6mmPPC AI...?

[Alex Wheeler]

6mm firewalker

 

[BoydAllen]

Just a simple question from a guy who's far less expert than most on this forum: Does the neck length really matter that much? Here's why I ask: The Wilson chamber-type neck-sizing die that I use only sizes down the last .1875" of the neck, stopping well short of the shoulder while still providing plenty of bearing surface for bullet/neck contact. This leaves some of the neck (about .10") expanded, which I assume improves the centering of the case in the chamber.

From an accuracy point of view, I do not think that neck length is an issue, but there is an advantage as far as barrel life goes. There is a something called Turbulence Point theory. The upshot of it is that if you project the angles of the inside of the shoulder to the center line of the neck, from opposite sides, that having them meet within the neck will result in longer throat life. An example might be comparing the .243 with the 6mm Rem. as far as barrel life.

Recently a new case has made its way into the field of long range benchrest, the BRA Which is an Ackleyized version of the 6mm BR Norma/Lapua case that has had its shoulder angle increased from 30 degrees to 40 degrees with the same neck length as the parent case. This case has slightly less (1 gr. ?) capacity than the Dasher that has the same shoulder angle but a shorter neck, and preliminary comparisons show that visible throat change comes sooner with the Dasher than the BRA.

As an aside, the old thing about having bullets engage necks one caliber in length is something that was probably more about their being secure for handling and feeding from a magazine, and has nothing to do with modern benchrest practice. When my .060 freebore (a historically common specification) 6PPC was new, my bullet of choice, a double radius ogive 67 gr. FB is only in the case neck a little under .140" and that has never been a problem. It may even be an advantage.

 

[TAJ45]

From an accuracy point of view, I do not think that neck length is an issue, but there is an advantage as far as barrel life goes. There is a something called Turbulence Point theory. The upshot of it is that if you project the angles of the inside of the shoulder to the center line of the neck, from opposite sides, that having them meet within the neck will result in longer throat life. An example might be comparing the .243 with the 6mm Rem. as far as barrel life.

Recently a new case has made its way into the field of long range benchrest, the BRA Which is an Ackleyized version of the 6mm BR Norma/Lapua case that has had its shoulder angle increased from 30 degrees to 40 degrees with the same neck length as the parent case. This case has slightly less (1 gr. ?) capacity than the Dasher that has the same shoulder angle but a shorter neck, and preliminary comparisons show that visible throat change comes sooner with the Dasher than the BRA.

On top of the .243 to 6mm Rem comparison, the Remmie holds several grains more powder which would further bolster your statement.
From a first hand, real world anecdotal perspective:.I have a Bud who has hundreds of thousands of rds launched in the dog fields of yore using well smithed barrels on the top tier actions. Apples to apples, he said he always got better bbl life from the 6mm REM over the .243, AI to AI or original configuration to original. Maybe neck length considered with the shoulder angle is a viable variable to consider.

 

[gunsandgunsmithing]

On top of the .243 to 6mm Rem comparison, the Remmie holds several grains more powder which would further bolster your statement.
From a first hand, real world anecdotal perspective:.I have a Bud who has hundreds of thousands of rds launched in the dog fields of yore using well smithed barrels on the top tier actions. Apples to apples, he said he always got better bbl life from the 6mm REM over the .243, AI to AI or original configuration to original. Maybe neck length considered with the shoulder angle is a viable variable to consider.

I don't know...There are lots of variables in terms of barrel life other than neck length and shoulder angle. If the gains were large, it'd be a bigger issue, but I don't think they are, if they even exist. If long barrel life is the goal, one of the small 30's excel here, or one could simply load down to save barrel life. These small cartridges used in short range br are not model T's, but rather, they're top fuel dragsters and like pressure. It's but one price we pay for tiny groups. Again, if the difference is considerable and not at all subjective to other factors,...that's another story. I just don't think it is.

 

[TAJ45]

[QUOTE="gunsandgunsmithing, post: 37003642,. Again, if the difference is considerable and not at all subjective to other factors,...that's another story. I just don't think it is.[/QUOTE]

 

[TAJ45]

You may well be right......time will tell -
maybe.

 

[gunsandgunsmithing]

JMHO, but I think the op is too hung up on a "per caliber" neck length. A 6 Grendel AI is almost exactly what he's described, sans about .005" of neck length, and that's somewhat contingent on reamer design and how you form brass. Fireforming without a bullet, but with pistol powder and tissue or cream of wheat can yield a considerably longer neck..Much more than the small .005" we're talking about.

This is how Jackie Schmidt forms brass for a 30BR with a neck that's .050" longer than standard.

 

[flatlander]

Several years ago, a good friend of mine wanted a barrel for the 6mm AR Turbo 40* Improved for an AR15 Match Rifle upper he wanted to build for NRA across the course highpower shooting. Don't recall the exact details now, but he couldn't get just a barrel, so rather than spring for a complete upper, he talked with both John Holliger of White Oak Precision, and Dave Kiff of PTG. The resulting reamer was called the 6 RAT. He had the PTG reamer sent to Holliger, and a 28" AR MR bbl was done for him on either a Bartlein or Krieger blank. I had a nearly identical bbl done by John for my own AR MR. My friend got with Hornady to have dies made, and sold them for a few years before turning the whole thing over to Lee Wells, who made a couple of very minor changes to the reamer print & re-named it 6 FAT RAT.

I had PTG grind a reamer to Greg's original 6 RAT print, and have done several AR15 bbls, as well as a few barrels for bolt rifles (CZ527 7.62x39 carbine first, more recently a Howa Mini in 6.5 Grendel). The RAT's neck is only .210" in length, but it works quite well in both applications - AR15s & bolt rifles. Simple to form, dies are still available, and it shoots great.

 

[rangertim]

Alex is Correct on the name it's a Firewallker I have a Barrel and 50 piece of Sako Brass and a bullet Seater but no FL Die to size the cases, I have always wanted to play with this 40 degree PPC to see how will it would do as s 200 yd VFS It looks Interesting LOL ! and now this 40 deg 6BRA as sparked more interest in this firewallker !

 

[TAJ45]

Heck, if we're going to do custom reamers and dies, why not a 50° shoulder, thereby increasing the capacity and bury the turbulence point that much further?

Orrrr, check W'by dimensions and do radiused shoulders and run the appropriate reamer in really short.
IF the case dims will allow. Just a wild thought. Heading to case specs now.