Headstamps for 5.56

[rero360]

I've recently decided to wade into reloading for 5.56 and I have some questions. I'm looking to develop a MK 262 clone for my two ARs, a 16" midlength and a 12.5" pistol, both BCMs, 1/7, one a BFH and one standard, I have just over 1K of Sierra 77gr MKs to play with. I haven't purchased primers or powder yet, pretty scarce these days, been looking at TAC for powder and will probably use the CCI NATO primers. My questions really revolve around the brass, I have just over 1500 pieces of brass, mixed between PPU, PMC, LC, and FC, in that order of quantity with another 360 rounds of PMC sitting around. Is any of those types of brass absolute junk or are they all good to reload? Also, should I really stick to one headstamp or does it really not matter? I'm looking to get 1.25 MOA or better at the highest velocity I can get before I start to experience pressure signs. This Ammo will be for SD and longer range shooting than the 55gr range ammo that I've been shooting.

I know with my .308 bolt gun I stick to Black Hills brass and I have a couple hundred pieces of Luapa brass sitting aside for when the BH gets worn out, I'm just curious if separating by headstamp is as vital for the semis as I'm expecting 1.25MOA or better as apposed to the .8 to .3 that I get with the bolt gun depending on how I'm doing that particular day?

I plan on once I build up the load, load up 14 mags worth just to stash for a rainy day and reload the rest for actual training/ practice.

 

[Pinecone]

5.56 brass does not seem to vary as much in case capacity as .308 brass.

But a Mk262 load is pushing the pressure pretty high, so even small variation may lead to issues.

Personally, for a Mk262 load, I would stick with a single brand of brass.

 

[woojos]

Can't answer definitively, but I had a huge box of 5.56 brass mostly LC and FC. I took all the mixed LC headstamps, processed them, and worked up a load, then shot about 250 or so from a stock 700 bolt gun with excellent results. When I verified my load I put 10 through 1 ragged hole about half moa. A lot of it was deswaged, so some had been fired more than once.

I'm going to use the FC headstamps for my SPR. Haven't worked up a load for that yet. I'd like to find a ball powder that meters well on the Dillon and see if I can come up with a faster way to load, but like you said powder is scarce these days.

FC and LC may come from the same plant, somebody else could probably answer that. The case capacity will probably differ the most between headstamps so if it's accuracy you are after, I'd just pick the headstamp you have most of and use that. 1.25 MOA gives you some wiggle room, so you may be able to get away with mixing them.

Somebody has probably done this experiment though.

 

[bigedp51]

Actually there is enough internal case volume between .223/5.56 cartridge cases to cause 6,000 psi difference in chamber pressure with the same powder charge as the Quickload charts below indicate.

Below Lake City cases with 30.6 grains of H2O capacity.

Below Israeli IMI cases with 28.8 grains of H2O capacity.

And to answer your question Lake City cases are harder in the base and made to much higher standards than commercial cases. Meaning your best bet would be to use the Lake City cases with your warm MK 262 clone loads.

A few weeks ago at the Accurate Shooter forum one of the forum members ended a "discussion" I was having with someone who was saying Lapua brass was harder than Lake city. The forum member had a Rockwell hardness tester and the base of the Lake City cases were the hardest with Federal and Remington being the softest.

 

[xdeano]

You can measure the internal capacity of the various brass and find out which brass is going to give you more/less room which will correspond to how much pressure and potential velocity a give company will reach.

I use a digital scale, weigh the brass, write it down, then use a syringe with water to fill case, write down. Then subtract the one value from the other. Do at least 10 pieces of a given head stamp, average. This will give you slight variations in brass capacities.

Deano

 

[bigedp51]

The case capacity will not tell him how hard the base of the case is and MK 262 cartridge cases must meet milspec standards.

The bucket below is 95% full of Federal cases with soft brass and over sized primer pockets after the first firing, meaning never reloaded.

 

[sinister]

Mark 262 brass also has crimped primers, so anything you choose to hot-rod or push to military pressures and velocities may drop cups and anvils into your lower.

 

[xdeano]

I realize this, and didn't post that because i was writing on my phone and submitted before the previous person submitted before me. But I will concur that LC brass is much harder then the FC, RP, Win, etc that is out there.
Xdeano

The case capacity will not tell him how hard the base of the case is and MK 262 cartridge cases must meet milspec standards.

The bucket below is 95% full of Federal cases with soft brass and over sized primer pockets after the first firing, meaning never reloaded.

 

[rero360]

Thank you gentlemen for the replies, I suppose I can work up loads for each type of brass and see where I see good accuracy and where I start to see pressure signs. Unfortunately I only have 214 pieces of LC, 109 of FC, 743 of PPU and 763 of PMC, so I'm kind of hoping I get good results out of either the PPU or PMC, but if the LC is the winner than so be it, I'll just try and source some more some where.

 

[woojos]

Actually there is enough internal case volume between .223/5.56 cartridge cases to cause 6,000 psi difference in chamber pressure with the same powder charge as the Quickload charts below indicate.

Below Lake City cases with 30.6 grains of H2O capacity.

Below Israeli IMI cases with 28.8 grains of H2O capacity.

And to answer your question Lake City cases are harder in the base and made to much higher standards than commercial cases. Meaning your best bet would be to use the Lake City cases with your warm MK 262 clone loads.

A few weeks ago at the Accurate Shooter forum one of the forum members ended a "discussion" I was having with someone who was saying Lapua brass was harder than Lake city. The forum member had a Rockwell hardness tester and the base of the Lake City cases were the hardest with Federal and Remington being the softest.

Thanks x2 for this.

Probably the topic for another thread, but has anybody tested neck hardness as a function of # firings to figure out how many firings you can get away with, before having to anneal?

 

[sinister]

 

[Victor N TN]

Good data. Thanks for sharing.