26" McGowen barreled 6mm Grendel upper

[bj139]

When I read that my eyes jumped forward to the capitalized name and I missed the "us".
Small thing that make no diff in the meaning.

[Popeye212]

Named mine Frosty when I took the barrel out the freezer so I could get it in the receiver. It immediately frosted up and put gloves on to handle it. Hair dryer on the receiver she slid right in. So she is technically semi-cryogenic..

[bj139]

Named mine Frosty when I took the barrel out the freezer so I could get it in the receiver. It immediately frosted up and put gloves on to handle it. Hair dryer on the receiver she slid right in. So she is technically semi-cryogenic..

Let us know if it shoots any better.
I ran out of safe space so maybe I could convert my standing freezer into a gun safe.
I could stress relieve all the parts at once.
Who needs food anyway?

[soloelcap]

Stone, I have 2 McGowen 6mm Grendel barrels both 20", 1 mid wt and the other is a heavy barrel .875 at the gas block. I ordered the heavy last fall when the ran the Halloween special, I've ran enough rounds through it for break in using the 105 RDF with good results so far. I'm assuming they used the same reamer for my barrel as yours which I'm finding was designed to work well with mag length rounds.
I get 2.275 Oal touching the lands 105 RDF. I'm using a Sinclair seating depth gauge to measure.
So far I've tried with this barrel XBR, CFE and RL15, all velocities around 2,500 fps for break in. RL15 showing the best results. I have Quick Load which says this bullet wt in a 20" barrel starts to max out around or blw 2,700 fps. I tend to trust QL as you can customize the BA to match the velocities you are actually getting and double check the results.
Today I'm starting serious load development using the 105 RDF and RL15 as I have half a box left. I have charges all the way up to 28.5 with a .015" jump, Hornady brass 7 1/2 primer.

[Popeye212]

Let us know if it shoots any better.
I ran out of safe space so maybe I could convert my standing freezer into a gun safe.
I could stress relieve all the parts at once.
Who needs food anyway?

Haven't shot it yet. Pick up the Midas for it Saturday break her in next week then we will see what she can do. Food???? Naaah it's overrated probably eat too much anyway. Save money on groceries and buy more bullets,powder,lowers,barrels........etc.

[soloelcap]

When did you order / receive? I think I ordered mine the last week in Oct and got it in early December. I would think they would be the same reamer, but my throat is much shorter. Made dummies starting at 2.31 and then took it down in 0.010 increments. Everything stuck until I got to 2.205 (2.220 stuck and then i overseated the next at 2.205 shooting for 2.210. That dropped and I've been loading the RDFs at 2.200. Strange I would be so far off from yours when they were made around the same time. Maybe the tip of the reamer broke off when the made mine and yours got made with a shiny new reamer

I've let mine sit for the week since the kaboom. Have other projects to keep me busy and it'll probably be another week or two before I can put my face near the chamber. I've got a ladder of N540 worked up and think I might poke around with N140 which did pretty well with the random break in loads and has pretty low temp sensitivity according to "the chart." Nonetheless, I'm going to back off the speed. Whitley seems to get the good accuracy in the mid 2700s out of his 26"ers so I'm going to shoot for that area despite getting around 100 fps more in my barrel.

Definitely looking forward to seeing your results!

Looking back at your post about buying that barrel from McGowen I ordered mine a week or so before. I think it is a bit difficult to figure out when the bullet is touching the lands with your method of seeing when it gets stuck. Using the Sinclair gauge or the Hornady LNL OAL Gauge is way more accurate.

Load testing with 105 RDF and RL15 were almost unbelievable, either I don't know how the shoot groups, my barrel is a tomato stake or my Vortex Viper scope is jacked up, maybe all the above.
27.8 RL15 3 shot Av 2663 Sd 5 Es 11 3 1/2" group with 2 1/2" vertical spread
28.0 RL15 3 shot Av 2688 sd 19 es 38 1/2" group, go figure. Pressure signs, ejector imprint right where QL says danger.
The work up loads were all over the place, nothing under 1 Moa. I went in .5 grain increments until I was close to max. All brass is Hornady match prepped, weight sorted ect. Rem 7 1/2 primers. I weighed all the brass after shooting this horror show, nothing changed and the primer pockets are still tight, I even cut a couple cases in half to see if there was any signs of case head separation or doughnut.

