Effect of Powder Coating on bullet velocity

[Snakeoil]

A little background info first.

We are shooting Springfield '03's out to 500 yds. My friend and shooting partner, who is serious rifle shooter (Camp Perry, Palma, Military Team and now Class F) is my shooting partner and other than shooting BPCR about 15 years ago and muzzleloaders prior to that, is not much of a lead bullet guy. So, when he started out, he bought some 170gr. powder coated bullets. He put 18 gr of 2400 behind them and with a 10X Unertl on the rifle, he could not get those bullets to shoot worth a damn. He's 86 and my first thought was he's either not seeing well or making rookie mistakes because of his age. I was hesitant to coach him because he's forgotten more about rifle shooting than I'll ever know. We thought it might be his rifle, an 03A3 which has a 2 groove barrel. But none of us have ever seen an 03 or 03A3 with a good original barrel that would not shoot. So, we started with the basics. We gave him the bullet we were using, a 315 SAECO from Meisters. That made the difference. When he does his part and I do mine in reading the wind and mirage, the bullet finds it's mark and all my concerns went away.

We were talking a few weeks later and he said that he later put those PC bullets over a chronograph after that first day and said he was seeing very high velocities. I want to say he said 2700 fps, but he might have said 2400 and my memory is screwing with me. Regardless, 18 gr. of 2400 is pretty much a 1700 fps load in my 03 and anyone else's 03 that is shooting that bullet and powder charge.

So, he gave me some of those PC bullets and I plan to work up some loads and put them over the chrono. Before I do, since I have zero experience with PC bullets, is an increase in velocity between lubed lead and PC bullets normal as reported by my friend? I'm asking because I may start with a significantly reduced load as a starting point if that is the case.

Thanks,

 

[Ian]

Typically, the coating will actually drop velocity until you start to reach full-power jacketed loads. At 1700 fps/2400 I would expect to need about 5-7% more powder to equal the same velocity with same bullet and alloy that's not coated. You can't put enough 2400 to get 2400 or 2700 fps out of an '06 without blowing it up.

 

[fiver]

Ian...?
you can put enough 2400 in an 0-6 case to get close to or at 2400 fps.
your gonna be a bit dicey looking for pressure signs much after 30grs but you can do it.
27grs. will get you over 2100 fps with only about 35 cup in pressure.
2400 was considered a rifle powder when it was first made and has a pressure line similar to unique in larger cases.

explain PC to your friend like it is a moly coated jacketed bullet, only without the moly transfer to the barrel.

 

[Ian]

215 grains at 2700 fps? With A2400?

 

[fiver]

170gr. is the number I thought we were talking about?

 

[Ian]

Maybe. He talked about 170 grain and Saeco 315 which is usually about 215 grains and didn't specify which were chrono'd and which he was given to try. 170 is a lot more reasonable. Regardless, PC alone isn't going to jump the velocity up by 1,000 fps.

 

[JWFilips]

Ian is she wearing a "Big Hat"?

 

[Gary]

That's 'SUM"burero!! Taco and brew, sounds good to me.

 

[Brad]

Nice hat Ian!

Anything over 2000 fps with 2400 is well into my “hell no” zone. Pressure curve just isn’t cast friendly.

And Ian is right, the coating will reduce velocity. With the same load.

 

[Snakeoil]

Okay, I see that I was not clear for some. I should have left out the background stuff and stuck to the specifics.

Bullet is a SAECO 315 is a 170 gr truncated cone bullet with GC. We use 18gr of 2400 and get a nominal 1700 fps out of a standard Springfield 03.

PC bullet is a 170 gr RNFP. Looks like a bore rider to me. With the same 18gr of 2400, he said he was getting 2400 fps or more over his chrono. The chrono is new and same as the one I have. Maybe he is confusing results from another cartridge loading. I hope so.

So, you are saying that PC will reduce velocity a bit compared to an equivalent weight, conventionally lubed lead bullet? Damn. If he is not confusing a results from a different load, then he either has a issue with his powder measure or he is doing something seriously wrong. I know he can be a bit forgetful. Not unexpected at 86. Guess I'll load up some rounds with 18 gr of 2400 and that PC bullet and see what they look like over the chrono. Will be doing that on Wed.

