6.5 CSS Barrel, .295 or .300?

[Schwag173]

I'm trading e-mails with Lothar-Walther about having an AR barrel made. They are calling the Grendel the "6.5 CSS" and asked if I wanted a .295" or .300" neck.

Before sinking $600 into this thing I was hoping you guys could educate me on this.

What I want to end up with is an 18" LW50 stainless barrel that will be as accurate with 6.5 Grendel reloads as my 16" LW50 stainless barrel is with .223 reloads (Larue Tactical Stealth upper group). My mainstay load will be in the 120-123 grain zone, but I'd like the versatility to plus up to 130-140 for the occasional hunting load. For rifling I was thinking 1-in-8.75" and have no idea about the .295" or .300" neck.

Am I in the ballpark on rifling? And please clue me in on the neck dimensions.

Thanks.

[Drifter]

In theory, the tighter .295" neck could potentially be slightly more accurate, perhaps a "match" version of the cartridge. Also, brass is worked less when resized. But it could be a little less reliable (regarding feeding, extraction, etc). The steel-cased ammo expected to become available probably won't work well in a .295" neck.

Thus, in theory, the .300" of the true Grendel chamber would lean the opposite way.

In reality, I've noticed no difference in accuracy nor reliability between the .300" neck of the Grendel and the .295" neck of the 264 LBC.

If I had to make the choice, I would probably choose the .295" neck in hopes of working the brass a little less, as I use my 6.5's exclusively for precision shooting and load my own ammo.

But if you plan to use the rifle for protection, self defense, etc., and / or plan to use steel-cased ammo, the .300" neck would likely be the better choice.

[Schwag173]

In reality, I've noticed no difference in accuracy nor reliability between the .300" neck of the Grendel and the .295" neck of the 264 LBC.

If I had to make the choice, I would probably choose the .295" neck in hopes of working the brass a little less, as I use my 6.5's exclusively for precision shooting and load my own ammo.

But if you plan to use the rifle for protection, self defense, etc., and / or plan to use steel-cased ammo, the .300" neck would likely be the better choice.

So, if I load my own brass-cased ammo I should have better accuracy with .295". I can live with that. I DO, however, require reliable functioning because without it - what's the point of having an AR? Can you give me an idea of how much more finicky the .295" neck is? I'm not a benchrest or competition handloader by any stretch of the imagination but I've never had fail-to-fire with my handloads through my Larue, either (and I cloverleaf with it). If I load well enough for the Larue 5.56 do you suppose I'll have similar luck with the .295"-necked 6.5?

[stokesrj]

I also have both .295 and .300 neck chambers, and can distinguish no difference in reliability or accuracy when fired from an AR. I can detect beter accuracy in the .295 neck when fired from my Panda Bolt action, which is a bench rest action. If you aren't concerned with full auto fire and clean your rifle every 200 rounds or so, and don't plan on firing steel cased amo, the .295 make sense.

You should get similar results to what you get with your Larue. Not all loads will clover leaf but then they won't in your Larue either.

Bob

[Schwag173]

Not all loads will clover leaf but then they won't in your Larue either.

OK, that brings me to rifling twist ... Am I on the right track with 1-in-8.75"?

[bwaites]

I should interject that the SAAMI chamber is .300 neck, the steel case ammo coming is based around the SAAMI chamber, and all future brass and factory ammo will be based around the SAAMI chamber.

Here are some targets shot with my .300 neck, SAAMI chambered rifles, both a 28 inch and a 19.5 inch:



28" That's a .21 group, shot in the first 50 rounds out of that barrel, while shooting load development rounds. It was the tightest group, but 2 others with that load were under .5 as well.





19.5"

Both are 5 shots. The "flyer" in the last two was me. I shot the group, then came down 1 MOA to make sure I had the scope zeroed for 100.

Once you fire the cases one time, and then PROPERLY resize, using the correct bushing for your neck diameter, there is no difference in how much you work the brass. That said, I have 20+ reloadings on some of my Lapua brass, and still can't tell the difference in accuracy over once fired brass.

I would lean towards an 1:8 for an 18 inch or shorter barrel.

[Drifter]

Once you fire the cases one time, and then PROPERLY resize, using the correct bushing for your neck diameter, there is no difference in how much you work the brass.

Not sure that I follow what you're saying.

A loaded cartridge measures somewhere in the neighborhood of 0.290" at the neck. When fired, the neck expands to fill the chamber, whether it be 0.295" or 0.300", then springs back maybe a couple of thousandths less than chamber size.

After resizing, an empty case neck will measure ~0.288 (depending upon brass, dies, and / or bushing size being used). A loaded round puts the neck back to ~0.290", and when fired, it expands to chamber size again.

Assuming that the previous two paragraphs are correct (with latitude given that measurements are estimations for the basis of discussion, and some might vary by ~0.002" in reality), how is resized brass not being worked more in a chamber with a larger neck?

[Whelenon]

I love it, the discussion is about a couple of thousands and I don't mean that in a negative way. The Horde can get together and debate the Grendel with so much attention to detail. It's a wonderful thing.

Personally, I'd go with the .300 neck, simply because it's the SAAMI spec. and all futrue ammo will be produced to meet it.

[bwaites]

In theory, I suppose it is, but unless you are sizing down to .280 or so, do you really think the difference in expansion from .295 to .300 is an issue with brass life? 5/1000ths?

Remember, many of us have 15+ reloads on brass, WITHOUT annealing. I have the first 200 pieces of brass I ever bought, still in rotation. Some of those have been resized 20+ times. I lose 1-3/100 pieces to cracked necks each time I reload them after 10-15 reloads. (Actually, that rate has dropped since I stopped using Lee dies, but I still count it as an average.)

