Considering a 13.9” upper to go with my 18” 6.5 Grendel.. thoughts?

[thedude824]

I recently built an 18” 6.5 Grendel with a NightForce NX8 2.5-20x

I went with the superlative arms piston system, but the BCG is tight in the upper so I may swap it over to DI with a superlative arms adjustable gas black and JP FMOS.
After researching the round more it really seems to be great at everything. So I’m thinking it may be cool to build a 13.9” SBR upper to have superior capabilities compared to my 300blk out and 14.5” AR and far less blast and recoil than my 13” SCAR 17. If I do that it makes total sense to swap the superlative piston to the SBR and I would use a VLTOR MUR upper since the BCG fits perfectly in that upper (my 14.5” AR setup). What I’m really wanting input on is… optic arrangement. While I’d have the 18” upper for long range, the 13.9” should be very capable out to distance. So I was thinking of trying the Steiner T6XI 2.5-15x with an RMR mounted on top. I’ve never used a top mounted or offset RMR, but I’m sure I can train to become accustomed to it. I thought this set up would make more sense than another LPVO. I’ve got a Trijicon Credo 1-6x on my 14.5” AR and a Trijicon Credo HX 1-8x on my SBR SCAR 17. Thoughts?
Use would be run and gun and up to whatever distance the rifle is capable. I’m thinking of trying the Lehigh 110 grain copper solids and the 110 grain controlled chaos.

 

[TonyTheTiger]

Sounds like a lot of overlap with the 18". Like, so much overlap that it'll do 95% of the same thing and you'll end up just shooting one of them.

 

[thedude824]

Sounds like a lot of overlap with the 18". Like, so much overlap that it'll do 95% of the same thing and you'll end up just shooting one of them.

I thought that might be the case. I guess that’s the risk when using a do it all cartridge. Reading last night I think I saw mention of roughly 20 fps per inch? Is that right? Makes the added length of the 18” kind of pointless I guess.

 

[TonyTheTiger]

I don't have my data in front of me, and most of it is for 5.56, but 20-30fps per inch is a close enough average for barrels between 14" and 24" if memory serves. There are exceptions to every rule of course, and things get a bit more dramatic once you get really short.

 

[thedude824]

I’m going to shoot this set up a little more Tuesday hopefully. If the BCG is totally smooth afterward I’ll just wait on the Craddock 13.9” Pangris to come back in stock and pick up a CMT UHPR 12.5” rail.
If there’s still binding I’ll pick up a Vltor MUR to mount the 13.9” barrel and CMT UHPR rail. I’ll swap the superlative arms system to this upper since I know the BCG functions as intended in the MUR upper.
I’ll use a superlative arms adjustable gas block and a new bolt carrier with the Rexus bolt with the 18” upper. I was originally set on the JP FMOS, but might consider the chrome microbest. I guess we will see. It’s unfortunate I didn’t see how effective the 6.5 Grendel could be from shorter barrels. Oh well
Any thoughts or suggestions?
I was also thinking of keeping the NX8 2.5-20x on the 13.9” upper and perhaps an offset RMR? The scope knobs and objective lense are too tall for an RMR mounted on the top of the scope ring mount.

 

[Jsp556]

Sounds like a lot of overlap with the 18". Like, so much overlap that it'll do 95% of the same thing and you'll end up just shooting one of them.

But a lot of us do it anyway. 16” 556 & 223 wylde, 16 & 18” 6.5 Grendel, & 16” 308’s seem to keep filling up my safes. I have a lot of others but for some reason those keep piling up.

 

[TonyTheTiger]

But a lot of us do it anyway. 16” 556 & 223 wylde, 16 & 18” 6.5 Grendel, & 16” 308’s seem to keep filling up my safes. I have a lot of others but for some reason those keep piling up.

For sure, I've done it too many times. Enough that I have great difficulty coming up with a reason to assemble another rifle these days. When I do think I need to clone something I already have, I make sure they have way different optics so I can at least pretend that the intended use case makes it different from the last rifle.

 

[hlee]

I thought that might be the case. I guess that’s the risk when using a do it all cartridge. Reading last night I think I saw mention of roughly 20 fps per inch? Is that right? Makes the added length of the 18” kind of pointless I guess.

20-25 fps per inch with the 6.5 Grendel has been my experience when going from a 22” to an 18” and then to a 12”…. And, my 12” gets pretty much all of the shooting time, even though the 22” is objectively more precise. The 12” is “good enough” with a lot more up side…

But, the 22” almost shoots itself. It’s a shame how much it sits in the safe.

 

[Bluedog82]

20-25 fps per inch with the 6.5 Grendel has been my experience when going from a 22” to an 18” and then to a 12”…. And, my 12” gets pretty much all of the shooting time, even though the 22” is objectively more precise. The 12” is “good enough” with a lot more up side…

But, the 22” almost shoots itself. It’s a shame how much it sits in the safe.

Once you realize what you can “get away with” length wise, and still make hits at extended range, it’s hard to put the cat back in the bag. Regardless of what caliber.

 

[TonyTheTiger]

Bringing this one back up. Had my 12.8" Grendel and my brother's 18" JP Grendel out to 770yds last Saturday. And my 6mm for what its worth. Pretty interesting comparison, both guns using ammo I loaded with 123ELD's, the hit percentage was almost identical. I was at 10.2 and 2 mils for elevation and wind respectively, 18" was 25moa elevation, whatever that means.
My target stand had sunk into the mud a bit in the spring thaw so the target was neither swinging nor singing, so no advantage in target reaction from either gun.
The 18" was so much nicer to shoot it wasn't even funny, even though gun weights are very close. Both have brakes, but the RLGS vs. MLGS, having the blast 5" further away, and having a real stock on the 18" helped a ton.
I don't remember load data, but when he shot his ammo in my gun it went from 10.2 to 9.6 mils of elevation, so either I loaded his ammo way hotter than mine, the POI differed between loads or his personal POI was different than mine. But his loads definitely recoiled a bit harder. I remember backing my loads away from max because of brass wear and tear and the fairly unpleasant recoil.

