.308 load test

[Nature Boy]

I had a great .5 MOA load that used federal 210M primers but since I can't find them I'm trying to find an equivalent with a CCI BR primer. I also broke out some new, never fired, LC 15 brass, which I ran through the sizer. I decided to use 10 round groups and shot them round robin style. Interested to hear what the results say to you guys.

I decided to stay in the range of the previous load and work off of that in 0.3g increments, up and down.

I used:
168 AMAX
H4895
OAL 2.895-to the lands
5 groups, 38.7 - 39.9



I note that some of the groups had what looks like smaller groups within, which made me think I had some parallax that I hadn't fully dialed out, but I kept checking and pretty sure that wasn't the case. Group A has a pronounced vertical stringing that the other groups didn't.

Again. Curious what it says to the experts here. 50 rounds for load development can get expensive, but it was interesting and if I can learn something then it's worth it.

 

[macgrumpy]

Actually group A is probably the best group based on the OCW process but I'd recommend pushing your powder charge up to 41 grains plus or minus a couple of .3 grain intervals (40.4, 40.7, 41.0, 41.3, 41.6).

I ran your entire target through a target analysis program that I have and the smallest vertical spread is group D. Group A has a vertical spread that is right in the middle of all the groups. Also, group 'A's center is approx. .001" above the center of entire 50 shot group so technically 'A' is the group that is closest to the center of the entire series of shots.

 

[Nature Boy]

Thank you for doing that macgrumpy. I'm loading some more this morning. I'll make some more of group A and extend the test toward the higher loads

 

[Bart B.]

How many times did your earlier group shoot .5 MOA.

In my opinion, they're all equal. Knowing the most accurate benchrest rifles have almost a 4X spread in 5-shot group sizes at 100 yards, a single 5-shot group with a given load is not very meaningful for the load's accuracy.

On the other hand, when all groups are close to the same size (as those 5 are) within about 10% in extreme spread across a couple grains of powder, your rifle is probably much more accurate than the group show. Your own marksmanship skills may be making them the sizes they are. All loads may well be near equally accurate. I've not seen any significant change in 100 yard accuracy testing .308 Win loads across a 2 grain spread in charge weight across several barrels.

I cannot shoot very accurate with a rifle held against my shoulder as it rests on bags atop a bench I'm sitting at. A Nat'l Champion suggested I test ammo slung up in prone with a bag under the stock fore end and heel. Testing that way, my groups were half to a quarter the size of those shot with a hand held rifle atop a bench.

Most folks have a more repeatable shooting position in prone as I mentioned above. Benchresters know their rifles shoot most accurate in free recoil untouched by them except for a finger on the 2-ounce trigger. If they shoulder them, they shoot much larger groups.

 

[Nature Boy]

I wouldn't argue that fact Bart. The biggest variable is me for sure. I think what I'm learning the most with this excercise is what I've known already, that 3 round groups are a waste. I almost always shoot 5 round groups and even that can be deceiving as these 10 round groups show with this bi modal pattern exhibited by some of them

However, I shot enough of that 0.5 MOA load to feel it was the most consistent I've found to date, shooting sub 0.5 multiple times at 100 and 200 yards. The only missing variable right now is the 210m primer.....hence my excercise above to find an equivelant.

I guess I should also note I'm shooting off a bench with a bipod and rear bag

 

[macgrumpy]

Make sure that you have something soft under the bipod feet, I usually put a small piec of carpet or heavy rubber under the feet.

If you graph the impacts of all 50 shots on a spreadsheet you find that the groups moved from a position farthest away from the point of aim horizontally but closer vertically, up, and then closer horizontally, and then straight down to almost the point of aim. To me it seems like the groups are moving towards the point of aim as you increase the powder charge.

 

[Gtscotty]

I've not seen any significant change in 100 yard accuracy testing .308 Win loads across a 2 grain spread in charge weight across several barrels.

Bart, are you saying you've seen certain 2 gr windows in .308 loads (such as you might expect to find at the top of the barrel's deflection where muzzle movement slows and reverses direction) where accuracy is equal throughout the window? Or are you saying that accuracy is the same across any given 2gr load window in your .308 loads at 100 yds?

 

[Bart B.]