I simply don't think that the theory of the tighter neck in the .295 chamber is a "real world" issue, while the difference in neck geometry between the two has been shown to have been part of the issue when Hornady released their ammo, (since corrected we believe) and Bill Alexander has cautioned us regarding the steel case ammo coming.

[texasgrunt]

In my opinion, as a pure novice in the long range precision game but a former USMC marksmanship instructor, unless you are competing on a serious level I would go with the more reliably functioning .300 Grendel spec. It is what Bill A developed after a Shiite load of testing in AR platforms. I have a LW barrel with the .300 chamber and mine shoots .5 or less groups (100 yards) consistantly.

I am building #2 precision Grendel and I am going with the .300 and a 1:8" twist in a 22" pipe.

Grunt

[Schwag173]

OK, I'm sold on the .300 neck. As for rifling I was under the impression that 1:8.75" was nearly perfect for a 120ish-grain bullet. You really think I should go 1:8? Again; 18" barrel, polygonal rifling, and the occasional desire to load 130-140 grainers for deer hunting.

[leopard6.5]

Schwag173: My Satern Spartan 18" barrel is 1-8.75 if that helps but I think from what Bill A. has said before that they are optimized for the 120 ish range bullets.

You may need to go closer to 1-8 to stabilize the heavier bullets.
You really should give Bill A. a call and have a conversation with him just to get his imput before you buy.
I never shoot anything heavier than 123 gr. so the 1-8.75 works fine for me.

Good luck.

Lee

[BjornF16]

Not sure you really need 130-140 grain bullets for deer hunting. I've used the 129 SST in my 19.5" successfully (I know almost 130, but with 9" twist) and, most recently, the 115 grain Berger with my 18" Grendel. I think 100-123 grain bullets are probably the most used for deer hunting with Grendel with barrels up to 18" (100 grn TTSX, 115 grn Berger, 120 grn TSX, 120 grn Nosler Ballistic Tip, 123 grn AMAX). In my 18" I am planning on 123 grn or less.

I don't think it will really matter between 8" twist and 8.75" twist. IIRC, someone on these boards had alluded the Satern barrels performed best with 8.75" twist. I don't really know how the polygonal rifling with affect the ballistics in regards to twist...

If you look at AA barrel/bolt combos, they have a several 18" barrels with 8.75" twist; the shorter barrels have 8" while the longer barrels wear 9".

I don't think you'll go wrong with either twist in your 18" barrel, but I'd seek advice from LW regarding twist and the polygonal rifling...there may be a "sweet" spot.

[LR1955]

Guys:

For the last five or six years of discussions on the Grendel forum, I have not once heard of a reliability issue that was traced to a .295 verses a .300 neck. Not one. The majority of reliability issues concern chambers not cut to the proper headspace, gas system problems, magazine problems, feed ramp problems, and with reloading -- that guys do not bump the brass sufficiently.

Not once has a .295 neck diameter been the problem in reliability. Because of this, I believe that there is no problem having a .295 neck and if anything it will probably mean that your dollar a piece brass will last another couple of firings.

I think guys are also making a false assumption Wolf Steel Case will be made too large to fit a .295 chamber. So far, I haven't found any factory loaded or virgin brass that would not fit into any chamber -- match grade or service grade. I have had factory loads (match and service) that would not chamber because the bullet was seated out too long for a short throated match chamber but the brass itself chambered perfectly. This is because virgin brass is deliberately made small in order to fit a huge variance in chamber dimensions.

I do believe that a .300 chamber may relieve some of the initial gas pressure faster and that there is more a potential that such a loose chamber will go a bit longer before shearing a bolt lug than a .295 chamber. Alexander uses a .300 to fit a variety of loads and his compound throat makes up for the larger neck diameter in terms of consistent accuracy.

I would go with a Lothar Walther barrel over a Shaw any day of the week and would get something like a 8.5 twist in an instant. I would not get anal between a 8 and 9 twist. In this case, the quality of the barrel weighs a thousand times more than a 8, 8.5 or 9 twist barrel.

One thing about LW barrels and LW -- you will get your barrel within ten days and it will shoot much better than a Shaw.

LR1955

[BjornF16]

Originally posted by Bill Alexander.
When we were first working on the Grendel we followed what everyone said about 6.5 calibers and made the barrels with 8 twist rifling. Some barrels would shoot but more often than not the groups were open and the guns were tempremental. One of the very early test rigs had run a 9 twist and it actually shot well despite a less than optimum chamber so out of frustration we ignored conventional wisdom and build some 9 twist units at 24" and 20" barrel lengths. The change in accuracy for the group as a whole was unquestionable. Subsequent production of 9 twist barrels has proven that this is optimum for the caliber.

One of the contributors to the 9 twist is actually the Grendel itself. Pressure limits the ability to slug the bullet to the grooves and the case capacity holds the round to lighter bullets. The 168 grain roundnose nickel steel projectiles are simply not a consideration any more than the 142 and 155 grain SMKs

We have tested barrels as short as 14.5" in 9 twist (not recommended use 1:7.5 this short) with projectiles up to 152 grains and both accuracy and stability are maintained. Equally we have run 9 twist barrels out to 1600 yards (12" group) and the round remains stable and it would appear accurate through the transition velocity. Longer 8 twist barrels often demand velocity reduction for best accuracy

It is our conclusion that the 9 twist offers the best solution for the Grendel for barrels of 20" and longer while the 18" and shorter barrels thrive on 7.5 twist.

From another thread and posted this am...