All in all, the short guns absolutely perform, and they are neat, but if I could only have one and wanted it to be as versatile and enjoyable as possible I wouldn't do a shorty. I'd probably split the difference and go 16" RLGS and make both the other lengths obsolete.

 

[LRRPF52]

Yup. I don’t notice much difference in hit probability between 12” and 18”, and I’ve had a lot of 18” Grendels, still do.

I pretty much always take the 12” #1, 17.6” #2, and 18” LaRue #3 for intermediate/LR work. If I could only grab one, it would be the 12” due to portability and suppressed.

If it was only carrying the rifle from the vehicle to the bench, then it would be the 24” Grendel or 22” .260 Rem. I haven’t taken the 24” Grendel out since 2015 I think. Just took the .260 Rem Bartlein barrel/GAP-build out last time with my youngest son, since he’s been asking about it. Time of Flight to 780yds is insta-connect with the .260 Rem and 130gr ELD-M Match ammo. Also weighs 14lbs.

My original 16” AA Grendel barrel averaged higher speeds than any of the 18” Grendels I’ve had. Just depends on rifling and other factors. Differences are meaningless, just interesting to note.

The LaRue 18” with that Tranquilo brake is the smoothest to shoot, very easy self-spot, brake not obnoxious.

20” is fun too.

Shooting 100gr ELD-VT from the 12” is really pleasant. Suppressor is noticeably quieter as well, vs 123gr. Cough vs bark. 90gr TNT is really nice handling from the 12” as well. I tame the 12” gas system with a Bootleg carrier, set to fully-suppressed position.

 

[912173]

I've noticed with shorter barrels, it's not so much a difference in overall hit probability, but the wheels seem to just fall off sooner. I mostly notice it near the max effective range.

 

[Bluedog82]

I've noticed with shorter barrels, it's not so much a difference in overall hit probability, but the wheels seem to just fall off sooner. I mostly notice it near the max effective range.

Which makes perfect sense, given the drop in velocity.

 

[Bakwa]

12.5" Grendel is the sweet spot.

I almost got rid of my LMT MWS because of my 12.5 G, but instead I'm going to build out a MRGG-A with it just to make sure their isn't a place for it in my stable.

I really want to build a 10" Grendel as a truck gun "pistol" too, but want to ensure reliability so I' slow rolling that.
With the introduction of 338ARC, I might just wait on those to catch on and build out a Mixtape/ICAR instead, but I digress...
Build more short Grendels!

 

[LRRPF52]

I've noticed with shorter barrels, it's not so much a difference in overall hit probability, but the wheels seem to just fall off sooner. I mostly notice it near the max effective range.

I think the twist rate is more of a factor here than the barrel length.

Spin Grendel with 1/7" or 1/7.5" and it stays stable surprisingly-well at distance. I first noticed that with the 16” AA MLGS 1/7.5 twist barrel shooting 123gr A-MAX out to 1200yds in 2012-ish. I had handicapped it to only 600yds at the time, until some weird guys challenged me to shoot out to 1200yds out near Stansbury on the SW end of the Salt Lake.

I suspect most of the shorter Grendel barrels out there today have 1/8" twist.

 

[thedude824]

I think I’m going to put the 13.9” on hold and get into night vision. It really seems like a 13.9” would essentially make my 14.5” 556 and 13” SCAR 17 completely unnecessary. Better in nearly every respect compared to 556 with similar recoil. Less recoil, less concussion/blast especially suppressed, more effective range, flatter trajectory, faster follow up… the only thing the other 2 have is cheaper bulk ammo, but I load all of mine anyway so that’s essentially moot.
At least a PVS27 will require the longer rail on the 18” gun lol.
I tend to need justification for my systems to keep the spending under control and I really don’t want to part with any of my rifles.
If I WERE to go with the 13.9” I was thinking of trying the Steiner T6XI 2.5-15 or the 3-18 in an ADM Delta mount with the diving board to mount a Trijicon RMR on top?? Or what would you guys do for a “do it all” rifle? I’m a pretty muscular guy so weight isn’t a huge issue.

 

[Bluedog82]

I think I’m going to put the 13.9” on hold and get into night vision. It really seems like a 13.9” would essentially make my 14.5” 556 and 13” SCAR 17 completely unnecessary. Better in nearly every respect compared to 556 with similar recoil. Less recoil, less concussion/blast especially suppressed, more effective range, flatter trajectory, faster follow up… the only thing the other 2 have is cheaper bulk ammo, but I load all of mine anyway so that’s essentially moot.
At least a PVS27 will require the longer rail on the 18” gun lol.
I tend to need justification for my systems to keep the spending under control and I really don’t want to part with any of my rifles.
If I WERE to go with the 13.9” I was thinking of trying the Steiner T6XI 2.5-15 or the 3-18 in an ADM Delta mount with the diving board to mount a Trijicon RMR on top?? Or what would you guys do for a “do it all” rifle? I’m a pretty muscular guy so weight isn’t a huge issue.

Be advised that 13.9s only “make sense” with certain suppressors and mounts, like Dead Air. For instance, my Griffin muzzle devices on my 13.9 and 14.5 put the can at almost exactly the same OAL.

 

[Gtscotty]

I'd second the 12"-12.5" recommendation, that's a nice spot for suppressed ARCs and Grendel's, and provides just enough difference from an 18" that most of us can, with minimal mental acrobatics, rationalize "needing" both.