Help with first chrony data

[GSoD]

Hey all,

So I bought a chronograph and ran my latest reloads through it. Can you help me interpret the data below?

I fired three loads of Varget at 44.4g, 44.5g, and 44.6g (each with federal brass, cci primers & 175g Sierra MatchKing in .308). I'm reloading with off the shelf Lyman and RCBS equipment and lee dies. I didn't seperate brass or bullets by volume or weight.

Its being shot out of a Rem700P, off a bench with rests at both ends on a virtually windless day.

I haven't played with getting closer to the lands because I want it to magazine feed so I've kept it at the book length.

I posted the velocities, group sizes, standard deviation etc.

I'm wanting to use this as my long range target round.

I'm thinking 44.6 grains is in a good spot.

Do you figure the velocities and deviations acceptable?

Any help appreciated.

Thanks,

ST

***44.4 GRAINS***
GROUP1 shot at 100 yards
Shot 1 2702 fps
Shot 2 2718 fps
Shot 3 2728 fps
Shot 4 2726 fps
Shot 5 2764 fps

Avg Vel Grp1 2727.6 fps
5 Shot Group Size 1.2 inches
5 Shot Group MOA 1.256 MOA
GROUP2 shot at 100 yards
Shot 6 2710 fps
Shot 7 2784 fps
Shot 8 2812 fps
Shot 9 2799 fps
Shot 10 2821 fps

Avg Vel Grp2 2785.2 fps
5 Shot Group Size 0.547 inches
5 Shot Group MOA 0.573 MOA

Avg Vel Total 2756.4 fps
Velocity Spread 119 fps
10 Sht AVG Grp Sz 0.8735 inches
10 Shot AVG MOA 0.915 MOA
Bias Standard Dev 42.68 fps

***44.5 GRAINs***

GROUP1 shot at 100 yards
Shot 1 2821 fps
Shot 2 2821 fps
Shot 3 2821 fps
Shot 4 2801 fps
Shot 5 2775 fps

Avg Vel Grp1 2807.8 fps
5 Shot Group Size 0.56 inches
5 Shot Group MOA 0.586 MOA

GROUP2 shot at 100 yards
Shot 6 2754 fps
Shot 7 2702 fps
Shot 8 2669 fps
Shot 9 2655 fps
Shot 10 2629 fps

Avg Vel Grp2 2681.8 fps
5 Shot Group Size 0.992 inches
5 Shot Group MOA 1.039 MOA

Avg Vel Total 2744.8 fps
Velocity Spread 192 fps
10 Sht AVG Grp Sz 0.776 inches
10 Shot AVG MOA 0.812 MOA
Bias Standard Dev 71.15 fps

****44.6 GRAINS****
GROUP1 shot at 100 yards
Shot 1 2603 fps
Shot 2 2652 fps
Shot 3 2680 fps
Shot 4 2741 fps
Shot 5 2731 fps

Avg Vel Grp1 2681.4 fps
5 Shot Group Size 0.553 inches
5 Shot Group MOA 0.579 MOA

GROUP2 shot at 100 yards
Shot 6 2773 fps
Shot 7 2746 fps
Shot 8 2709 fps
Shot 9 2723 fps
Shot 10 2743 fps

Avg Vel Grp2 2738.8 fps
5 Shot Group Size 0.762
5 Shot Group MOA 0.798

Avg Vel Total 2710.1 fps
Velocity Spread 170 fps
10 Sht AVG Grp Sz 0.6575 inches
10 Shot AVG MOA 0.688 MOA
Bias Standard Dev 48.62 fps

 

[Gatehouse]

Which is what?

 

[Eagleye]

If I read your post correctly, you are only changing your charge by .1 grain per load. In a 308 size case, you are unlikely to see any measurable difference with .2 grains. I would be varying those loads in .5 gr increments, and then fine tune it once I had empirical evidence that it shot better around one charge. Regards, Eagleye.

 

[GSoD]

If I read your post correctly, you are only changing your charge by .1 grain per load. In a 308 size case, you are unlikely to see any measurable difference with .2 grains. I would be varying those loads in .5 gr increments, and then fine tune it once I had empirical evidence that it shot better around one charge. Regards, Eagleye.