Gtscotty,

I'm saying I've seen certain 2-grain windows in .308 loads where accuracy is equal throughout the window at 100, as well as 200 and 300 yards. Having shot 41 through 43 grains of IMR4064 under Sierra 168's in dozens of 10-shot groups of different charge weights and no discernable difference in accuracy, I conclude at short range, the difference is insignificant.

Shoot five 10-shot groups for each 1/2 grain step in a 2-grain spread, then measure the groups. That'll show you what really happens a lot better than one or two single few-shot test groups. 100 shots tells the whole story; 5 or 10 just one small part of it.

No idea where in the muzzle axis swing where that happens, but I doubt it's at either extreme (top or bottom) where lots of folks think its the best place for them to leave. I don't want my bullets to leave at either of those places because half of them will be negatively compensated for their muzzle velocity. Bullet best compensated for their muzzle velocity leave on the muzzle axis upswing; anywhere in that place will work fine. Faster average velocities will leave in a lower spread and slower average ones in a higher spread.

 

[Gtscotty]

Gtscotty,

I'm saying I've seen certain 2-grain windows in .308 loads where accuracy is equal throughout the window at 100, as well as 200 and 300 yards. Having shot 41 through 43 grains of IMR4064 under Sierra 168's in dozens of 10-shot groups of different charge weights and no discernable difference in accuracy, I conclude at short range, the difference is insignificant.

Shoot five 10-shot groups for each 1/2 grain step in a 2-grain spread, then measure the groups. That'll show you what really happens a lot better than one or two single few-shot test groups. 100 shots tells the whole story; 5 or 10 just one small part of it.

No idea where in the muzzle axis swing where that happens, but I doubt it's at either extreme (top or bottom) where lots of folks think its the best place for them to leave. I don't want my bullets to leave at either of those places because half of them will be negatively compensated for their muzzle velocity. Bullet best compensated for their muzzle velocity leave on the muzzle axis upswing; anywhere in that place will work fine. Faster average velocities will leave in a lower spread and slower average ones in a higher spread.

Ok, I've seen similar windows in my load workups, i believe the OCW method is based on finding these windows. Most folks believe that the best time for the bullet to exit would be near the end of the barrel swing because that is where the barrel is decelerating and changing direction, therefore the change in muzzle direction over a given time period will be smaller than mid swing when the barrel is at a higher average velocity. The bullet velocity compensating for barrel swing by faster bullets exiting lower might have some effect, but i would not expect it to be a major effect compared to the effect of exiting during the dwell time when barrel muzzle moves around the maxima point of its travel .


Nature Boy,

In another thread you had mentioned that you wanted to try around 43gr Varget and 178gr Amaxes. Did you ever play around with the heavier Amaxes and Varget? If so, what did the results look like?

 

[Nature Boy]

I did shoot that load Gscotty, the one you did so well with, and results were so so. I may try is again as I still have the components to run more.

 

[Nature Boy]

Macgrumpy. I'm using an atlas bipod and always put a folded towel under the feet

 

[Walkalong]

I'm trying to find an equivalent with a CCI BR primer. I also broke out some new, never fired, LC 15 brass, which I ran through the sizer.

So, you changed two things at the same time. Not that I haven't done that, but it opens the door to questions.

Bart is right, one group means nothing, and I have posted that before, but we still see folks post some targets with one group from each load and then they declare a winner.

Groups must be repeatable, but the human factor makes it hard to shoot the best group the rifle/load has in it every time. The better shooters do the best job of getting the most out of a rifle/load consistently. They simple make fewer mistakes than most shooters.

 

[Nature Boy]

Yes, I changed 2 things. Figured since I was starting from scratch, what the heck

It does bring up another question. Since the cases are new, never fired, there's more head space than the normal .003" shoulder bump back from once fired. They measured .005 from fired cases, for what it's worth

 

[murf]

and new cases commonly shoot more accurate than fired ones. it seems you are having good luck with mag primers, so try 215m federals, 9.5m remington and/or 250 cci primers. surely one of those will get you back down to .5 moa.

luck,

murf

 

[Bart B.]

Nature Boy,

Were those .5 MOA groups:

* smallest ones fired?

* average of all groups fired?

I ask because I don't think any rifle shoots the same size groups all the time. So, what's the sizes of the other groups when one .5 MOA shows up?

