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 Polymer coated bullets, and leading 
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Location: Everett
Joined: Thu Aug 13, 2020
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Real Name: Nathan
So, I happened to pick up some 217gr 30 cal projectiles from SW in Bellingham. 500 in a box for a good price(about 70 bucks). Figured I load them up for 300 BO subsonic affordable plinking load.

Bought them, got them home and didn't think about bullet diameter when I first bought them. It also wasn't on the package. Measured them out to a diameter of .310. Thought to myself, shit! So I went ahead and bought a bullet sizing die, as I'm slowly building up the tools for casting in the future. Figured might as well get it now. Put them all through the sizing die and none of the polymer came off the bearing surface. They all came out to .308 some .307.

Went to test fit one into a case. Took about .002 off the bullet, polymer and lead on the outside of the case. Neck tension on factory die is .305. Tested .306, same out come. tested .3075 no coating came off, seated just fine.

My question is, should I crimp these bullets with a crimp die? I'm going to be firing them in a semi auto. So, I'm skeptical that they may cause leading in the barrel, and/or the bullet to seat deeper if not crimped while cycling in a AR.

I clean after every 300 to 500 rounds with copper plated bullets. But, if these could cause leading, I may end up cleaning after every 100 round lots are fired.


Mon Sep 27, 2021 12:12 am
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Location: Renton, WA
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Whether or not to crimp would depend on how tight the bullets feel to you (neck tension). If you push a round against the table (bullet down), does the OAL decrease? They may be okay without crimp; I don’t crimp most of my AR ammo.

When I load coated 300BLK bullets, I use a Lee universal flaring die to bell the case slightly, which allows the bullet to enter without damage. Then I use a Lee factory crimp die to push it all back together and crimp it a bit.

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Mon Sep 27, 2021 6:27 am
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Good info, I haven’t bought polymer bullets nor loaded for subs…. YET. :wink05:

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Mon Sep 27, 2021 7:16 am
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MadPick wrote:
Whether or not to crimp would depend on how tight the bullets feel to you (neck tension). If you push a round against the table (bullet down), does the OAL decrease? They may be okay without crimp; I don’t crimp most of my AR ammo.

When I load coated 300BLK bullets, I use a Lee universal flaring die to bell the case slightly, which allows the bullet to enter without damage. Then I use a Lee factory crimp die to push it all back together and crimp it a bit.
I use the same method and have not observed any leading.


Mon Sep 27, 2021 11:03 am
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Location: Everett
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Madpick, I will have to test this when I get the chance. However, there maybe a variable to the OAL with most of the bullets having lead nose and not much polymer coating on the tips. Much like a SP from Hornady or Sierra.

However, I do have ogive measurement tools. Which could help with that measurement. More tests are in order before a mass load session, that's for sure.


Mon Sep 27, 2021 2:58 pm
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It doesn't matter if there is OAL variation; we are just talking about a single cartridge here. Measure its OAL, then push it down on the table, then measure it again. Did it get shorter, i.e. did the bullet push into the case at all? That's what you're checking for.

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Mon Sep 27, 2021 3:32 pm
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I crimp everything I load so that I do not have to worry about neck tension. I have been using powder coated bullets for quire a while and getting no leading. You got by lucky this time reloading you need to get the universal flaring die as it will save you a lot of grief. Your oal for a magazine fed firearm is what fits the mag and feeds.


Mon Sep 27, 2021 10:08 pm
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NWReloadN89 wrote:
So, I happened to pick up some 217gr 30 cal projectiles from SW in Bellingham. 500 in a box for a good price(about 70 bucks). Figured I load them up for 300 BO subsonic affordable plinking load.

Bought them, got them home and didn't think about bullet diameter when I first bought them. It also wasn't on the package. Measured them out to a diameter of .310. Thought to myself, shit! So I went ahead and bought a bullet sizing die, as I'm slowly building up the tools for casting in the future. Figured might as well get it now. Put them all through the sizing die and none of the polymer came off the bearing surface. They all came out to .308 some .307.

Went to test fit one into a case. Took about .002 off the bullet, polymer and lead on the outside of the case. Neck tension on factory die is .305. Tested .306, same out come. tested .3075 no coating came off, seated just fine.

My question is, should I crimp these bullets with a crimp die? I'm going to be firing them in a semi auto. So, I'm skeptical that they may cause leading in the barrel, and/or the bullet to seat deeper if not crimped while cycling in a AR.

I clean after every 300 to 500 rounds with copper plated bullets. But, if these could cause leading, I may end up cleaning after every 100 round lots are fired.


Should've done your research before sizing all the bullets too small. At this point you'll probably get some leading no matter what; .307-.308 is too small for a good bore seal in a low pressure subsonic load. At .310" you would've been fine.

Absolutely do not crimp. Coated bullets should never be crimped if you can avoid it; a crimp cuts into the coating but also is likely to scrape some coating off as the bullet leaves the case. Crimp is generally unnecessary in this application anyway unless your bullets are way too soft, or you don't have enough neck tension.

Personally I want the die to set sized neck diameter at .307", and a sized bullet diameter of .309"-.311". You have to play with diameter a bit sometimes to figure out what works best with your rifle, but the general rule is you need bullet diameter to be at least .001" larger than the bore.

Done right, you can shoot coated bullets indefinitely without cleaning the bore, but in this case with the small bullets, you'll have to keep an eye on leading. If it happens, wrap some strands from a copper chore boy pad around an undersized bore brush so that it's a tight fit from the chamber end; a few strokes back and forth will take care of it.
Don't shoot these undersized bullets through a suppressor.


Mon Sep 27, 2021 11:48 pm
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