I had done that before I got the chronograph, thats how I got into this ballpark. It shot the best groups at 44.4 and 44.7. So I thought I would try in between to see if there were improvements. Which these are.

 

[Gatehouse]

I had done that before I got the chronograph, thats how I got into this ballpark. It shot the best groups at 44.4 and 44.7. So I thought I would try in between to see if there were improvements. Which these are.

If you had an improvement in accuracy, then just load wiht that charge...You won't get much (if nay) consistent velocity gain with that small an amount of powder.

 

[maynard]

If you plan to use this as a long range load you need to sort your brass into at least 1 gr batches. If your brass is +/- 5 grains your results will be all over the place, not only in velocity buy POI at long range.
Also most long range target shooting is done single loading so forget about the mag length. Worry about AOL once you find the load that work best.

 

[BattleRife]

I fired three loads of Varget at 44.4g, 44.5g, and 44.6g

Please do not abbreviate 'grains' as 'g'. 'g' Stands for 'grams', and there are people who do their loading in metric, so you are asking for confusion doing this. Most people shorten grains to 'grs'.

There also appears to be a problem with your math, as MOA numbers should be smaller than the group size in inches at 100 yards. For example, 1.2" @ 100yds is 1.15 MOA.

I am a little surprised you can be getting half-inch groups with almost 200fps of extreme spread. I generally consider any spread over 75fps in 10 shots to be undesireable, even for plate shooting ammo. But, if it works, it works.

Your velocities also seem a little high to me, a 175gr bullet at 2800 fps is .30-06 territory or better, but I have never loaded Varget. I know that if I was seeing numbers like those in my M14 I couldn't sleep at night wondering what I was doing to my op rod.

 

[Shelldrake]

I agree with BattleRifle for the most part. Your velocities are high for that bullet, and your powder charges are also high. The Sierra manual tops out at 41.7gr for the 175gr Match King.

My best load has been 41.0gr of Varget with a velocity of just under 2500fps with a SD of around 15. That's good enough for me and groups well all the way out to 800m. With your velocity spread of over 100fps, you can expect your group to open up greatly as the distance increases. You should be able to find a load with a low SD and a lower extreme spread. I suggest backing off your loads.

Are your primers flattening?

 

[Shelldrake]

Also, I chrono and average 10 shots. With a larger pool of shots, then your computations have more assurance than using 5 numbers.

 

[Boomer]

How did you determine that you were using safe powder charges? Unless your rifle chamber is cut in such a way that the bullet does not extend into the powder capacity I think you are playing with fire with that combination. If your rifle is built to SAAMI standards stop, pull those loads and start at a safer level.

My preference with rifle cartridges is to increase the power charge from a safe starting point (determined from a loading manual) in 1 gr increments until I have determined the maximum safe load, then work backwards from that point to find the best accuracy. I also think that varying the powder charge weight by a tenth of a grain with .308 capacity cartridges is of little value.

 

[GSoD]

How did you determine that you were using safe powder charges?"

I don't have it in front of me, but I was using the Lyman reloading manual which, if I recall correctly, says max load is 45Grains of Varget for 175Grain projectile.

So I started at 41Grains and worked up 5 shot groups in .3 grain increments looking for pressure signs. I didn't see any, or didn't know what I'm looking for, and got the best groups at 44.4 and 44.7. So then I worked up 10 round batches at 44.4, 44.5 & 44.6 to see if something tighter would emerge.


"I think you are playing with fire with that combination."
It is a manual suggested combination and is similar to other loads I've read of people using.

"My preference with rifle cartridges is to increase the power charge from a safe starting point (determined from a loading manual)."

I did that.

"I also think that varying the powder charge weight by a tenth of a grain with .308 capacity cartridges is of little value."

I'm starting to get that impression as well.

On another board it was suggested that my chrony is giving inaccurate readings because of the time of day I used it.

I used it on a cloudless day, but near dusk. The sun was setting to the left of the machine with sunlight coming through some trees. It was suggested I perhaps try again on a cloudy day earlier in the day so the chrony can see the bullet best.

Any thoughts on this theory?

 

[GSoD]

Please do not abbreviate 'grains' as 'g'. 'g' Stands for 'grams', and there are people who do their loading in metric, so you are asking for confusion doing this. Most people shorten grains to 'grs'."