Conclusion is 105 RDF was used to break in the barrel, the rest of the box is not worth wasting time on, trash can. I have 4 boxes of 105 Hybrids that I know work in my other McGowen barrel and some 95 TMK's. The 95's I'm finding are the ticket for this case capacity and barrel length to get the speed needed to give this round an advantage at 600 yrds in competition.

[Sticks]

Looking back at your post about buying that barrel from McGowen I ordered mine a week or so before. I think it is a bit difficult to figure out when the bullet is touching the lands with your method of seeing when it gets stuck. Using the Sinclair gauge or the Hornady LNL OAL Gauge is way more accurate....

I found that LNL gauge to be inaccurate. The modified case is SAAMI spec case length of 1.510. My resized cases for the AR is 1.515, fired case length between 2 of my ARs is 1.518 to 1.525 (not exactly sure where the chamber measures out).

Anyhow - I was getting bad intel from the tool. I could not find the math to do the conversion from bolt face to lands, so I also use a sized case with a slightly crimped neck to chamber with a seated bullet and remove to get measurements. Rinse and repeat several times until I get 3 matching measurements and give myself .005 fluff room.

Hornady LNL curved tool and modified case for sale!

p.s - Send me your 105 RDFs if you are donating to the landfill. I may start chasing lighter faster for my shooting matches.

[soloelcap]

The very reason that I use the Sinclair gauge, you use a sized case and the bullet to measure and then make a dummy round with that case and bullet. The LNL looks to be a PIA due to having to get the modified case for every different round you need. The Sinclair tool works for everything even 17 cal.

pm me on where to send the bullets and you can pay me back for shipping.

[Crusty]

I don't understand how those Superlative gas blocks are any different than a leaky traditional gas block, which I have personally seen (more than once) turn a rifle group into a shotgun pattern. The high pressure gas that's exhausted from them could have been used to propel the bullet faster, or at least present a similar volume of gas at a similar pressure to each bullet in a group.

[Sticks]

The thought behind them was to be used with a suppressor and not have the gas in the face.

IIRC there was initial gas reduction - no bleed, then you get into the bleed off section.

[Tex Nomex]

I don't understand how those Superlative gas blocks are any different than a leaky traditional gas block, which I have personally seen (more than once) turn a rifle group into a shotgun pattern. The high pressure gas that's exhausted from them could have been used to propel the bullet faster, or at least present a similar volume of gas at a similar pressure to each bullet in a group.

The SA gas block can be used either way, as a traditional gas restriction/cut-off or as a pressure release to atmosphere.
The SA piston system is the same.

Here's Michael Bell's SA Gas Block Test Video It's small sample sizes, but it seems venting allows for more consistent bullet velocities overall and average velocities are the same as a non-suppressed rifle with the adjustable block dialed wide open/non-vented. BCG also runs cooler when vented.
YMMV

[soloelcap]

I"m over testing the 105 RDF's, for whatever reason they don't work in this barrel.

I have a clamp on gas block for this and most all my builds, I can get the same results of shutting gas down by clocking it slightly one way or the other and I use a bolt carrier weight to slow down (delay) the unlocking. You can delay the unlocking by moving the gas port forward rifle length +2", didn't you special order that on your barrel?

Leaky gas blocks, over or under gassed, ect are not going to make groups open up, gas makes the rifle function(cycle) properly, after so many rounds the leak seals itself with carbon.

I have 95 TMK's BN coated RL15 28.0-29.6 Hornady brass 7 1/2 primer for testing tomorrow. Let you know how they shoot.