Help me with this. Is a rifle length gas system marginal on an 18" Grendel? I am under the impression that both work reliably with normal Grendel ammo, so please let me know if you have reason to believe that's not the case. No judgment from me if you simply prefer the shorter gas system so you don't have to think about it (I have a carbine-length system on my 16" 5.56 for exactly that reason), I'm just curious.
6.5 Grendel Barrel
- Thread starter Okie_Poke
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Help me with this. Is a rifle length gas system marginal on an 18" Grendel? I am under the impression that both work reliably with normal Grendel ammo, so please let me know if you have reason to believe that's not the case. No judgment from me if you simply prefer the shorter gas system so you don't have to think about it (I have a carbine-length system on my 16" 5.56 for exactly that reason), I'm just curious.
js8588
Member
Rifle length on an 18 Grendel is probably fine. Intermediate or midlength just makes me happier. Little more dwell time. I'm someone who refuses to mess with adjustable gas blocks/gas keys/triggers because I'm concerned about introducing another possible failure point. A little overgassed but also more reliable? Yeah, that's for me. LRRPF52 over on the Grendel Forum & Snipers Hide thinks highly of Rifle length gas on an 18 inch 6.5 Grendel and the guy knows more than I ever will.
Thanks. This makes sense and I totally get the sentiment.
Varminterror
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No, rifle length gas in an 18” can run fine. But… in an AR, we’re balancing gas and mass, and with a short dwell time of a nominal 12” gas system and 18” barrel, shorter than that of a 9” gas system, meaning much less dwell time and much lower operating pressure, we don’t have as much latitude.
But I recognize my personal sentiment is a bit dated - I’ve always preferred to have an over-gassed system, then throttle gas by an adjustable gas block until I get the impulse I want for recoil, based on the operating mass I design to get it. But modern era popular sentiment is longer gas, longer recoil systems, and trending towards heavier reciprocating mass. I like high mass for a pleasure rifle, but I also recognize that we can make a LOT of different combinations work without issues.
Some AR designs operate on a wide operating band, like a 6 lane highway. Some are more like a sidewalk. Rifle gas system on an 18” Grendel barrel is more like a two lane road with a wide shoulder and a center turning lane. Not as generous and forgiving as it could be, but not razor thin either.
Personally I think you will get better performance on GAME with a 6.8 SPC barrel and my second choice would be 5.56 with plain old 55 gr SP, keeping range in mind. This has been my experience as well as the experience of many others.
The larger 6.8 diameter increases terminal performance, this being the correct observation of the original military evaluation during SPC development when tested vs. 6.5 diameter bullets on actual flesh and bone. Source: American Rifleman, Remington's 6.8X43 History And Development, Dec. 2021 : https://www.americanrifleman.org/content/remington-s-6-8x43-mm-spc-history-performance/
"Many 6 mm, 6.5 mm, 6.8 mm, 7 mm, and 7.62 mm cartridges were considered and tested, but it was ultimately decided that the 6.8x43 mm Special Purpose Cartridge (SPC), with a 115-gr. bullet moving at 2600 f.p.s. from the muzzle offered the best combination of accuracy, lethality and reliability."
6.8 SPC is also likely to have a slight energy advantage at ranges where almost all game is shot with these rifles, due to higher muzzle velocities acheived bullet weight-for bullet weight. Hodgdon shows 2608 for Grrendel vs. 2711 for the 6.8 SPC for 110 gr. loads for example.
6.5 is a better target round, being higher in BC though slightly slower. Its larger head means less metal on the bolt and weaker bolts.
Published in Shotgun News, July 31, 2006:
"Its head and body diameters are larger than 5.56 (0.378 inch), but smaller than 7.62x39mm (0.445 inch). This thoroughly obsolete cartridge was chosen as the parent case because its smaller head diameter (0.422 inch) required less metal to be cut from the bolt head compared to the PPC or 7.62x39mm cases, which improves bolt service life."
6.8 SPC feeds and functions very slick through an AR. I dont know if anyone has ever done a military style evaluation of mean rounds between stoppages, but if they did 6.8 SPC would win every time.
SO for hunting, and reliability 6.8 SPC is slightly ahead, for paper punching 6.5 G gets the nod here.
The larger 6.8 diameter increases terminal performance, this being the correct observation of the original military evaluation during SPC development when tested vs. 6.5 diameter bullets on actual flesh and bone. Source: American Rifleman, Remington's 6.8X43 History And Development, Dec. 2021 : https://www.americanrifleman.org/content/remington-s-6-8x43-mm-spc-history-performance/
"Many 6 mm, 6.5 mm, 6.8 mm, 7 mm, and 7.62 mm cartridges were considered and tested, but it was ultimately decided that the 6.8x43 mm Special Purpose Cartridge (SPC), with a 115-gr. bullet moving at 2600 f.p.s. from the muzzle offered the best combination of accuracy, lethality and reliability."
6.8 SPC is also likely to have a slight energy advantage at ranges where almost all game is shot with these rifles, due to higher muzzle velocities acheived bullet weight-for bullet weight. Hodgdon shows 2608 for Grrendel vs. 2711 for the 6.8 SPC for 110 gr. loads for example.
6.5 is a better target round, being higher in BC though slightly slower. Its larger head means less metal on the bolt and weaker bolts.
Published in Shotgun News, July 31, 2006:
"Its head and body diameters are larger than 5.56 (0.378 inch), but smaller than 7.62x39mm (0.445 inch). This thoroughly obsolete cartridge was chosen as the parent case because its smaller head diameter (0.422 inch) required less metal to be cut from the bolt head compared to the PPC or 7.62x39mm cases, which improves bolt service life."
6.8 SPC feeds and functions very slick through an AR. I dont know if anyone has ever done a military style evaluation of mean rounds between stoppages, but if they did 6.8 SPC would win every time.
SO for hunting, and reliability 6.8 SPC is slightly ahead, for paper punching 6.5 G gets the nod here.
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Varminterror
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I’ve been killing game with both of these since they first hit the streets, back when we had to order custom reamers and have barrels made for the SPC, and could only get Grendel barrels and dies through Bill. Anyone talking about a difference on game between Grendel and SPC has bought a lot of online BS, hook, line, and sinker. Same deal bringing up the “thinner bolt head issue,” we’ve been doing this for 20yrs, the “fragile Grendel bolt issue” only exists on the Internet.
@rizbunk77: I agonized over 6.8 vs 6.5 about 8ish years ago when I first built this rifle. I picked 6.5 then and see no need to revisit the topic. I’m firmly in the “no game animal can tell the difference” camp, and I have dies, components, magazines, and bolts for the grendel. I appreciate your input, but as I stated in my OP I’m only looking to upgrade a barrel here, not switch chambering.
FWIW, the only time I’ve had trouble with Grendel feeding is when I learned the hard way that different bullet profiles have to be seated to different lengths, even in an AR. In a Grendel AR you can’t just seat the bullets under magazine length and assume you’re off the lands. 120 sierra pro hunters, for example, need to be seated quite a bit deeper, at least in my current barrel. That experience about 8 years ago is why I now have a Hornady/Stoney point overall length gauge.
FWIW, the only time I’ve had trouble with Grendel feeding is when I learned the hard way that different bullet profiles have to be seated to different lengths, even in an AR. In a Grendel AR you can’t just seat the bullets under magazine length and assume you’re off the lands. 120 sierra pro hunters, for example, need to be seated quite a bit deeper, at least in my current barrel. That experience about 8 years ago is why I now have a Hornady/Stoney point overall length gauge.
That sounds great.
