Centerfire's G-ride

[centerfire]

My foray into Grendel, parts and notes as follows:

Mega Machine ambi receiver set
Proof Research 20" CF barrel
SLR 15" Ion UL HG
2A Ti gas block
LT MBT trigger
AA Bolt, Toolcraft carrier
BCM receiver extension
BCG Mod 3 grip
Carbine Buffer, 1 tungsten/2 steel weights, 3.8oz, (H1 weight)
Std carbine buffer spring
V7 Ti pins and lw fwd Asst
B5 SOPMOD stock (not pictured)
Geisele CH
Seekins ambi safety and oversized BHO
Bushnell 4.5-18x44 LRHSi
Badger Ordnance 20MOA, 1.4" mount
GA Recce 7 silencer (not pictured)

Build notes: The upper receiver was true and required no additional work; barrel has interference fit to receiver and set in loctite adhesive. Gas block was too close to HG so MLOK slot was relieved to eliminate contact. The gas block and HG contact caused initial accuracy issues which went away after material removal. The .850 GB and 1.30" ID HG are very close.
MBT trigger is heavier than I prefer, I like it's feel but I will probably change it out for an AR Gold trigger. It's a shame since the $99 MBT sale started this entire build.
Extractor gouged brass rims, I broke the corners but it still needs a bit more work. Ejector spring trimmed. The added Tungsten buffer weight is a little too much for initial load work up but probably perfect with the silencer. I am working on load dev and haven't shot it with the silencer yet. I didn't measure the gas port but it is perfect; brass piles up at 1 o'clock, -1' with H1 vs carbine buffers.





Initial Load Dev:
DA 3331, 55 deg, RH 35, 6mph
6.5gr Hornady Custom SST Factory
Avg 2458
ES 35.8
SD 13.85

DA 4030, 67deg, RH 21, 11mph
6.5gr Hornady Custom SST Factory
Avg 2464
ES 56.19
SD 22.44

123gr ELD-M 1.666" comp (touching inside mag)
H4895
27.4gr
Avg 2412
ES 33.56
SD 12.24

27.6
Avg 2430
ES 19.53
SD 8.48

27.8
Avg 2440 (3 shot group)
ERRor

28.0C
Avg 2465
ES 27.57
SD 10.67

IMR 8208XBR
27.4
Avg 2379
ES 20.09
SD 9.21

27.6
Avg 2407
ES 27.7
SD 10.44

27.8
Avg 2436
ES 32.20
SD 12.8

28.0
Avg 2444
ES 27.51
SD 11.53

Load dev notes: H4895 looks good on paper and has very consistent performance, however, it is bulky and I ran into pressure as soon as the charge became compressed. I want to love this powder but it is inappropriate for the 123gr ELD-M bullet. 8208 builds velocity even slower than H4895, both show pressure at 28.2 grains. The initial ladder for both had dented shoulders low in the work up. Accuracy for both powders was mediocre at best...moving on.

I did a single shot ladder of LeverEvolution from 29.2gr to 31.4C. The top of the ladder was 2574fps and just starting to show pressure (swipes). Half MOA nodes present. This powder is very fine and royal PITA in my throwers, I want to hate it but it looks like a performer.

[Sticks]

Go big or go home.

I'd put some witness marks (sharpie or something will rub off easy) on your handguard where you relieved for the GB to make sure you are not contacting during recoil, and preload with the bipod.

Nice write up.

Your starting to see pressure is actually you have had pressure for a while. With Grendel, normal pressure warnings mean it's too late, you passed the safe zone a while ago.

[centerfire]

I actually found the contact using a white paint pen. The GB cleared the rail but was closer than I thought it should be. It only made contact under recoil so I opened up the inside edge of the MLOK directly under the GB. Pic rails didn't fit under the GB anyway.

You're right about the pressure. I'm working up from known data and velocities and haven't found a good load yet. The chamber is a little short and I'm going to adjust the COAL to hopefully bring down pressure. Klem was right though, 8208 and H4895 are too fast for 123gr ELDm. LVR makes velocity well under the pressure signs. Also, I don't think this barrel likes to be pushed like that, the best accuracy was with lower pressure loads.

[NightFisher]

How long did it take them to ship your MBT Trigger at the "I got plenty of time" price? I ordered a couple a month ago and still haven't seen them....

[centerfire]

I bought the trigger a year ago, I think two weeks maybe? Certainly not months, I'd call them.

I think the MBT is a terrific $100 trigger, I have another in a SBR and it's phenomenal. I wouldn't put another one in a precision gun though.

[LRRPF52]

Is that last load set with 8208 30.0gr a typo?

27.8
Avg 2436
ES 32.20
SD 12.8

30.0
Avg 2444
ES 27.51
SD 11.53

[centerfire]

Yes, it should be 28.0. I edited the post, thanks for catching it.

[centerfire]

I haven't updated this thread in a while. I made some changes to the rifle worth noting.

First, I was getting some bolt over base failures with the suppressor. Between that and just feeling kind of harsh for an AR15, I went to a Sprinco Red buffer spring and that seems to have dramatically settled the action down. I previously tried an H2 but it still felt harsh. The rifle locks back on an empty magazine and cycles fine without the suppressor too.

Second, as much as I like the MBT trigger it just wasn't right for this gun. I switched to an AR Gold trigger like I have in other rifles. The MBT was just too heavy for me to be able to switch between platforms with lighter triggers.

Third, I went from a minimalist single port brake to a 6.5 specific two port brake. The two port brake I've had on a while, I'm not sure it was a worthwhile purchase but it is on there nonetheless.

[Sticks]

How's the accuracy?

[centerfire]

About an inch with ELDM using H4895 and 8208. Velocity has been poor with that combination and I'm just getting back around to working up 107 TMK with A2520. Initial ladder looks like sub 1" easily. I'll post targets when I'm done.

[muvef]

Very nice set up.