Abrasiveness of PC bullets

[Oreo]

This is a train-wreck of a thread. Tons of speculation, and inaccurate explanations, with zero factual, citeable sources. Its disgraceful and misleading.

BangerJim, you're experienced with powder coating so you have a lot of knowledge but you act like a salesman the way you summarily dismiss the idea that some folks might have discovered a serious problem. I trust your view of that matter about as much.

This discussion needs to be framed properly to have any merit at all. So first, each individual powder needs to be treated as an individual which may have totally different properties then any other powder product. Second, no more speculation about what's in these powders. One particular black may be fine and another may be a problem. To know for sure we need reliable source data about each specific product's contents. Without that y'all are just guessing.

Someone in another thread who seemed to have some scientific understanding of how abrasion works described the phenomena as a cube of velocity. Its beyond my knowledge base but if that is the case BangerJim's palm test, or any test involving a drill is woefully inadequate and misleading.

There are lots of folks having wonderful results with powder coated boolits and I mean not to discourage anyone. It is imperative to be open minded about potential problems though. Discussing them frankly, and examining them scientifically is necessary to reach firm conclusions.

[Oreo]

There was another thread I read a while back with dramatically accelerated barrel wear shooting PC. The barrel was a drop in conventional rifled in a Glock and the owner was sizing to .356" My suspicion after reading the thread is that the issue was sizing too small and that .357" should have been used.

With lubed boolits, if you size too small you get leading and are encouraged to immediately deal with it. But with PC if you go too small, there is really no symptom. And the same forces that cut the boolit can erode the rifling in the barrel.

The basic concept that is in play is that if the boolit seals the bore, the gasses expand, but do not flow over contact surfaces, thus their ability to transmit heat to the metals involved is quite minimal. Once there is a gap to flow through, gasses can accelerate past at *insane* velocities and impart dramatically more combustion exposure to the materials involved. Lead being weaker than steel of the barrel, lead "gas cuts" and turns into a headache LONG before any barrel damage can occur. But if this problem pops up with a PC boolit, the first symptom you would see is rifling and chamber erosion- and by then it's ugly.

I could be interpreting this whole thing wrong, but if I'm right, the solution is simple, and carries virtually no risk: Make sure not to use a boolit too small.

I believe your hypothesis is wrong. High speed photography clearly shows that jacketed bullets universally leak gasses far more then lead boolits without the exaggerated barrel wear we're discussing in this thread.

[Maximumbob54]

Add to that anything has to be better that leaded barrels that need to be scoured all the time.

[waksupi]

Add to that anything has to be better that leaded barrels that need to be scoured all the time.

If you are getting leading, you are doing something wrong. I have guns with hundreds of rounds through them, no cleaning, and the bores are bright.

As far as bore wear, you guys are doing the empirical testing, so take all accounts equally. Regardless of one claim I saw of thousands of people using this method, I am willing to bet there are only maybe 100 experimenting with it at the time. Observe, and learn.

[totalloser]

Oreo, I'm sorry you are offended, but gas cutting is a reality. There are very few ways to directly observe occurrence in the bore since very few devices are capable of surviving the pressures. The likely reason for a jacketed bullet not causing such erosion is the very high conductivity of copper, and increased tensile strength resisting deformation. This means that gas escaping from said barrel will not pass the rifling, but instead, the valleys between the rifling. Thus no flame cutting on the rifling itself. A boolit loose in the bore likely will sway side to side as it travels down the barrel since there is inadequate contact with the rifling, and thus exposes the rifling to gas passage.

Do you really think it bad advice to suggest erring on larger rather than smaller? We KNOW that with lubed, that is a very very bad idea. If PC was causing such damage, I think we would hear about it, so I am speculating as to another cause. Perhaps you would like to venture the cause of this instance.

http://castboolits.gunloads.com/show...+barrel+damage

Since the gunpowder and the coating are relatively proven, short of improper boolit size I see only one other potential cause: metallurgy of the barrel. Well I can almost rule that one out too since if the heat treatment was the issue the barrel would probably fail dramatically since most steels untreated are barely in the range of cold rolled mild steel before treatment.

I think it would be foolish to not consider this issue when PCing. Look at the pictures.

[bangerjim]

I am out of here.

Do what the heck you want with whatever you have.

banger

[lka]

We don't need to get upset at each-other, the way I figure if it eats one of my barrels then I'll replace it, no harm. If i do replace a barrel then I'll decide to keep doing it or not. One thing for sure is it has added a little excitement to my hobby. It's fun to experiment with new things and even funner when others are doing it too and reporting their findings. If I do have a barrel go I'll be sure to let the Community here know but bottom line, were all on the same team here

[Oreo]

Oreo, I'm sorry you are offended...

I'm not offended and I apologize if it came across that way. I also apologize to anyone else I offended.

You are correct that gas cutting it real. I just don't think it's the cause of the abnormal barrel wear with powder coated bullets. I may be wrong. My point was to draw attention to what happens with jacketed bullets which are usually loaded to higher pressures then cast boolits. In this case we have some evidence of what is happening via high speed video that is directly applicable to the conversation here.

ETA: I reread your post and what you're talking about is not just a little undersized (grooves) but ridiculously undersized so that boolits don't even make solid contact with the lands. I guess anything could happen in that case but I would entirely dismiss it as not germane. That's right up there with shooting 9mm ammo in a 40cal gun and wondering why the ejected brass looks funny.

