Let me get the particulars out of the way first.
Rifle I'm working with is a 10 FCP HS in .308 flavor, with EGW rail and a Nikon m-308 scope. So far this set up is far more accurate than I could claim by my skill. To date, it has shot FGMM 168's @ 100 yards in groups that can be covered by a dime. Had one group @ 200 yards I could cover with a quarter. Great Rifle and set up. (All powder is measured and weighed not just dropped and all cases are the same and trimmed to same length. So processing is identical in my home rolled)
Now for rolling my own. I have been reloading for target and hunting since the mid 80's and enjoy the process. This rifle and my desire to work it and my skill set has me going to the next level. I've already determined it's head space and distance to lands via RCBS precision mic, which I also worked up great loads for my .308 Edge (yes it's the early one and the box says Edge - lol) I have been having great luck with IMR's 4064 (old stand by) and have had great luck with their 8208 XBR. Worked up loads to find this (10 FCP) rifles likes and am working on seating depth. I used the FGMM as a benchmark, but as we all know, the recipe is top secret (lol). I found the FGMM 168's to be .005 off lands, so I started there expecting to find this to maybe .010 to be the sweet spot. Well, wouldn't you know it, this thing likes .015 to .020 jump. I know every rifle like every woman is unique, but with the same bullet weight (SMK or Nosler Custom Comp) and seating depth and approx. the same FPS as the FGMM, I was expecting a little closer. The .005 and .010 loads were still 1 moa or less, but the .015 and .020 were dime size or less.
The other thing I found was my dope for the FGMM was nuts on but the home rolled were all consistently slightly high and left regardless of jump. However, the .020 and .025 versions were getting closer in to the POA-POI like the FGMM. This got me to thinking (dangerous lol) and wondering if I wasn't pushing the home rolled a little faster or was it just the harmonics of the time. All of my home rolled were predictable high left weather .005 or .025 jump, just a little closer with the longer jump.
I really need to get a chrono, but this is fun and keeps me out of trouble.....lol. Oh, and i have no signs of over pressure or other issues some get with working up loads. (I think mostly due to careful work ups and getting head space dialed)
What I'd really like to do is dial up a load that is as consistent as the FGMM. I know a chrono would help, but am wondering if this high, left dime size groupings (.010 and .015) I'm getting could be reduced a bit (thinking I'm pushing a bit fast) and to that idea, the reason the .020 and .025 jump is coming back to POA-POI closer due to maybe slight drop is pressure with more jump, slower FPS.
Sorry for the long post, but this is just getting fun. Luckily, I have sufficient components to keep testing and having fun.
Any help or guidance from you all that have been into this precision game is appreciated.
sounds to me like your doing well without any advise or opinions from others.
im not sure how much improvment you can or even should expect.
i have a question. does a few 10ths or even a half grain of powder impact where your
shots land on the target at 100 yds? in other words would say 40 gr. 40.1 40.2 40.3 etc.
make for a larger group?
yobuck,
I did my powder load work up first before seating depth. And yes there was slight changes. I have found the 8208 to be stable, not temp sensitive and very forgiving. But as for this rifle/load/weight, 41.0 to 41.6 in .2gr increases was it's happy place. Not being smart enough to dope this on my optics and leave well enough alone, I doped for the FGMM 168's as a known performer, then started to work these seating depths. Never was that smart....lol, just ask the wife after 30+ years. LOL Funny thing is if I left the dope as is, I could compensate my POA hold and not have a problem due to the high/left POI being very consistent. Just thought it was funny how the .020 and .025 jumps brought the POI back in about 1/2 closer than the .005 to .015 flavors even though the spread was larger.
I may not know every rifle, but will dang sure know mine and its likes. Someone said to me that this sounds like a lot of work.....work?, you mean going to the range and shooting, reloading, enjoying the outdoors.....sign me up and put me in for over time!!! LOL
Sounds to me like all you need to do is adjust your scope so that your poa is the poi. Why make things more complicated than they need to be by holding over for a factory load zero that you will probly never shoot again because you have such a great load developed with your hand loads. Why shoot factory stuff when you can reload with better accuracy and less cost?
stomp442,
thanks and that's probably what I'll do. My wife says I think like and engineer with the brains of a 12 year old.....LMAO. But, hey at my age it's fun to "play". Funny when what you expect to happen thru known data gets thrown out the window....lol. I was expecting to see tight groups near max powder and short jumps. Guess this tight chambered girl wants it a bit easier and bit more foreplay...so to speak. Can't wait to load up some 175's and stretch its legs a bit.
What you are seeing is the effect of COAL on the OBT (Optimum Barrel Time). Your bullet is leaving on varying stages of the barrel 'whip'.
Look it up on Google for some very interesting reading.
Your wife is going to want to kill me for pointing you down that path. :)
I've done quite a bit of load testing with the .308, and I found the same thing as you. FGMM 168's will bug hole for me and they are only about a couple thou. off the lands, however in my own load testing using the 168 sierras, I found the tightest groups at about .020 off the lands. Not only that but the poi was a little different than the FGMM. I even used a chrono to get the speed matched, but that didn't help. I chalked it up to different powder's will create different explosion's in the barrel thus changing the way the barrel reacts.
