Large vs small primers

[gorillamotors]

Since I cannot find any good quality 6mm ARC brass (forget Hornady too soft) I have been case forming 6.5 grendel, 220 russian, and 7.62x39 Lapua brass. Has anyone done any testing on which primer is best suited for the ELR 6ARC. Large or small?

[CZ527 Guy]

Large primer will essentially weaken the case head a bit, increasing the likelihood of blown out primer pockets due to thinner wall. For this reason, when I am pushing pressure, I favor small rifle primers for these smaller powder capacity cartridges. That being said small rifle primers vary a lot within themselves. Thickness of the cups is one variation along with hardness that will determine max pressure suitability along with force required by the firing pin to successfully fire the primer.

Then some primers fire hotter than others. Certain primers tend to work better with ball powders while others work perhaps a bit better with extruded powders.

See link for your consideration. http://www.jamescalhoon.com/primers_and_pressure.php

[CZ527 Guy]

I went with the Lapua 220 russian brass and while I am pleased with this brass I am not saying it is substantially tougher than Hornady brass. The Lapua brass is substantially more consistent in my experience. and yes a bit more robust. My observation is case capacity looks to be near identical in my lot's of 220 Russian brass vs the Hornady 6 ARC case head stamping.


6.5 Grendel is another good choice in the lapua brass though I have not yet tried it as a parent brass for 6mm arc. My understanding is the Lapua 6.5 grendel parent is a bit easier or more so straight forward to form & may have slightly more case capacity.

Keep us posted on your results if you would.

Thank you!

[CZ527 Guy]

One more difference to be noted between the Lapua 220 russian VS the Hornady brass is the size of the flash hole diameter.

Think the Lapua runs roughly .060" Vs the Hornady at .080" Performance wise I am not noticing a difference between flash hole diameter thus far.

Just be aware you may need a smaller primer extraction pin when sizing & decapping with the Lapua brass. Hornady offers a smaller pin & Whidden the smaller pin is standard.

https://www.whiddengunworks.com/product/...ur-caliber

[gkf]

I went with the Lapua 220 russian brass and while I am pleased with this brass I am not saying it is substantially tougher than Hornady brass. The Lapua brass is substantially more consistent in my experience. and yes a bit more robust. My observation is case capacity looks to be near identical in my lot's of 220 Russian brass vs the Hornady 6 ARC case head stamping.


6.5 Grendel is another good choice in the lapua brass though I have not yet tried it as a parent brass for 6mm arc. My understanding is the Lapua 6.5 grendel parent is a bit easier or more so straight forward to form & may have slightly more case capacity.

Keep us posted on your results if you would. 

Thank you!

Hey CZ527, are able to just use a FL sizing die, or do you need hyrdroform or fire form 220 Russian?

[gorillamotors]

I don't know about CZ but all I use is a 6ARC Hornady FL sizing die (I put a smaller pin in) to reform Lapua 220 Russian. I destroyed a few cases because I went toooo fast. Just slowww it down and it will be fine.

[CZ527 Guy]

Their are at least 4 ways to firearm 220 Russian to 6mm ARC. & yes I suppose Hydroforming may be a good option as well.

While I waited nearly 6 months for my Pacnor barrel for a CZ 527 action I purchased a Savage AXIS in 6mm ARC largely for fire forming.

A few fire forming options summarized below. May recommend looking up fire-forming 6ppc if you want more info on fire forming.

1.) Work up a load with a faster burning powder & load with a light inexpensive 224 cal bullet & fire form away. Then trim to length & debur.

2.) Work up a load with a faster burning powder & load & somehow contain with wax & fire form away. Then trim to length & debur.

3.) Trim length a bit. Neck up to .243 . Work up a load with a faster burning powder & jam 6mm bullet in to lands & fire form away.

4.) Trim length a bit. Neck up to .264, neck back down to .243, creating a small false shoulder Work up a load with a faster burning powder & load 6mm bullet off the lands & fire form away.

I tried 1.) & 3.) above with fine success. Found 1st option worked out best in terms of getting OAL correct when trimming brass. BTW the Little crow trimmer was very handy for trimming after fire forming. https://www.midwayusa.com/product/101285306?pid=741578

[gkf]

Thanks gorillamotors.  I am going to give your method a shot.

