 50 meters.
The rest exceeded that grouping, and that's the best of that label.

15 mm is about 0.59 inches measured outside of hole to outside of hole at widest point.
Subtract 0.21 inch and you get a ten shot group of 0.38 inches center to center.
That's better than I can do for 10 shots at 50 yards.

Thank Tim.
He was the one that pointed out I was basing my opinion on unsupported information.
No documentation of barrel wear during break-in to substantiate my thoughts.
I like hard data. Difficult to argue with images taken of the same spot at 100 shot intervals.

Checking for improvement, early morning before the wind picks up.
SK Biathlon Sport at 50 yards.

CZ 455 Varmint, heavy bags, new barrel





Still not producing consistent results.
Group average size is dropping but aggregate almost the same.



How much and where does the burn residue end up in the bore?
Good question. Before cleaning, after this mornings session,
pulled the barrel, grabbed a camera and played with focal length and lighting.
managed to get a few images that best illustrates the answer.













And the answer is, a lot of residue and everywhere from the leade to the muzzle, top, bottom and sides.
That explains the wear patterns showing up all through the bore.
Heavier clumps in different spots, biggest on the bottom of the barrel.

Time for a comparison



Shots 1 through 50 with SKBS.

Then shots 200 through 250



Second box shows better results than the first.
Each target shows improvement with progressively smaller groups sizes.
Still slinging strays, but significant improvement with increased number of rounds sent.
0.45 inch best group on the first target, 0.3 inch on the second.
Hopefully that rate of improvement holds up.



The leade as received from the factory

and after 300 rounds, the lands still appear rough
but the grooves show polishing has occured.



Link to borescope images after 300 rounds https://photos.app.goo.gl/LVPSsHLJSs64pfaS9

@JM... I've read about Flitz and JB being used to polish the bore on a rifle,
but never tried it. I'd rather purchase a custom barrel that is
already as good as it is going to be, as opposed to attempting
to improve a hammer forged factory barrel to obtain better results.

Some days all you can do is laugh.
Bulk 22lr at 50 yards in a 6 to 10 mph swinging tailwind is one of 'em.

Federal 36 grain CPHP







Shifting wind direction and speed with poor quality cartridges threw some amazing strays.




The next 50 sent were Remington Thunderbolts









And the Thunderbolts were better quality than the Federals.
Even with the ridiculous wind conditions.

Doesn't matter, just an excuse to put another hundred through the barrel.




Above after 400

Below as shipped



Now, even the tool marks in the leade are showing smoothing.

@JM.... I rubbed the nose of an unfired wax coated lead 22lr
on a piece of polished steel and showed no abrasion.
Did the same thing with a copper washed 22lr and again, no scratches.
It looks to be that the burn residue is providing the abrasive
and the bullets are doing the work of dragging it through the bore.
The more shots sent, the more smoothing is taking place.
Doesn't matter hi-v or subsonic, only round count.
Results have improved when using the SK Biathlon after 200 shots.
Next test for accuracy will be at 500 shots.

No assumptions Tim.
As you pointed out, I have no real documentation of barrel break-in or wear during the first 1000 shots.
I'm not using anything but a nylon brush and patches to eliminate any claims that the bronze brush
was responsible for the linear abrasion marks. Will the barrel show wear and/or improved results?
Not my responsibility to draw that conclusion. I can comment on what looks to be happening,
but the final decision will have to be made by those comparing the images for themselves.
I've never seen a long term borescope project like this with rimfire, where all the images are available to view.
I'm doing my best to provide a full record of the bore finish after each 100 shots.
Also providing an image of every target shot during the process.
That's as good as I can do, as I have no access to a test tunnel.
If you'd like, I wouldn't mind a duplication of the process being done by y'erself.
Set it up, use a different cleaning method, indoors from a fixture, and document what occurs.
Two sets of independent data is just good research procedure.

Have I seen changes to the bore during the first 400 shots? Yes.
Has there been improvement in the results on target with the SK? Yes.
Have some of the burrs that were visible in the initial images been removed? Yes.
Is primer residue capable of acting as an abrasive and cutting into a steel surface? Sure looks like it.
If you hand lap the bore on a custom barrel, don't you coat the lead lap with an abrasive to smooth the rifling? I believe so.
So far what I've seen indicates accuracy is improving and the bore in this factory barrel is being smoothed out.
What will happen after 1000 rounds remains to be seen.

knock yourself out

Can do Tim....good thing I'm easily entertained.


Tim? What happened?
You offered some useful criticisms, then deleted them? Why?

@AGrizz...that's my problem, couldn't find any documentation of rimfire barrel wear during the first 1000 shots.
Plenty of opinions as to what is occurring and claims of improved accuracy after 2 bricks of 22lr sent.
However, no actual documentation of change over time. That's what Tim pointed out in a previous thread.
I was basing my comments on unsubstantiated information. A search of the internet showed he was correct.
Opinions and anecdotal evidence aplenty, hard data/images none with rimfire. When ya' can't trust y'er information
ya' have to try it for y'erself. I've been doing that with rimfire for about 9 years .
Determining if those internet rimfire truisms are based on fact or wishful thinking.
Things like free floated barrels, find the brand y'er rifle likes, sub-moa all day long,
precision shooting with 17hmr and 22wmr, consistent accuracy at 200 yards, supersonic transition.
Try 'em, document 'em, figure out what works and what are incorrect conclusions based on minimal data.
Everyone needs a hobby, rimfire keeps me occupied.

I think Tim might be a bit annoyed that I don't agree with his opinions/experiences.

It's possible I might have pissed him off-fa-fa.



I do affect some folks that way.
Likely because I question everything.

I torque the barrel screws at 34 inch/lbs.
Produces best results in my A and B model 455 receivers.