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+--- Thread: 18 vs 20" (/showthread.php?tid=7141)
18 vs 20" - cst - 01-23-2014
Can you guys post your average velocities for 18 and 20" barrels with 123 gr. Amax or 123 scenars?
I see such a wide range of velocities and barrel lengths its really throwing me off. I sometimes see 22"+ lengths have velocities you would expect from a 18 so I'm a little confused on whch length to get....I'll be shooting out to 800yards on a regular basis..occasionally 1000.(But i got a bolt gun for that!) thanks!
18 vs 20" - explorecaves - 01-23-2014
It is in Volume 2 of the grendel reloading book: IIRC (do not have it in front of me at the moment), ~8fps per inch difference between 18"-24" barrels, and ~23 fps per inch for 10.5" - 18" barrels... (20" barrel might be the transition point?)
18 vs 20" - Onewolf - 01-23-2014
My 20" LBC is around 2490 fps with Scenar 123, 31.8gr CFE223, CCI #450 primer. I shot it at 500/600/800/1000 yds on Monday. It was 11.1 mils of elevation at 1000 yds with a 20MOA mount zeroed at 100yds.
18 vs 20" - CPT.CRAZY - 01-23-2014
All barrels will produce different velocities with the same load. My 24" will get roughly the same velocity as my buddies 20".
18 vs 20" - bigbear_98 - 01-23-2014
My 20" krieger is ~2440 with factory hornady 123 sst.
18 vs 20" - bwaites - 01-23-2014
Don't forget that most chrony's have at least a 5% slop factor, so measuring velocities on different chrony's will lead to vastly different numbers!
18 vs 20" - JASmith - 01-23-2014
The chart at http://www.65grendel.com/forum/showthread.php?3007-Barrel-Length-and-Velocity tells us that, on average, the differences in chambers and bores will likely overwhelm the small average increase one gets by going from 18" to 20" barrels.
The difference in average velocity is about 2% which tells us that the point made by BWaites above needs to really be taken into account when making comparisons.
There is a lot more on this in both Volume 1 and Volume 2 of the 6.5 Grendel Reloading Handbook.
18 vs 20" - cst - 01-23-2014
I get the differences between 18 vs 20 is small....but I need more real world data on the muzzle velocities. I know there is a lot of variables that come into play when it comes to MV....buy I'm trying to figure out an average MV for barrel length..
..trying to justify if there is that much of an advantage going to 20 and give up some of the handiness of a 18.... as well as effwctiveness at 800-1000yards at the range.. in other words. .if its only gonna change 50fps over 2 inches why go with a 20"
18 vs 20" - JASmith - 01-23-2014
cst Wrote:I get the differences between 18 vs 20 is small....but I need more real world data on the muzzle velocities. I know there is a lot of variables that come into play when it comes to MV....buy I'm trying to figure out an average MV for barrel length..
..trying to justify if there is that much of an advantage going to 20 and give up some of the handiness of a 18.... as well as effwctiveness at 800-1000yards at the range.. in other words. .if its only gonna change 50fps over 2 inches why go with a 20"
And the Grendel Reloading handbook shows that that velocity makes diddly squat difference in the hunting arena.
Go with the barrel you feel most comfortable with!
18 vs 20" - Onewolf - 01-23-2014
cst Wrote:..trying to justify if there is that much of an advantage going to 20 and give up some of the handiness of a 18.... as well as effwctiveness at 800-1000yards at the range.. in other words. .if its only gonna change 50fps over 2 inches why go with a 20"
Because 50fps may be the difference between going transonic or not at the distances you plan to shoot?
18 vs 20" - JASmith - 01-23-2014
Onewolf Wrote:Because 50fps may be the difference between going transonic or not at the distances you plan to shoot?
Excellent point! We need to remember that very few hunters should contemplate shots at ranges greater than about 500 yards with any rifle or cartridge.
Long range competitive shooting is an entirely different matter. Range to transonic transition is one challenge. The other major challenge is wind drift. The competitive shooter needs as much velocity as he can get because a difference of 0.2" can make a point or two difference in one's score. One point can be a big deal in top-level competitions.
If one feels compelled to use the Grendel for serious long range competition, then a 26" or 28" barrel makes a lot more sense. We see a bit more than 150 ft/sec increase when going from 18" to 28" and this is important to the F-class shooter who can use a 22lb rifle and doesn't to go through a lot of movement. Even, then one needs to ask why use the Grendel at these ranges unless minimum recoil is important.
BTW -- I am very much interested in the "WHY" so please come forward with your thoughts, knowledge, and analyses!
18 vs 20" - LRRPF52 - 01-23-2014
There are 14.5" barrels that will average 2420fps with factory 123gr A-MAX, while my 16" averages 2470fps with the 123gr A-MAX last time I chrono'd it.
I'm getting amazing results with CFE under the 123gr A-MAX as well, by loading it out longer. I also recently realized that my Hornady dies came with a large .071" de-capping pin, so it is opening up my Lapua brass flash holes, which may be giving me a little more oomph, but I still get mid-high 2400's with different factory 123gr loads. Precision Firearms 123gr Scenars clocked 2450fps average for me, with 7fps ES, and are very accurate.
As a sanity check opportunity, I got challenged to making hits at 1200yds last summer by some guys that were out trying to hit at that distance and farther. When I dialed in the atmospheric conditions, my ballistic program told me 14.4 Mils elevation, and it was spot-on. My first round was just off the left edge of the target, and it looked like a hit to them. There just happened to be no wind at that time in the day, and I put the remaining 4 rounds on-target as fast as I could index the reticle and break the trigger.