CZ527-Thanks for the info.  If direct resizing method doesn't work for me, I think I am going to order the Whidden Hydroforming die.  The trimmer you linked looked interesting.  I am currently using a Frankford Arsenal Case trimmer, but there is so little of the case exposed, it is very difficult to make larger trims, ie reformed grendel brass.

[StoneHendge]

I have extensively used Starline 7.62x39 brass, primarily to use up an oversupply of LRPs in a tight primer market. I've had great accuracy and success, but I don't chase velocity since I use them for practice rounds. What I have found is that with the larger spark, peak pressure comes a little earlier and thus, not as much powder can be used. It seems that the faster the powder, the earlier the (relative) peak. The end result is having to accept lower velocity, which is fine for me since paper at 100 yards doesn't care what the velocity is and steel out to 500 remains well within reach. Using milder loads, some primer pockets start to go around 5-6x, but loss of brass resilience in the neck (and hence neck tension) is what sends most brass to the scrap yard (note that I don't anneal).

[r.tenorio671]

...check out post #24 in this thread >>> https://6mmarc.com/showthread.php?tid=124&page=2

...both times I've been able to get Starline 6.5G brass from Brownell's it was during late night, pre-dawn surfing, probably when their systems do inventory updates. The only problem has been it's only been the 100 qty bags and they have a 2 bag limit. What's interesting is although I have set up alert notifications for when it comes back in stock, I came across it before I received any notice. It must run out really fast as I never receive the notices after I get my order in.

[Keycap]

What's the popular consensus in the difference between starline and lapua?

[r.tenorio671]

What's the popular consensus in the difference between starline and lapua?

...pricing 

...for the cost of Lapua brass one could just buy HDY ammo, which is becoming more available than the Lapua new brass, although both are still relatively limited...

[Keycap]

You are saying they are the same quality, just the lapua costs more?

[r.tenorio671]

You are saying they are the same quality, just the lapua costs more?

...not making a statement about the quality of either, just stating that the average cost of single Lapua 6.5 Grendel  casing runs between $1.10 - $1.50 each, depending on source.  Norma & Nosler brass is even more, many in the 6.5G community infer the Norma brass is "better" than the Lapua brass, for use in 6.5G at least...

Hornady 6ARC ammo is averaging $1.30 - $1.70 per round, depending on source.  In these days of limited supply of ammo & components, it makes economic sense to get the Hornady ammo, if you can. A person can get at least 1 reload out of the brass left from the ammo, more if they are not loading to the max charge limit for their chamber. One would still be ahead "economically" on that 1st reloading as only the primer, powder & projectile are a cost item.

[Dino11]

I loaded a batch of ammo yesterday using Hornady brass... It was load number 12 for that brass. I anneal the brass each time, the primer pockets are still tight. Not loaded to max load each time... but pretty damn close.

Some of my brass is loaded to bolt gun specs for my bolt gun, that brass is holding up well to. I do keep gas gun and bolt gun brass segregated.

[Teats]

I have hydroform 6 arc brass.
My 1st 10 rounds were interesting. Very low ejection force ??
Are the casings using my gas to fully fireform ?
Now comes the most interesting part.
I compared the fired casings to factory, and measuring, the appear to be identical, BUT....
When I fl resized, I get what feels like a 2 stage ram cycle, and my brass has a ring that looks like a belted magnums casing.
3 out of the 10, I have to use a rubber mallet on my charging handle to eject ! The other casing, I can eject by hand, but I almost can't.
I am going to fire a few resized casing, and unfired form casings, and experiment on just neck sizing with the expander set way low.

[grayfox]

"A tip on fire forming I read years ago said to use heavy for cal bullets and lighter loads for Fire forming, "
This tip on fire forming, there may be a couple of pointers to be cautious about...
Might be ok-no problem in bolt action guns like your 7-STW no doubt is, but on gas guns you may have to be careful. Also, in the 6Arc as with many ARs the pressure limit is below normal bolt-gun values, in 6Arc case, 52 ksi, any load not specifically on the charts may be too hot unless you know what your barrel does with the load... for brass with a different volume than what the mfr used in their table, this is definitely the case.

So be careful