Hornady releases 6mm ARC

[abersfelderami]

Chamber has "headspace,
brass has "dimensions".

 

[abersfelderami]

Length of the brass (variable) + length of the "headspace clearance" (variable)= length of the "headspace" of the chamber (fixed).

 

[TAJ45]

Headspace is a fixed chamber dimension on a rifle. The SAAMI definition is quite clear that the headspace measurement is taken from the firearm and it is not taken from the case used in the firearm.

When I bump the shoulder on my cases 0.0015-0.002" so that they chamber freely, the headspace of my rifle has not changed.

We are cutting this pretty fine but I gave to agree: The headspace is machined into the action, bolt. The cases are sized to conform to whatever degree the reloader desires. Click, no click, bolt falling nearly freely....jmo.

 

[johara1]

Headspace is a fixed chamber dimension on a rifle. The SAAMI definition is quite clear that the headspace measurement is taken from the firearm and it is not taken from the case used in the firearm.

When I bump the shoulder on my cases 0.0015-0.002" so that they chamber freely, the headspace of my rifle has not changed.

But the head space on your case did...... Shoulder bump is an other new term...... What do you use a stub for to measure the set back on the case head space...... jim

 

[FrankG]

2885fps! Wow!

I have a 243LBC AR 40 and 26" barrel. I get about 2750fps with 28gr of H4895 and 105gr bullet. I had to decrease my load when I used more powder because I shed lugs in two bolts.

Was Brady using Hornady factory ammo or reloads?

He was using handloads. Shot the rifle again this past weekend. 1/2moa and a SD of 8.1 I think he said. Yes the velocity was correct at 2885fps.

I have to correct my original post...his gas system is +1". Not standard rifle length.

Brady did shoot box ammo (108Amax) thru his gun but didn't chronograph the muzzle velocities but the electronic target at 600 yards said the bullets where hitting it at 1860fps. So working the numbers backwards with JBM ballistics that gave him 11.4moa for come ups from a 200 yard zero which he pretty much had and according to velocity that works out to 2835fps at the muzzle. Probably not a accurate to figure it but as close as I can right now. So faster than what Hornady listed it as 2750fps. The box Hornady ammo had a SD on the electronic target 14.2. Which for virgin brass and box ammo...nothing wrong with that.

The picture of the attached target is with his handloads at 600 yards. He said he got caught in a couple of wind changes but still pretty nice. 149-9x.

His handloads had the 105BTHP. I had to correct this post.

Later, Frank

 

[johara1]

Headspace is a fixed chamber dimension on a rifle. The SAAMI definition is quite clear that the headspace measurement is taken from the firearm and it is not taken from the case used in the firearm.

When I bump the shoulder on my cases 0.0015-0.002" so that they chamber freely, the headspace of my rifle has not changed.

You are wrong head space one the chamber is a standard set of the head space gage only. head space on the case is set with the die to fit the chamber. Bumping the shoulder back is a new new term and it derived from bump dies that were a POS.from the days they made them from a neck die that didn't support the sides of the case and when you set the shoulder back it bulged the sides of the case. there is no way to set the shoulder back without supporting the sides of the case to set the head space need for easy chambering.... jim

 

[johara1]

He was using handloads. Shot the rifle again this past weekend. 1/2moa and a SD of 8.1 I think he said. Yes the velocity was correct at 2885fps.

I have to correct my original post...his gas system is +1". Not standard rifle length.

Brady did shoot box ammo (105gr BTHP) thru his gun but didn't chronograph the muzzle velocities but the electronic target at 600 yards said the bullets where hitting it at 1860fps. So working the numbers backwards with JBM ballistics that gave him 11.4moa for come ups from a 200 yard zero which he pretty much had and according to velocity that works out to 2835fps at the muzzle. Probably not a accurate to figure it but as close as I can right now. So faster than what Hornady listed it as 2750fps. The box Hornady ammo had a SD on the electronic target 14.2. Which for virgin brass and box ammo...nothing wrong with that.

The picture of the attached target is with his handloads at 600 yards. He said he got caught in a couple of wind changes but still pretty nice. 149-9x.

Later, Frank

Frank, I tried the 110's in a BR Imp. with H4350 and it shoots very small at 2900+ Sub..1...... jim

 

[Winny94]

The 6mm ARC is not interchangeable with the 6mm AR or the 6mm Grendel. The headspace is different.

no one said it was interchangeable, but for all intents and purposes, its ballistically identical

 

[Winny94]

I re-read Brownell's introduction of the 6mm ARC. They stated that it was necked down 6.5 Grendel. WD

https://www.brownells.com/guntech/6mm-arc/detail.htm?lid=18076

They said it was "based on" a necked down grendel

 

[Winny94]

I have a question. Hornady has made the CM a marketing sucess and may do the same with ARC. But, why not do the long overlooked obvious and promote the 6BR with cases and factory ammo and getting the rifle manufacturers to produce factory rifles.The CM is no real gain over existing cartridges in its class such as the .260 and 6.5x47. The 6BR has nothing else like it available. Maybe its the jealousy thing because it was an original from Remington who has totally fumbled the ball with it.My point is, fill a void, we do not need more of the same things that offer no real gain. But, kudos to Hornady for slick marketing.

