Grendel Short Barrel Group Buy Orders

[cory]

I think we'd greatly appreciate the offer. I personally will jump on it.

Update barrel count and score.

[cory]

Here's the PF Phalanx BCG we're talking about.

https://secure.wf-api.com/www.precisionfirearms.com/m8/6.5%20Grendel%20Bolt%20and%20Carrier%20Group--6-5-grendel-bolt-and-carrier-group.html

[cory]

I talked Mark about a rough price at 25 units. I'm going to update the order form to reflect the PF Nitrided BCG. If you've already ordered and want one, just let me know I'll add it.

[cory]

In light of recent events I've saved the first few informational posts to a file. If the forum was to crash again look for this thread in the Snipershide Group Buy forum and eventually over at Arfcomm.

[biodsl]

Cory...is the BCG available to folks not in the short barrel group buy?

[keystone183]

Cory...is the BCG available to folks not in the short barrel group buy?

+1....(maybe 2)

[cory]

I've a couple of emails about ordering the BCGs separately.

It'll be just like the Spikes Tactical Parts. If we hit 25 barrels, I'll take orders for BCGs and Spikes absent a barrel. If we don't hit the 25 barrels, the group buy won't happen all the way around.

However, I'm confident it'll happen. It may just take a few more weeks.

[cory]

We're at 12 barrels, gents. We just need a few more orders to make this thing happen. Send me an order and just consider it an early christmas present to yourself. Submit an eForm 1 for your SBR soon and you'll likely have your tax stamp before christmas if they keep processing them at the pace they are now.

[Bronson90]

I'm really interested in getting in on the group buy but can’t seem to find any empirical load information that details what one could expect from the different lengths being offered... My searches yield a lot of people talking but no one discussing load or performance specifics.

I’m thinking that I would go with a 12.5” but then need to settle on a gas system length. Is 1:8 fast enough to stabilize a 123gr – 140gr bullet in a 10.5” – 12.5” barrel? Right now I have a 16.5" 1:8 Lilja and unfortunately my busy work schedule has precluded me from finalizing a load for it. I have had decent success with CFE223 & AR-Comp so far, but need more time with it before I can finalize the load…

I've run a few different scenarios through QL with the 12.5” barrel with the 123gr SST & AR-Comp and honestly haven’t been too impressed thus far…

Any feedback will greatly appreciated!!!

[cory]

JASmith is the resident expert on QL, here. He'll tell you quickly that QL has to be tweeked before you'll get accurate predictions using the Grendel.

Here's a post from Variable, form the group buy thread before this one. Where he found a quote from Bill Alexander. Based on this I think the 1:8 twist in the Lilja Button SS barrel, will be more than sufficient.

Regarding twist rates: I just found this quote (of a quote of a quote...LOL) from Bill Alexander that I found back on Sniper's Hide long ago. It may even have been from the old board. I dunno, but it is pertinent, so anywhooo:


The stability of the projectile is given by the rate of rotation and is usually expressed as radians per second. It is for most purposes independent of the forward velocity, but in the case of a rifle the spin is created by the rifling. Longer barrels producing more velocity can therefore use a slower twist rate to produce the same rate of rotation.

Barrel materials and the shape of the rifling will also effect how the projectile is stabilized and the complexity of the choices is then extended by the economics of tooling and the process by which the rifling is formed.

For Grendel the following set ups are used.

- 28" cut rifled stainless 5 groove 5R 1 in 9
- 24 cut rifled stainless 5 groove 5R 1 in 9
- 24" button rifled stainless 6 groove 1 in 9
- 20" cut rifled stainless 5 groove 5R 1 in 9
- 19.5" button rifled stainless 6 groove 1 in 9
- 18" chrome lined 6 groove 1 in 7 1/2
- 18" stainless 6 groove 1 in 8 1/2
- 16" cut rifled stainless 5 groove 5R 1 in 8
- 16" chrome lined 6 groove 1 in 7 1/2
- 16" button rifled stainless 1 in 8 1/2
- 14.5" chrome lined 1 in 7 1/2
- 10.5" chrome lined 1 in 7 1/2

As can be seen from the above, there are some anomalies. The chrome lined barrels like a fast twist rate and at 18" the 1 in 7 1/2 that Sabre produces, produces very fine accuracy. Interestingly the 14.5" barrel with the same twist is also very accurate as is the 10.5" barrel. When we ran the 16" stainless button barrel in 1 in 7 1/2 the accuracy was marginal but 1 in 8 1/2 works well for both the 16' and 18" . The oddity is the cut rifled barrels. These can run slower than anything else but do not seem to care about faster twists either. We have set up 16" barrels at 1 in 9 with great success equally 24" barrels will stabilize 140 grain projectiles at 1 in 10 but this is not at minus 60 at sea level, so we edged towards caution.

Bill Alexander

Here's a link where bjorn quoted variable in some of his chrono data with his 10.5" chrome lined Grendel with factory Ammo.

http://www.65grendel.com/forum/showthread.php?8805-Lilja-Short-Barrel/page2

As far as loading for a 11.5" or 12.5" Grendel, we may be in unfamiliar territory. However, I'm confident that between CFE and 8208, I'm going to be very happy.