[totalloser]

Oh good. I'm not either. But this single case IMO raises a concern that there may be an issue to consider that is applicable to PC boolits specifically. I agree that .001" undersize won't send it bouncing between the rifling. What I'm thinking is that variations in bore friction allow for the projectile to cock from side to side as it travels the bore due to deformation of the lead. This is highly speculative, I realize, but clearly there was a problem, and this is the best guess I can venture.

I am talking about just a little undersized since that was the case scenario. .356" in a 9mm. Most folks who go to PC did so coming from lubrisize or pan lube, so we already size .001" over since you can't get away with not doing do due to lead gas cutting. This *appears* to be an issue that is specific to PC that give a surface appearance of abrasion which I *highly* doubt as the actual cause, but would seem to pertain to the discussion.

Perhaps there is something else going on here, but the only weird thing I can nail down is .001" too small destroying the rifling in relatively short order. IF this is what is going on (which it might not) then it is important to not go undersize with PC. Which most folks do not do.

I have shot as many (or way more) as the OP in that linked thread out of several barrels with ZERO noticeable wear- and I'd like to keep it that way and hopefully with a discussion such as this, help prevent someone else from having a similar failure.

The reason I came to the conclusion that flame erosion could be the problem is that flame erosion does take place in the chamber- like in rifles eroding over time. But the flame front in a barrel should mimic a zero g flame since it happens so quickly that issues like gravity can hardly have an effect. The heat charge does expand and travel, but the mechanism doesn't direct the force to cut. A loose fit, I am suggesting, *might* direct the flame to cut. The pressures and temperatures are certainly there for eroding metal, but resisted by the controlled expansion of the bullet walking away from the charge.

I did not mean to offend either, but I can be a lot more abrasive than a PC boolit ever hopes to be!

Two last thoughts: Calcite in HF black was noted in Bangerjim's thread as being a component not common to other PC- I wonder if calcite could act as an oxidizer under combustion pressures? HF black was used in the case thread I linked also- and his scratch test demonstrates there is an obvious difference between the two HF black PC's.

And Aluminum gas checks should be on the radar too since aluminum surface oxidizes within seconds- that's why in TIG welding, you brush the surface *right* before you start the weld.

[Oreo]

Was there evidence of calcite in hf black, or was someone just supposing?

[bangerjim]

Was there evidence of calcite in hf black, or was someone just supposing?

It is listed in the MSDS sheet.

Titanium dioxide in red/yel/wht.

banger

[IllinoisCoyoteHunter]

Bump for some scientific testing...

[totalloser]

You know, I have been stewing on it a while after realizing I missed a relatively obvious potential cause of these dramatic worn out barrels; Shooter shot WAY more through them than they realized, then shot a bunch of PC and looked at the barrel. "OMG it's worn out now!" Well maybe it was the 500 PC, or maybe it was the 20,000 steel jacketed russian junk that sailed down the bore BEFORE the PC was ever used. Seems a little more plausible considering the rarity of failure and the commonality of the success.

Considering the infrequency of such issues, I'd almost be suspicious of more dramatic creativity. Once upon a time I had a spirited discussion with a buddy of mine about the detriment of "polishing" the rifling with a dremel. My point is, who knows?

I'm still too nervous to PC black though.

[KYShooter73]

You know, I have been stewing on it a while after realizing I missed a relatively obvious potential cause of these dramatic worn out barrels; Shooter shot WAY more through them than they realized, then shot a bunch of PC and looked at the barrel. "OMG it's worn out now!" Well maybe it was the 500 PC, or maybe it was the 20,000 steel jacketed russian junk that sailed down the bore BEFORE the PC was ever used. Seems a little more plausible considering the rarity of failure and the commonality of the success.

I'm still too nervous to PC black though.

That barrel was completely new, only fired the HF Black PC through it. The more I think, the more Im believing that gas cutting was the culprit. I used a .309-170 boolit in it some. I measured some prior to coating, and they were dropping a little out of round and at about .307 at the smallest point. Could be, still dunno.

ON A BETTER NOTE: I PC'd some of the 312-155 in HF Red, gas checked them, sized to .311. 15.7gn of Win296. 1.4 inch 10 round group at 100 yards.

[IllinoisCoyoteHunter]

I've never seen steel-jacketed bullets before...

[Oreo]

I've come across quite a few while mining range lead. In fact, I found a single 9mm bullet that had a steel jacket AND a steel core with a thin intermediary of lead.

[Love Life]

If somebody will cast and coat 5,000 9mm bullets with HF black, and send them to me, I will shoot them and report back on barrel wear...

[totalloser]

I was referring to the glock drop in scenario, but in the case of KYShooter73 I'd be more suspicious of the gas checks if uncoated aluminum. As noted, aluminum surface oxidizes literally within seconds. This surface oxidation protects the metal under it making people think that aluminum does not oxidize even though it oxidizes RAPIDLY. And the oxidation is what most sand paper uses for grit.

Steel jackets are quite common in russian ammo- cuts barrel life in half and wears the whole length of the barrel. Usually copper washed (very thin) to trick the consumer/protect from rust.

That's a pretty snug group for home cast at .30 velocities. Nice.

[KYShooter73]

I was referring to the glock drop in scenario, but in the case of KYShooter73 I'd be more suspicious of the gas checks if uncoated aluminum. As noted, aluminum surface oxidizes literally within seconds. This surface oxidation protects the metal under it making people think that aluminum does not oxidize even though it oxidizes RAPIDLY. And the oxidation is what most sand paper uses for grit.

That is certainly a possibility as well. I noted that down as one scenario in my original thread about my barrel. If I ever start turning a profit in my office again, I'll get a checkmaker and make my own copper checks. Got one for .35, should have bought the .30 cal instead.