 

[Nature Boy]

Bart. I stumbled on this load as I was trying some Berger VLDs for the first time, as documented on this thread. It has data on the results of this load.

http://www.thehighroad.org/showthread.php?t=795012

I should have kept more accurate records and I could answer your question with actual data. As it is, I can say fairly confidently that I loaded somewhere around 300-400 rounds with this load combo and had no 5 shot group higher than 0.600-ish MOA and a low of 0.350-ish MOA. That's both at 100 and 200 yards. It was great while it lasted, hoping to find the magic again. Headed to the range after church.

 

[macgrumpy]

I've looked over some of my notes and it appears that my best 175gr Berger VLD load in my 22" barreled M1A loaded model rifle used 40.5gr of IMR 3031, I actually got some very nice groups at 100 yards from a bench with a bipod and sandbags. Quite often I got sub-MOA but the average was 1" plus or minus a few tenths of an inch. I don't have a bolt rifle to test this load in but my QuickLoad software estimates that the chamber pressure would still be safe (on the hot end of the SAAMI spec but safe) and depending on your case volume you might be able to go as high as 42gr with a COAL of 2.82". As always, if you choose to test loads that hot work up to it slowly and look for pressure signs, QuickLoad says that 42gr would produce a max pressure of around 60,000 - 61,000 PSI so 42gr would be right at the top end of the SAAMI safety spec.

 

[Bart B.]

macgrumpy,

I may be weird but I've never use average group sizes to represent accuracy. Biggest group shot tells me the accuracy one can count on almost all the time. So your 1" plus or minus a few tenths of an inch tells me the accuracy is about 1.25 inch.

Gtscotty,

The optimum charge weight and barrel time theories are based on when the shock wave going back and forth in the barrel is at the breech end so there's no .0001" or so enlargement at the muzzle doesn't hurt accuracy. The theory's based on the speed of sound in barrel steel being about 18,000 fps per second. Yet I've seen speeds of 10,400 and 14,900 fps in pipe which is what barrels are like. My calculations of shock wave location versus bullet exit very different that the creator of that optimum charge weight theory publishes.

I've shot 7.62 NATO Garand barrels cleaned from the muzzle that's opened up .0010 to .0020 inch from cleaning rod wear that shot inside 4 to 5 inches at 600 yards when new and still did with that much wear after a couple thousand rounds through them and cleaned every 40 to 80 shots with a bare steel rod.

One mechanical engineer has shown that bullets exiting at the extremes of barrel whip have some of the slower ones exiting at a lower angle than faster ones leaving at a higher angle; opposite of what's needed. All bullets must leave on the upswing of the bore axis someplace where all the slower ones are launched at a higher angle than the faster ones that leave at a lower angle. Shown in:

http://www.varmintal.com/aeste.htm#Modes

 

[macgrumpy]

Whatever, what is it with you guys on this forum? Everybody has an axe to grind, I don't really care what you consider to be a true group size, that's not the topic of the conversation and I certainly didn't make it the topic of my post. I simply said that I can get sub-MOA groups quite often but we all know that unless the sample size is at least 20 rounds we aren't seeing a true representation of the group size.

 

[Bart B.]

... we all know that unless the sample size is at least 20 rounds we aren't seeing a true representation of the group size.

If that's true, few of us mention it.

A lot of people claim their stuff's accuracy is the smallest group fired. And the majority use a single few-shot group to represent the performance of a load.

I doubt that'll change; been that way for decades.

 

[Walkalong]

Guys, do you think we could get back on topic and try to help Nature Boy with his primer question?

 

[Nature Boy]

I thought I was doing better by using 10 round groups. Are you saying I need to use 20 round groups to determine my loads accuracy?

Bart, take a look at the thread I linked to if you haven't. I generally let the data determine how me, my rifle and my loads are performing. I'm not using the best group be the indicator.

I loaded up 25 more from Group A and shot some 5 round groups with it. All of them were +1 MOA

 

[Bart B.]

Yes, shoot at least 20 rounds.

Shoot all 25 in one group; waiting 'till the barrel cools down every 4 to 5 shots if needed. It'll probably be larger than any single 5-shot group, but such is life.

 

[Nature Boy]

I'll probably need to get a new barrel on order and find a deal on bulk 168 AMAX

 

[Bart B.]

How many rounds does your barrel have through it?