As a sidenote, since Ian mentioned the limits of 2400 in a .30-06, a few weeks ago, we had a member fire a round that blasted both both him and his spotter with a major shock wave. Rifle was a Spfld rebarrled in .308. His standard load is 17gr of 2400 with a 170 gr bullet like most of us use. The bolt would not budge. So, we hammered the bolt open with a piece of firewood and found that the brass had flowed into the bolt face. The flash hole in the primer pocket was about twice its normal size. The primer came out as a thin flat disc, including the anvil. The suspicion is a double charge. Fortunately, it was a Spfld and not a Rolling Block. So, 34 gr of 2400 is what we think went off in that rifle. I asked Alliant if they could estimate the pressure that the rifle saw with that load and they could not.

 

[Brad]

Yes, reduced velocity. Take a set load and shoot it over the chronograph. One with traditional lube and the other with PC. The PC will likely be going slower. The lower friction means lower pressure and therefore slower.

 

[Snakeoil]

Okay. Thanks. I thought that PC would provide reduced friction. Guess I need to politely check on what he may or may not be doing with his loads.

So, that question answered, here's a follow on question based upon the characteristics of PC.

Since PC precludes the need for lube and also prevents leading, is there any ballistic advantage to selecting a bullet without lube grooves or other surface characteristics? I'm thinking a smooth bullet will maintain more velocity due to reduced eddy currents at the various grooves, lands, etc. I see a quasi-jacketed bullet, only with a flat or GC base will shoot better. Or am I splitting hairs here?

 

[waco]

I thought that PC would provide reduced friction.

It does. That's why it builds less pressure and you get lower velocities.
Lube grooves are a good thing. They provide a place for lead to disperse while being fired. A non lube groove bullet has nowhere for the lead to go except the base...

 

[Snakeoil]

Interesting. Never considered where the lead had to go when it encountered the lands. But you are right, with a bullet sized to groove diameter, there is no place for the lead to go but in the lube grooves or out the back to produce whiskers at the base. I wonder if this is why that 315 SAECO shoots so well. Plenty of grooves into which the lead can flow when it encounters the lands making any whiskers at the base minimal.

 

[fiver]

Boyles law.
it's the same as using a 1oz load in a shotgun.
the projectile moves further away faster so the pressure behind it drops off quicker.
you need more gas to keep the pressure up to gain the velocity back.

as far as a slick side bullet?
meah maybe maybe not so much.
on a short bearing surface bullet at lower velocities your probably okay. [maybe even more okayish if it has a slight bevel base]
what happens is the lands still engrave the side of the bullet and the lead needs somewhere to go the only place it has is to push the displaced lead to the back of the bullet.
unless there is some grooves to take up that displaced metal [think relief grooves like the all copper bullets have] it will get stuck out the bottom causing,,,, well,,,? whatever little tails of lead causes.

 

[RicinYakima]

"As a sidenote, since Ian mentioned the limits of 2400 in a .30-06, a few weeks ago, we had a member fire a round that blasted both both him and his spotter with a major shock wave. Rifle was a Spfld rebarrled in .308. His standard load is 17gr of 2400 with a 170 gr bullet like most of us use. The bolt would not budge. So, we hammered the bolt open with a piece of firewood and found that the brass had flowed into the bolt face. The flash hole in the primer pocket was about twice its normal size. The primer came out as a thin flat disc, including the anvil. The suspicion is a double charge. Fortunately, it was a Spfld and not a Rolling Block. So, 34 gr of 2400 is what we think went off in that rifle. I asked Alliant if they could estimate the pressure that the rifle saw with that load and they could not."

A 34.6 grain load in 30/06 with the FA 173 grain boat tail was listed at 51,000 CUP in the early 1950's. Our target load in '03's is 16 grains with the 200 grain cast bullet. I have seen two double charges of 32 grains. Luckily both were Remington WW2 actions that bulged the barrel shank's square threads into the receiver requiring machining to remove the barrel. Both case heads failed releasing gas into the action and both blew the magazine floor plates out and cracked the stocks. Both shooters had powder burns and splinters in their right hands. Cone breeched actions are not the ones to be shooting when this happens.

Reduced case volume and a cast bullet in the 308 must be making enough for the primer to blow.

 

[KeithB]

I wonder if a surface roughness or texture might act like dimples on a golf ball and break up the boundary layer drag? Not really my field, just curious.

