Why is Rimfire Ammo Dirtier than Centerfire?

[ChanceMcCall]

I'm embarrassed to admit I don't know. Could it be made cleaner? How?

I have been shooting .22 rounds for over 60 years and have never considered the why. I just know rimfire guns need cleaned far more often to be reliable, especially semi automatic ones.

[Ol` Joe]

Heat and pressure. Centerfires operate at much higher temps and in most cases more then double the pressure

[jaia]

1) Primer and powder of rimfire often produce an incomplete burn leaving much residue

2) The number of shots fired per session.

3) Incomplete seal of brass to chamber allows burn residue to blow back into the receiver

4) Semiauto is direct blowback operated, all that incomplete burn residue ends up in the receiver

[NIB]

In addition I'll add.........

In ratio of Primer/Powder Rimfire is much higher % Primer vs % Powder than CF is.

Both use glass in the Primer to facilitate Primer Ignition. (Look at CF Primer Patents.)

Rimfire uses a greater percentage of glass in its Primer composition (double+) vs CF.

In semi-autos I believe much of the gritty residue comes from the "Blown Back" glass surrounded by blackened primer/powder residue. Take a close look at this residue in the sunshine for the glasses reflective sparkle.

I once took apart a German SK 22lr and found small tubular Vihtavuori powder (the brand they use). In open air it burned very cleanly. As for SK I'd say any dirt would come from the primer.

As for..lets say, Remington? (Picking on them). You may find tiny wafers/compressed spherical propellant that has failed to fully burn which likely comes from inefficient poorly fabricated propellants, in addition to the grit.

In semi-auto rimfire their blow-back action is like a shovel back filling itself (a little every shot) whereas a locking action rimfire will plow out a high majority of (every shots) residue past the muzzle.

[Al the Infidel]

Originally Posted by jaia

1) Primer and powder of rimfire often produce an incomplete burn leaving much residue

That and cf is hotter, better burn, less unburnt soot and whatever magic ingredients rf has.

[NIB]

Originally Posted by jaia

Incomplete seal of brass to chamber allows burn residue to blow back into the receiver

Yes jaia...How many times do we see that blackened edge of the case mouth indicating poor sealing and gas leakage. I certainly see it often in my Marlin 60. Of course a semi-auto chamber is not as tight due largely from its method of operation.

There must be some pressure left in the blow-back design pushing gun shot residue into them as their actions are the dirtiest of all.

I wonder if it would be correct thinking that there is some pressure still in the action/barrel of these designs and as such the case edge powder burn happens during this pressurized interval while the bolt is traveling rearward? This happening above and beyond the known generally larger semi-auto chamber.

I have also had the thought (right or wrong?) that during the bolt rear travel volume increases in the chamber/barrel reducing pressure/temperature which may allow the burn to subside leaving a few extra unburnts?

I may be way off on that thought...or...am I?

One thing for sure, if the highest grade cartridges are used semi-autos will stay cleaner.

[lessisbest]

Originally Posted by ChanceMcCall

I'm embarrassed to admit I don't know. Could it be made cleaner? How?

I have been shooting .22 rounds for over 60 years and have never considered the why. I just know rimfire guns need cleaned far more often to be reliable, especially semi automatic ones.

All the reasons as to why .22 ammo burns dirty apply to semi autos. Do .22 bolt and lever guns burn cleaner? After all, the shell stays seated in the chamber until YOU, the shooter, decide to take it out. By that time all powder has been burned.

[springer1]

What are those white crispy specks (about the size of a small salt particle) that I keep cleaning out of the front part of the bolt & receiver? I use Eley ammo.

[NIB]

Does it sparkle in bright light? It could be glass..I'm not sure what else it would be?

[jaia]

Without actual chemical analysis, I can offer an educated guess... combustion residue.
It's going to be a combination of primer/powder/lubricant both burnt and unburnt.
Yep, Captain Obvious strikes again.

[Nick7274]

I always just assumed that the biggest factor is because I shoot a lot more .22 ammo when I go shooting than I do centerfire. I can shoot 200-500 rounds of .22lr (depending on the barrel) before it really needs a good cleaning. If I put that many rounds through an AR it's going to need a good cleaning also.

[eflyguy]

When I bought my first 10/22 (used, and my first .22), I thought the previous owner must have put 1000 rounds through it without ever cleaning it. The forward area of the receiver and bolt were covered in grit, I wondered if it has been used at the beach!

I stripped and cleaned it, but after our first trip to the range and ~150 rds, it looked and felt about as bad as it was when I had first purchased it.

Needs another cleaning since our last match, I'll try to capture some of the grit, clean it up, and look at it thru my digital microscope.

[springer1]

Originally Posted by Nick7274

I always just assumed that the biggest factor is because I shoot a lot more .22 ammo when I go shooting than I do centerfire. I can shoot 200-500 rounds of .22lr (depending on the barrel) before it really needs a good cleaning. If I put that many rounds through an AR it's going to need a good cleaning also.

Bingo +1. Also, Jala - I don't buy in to the idea the white specks in the receiver I see are combustion residue that get blown past the length of the chamber & seated bullet case (which is tight in it), and then make two 90 degree turns around the compressed rim to get into the bolt channel. I don't see any scores on the brass - I could buy that if it were gasses, but particles - nah.

Maybe its lube or grease that was against the base of the brass that the ignition heat crystalized into something, maybe something else, I donno. They are not clear, rather white and crunchy - easy to crush.

[jaia]

Okay...I can see y'er point Springer.
But how about residue that is on the inside and outside of the brass,
that when the bolt cycles, knocks the case around in the receiver
before pitching it out the port. Could that lead to particles ending up there?

Another thought is moisture reacting with remaining unburnt primer/powder
producing another chemical in crystalline format as it dries. Maybe.

[SteelPig]

How about the roll crimp and healed projectile.
RF headspaces on the rim not the case mouth so blow by is natural. The case does not start to seal until after expansion.