[Bronson90]

I had previously read all of that and some of those comments have me unconvinced that 1:8 is a suitable twist for a 10.5" - 12.5" barrel. Based on Bills comments alone I would only be comfortable with a 1:7 twist for a 10.5" - 12.5" barrel; especially knowing that I am going to be shooting it suppressed and making the wrong decision equals a baffle strike...

Some of the better the velocities I am seeing in QL are in the 2,150 - 2,225 fps range through a 12.5" barrel, but they all have seemingly have high percentages (3% - 8%) of un-burned powder. On the flip side, all of the loads that I ran that were 100% burns are only getting me in the 1,950 - 2,075 fps range in a 12.5" barrel...

[cory]

This "we ran the 16" stainless button barrel in 1 in 7 1/2 the accuracy was marginal but 1 in 8 1/2 works well for both the 16" and 18"."

This leads me to believe that a 7" twist could hurt accuracy being to fast before an 8" twist didn't stabilize a 140gr bullet being to slow.

[Variable]

I had previously read all of that and some of those comments have me unconvinced that 1:8 is a suitable twist for a 10.5" - 12.5" barrel. Based on Bills comments alone I would only be comfortable with a 1:7 twist for a 10.5" - 12.5" barrel; especially knowing that I am going to be shooting it suppressed and making the wrong decision equals a baffle strike...

Some of the better the velocities I am seeing in QL are in the 2,150 - 2,225 fps range through a 12.5" barrel, but they all have seemingly have high percentages (3% - 8%) of un-burned powder. On the flip side, all of the loads that I ran that were 100% burns are only getting me in the 1,950 - 2,075 fps range in a 12.5" barrel...

QL is expressly verbotten by Bill A., as it frequently gives wildly innaccurate and sometimes dangerous results in relation to the Grendel. It's only used as a last resort FWIW.

Here is some actual chrono data posted by David Fortier (Gunwritr) from a 12.5" Grendel a while back:

"Alexander Arms 12.5 inch 6.5mm Grendel
Alexander Arms 100 grain Berger OTM 2470
Alexander Arms 123 grain Scenar OTM 2330
Velocity figures are 10 shot averages recorded on an Oehler 35P placed 12 feet from the muzzle 1,030 feet above Sea Level at an ambient temperature of 30 degrees F."

http://www.ar15.com/forums/t_3_121/533217__ARCHIVED_THREAD____Looking_for_6_5_Grendel_Chronograph_results.html&page=1#i5053498

FWIW, your 2100-2200 fps numbers from QL are what I actually see with factory ammo out of my 10.5" barrel. The extra two inches of barrel (12.5") on a tube that short will definitely net you more than that.

12.5" barrel: I can't find the dang post now, but someone reported getting 2350fps with the Hornady factory load. That may have included freebore boost from the can or not, I don't know. I do know that 2350fps with a 123gr. Hornady pill is exactly the target I'll be shooting for. 2300fps will make my desired threshold of 400yds, but I'm hoping for more wiggle room. I'll just have to wait and see.

[Bronson90]

QL is expressly verbotten by Bill A., as it frequently gives wildly innaccurate and sometimes dangerous results in relation to the Grendel. It's only used as a last resort FWIW.

Here is some actual chrono data posted by David Fortier (Gunwritr) from a 12.5" Grendel a while back:

"Alexander Arms 12.5 inch 6.5mm Grendel
Alexander Arms 100 grain Berger OTM 2470
Alexander Arms 123 grain Scenar OTM 2330
Velocity figures are 10 shot averages recorded on an Oehler 35P placed 12 feet from the muzzle 1,030 feet above Sea Level at an ambient temperature of 30 degrees F."

http://www.ar15.com/forums/t_3_121/533217__ARCHIVED_THREAD____Looking_for_6_5_Grendel_Chronograph_results.html&page=1#i5053498

FWIW, your 2100-2200 fps numbers from QL are what I actually see with factory ammo out of my 10.5" barrel. The extra two inches of barrel (12.5") on a tube that short will definitely net you more than that.

12.5" barrel: I can't find the dang post now, but someone reported getting 2350fps with the Hornady factory load. That may have included freebore boost from the can or not, I don't know. I do know that 2350fps with a 123gr. Hornady pill is exactly the target I'll be shooting for. 2300fps will make my desired threshold of 400yds, but I'm hoping for more wiggle room. I'll just have to wait and see.

Ok, what are your thoughts about twist???

[Variable]

Ok, what are your thoughts about twist???

"Punt!!!"

Seriously though, I don't know. In my gut I think we'd be okay at 1-in-8" twist. I couldn't definitively say though.

I know that the 160gr. "telephone" poles (Hornady 160gr. RN) stabilize just fine in my 1-in-7.5" twist 10.5" barrel.

I think Txgunner00 was running them in his 1-in-8" barrel too.

Long pause for searching..........


ETA: "Rapier" and "Txgunner00" were getting round holes with the Hornady 160gr. at subsonic velocities in this thread: http://www.65grendel.com/forum/showt...ll=1#post10010