The only rifle I have that keeps the same basic point of impact with different ammo, but very close in speeds is the .22lr. Faster rounds will impact higher than the slower rounds.
When ever I know that I'm changing ammo or any variable to my home rolled, I always have to re zero my scope, it might not make much difference if your shooting a deer at 100 yards but, it will screw things up big time when your shooting at a woodchuck at 500 yards LOL.
Last edited by DanSavage; 05-29-2013 at 04:47 PM.
DanS,
Thanks for your post also. Those FGMM are some black art for sure. This rifle and those rounds are scary accurate. But like you, I can roll my own and dope to those. I've actually had real good luck with the two work ups with the 8208 & 4064. The nice thing about the 8208 is great metering and have a good load for the .223 also. It burns clean and haven't had any issues. Will have to work up some 175's for reaching out a bit further......this rifle is definitely capable.
Kelbro, no worries, she's been with me for enough years to know I can read/devour tech stuff like eating a bag of chips, but give me a novel and turn out the lights, I'm asleep. LOL I have seen this and the high speed footage of the harmonic vibration. It's all about the nodes eh? We had the same thing with vibration on turbine blades in jet engines. Of course those tend to get real critical real quick!
Well, I'll dope to my loads that this rifle likes and work on my skills....practice, practice, practice! Heck, even have her working on her breathing and trigger control with her new rifle. She's a "nut" too! I could have done so much worse......She's a keeper and my best friend!
K. The more jump the bullet has the faster it’s travelling when it engages the rifling which will make the barrel oscillations different than if the bullet is almost kissed(5 thou off the lands). So yeah,bullet jump will affect velocity and the node.
Now you don’t need a chrono to press up a decent load however to get real precision you will need one. Especially at ranges beyond 600 meters. But for now I would tune the load you’ve got. Increase powder charge by 0.2 grains from what you’ve got now and shoot 5-7 shot groups at each subsequent powder charge increase.
Gives you the opportunity to establish your actual max charge too,rather than depend on some arbitrary number in the load books. I suggest a 20-30 thou jump and whatever node is near 2800ft/s velocity.
Just my opinion
If it's shooting as good as it sounds, Shoot it!
What a chrono will tell you:
#1 Velocity
#2 Consistency via SD/ES: I use this to tune my loads in for consistency from 100-1200yds for the type of competition i do, but wouldn't change it if i was trying to simply hit targets (regardless of type) across those ranges.
What groups tell you:
3 shots nice and tight: Rifle is tight
5 or more shots nice and tight: Rifle and Shooter is tight
If you can get 10rds in less than an MOA at any distance the rifle is extremely consistent. If you are looking for Bench Rest type groups the system probably isn't consistent enough to do it every time, but you can get lucky now and again.
I've read your post a couple of times and was trying to match your experience with FGMM 168 factory ammo with mine.
You obviously have measured your chamber to conclude where the jump for FGMM is.
All of the 168 FGMM SMK ammo that I have measured have an O.A.L. about 0.005 shorter than SAAMI - around 2.795 O.A.L.
I presume Federal does that so bolts will close in chambers that are precisely cut to SAAMI recommended O.A.L.
If your .308 is reading 0.005 off the rifling with FGMM ammo, your chamber should be right at SAAMI, so seating the same bullet back 0.015 off the rifling would get you an O.A.L. of 2.785.
I have only had one Savage barrel - a .308 rebarreled by the factory - that came with a chamber shorter than SAAMI by 0.006. The bolt would not close on FGMM 168s consistently without seating them back another 0.005. That lasted about 200 rounds before the bore eroded a bit.
Most of my Savage barrels have come from the factory with chambers at least 0.020 longer than SAAMI for their calibers.
Most of my Savages like to be at least 0.015 to 0.020 off the rifling. Some like being further off than that.
If you are loading with a O.A.L. shorter than SAAMI with 168 SMKs and hence shorter than FGMM, then I can't imagine why the fps from your reloads are consistently lower than FGMM ammo @ 2650 fps with a 24-inch barrel, especially since you are using IMR4064.
If your barrel is shorter than 24-in, the velocity of both the FGMM and your hand loads will be slower but relatively by the same degree.
FGMM has used IMR4064 powder for years - after they changed from RL-15 maybe 10 years ago.
I heard recently that they changed powders again but I haven't been able to validate that claim. If so, the powder they now use might be different and therefore your results might also be.
Seating the bullet deeper in the case increases the pressure and adds muzzle velocity - 0.010 deeper would increase mv by about 4-5 fps depending on the powder.
Seating the bullet out further decreases the pressure and drops the muzzle velocity - seating 0.010 further out would decrease mv by about 4-5 fps depending on the powder.
All that being said, if you are getting the accuracy you describe, don't sweat it.
You understand your rifle and use that understanding to tailor your loads to improve the accuracy.
If it means adding a few tenths of a grain to get a better result, do it unless you are seeing pressure signs.
However, I have never found the best accuracy at factory ammo velocities.
Velocity sells factory ammo, not accuracy although I think FGMM is the gold standard for .308 factory ammo.
All my .308s shoot much more accurately with the same bullets as factory ammos with my reloads than with factory ammo.
My best loads are all lower than factory claimed velocity by about 50 to 100 fps depending upon the rifle.
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