 

[fiver]

IMO the rotation, and air wave on the front of the nose would negate that.

a gold ball spins maybe 2000 rpm, and is travelling at like 174 mph. if it's given a good enough hit to go 400yds.
it's rotation is also into the wind/air so the dimples break up the drag behind the bullet.

 

[Gary]

I like my Loverin bullets.

 

[Ian]

The grooves are insignificant aerodynamically due to boundary layer effect. Vaughn proved this eons ago both empirically and with rocket math.

Slick-sided bullets coated with powder paint have to displace metal when they engrave. They also need to be throat size for alignment support and to mitigate slumping at launch in order to shoot straight and that means bigger than groove diameter. In the case of a grooveless, lead alloy monolith, when there is nowhere else for metal to move then the entire cross-section is squeezed down and the metal has no choice but to draw toward the ends. Drawing lengthwise causes deformities on the ends and fractures the microstructure of antimonial alloy through the whole length and diameter of the bullet, which weakens it. If the coating doesn't get completely raked off in the throat, the pressure alone of plasticizing the whole bullet transfers some of that paint to the bore in the form of really hard fouling. Pistols and low-velocity rifle loads seem to get away with coated slicks, but I know of no one who has with full-power rifle loads...they ALL do better with grooved bullets so just the surface of the driving bands gets squeezed by the throat and lands an that force is dissipated near the surface because the metal can easily flow into the grooves rather than be forced into the core of the bullet.

Frank Barnes discovered with HIS monolithic bullets that metal fouling was a huge issue and he solved it with...you guessed it...displacement grooves. The force of engraving and extruding a solid copper bullet caused excessive heat and abrasion of the bullet's surface and the atomized dust together with intense heat and pressure plated the copper on the bore at a very high rate. Also note that Barnes recommends a very long jump to the lands to mitigate the high engraving force of the tough, monolithic material.

Copper jacketed bullets do extrude lengthwise as they engrave, but they are very different from monolithic brass, copper, or lead alloy bullets. The jacket is filled with a very ductile core material which easily lets the bullet elongate as it is engraved, but the jacket acts as a container for the core and keeps it in a basic, uniform shape and prevents the core from bulging out unevenly at the ends. The jacket of course seals the bore and is tough enough and slippery enough to glide along and hold the lands without abrading much metal. The soft core and tough jacket make a very extrudable combination and engraves with relative ease, so there isn't excessive force on the bore to necessitate having displacement grooves. Jax are also typically of groove dimension or close to it so there is less metal to displace in the first place. Cannelures help too, I'm sure. The jacket doesn't need to fill the throat tightly to shoot well because it is tough and doesn't get squashed by initial launch pressure like cast bullets can. The toughness also allows the bullet to be groove size and rattle around through the throat like a pinball and find the center of the bore at the end without getting completely mangled up or getting an excessive amount of its surface blasted off by powder gas leaking around it before it moves forward enough that it can fully seal the bore.

Monoliths and jax are each systems with their own characteristics. Monoliths need displacement grooves.

Pc is a jacket in some ways and in some it isn't. It's a lubricant in some ways but not like a dynamic film lube at all. It hardens the very surface and makes it abrasion-resistant. It adds just a tiny bit of surface strength and slipperyness to help a bullet self-align in the throat if you don't stress it too much. It won't shear off if the transitions are gentle and it won't rub off on the bore if the compression and friction isn't too high. It will strengthen the land engraves against torsional and frictional forces, reducing heat at that critical contact point and allowing higher velocity than normal for cast bullets without especially tough alloy. Softer alloy is actually better (to a point) because it conforms easily and is flexible which promotes obturation (remember, obturation is a medical term that describes a blockage of a passage, we mean it as in seal the bore gas-tight and prevent blowby). Sealing the bore against gas means no cutting or washout, and that translates to better bullet integrity, balance, and groups. It also means no atomized PC/lead/carbon dust being melted and deposited on the bore in a rapidly increasing layer of hard fouling. Assuming the PC lead-alloy bullet system is set up correctly through fit, alloy choice, powder selection and charge, and all the other things we preach about with ordinary lubricated cast bullets which STILL apply. PC is also virtually immune to temperature and issues with bore consistency induced by grease/wax lubes. That ought to about cover it.