Flat primers

[bowhunter-tw]

Hey guys, what causes flat primers like this? Is flattening normal to some degree? These were not loaded hot, just loaded for fire forming

Ar15 platform 6.5 grendel type 2 bolt

21” barrel rifle length gas tube

cartridge 6mm AR

100gr core lokt

26gr H4895

also could not get bolt lock back with these and adjustable gas block. It was throwing brass about 3 o clock but not very far, maybe 2 feet. My 223 throws it 4-5ft out, thought this was interesting

[CouesPursuit]

Overpressure. 

I don't know the load but it sure looks hot in your gun, there are at least 3 pressure signs there -

Stiff bolt, flattened primers, ejector marks and some case swipe. Full stop, imo. 

[bowhunter-tw]

21 minutes ago, CouesPursuit said:

Overpressure. 

I don't know the load but it sure looks hot in your gun, there are at least 3 pressure signs there -

Stiff bolt, flattened primers, ejector marks and some case swipe. Full stop, imo. 

What is case swipe?

Edit: I looked it up. Maybe I’ll try a different powder and load weight and see if it shows any signs

[lancetkenyon]

Definitely more signs than just the flattened primer.

Velocity?  That can be a telling sign.  But not the only one.

Are you using normal primers or AR style/military primers?  ARs are rough on primers.  If you are using normal SRP primers, try the #41 primers or a magnum primer, which have a harder cup.

New barrel?  Could have a tight spot.

Solvent in chamber?  Doesn't allow the case to expand and grip the chamber wall, allowing the case to slam back into the volt face.

Too much headspace?  Again, this doesn't allow the chamber to force the case against the bolt face, allowing it to slam back into the bolt face and cause false signs of pressure.

Bullets jamming into the lands?  This will definitely spike pressure.

[bowhunter-tw]

1 hour ago, lancetkenyon said:

Definitely more signs than just the flattened primer.

Velocity?  That can be a telling sign.  But not the only one.

Are you using normal primers or AR style/military primers?  ARs are rough on primers.  If you are using normal SRP primers, try the #41 primers or a magnum primer, which have a harder cup.

New barrel?  Could have a tight spot.

Solvent in chamber?  Doesn't allow the case to expand and grip the chamber wall, allowing the case to slam back into the volt face.

Too much headspace?  Again, this doesn't allow the chamber to force the case against the bolt face, allowing it to slam back into the bolt face and cause false signs of pressure.

Bullets jamming into the lands?  This will definitely spike pressure.

This is the information I need, Thanks! 
 

Normal primers, when trying to form the cases it looked like I had .010-015 bump on the shoulder, huge bump so im guessing this could be part of it. Ive got the die set to bump .0025 after fire formed. 
 

havent shot through a chronograph, these were the first few rounds through this build for me. 

[Mike S]

With that much headspace during fire forming, the firing pin pushes the cartridge forward upon firing, the primer is then pushed back to the bolt face first, and when the case itself follows, the primer mushrooms and flattens badly. This can happen even with mild loads, but if those are ejector marks, I'd back off a half grain and see what your velocity is with the fireformed cases.

With that much headspace, if it were a bolt action, I'd probably jam the bullets and fireform with an appropriately reduced load. This would help minimize the initial case stretch in the web area and help extend case life.   AR's are hard on brass though and that's probably overkill

[lancetkenyon]

.010-.015" headspace is HUGE.  

If you are just forming brass, back that charge way down and blow them out.

[bowhunter-tw]

23 minutes ago, lancetkenyon said:

.010-.015" headspace is HUGE.  

If you are just forming brass, back that charge way down and blow them out.

What kind of charge could I go down to, like 10gr? I dont want to squib load but dont know around what pressure that would occur 

[PRDATR]

45 minutes ago, bowhunter-tw said:

What kind of charge could I go down to, like 10gr? I dont want to squib load but dont know around what pressure that would occur 

26 is at the low end already so maybe 24. 10 is way too low.

[CouesPursuit]

10% below MAX is a good starting point as a rule of thumb for most powders.

While not necessary or what you want in this case, no pun, H4895 specifically is known for being able to reduce much farther than that, up to 40% below MAX, making it a great powder for reduced recoil loads. Just an FYI. 

[bowhunter-tw]

25 minutes ago, CouesPursuit said:

10% below MAX is a good starting point as a rule of thumb for most powders.

While not necessary or what you want in this case, no pun, H4895 specifically is known for being able to reduce much farther than that, up to 40% below MAX, making it a great powder for reduced recoil loads. Just an FYI. 

Ive done 10% below for starting loads but havent done any fire forming brass from another caliber. I was un aware h4895 could go that low

[bowhunter-tw]

2 hours ago, lancetkenyon said:

.010-.015" headspace is HUGE.  

I figured so also; I adjusted the die to where it only necks down from 6.5 to 6mm so im not sure how else I could move the shoulder forward besides fire forming