Standard Deviation of 12 and FPS of 2660 Good Enough?

[hk dave]

Hey folks, fairly new to reloading, been working up a load for my GAP Custom 308.

Chrono Setup at 12'
175 SMK, 43.5gr Varget, Rem 9 1/2 Primer, FC Brass prepped and weighed with 2 grain variance

Shot 1: 2661 fps
Shot 2: 2666 fps
Shot 3: 2640 fps
Shot 4: 2666 fps
Shot 5: 2677 fps
Shot 6: 2661 fps
Shot 7: 2661 fps
Shot 8: 2645 fps
Shot 9: 2645 fps
Shot 10: 2677 fps

Median: 2660 fps
Standard Deviation: 12

Question #1: This good enough to play well at 1000 yards or do I need to tighten up my procedures further? I did not double weigh my charges so I'm guessing there could be as much as a .5 gr difference between rounds.

Question #2: The difference in G1 vs G7 BC at my 600 yard range was pretty big, almost half a mil... when using G7, I was hitting high by quite a bit, when using G1 I was barely hitting higher than my ballistic program said I would. Why is there such a variance between the two BCs? Is this an entirely different subject to learn on?

Question #3: Is muzzle velocity vs velocity at the chrono at 12' feet different? When I changed out my muzzle velocity on my ballistic program with G1 to 2680-2690 I was hitting dead center at 600 yards... anytime I used the recorded median fps or change to G7 BC, I hit high.

This is fun.

 

[Bear24]

If it were me and I wanted to be consistent at 1k I would make sure I had less than .5g difference in powder charge. I think that is all you are missing in your loading. I am shooting the same bullet, powder and brass you are but I use fed 210m primers and have a single digit SD. I am using 44.4g but plan on dropping my charge a little bit soon.

 

[ChrisGarrett]

Just my personal 'standard':

20-25 SD: Most factory ammo, but not all.

15-20 SD: Decent reloads for shorter ranges.

10-15 SD: Your're doing pretty well, but maybe not out past 1k.

Sub 10 SD: You're in the major leagues, so congrats.

Chris

 

[milo 2.0]

I'd let my groups or shooting decide if it meets your standard. Numbers are just that, numbers. My best load to date had the worst numbers of any of my loads, but it was a day in, day out performer, through all four seasons for 2 years.

 

[JSTARSZ]

Reloading has a tendency of bringing out the perfection for some. Bench Rest shooters are the most anal about their reloading then I have ever seen. They stress over the most minor of details imaginable to become competitive with their other anal shooters. I shoot long range on steel and use silhouette targets that are 30" tall x 18" wide which is about a human torso. I can tell you with a high degree of confidence that 2660fps and a a SD of 12 is pretty darn good for starting out. If you want to become anal about reloading start reading bench rest reloading books and brass prep will take lots of your time. I am in the good enough to work with what I am doing category and I would rather be out shooting that prepping my brass all the time.

 

[Layton]

Question #2: The difference in G1 vs G7 BC at my 600 yard range was pretty big, almost half a mil... when using G7, I was hitting high by quite a bit, when using G1 I was barely hitting higher than my ballistic program said I would. Why is there such a variance between the two BCs? Is this an entirely different subject to learn on?


This is fun.

What app are you using? A buddy of mine had a big discrepancy between his G1 and G7 with Shooter until he manually entered the est G7 for his SMKs.

L

edt: With the numbers you posted there is only a .5 mil or 18" difference in your ES at 1000y. Just fyi.

 

[nuclear_shooter]

I just plugged these into JBM for your highest and lowest velocity and you get a drop of -35.2 MOA for lowest and -34.1 MOA for highest at 1000 yards (I used the data for the Litz and not HPBT, not sure which you have). If you use the average (not to get picky but your median is 2661, and your average is 2660... I do this for a living) you get -34.7 which should only put your off by ~.5 MOA. Is that good enough for you?

 

[gvanhyning]

I'd let my groups or shooting decide if it meets your standard. Numbers are just that, numbers. My best load to date had the worst numbers of any of my loads, but it was a day in, day out performer, through all four seasons for 2 years.