Already been stated, the BR bolt face in a small frame AR is not reliable. Too many instances of shearing lugs

 

[Winny94]

Head space in chambering has nothing to do with the case at that point only the go gage and tape on it for no go. There hell it can't be changed with the sizing die, how do you set up a sizing die ? How do get the bolt to close freely? You size the case .0015 to .002 on most so you are setting head space. it has been a term for 65 years or more. .... So what do you call the clearance between the chamber size and a sized case? all the SAMI says is where to measure .... jim

Jim you can keep parroting the same wrong info and hope people just get bored and accept it (seems to work w/ the media), but that doesnt change the fact headspace is set in the chambering. Hence, if you close a no-go guage, you cant use it (as we all know the potential ramifications of shooting in an excess headspaced chamber) - all the case sizing in the world wont make an out of spec headspace chamber in spec.

 

[FrankG]

Frank, I tried the 110's in a BR Imp. with H4350 and it shoots very small at 2900+ Sub..1...... jim

Jim, The 110SMK or the 110ATIPs?

I've shot plenty of the 110ATIPs out of my 6BRA. Like you said...nice small groups!

I corrected my previous post.

His box ammo was the 108AMAX bullet and his handloads where 105BTHP Hornady's.

Later, Frank

 

[johara1]

Jim, The 110SMK or the 110ATIPs?

I've shot plenty of the 110ATIPs out of my 6BRA. Like you said...nice small groups!

I corrected my previous post.

His box ammo was the 108AMAX bullet and his handloads where 105BTHP Hornady's.


Later, Frank

Frank, I have shot both 110's and both shoot small at 2900 but the A tips shoot easy. I had the 110 SMK to 2960 before hard bolt lift but they didn't seem to shoot there. The A tips shot Three .020 groups with two different barrels a 7 twist and a 7.75. They sort very well bearing surface and base to ogive and over all length was scary uniform... jim

 

[johara1]

Jim you can keep parroting the same wrong info and hope people just get bored and accept it (seems to work w/ the media), but that doesnt change the fact headspace is set in the chambering. Hence, if you close a no-go guage, you cant use it (as we all know the potential ramifications of shooting in an excess headspaced chamber) - all the case sizing in the world wont make an out of spec headspace chamber in spec.

Here is where you are wrong so you run the reamer a little deep excessive head space ... right? Now I form a false shoulder and fire it and no excessive head space but the over all chamber length is longer but no big deal. Now I set the fired case back to get my correct head space for the case.... SAMI is just for factory cases right or wrong they have their dimensions. Dashers and BR IMP are all over the place, everyone has their own little changes but all will set there case head space with there die..... jim

 

[Winny94]

Here is where you are wrong so you run the reamer a little deep excessive head space ... right? Now I form a false shoulder and fire it and no excessive head space but the over all chamber length is longer but no big deal. Now I set the fired case back to get my correct head space for the case.... SAMI is just for factory cases right or wrong they have their dimensions. Dashers and BR IMP are all over the place, everyone has their own little changes but all will set there case head space with there die..... jim

Still not getting through to you. Not sure how many people can explain it in how many different ways. You're incorrect - headspace is set by the chamber. You can float in a certain range by how much you size your brass, but your limiting factor will be the chamber.

 

[TC260]

This is interesting. Many are saying Jim's wrong but nobody's provided the correct word to use for the case to chamber gap. If he's clearly using the wrong word, the right word should be simple.

 

[Winny94]

This is interesting. Many are saying Jim's wrong but nobody's provided the correct word to use for the case to chamber gap. If he's clearly using the wrong word, the right word should be simple.

Not sure anyone is saying hes using the wrong word - his definition of what that word means is wrong.

 

[TC260]

Fair enough. What is the right word for the gap between the case and the chamber?

 

[abersfelderami]

Headspace clearance.

 

[johara1]

Still not getting through to you. Not sure how many people can explain it in how many different ways. You're incorrect - headspace is set by the chamber. You can float in a certain range by how much you size your brass, but your limiting factor will be the chamber.

Here again you are wrong with nothing in the chamber you have no head space. this the same as we have used for 65 years I have been loading, no Sami BS then..... jim