Plastic Coating and Bullet Size

[Joshua]

My limited experience is all with 30 and 31 cal bullets. There are many here who have more experience than I. As Ian has mentioned a tapered nose that tries to find center is important. The two bullets I’m doing most of my higher velocity work both have this taper to them.

 

[Ian]

Try the longer MP bullet, only because I don't have that one...LOL! Some of these things only your rifle can tell what it likes best. All I'm trying to do is give some pointers based on what worked (and didn't work) for me.

Pound-casting an AR-15 is no different than any other rifle, it just may require pile-driving the butt or use of a cleaning rod and gentle taps from the muzzle while pulling the charging handle to eject the slug due to weak camming action. For now, just finding throat entrance diameter and using the NATO bullets will solve most of your fit issues because all the thinking has been done for you in the bullet design. It will work in pretty much any throat shape and size.

 

[fiver]

the nato bullet was taken for the longer 5.56 throat.
that nose shape works because the taper helps center it.
in the rifles we are talking about here the nose of the bullet does most of the work.

here is how I worked around my 1-8 twist AR's.
neck tension like Ian mentioned 1.5 thou. I get there with a LEE NS squish die.
cases are once fired for the proper neck tension and a slightly hardened anneal.
I modified the RCBS 22 cal mold so the nose right in front of the front drive band is 219, with the rest at 218.
I size to 225.
I use an alloy of 4% tin and 6% antimony [I'm sure something lighter like 3% tin and 4% antimony will work too]
slower powders like 4895/4064/CFE-223 start at 20grs to function the rifle and work towards 22.5

 

[Dimner]

Interesting to hear the NATO bullet was made to do the work for me with throat alignment. I probably have shot 300 various rounds using this bullet and have not been able to get it to work right.

Now, it should be said that I was having other problems during those tests. Some that I have sorted out already and others that you guys have enlightened to me too. So working with it again I am hopefull that I will get better results.

What is still troubling me about these NATO bullets is how deep they need to be seated so they are not engraved on the lands when they are secured by the bolt in the chamber. Especially for the 73gr NATO, a large portion of the bullet is seated in the shoulder of the brass.

During that period of time using the NATO bullets, I build my own 'modified case' for my hornady OAL Guage. After that, I started measuring where the NATO bullets engaged the lands. That's when I discovered different PC colors using the exact same application and bake methods resulted in an over all length difference that I was not expecting. I still don't know what causes these differences, some colors seem to apply and bake on thicker than others.

At first I thought perhaps it was a humidity issue. Meaning some humidity in the the different powder colors was causing coating differences during the shake and bake application. So I dropped two medium sized silica packets into each of the plastic containers that held my powder coat and air soft BBs.

I made sure to first bake the packets to remove all current moisture and then weigh them for a base line. Then after a week I weighed the packets that had been in each container. Similar gain in weight (moisture) for each packet. I also left two packets on the shelf next to my containers of powder coating. As expected the latter fully exposed packets gained more weight(moisture) than the packets stored in with the PC. And after all of this, the coatings that were applied baked on were very close (within 10%) of the original measurements. So moisture seems not to be the issue with the difference in powder coat thickness among different colors.

You guys may have already been aware of that, but I thought it was an interesting side quest to note.

But back to the topic at hand..... tonight I will post pictures after I do some pound casts with both weights of the NATO bullet. Also I will dig up my OAL measurements per color if that is interesting information for you guys.

 

[Ian]

Photos always welcome.

Where do suppose a 77-grain jacketed bullet fits? Max OAL is determined by the magazine, therefore much of the heavy jacketed bullet intrudes into the powder space as well. Don't worry about that too much right now.

 

[Spindrift]

Different colors might indeed give different thickness of the coat.
I have the MP227-65, it has worked very well in my .223 bolt gun, with both PC and regular lube. I would also suggest focusing on that bullet for now.

I tend to think your main issue has been the oversized PC bullets. The solution might be pretty simple. Size som MP bullets .225, and some .226. Load the MP-65 to 0,02in jump, using starting loads with one of the faster, non-spherical powders you have data for.

Good luck!

 

[popper]

Josh, this is what the cart should have been, for the 40K psi case. Calculated for peak pressure. Light 223 bullet gets hit hard. Plus it's way over pressure for normal 45 ACP.
Cal 0.3 0.223 0.4 0.45 .357
Acceleration 125 286 171 145 105

 

[fiver]

different powders do coat to a different thickness.
the amount of tin you have in the alloy will also influence how much powder the bullet takes.

think about putting bondo on a cars fender, a heavier gouging weight sandpaper allows more surface area for the bondo to grab onto.