+1^ ... I'd shoot some groups on paper or steel at 400 to 500 yards minimum and evaluate the groups. I'd be looking to see how much vertical dispersion there is in the group and decide if that is good enough.

 

[hk dave]

Reloading has a tendency of bringing out the perfection for some. Bench Rest shooters are the most anal about their reloading then I have ever seen. They stress over the most minor of details imaginable to become competitive with their other anal shooters. I shoot long range on steel and use silhouette targets that are 30" tall x 18" wide which is about a human torso. I can tell you with a high degree of confidence that 2660fps and a a SD of 12 is pretty darn good for starting out. If you want to become anal about reloading start reading bench rest reloading books and brass prep will take lots of your time. I am in the good enough to work with what I am doing category and I would rather be out shooting that prepping my brass all the time.

Seeing the varied responses, it looks like an SD of 12 is good enough for tactical shooting which is what I mostly do. Perhaps I should double weigh... it just make it so time consuming. My RCBS Chargemaster gets 1 out of 3 pours correct. haha

What app are you using? A buddy of mine had a big discrepancy between his G1 and G7 with Shooter until he manually entered the est G7 for his SMKs.

L

edt: With the numbers you posted there is only a .5 mil or 18" difference in your ES at 1000y. Just fyi.

Hmm this is interesting... it's really got me wondering whether there is something wrong with my software. I'm using Bulletflight and the difference is pretty big.

I'm going to go run the same figures in Ballistic and see what I get.

I just plugged these into JBM for your highest and lowest velocity and you get a drop of -35.2 MOA for lowest and -34.1 MOA for highest at 1000 yards (I used the data for the Litz and not HPBT, not sure which you have). If you use the average (not to get picky but your median is 2661, and your average is 2660... I do this for a living) you get -34.7 which should only put your off by ~.5 MOA. Is that good enough for you?

Half MOA would be great, but I think I'm getting more like a half mil which is huge.

+1^ ... I'd shoot some groups on paper or steel at 400 to 500 yards minimum and evaluate the groups. I'd be looking to see how much vertical dispersion there is in the group and decide if that is good enough.

Will do... now to find a place I can setup targets at 400-500 yards. My local range goes out to 600 yards and I can sort of get groups in the early morning when the steel still has fresh paint.

Thanks for all the responses... I really need to figure out why i'm getting such a difference in G1 vs G7. Time to go figure it out.

 

[nuclear_shooter]

Half MOA would be great, but I think I'm getting more like a half mil which is huge.
.

Sorry, I should have been more clear... you would get 1/2 MOA vertical dispersion from the change in velocity. This is NOT the difference between G1 and G7. How was your vertical dispersion? Generally G7 is thought of as 'better' for LR bullets. You can read more about it from experts here: JBM - Topics - Ballistic Coefficients. As for the distance from the chrono, most ballistic calculators (okay maybe not most but the ones I've dealt with) have a spot where you enter how far the muzzle you are. It does make a small difference, about 0.2 MOA according to a quick calculation using JBM.

 

[former naval person]

The question not asked, is what chronograph and what are the accuracy numbers for that particular chrono. With most hobby chrono's 12 is within the accuracy limits of the instrument...meaning that if you were getting identical readings for 10 or 15 shots...they still could be varying by chance 12 fps. You need to ask the accuracy level of that chrono in percent of fps. Then get your instrument verified. Probably your best indicator would be shooting drops at range. JMHO

 

[Layton]

Sorry, I should have been more clear... you would get 1/2 MOA vertical dispersion from the change in velocity. This is NOT the difference between G1 and G7. How was your vertical dispersion?

This is what I was getting at when I said you only have a .5 mil spread with your min and max velocities and I wasn't relating to the G1 or G7 bc's. My bad on not clarifying. Only way to get that down is to tighten up your ES. But is that good enough already is the question?

L

 

[JSTARSZ]

Here is an easy method that I use when I am getting inconsistent pours. I set the charge that it will average a little light in each pour and I fill a case with powder and use it to fill my powder scale until I get the weight I want. I guess I could buy a trickler but I am too cheap for that by my method works.

 

[nuclear_shooter]

Also keep in mind there is more to consider than just BC at 600 yards. Did you factor in humidity, temp, density altitude, et cetera?