Neck Diameter Various Brass Loaded Rounds?

[BluntForceTrauma]

What are you guys getting for neck diameter measurements of loaded rounds for various brands of brass?

Lapua?

Starline?

Hornady?

Federal?

PPU?

Wolf?

[A5BLASTER]

Stand by will get some data on remmy, ppu,wolf, federal, hornady, Starline handloads.

Wolf= 286
Federal factory ammo=286.5
Remmy factory ammo=284
Ppu factory ammo=287.5
Hornady handload=287
Hornady factory ammo=286.5
Starline handload= 287

Hope this helps BFT. You thinking about a spec change for your barrels?

[ricsmall]

.292” neck perhaps?

[FLshooter]

I only use Hornady cases. Mine are .2835 In.on the avg.

[BobinNC]

Starline 6.5 Grendel cases loaded w/120 Grain Speer Gold Dot 0.290" in new unfired brass

[Klem]

Lapua is .293" (thick brass at the neck; .013 - .0135")

[BluntForceTrauma]

Yes, am thinking about tighter neck spec for my barrels.

SAAMI 6.5 Grendel maximum loaded cartridge neck diameter is 0.293.

Following are my measurements, but I want independent verification in case I'm measuring wrong or my calipers are off. I get two different dimensions, depending whether I use the sharp "beak" of the calipers (smaller measurement) or the middle "fat" area of the calipers (usually 0.001 or even 0.002 larger measurement). Following dims are from the beak end and represent the largest dimension of any variation.

LOADED CARTRIDGE NECK DIAMETERS BY BRAND
Lapua = 0.291
Hornady = 0.289
Federal = 0.288
PPU = 0.286 (old production, prior to recall)
Wolf = 0.288
Starline = N/A

Almost every cartridge in the SAAMI book (well, the more recently developed cartridges) follow a similar dimensional scheme: If the SAAMI maximum loaded case neck is, oh, 0.295, then the SAAMI chamber minimum neck dimension at the "root" (the neck-shoulder junction) is typically 0.002 over -- which would give us 0.297 in our example -- and at the neck mouth it is 0.001 over, which would give 0.296.

Now, having discussed the Grendel chamber extensively with Bill Alexander in years past, he created the 0.300 neck because he anticipated that the lacquer coating on Wolf steel-case would be applied unevenly and also get gummy if a round sat too long in a very hot chamber. He also anticipated some form of military adoption and thus field use under dirty conditions. He also figured the compound throat would help center cartridges rattling around in the sloppy "machine-gun" chamber neck.

My questions: Are those considerations still valid? Can we do better? Why is it NO OTHER cartridge does this? A barrel maker named Randall Rausch who had a firm called AR15Barrels (don't know if he's still around) posted, years ago, a spreadsheet charting 223R/556N reamers from the blueprints of the major reamer manufacturers, and they all made reamers to SAAMI minimum spec (0.254 for five makers and 0.255 for one). These are semi-auto AR15 chambers and some, presumably, would have Wolf steel-case in 223R/556N fired from them! Now, it depends, of course, what is the average neck diameter of loaded 223R/556N rounds, but it has got me thinking....

[BluntForceTrauma]

Lapua is .293" (thick brass at the neck; .013 - .0135")

Klem, can you double-check your numbers? I get 0.291 for Lapua, at the largest. (0.0135 x 2 = 0.027 + 0.264 = 0.291)

Lapua making fat bullets?

[ricsmall]

John

Use the thicker section of the calipers to measure when possible. It can make a difference. I sometimes wish I had gone with the .295 neck on my reamer as it’s for bolt guns but I have cleaned up several chambers in AR rifles as well. May send it for regrind to .295 neck. I’ll measure some rounds first chance I get and report back and decide on my reamer. Thinking of re contouring a bolt gun barrel in a 700 Grendel. May set back and rechamber with .295 neck to see if it makes any measurable difference.

[BluntForceTrauma]

Ric, why 0.295 and not some other dimension?

[JASmith]

Remember that clearance at the neck is needed for the bullet to be safely released. This means that one will ALWAYS have slop n the neck region if the bullet is to be safely released.

That is why some neck size only in bolt guns so the case body is more concentric with the chamber. In other words, very little slop is present when neck size only is used.

Then, take a look at the very much smaller lateral clearance one gets as the ogive “just kisses” the compound throat.

That is part of the genius of the Grendel design.

The reason we see essentially no other cartridges with a compound throat is the higher pressure cartridges can get by with a single angle taper and the compound throat is a PITA for the reamer maker.

These arguments are less strong in bolt and other actions where latitude in seating depth allows easy set of optimum jump.

Some cartridges employ a tapered freebore and throat (single cone angle). The 50,000 psi working pressure in the Grendel is low enough that some help is needed to get the powder burning consistently. Hence Bill applied a more conventional taper for what would be the freebore. We all know this combination works very well, especially with the length constraints in the AR.

[BluntForceTrauma]

Then, take a look at the very much smaller lateral clearance one gets as the ogive “just kisses” the compound throat. That is part of the genius of the Grendel design. The reason we see essentially no other cartridges with a compound throat is the higher pressure cartridges can get by with a single angle taper and the compound throat is a PITA for the reamer maker.

Joe, I agree the 6.5 Grendel compound throat is genius and I have no intention of messing with it. I'm addressing only the issue of chamber neck dimensions.

By the way, I've asked reamer and barrel makers if the SAAMI compound throat reamer is more problematic. They just shrug their shoulders and say, "Not really." The reamer guys say, "We grind to spec, and specs is specs." The barrel makers say, "You chuck up the reamer and drill the chamber. A hole is a hole." I think the rumor about the compound throat being problematic was started by jealous competitors.

[A5BLASTER]

Joe, I agree the 6.5 Grendel compound throat is genius and I have no intention of messing with it. I'm addressing only the issue of chamber neck dimensions.

By the way, I've asked reamer and barrel makers if the SAAMI compound throat reamer is more problematic. They just shrug their shoulders and say, "Not really." The reamer guys say, "We grind to spec, and specs is specs." The barrel makers say, "You chuck up the reamer and drill the chamber. A hole is a hole." I think the rumor about the compound throat being problematic was started by jealous competitors.

That wouldn't be the first time that happened lol.

[Klem]

Klem, can you double-check your numbers? I get 0.291 for Lapua, at the largest. (0.0135 x 2 = 0.027 + 0.264 = 0.291)

Lapua making fat bullets?

Probably not, but they do make fat necks.



The bullet is a 107SMK

Note, in both cases the case is suspended...meaning there's enough pressure between the jaws to be confident in the reading.

With this degree of precision it also varies slightly depending on whether you take a few readings at different points of the compass.

Here are some 6.5 bullet diameters;
90TNT .26315
100NBT .26360
107SMK .26380 - .26395
120NBT .26360
123ELD .26390
130AR .26435
130TGK .26400
130ELD .26395
140ELD .26395

(these are not averages, I just measured one from each box).

[JASmith]

Joe, I agree the 6.5 Grendel compound throat is genius and I have no intention of messing with it. I'm addressing only the issue of chamber neck dimensions.

The point about the throat is that it renders concerns about neck tolerance for accuracy largely moot.

There is still the issue of working the brass more than needed. This exploration might help shed light on that.