 

[Ian]

I had about two hours left before dark so I checked, sized, and coated some .22s from the mould I just got from Paul. Didn't have time to prep brass so I grabbed some sized/primed/expanded cases out of my subsonic plinker stash Turns out these are S&B range pickups that had the rims set back badly from (probably) being shot in a stupid short AR pistol. I had FL resized them, dropped them in a takeoff Savage barrel, and planished the rims back into place. Who knows how consistent or accurate the headspace is after all that. Measure still set for 24.0 grains H335 so in it went. Seated to fit the magazine minus .020", checked they would chamber in the Mossberg, and got them on target amidst fierce suppressor mirage and near darkness.

Six on the first target (loaded an extra for a sighter) were unsized and five on the other were firm sized nose-first in a custom die I reamed. This is about the usual performance for this rifle, by the way, and it has a huge, long throat even for a 5.56x45mm NATO chamber.

 

[Bruce Drake]

I've had to adjust to the fact of either seating my PC bullets a hair deeper or nose-sizing the bullets in a separate process if the load is more accurate at the original COAL. The PC coating does change the bullet's nose profile of course. It is just another aspect that has to be adjusted for the bullet and the firearm. This bit of advise works across all calibers of PC coated bullets, not just the extremely demanding cast .22 caliber bullets for ARs.

 

[Dimner]

different powders do coat to a different thickness.
the amount of tin you have in the alloy will also influence how much powder the bullet takes.

think about putting bondo on a cars fender, a heavier gouging weight sandpaper allows more surface area for the bondo to grab onto.

Huh... had not known that. Makes sense, this alloy I'm using when I cast my NOE 70gr had about .5% more tin than I usually put in. Bullets came out with a little more... crystalization effect when light bounces off of it. That's the best way I can visually explain it. And yes, a bit more rough to the touch. I have noticed that these were coating a little bit thicker.

@Ian Nice looking groups, at least to me. That's about the best I have gotten so far in my quest, and it's with no consistency. I get those about 1 in 20 of the time. If I were able to shoot 1.25 groups with consistency, I would be done with this project. The load is for 100 yard CMP high power practice at the local sports club. Shooting with iron sights. So 1.25 would be great for me. I'm optimistic I can get there

So now onto some measurements of the chamber side and muzzle side.

not having done it with this method before, I may have measured in the wrong area, but here is a pic of where I measured the land engravings on the chamber side:



Normally I would do the pound cast method where you insert a cartridge with a slug that is a few thousands less that bore size, close the bolt, and whack a brass rod down the barrel so the slug expands to the dimensions of the first 1/2 of the barrel on back to the throat and such.

Here are the measurement results from the land engravings on the chamber side (C = control/unmolested)

• Green 1 - 219.5
• Green 2 - 221.5
• Green 3 - 219.5
• Green 4 - 219.5
• Green C - 223.5
• Blue 1 - 221.5
• Blue 2 - 221.0
• Blue C - 224.5

Measurements from the muzzle side:

• Muzzle 1 - 219.5
• Muzzle 2 - 219.5

Also, here are some pics. (I am bad at editing and resizing)

There you have it. Not sure if I am measuring in the right spot, I'd appreciate guidance if I am off.

 

[Ian]

Look at green #2 and #3, see that ring of lead pushed up? Measure the scraped part just in front of that ring. The throat entrance is doing the scraping and it will do the same when you pull the trigger unless you size them just a fuzz smaller than that (.0005 to .001".

 

[Dimner]

Look at green #2 and #3, see that ring of lead pushed up? Measure the scraped part just in front of that ring. The throat entrance is doing the scraping and it will do the same when you pull the trigger unless you size them just a fuzz smaller than that (.0005 to .001".

Well here is an interesting result...... I'm measuring these at 0.224 possibly 0.2245. Kind of explains why I am having such awful results with my previous tests.

So should I really be sizing these down to 0.2235? Actually at this time, I don't think I have any method to size smaller than 225.

 

[Dimner]

.... update... regular cast bullets (not coated) measure at 0.225

 

[fiver]

bleh.
that lead being pushed back that hard is kinda where my focus would go right off the bat.

cutting and scuffing like that might be happening when your firing the round, and if so, that's where your groups are going.

 

[Dimner]

I'll admit, those bullets were originally .226 sized and then PCed. So they were some thick bullets. I guess it's time to get a .224 sizer?

 

[Ian]

They were supposed to be big so you could see what was going on in there. Some throats are .227 so you never know until you do.

 

[Dimner]

Well, the question for me now is.... Do I try this again with bullets sized .225 -> PC -> sized again at .225 or do I wait and order a .224 from Al @ NOE.

If I had a range in my backyard, this wouldn't be a hard question... but I cant get to the range until March 2nd at the earliest.

 

[fiver]

I'd try the 225 size.

 

[Ian]

Yup.