I had just chrono'd that Hornady box ammo earlier that morning, so I took that series of events as an indication that the published BC is correct, my chrono is working and cranking out good numbers, and my velocity is what the chrono said it was, at least on that day, with that lot of 123gr A-MAX.
With these 2 new Grendel barrels I'm getting, one a 16" and one an 18", it wouldn't surprise me in the least if they were 100fps different than my current 16", which easily matches what 18" and a lot of 20" barrels do.
18 vs 20" - Nukes - 01-23-2014
Our 20" 1-8.5" Krieger sees a mean of 2593 fps (84° F) to 2644 fps (105° F) for AA factory load 123gn Scenars.
18 vs 20" - Onewolf - 01-24-2014
JASmith Wrote:Excellent point! We need to remember that very few hunters should contemplate shots at ranges greater than about 500 yards with any rifle or cartridge.
Long range competitive shooting is an entirely different matter. Range to transonic transition is one challenge. The other major challenge is wind drift. The competitive shooter needs as much velocity as he can get because a difference of 0.2" can make a point or two difference in one's score. One point can be a big deal in top-level competitions.
If one feels compelled to use the Grendel for serious long range competition, then a 26" or 28" barrel makes a lot more sense. We see a bit more than 150 ft/sec increase when going from 18" to 28" and this is important to the F-class shooter who can use a 22lb rifle and doesn't to go through a lot of movement. Even, then one needs to ask why use the Grendel at these ranges unless minimum recoil is important.
BTW -- I am very much interested in the "WHY" so please come forward with your thoughts, knowledge, and analyses!
My rationale for a Grendel with a 20" barrel is because the rifle is intended to shoot in our local long range field/tactical matches. About 50% of the shots are prone but the rest are not (sitting, kneeling, standing, behind obstructions, etc). Less than 10% of the shots in our matches are longer than 800yds so I was looking for a rifle that would be capable of shooting prone, but also good for non prone/unsupported positions and very capable of 800yd shots but able to stretch to 1000 yds. In the short time I've had my Grendel it appears that I made a great choice. 6 months ago there was one Grendel being shot in our LR club and now there are four.
18 vs 20" - LRRPF52 - 01-24-2014
Traditional long-barreled rifles suck for shooting positions with. You start figure 8-ing and your hit probability deteriorates with every moment once you set up the position. In that sense, a shorter AR15 with a medium profile barrel with a good quick-adjust sling will allow higher hit probability, especially with higher BC pills that buck the wind well.
This is one of the reasons why I like very lightweight handguards, such as carbon fiber or lightened aluminum units, with a stout medium contour barrel of high quality steel that doesn't walk or open up.
If you step outside of your comfort zone and work with the kneeling, or a hybrid kneeling/seated position with sling, you sill step into a different world, but you do have to be flexible, which I am not, so it takes an exceptional amount of physical training and stretching to get solid with some of the positions I have been working with lately. We need a whole new discipline of shooter's stretching and martial arts.
I'm not interested in shooting jackets and leather slings, but finding ways to achieve what a shooting jacket and sling do using practical tools and techniques that can be gotten into and out of quickly.
18 vs 20" - Kikn - 01-24-2014
I ran some factory 123sst through my 16" barrel last weekend on a 60°+ day and it was between 2468 and 2475. Tested with a chrony F1 @ about 10-15 feet or so from device
18 vs 20" - LRRPF52 - 01-24-2014
Kikn Wrote:I ran some factory 123sst through my 16" barrel last weekend on a 60°+ day and it was between 2468 and 2475. Tested with a chrony F1 @ about 10-15 feet or so from device
That's exactly where mine is, last reading taken at 80 F this summer. For my altitude, it retains energy much farther than I would have thought. It was supersonic out to 1318yds at 4400ft elevation.
18 vs 20" - ejkoechling - 01-24-2014
AA
18 vs 20" - bigbear_98 - 01-24-2014
LRRPF52 Wrote:As a sanity check opportunity, I got challenged to making hits at 1200yds last summer by some guys that were out trying to hit at that distance and farther. When I dialed in the atmospheric conditions, my ballistic program told me 14.4 Mils elevation, and it was spot-on. My first round was just off the left edge of the target, and it looked like a hit to them. There just happened to be no wind at that time in the day, and I put the remaining 4 rounds on-target as fast as I could index the reticle and break the trigger.
I set my chrono up last friday at 200 yards. It read 2160av. Then I was able to verify at 750. -24.75 on the chart, -25.75 actual. I trued the ballistic calculator and got hits on an 8" plate at 750 and 4" at 500.
ETA: I was at 935 elevation.
18 vs 20" - LRRPF52 - 01-24-2014
bigbear_98 Wrote:I set my chrono up last friday at 200 yards. It read 2160av. Then I was able to verify at 750. -24.75 on the chart, -25.75 actual. I trued the ballistic calculator and got hits on an 8" plate at 750 and 4" at 500.
ETA: I was at 935 elevation.
What barrel length and load were you shooting? Very nice. I just ran some basic numbers through Berger's program, and came up with almost duplicate of your 200yd and 750yd numbers. I put in the 123gr A-MAX at 2500fps, sea level, 59F, 100yd zero, 2.5" optic height.
200yds was 2167fps
750yds was -25.00 MOA
I was trying to figure out your mv and bullet based on what you posted. After adjusting based on your altitude, I put in 28.9" of mercury on the barometric pressure, and started tweaking it until I got 2490fps mv, 2169fps at 200yds, -24.77 MOA at 750yds.
What BC does your program kick out for you with the truing feature?