Will do from now on, thanks for the insight.

"There also appears to be a problem with your math, as MOA numbers should be smaller than the group size in inches at 100 yards. For example, 1.2" @ 100yds is 1.15 MOA."

I took my group reading in inches and multiplied it by 1.047. Is this wrong? How do you do it?"

"I am a little surprised you can be getting half-inch groups with almost 200fps of extreme spread. I generally consider any spread over 75fps in 10 shots to be undesireable, even for plate shooting ammo. But, if it works, it works."

This sort of input is half making me think I have a bit of a chrony inaccuracy perhaps caused by the conditions I deployed it in. Or I completely messed things up.

"Your velocities also seem a little high to me, a 175gr bullet at 2800 fps is .30-06 territory or better,"

Also making me think I have a bit of a chrony inaccuracy perhaps caused by the conditions I deployed it in. Or I completely messed things up.

 

[GSoD]

I agree with BattleRifle for the most part. Your velocities are high for that bullet, and your powder charges are also high. The Sierra manual tops out at 41.7gr for the 175gr Match King."

Weird, cuz I believe the Lyman manual suggested it topped out at 45grain and I've read about quite a few people running above 41grain.

Hmm, perhaps I will start from scratch with some cross referencing of manual materials.

"Are your primers flattening?

Nope everything on the case and primer looks good after every shot.

 

[Boomer]

The Chrony works by the "eye" detecting a shadow as the bullet passes over it and measuring the length of time that passes until the second eye detects the shadow caused by the passage of the bullet. Low light conditions would not be conducive to the eye recognizing the passage of the bullet. If it was way out I would think it should display an error, but this is not necessarily the case.

I have the Lyman 46th and 47th editions and neither has data for the 175 MK or Varget, but the Hodgdon #27 confirms that 45.0 is the maximum load for Varget with a 175 gr MK. I apologize for jumping to conclusions, I should of checked more than one source.

 

[stepnout kennels]

I have the Lyman 48th edition it dose say 308 win, max 45 grains of varget for a 175gr, HPBT and lists 2708 fps @ 59,300 psi. I also have a Hodgdon basic booklet which confirms max load of 308 win, 45grains of varget, 2690fps, 48,600psi. Notice the pressure difference. Both books called for a 24 inch barrel but the Brass and primers are different. This proves and confirms starting low and working up your load is critical to achieve save pressure in your firearm. I also have a 50th Sierra manual who do not even come close to this load as far as speed. I am quite sure when this book came out Varget was quite new and they really did not utilize Varget as much.

 

[BattleRife]

... MOA numbers should be smaller than the group size in inches at 100 yards. For example, 1.2" @ 100yds is 1.15 MOA."

I took my group reading in inches and multiplied it by 1.047. Is this wrong? How do you do it?"

At 100 yards, there are 1.047 inches per MOA, so you need to you need to take your measurement in inches and divide it by 1.047 to get your numbers in MOA.

As to how I do it, well, I shoot a ten-round group at 100 metres, take a measurement in millimeters, then divide by 29.1 (actually, I divide by 30, 'cuz I only do it in my head to one significant digit) to get MOA.

 

[GSoD]

Thought I would provide an update:

Looking at the numbers and the insight provided by this board and others I changed some things:
a) gave my rifle a really good copper cleaning which it hadn't had in a few rounds.
b) choronographed earlier in the day with more light and total overcast.
c) got a digital scale. I've never been really comfortable with my working of the balance beam so I got a Lyman 1000 grain scale.

I loaded up the same batches I ran through the last time and got much better numbers in terms of standard deviation and extreme spread (assuming I'm doing my math right). Here's the best one:

44.5 GRAINS

1) 2689 fps
2) 2692 fps
3) 2686 fps
4) 2681 fps
5) 2690 fps
6) 2692 fps
7) 2682 fps
8) 2694 fps
9) 2701 fps
10) 2691 fps

Avg Vel 2689.8 fps
Extreme Spread 20 fps
Deviation 5.55 fps
10 Shot group size 0.717 inches
10 Shot group MOA 0.685 MOA

The group size got pushed out just a little bit by two hits that landed on the outside edge of the grouping, otherwise it would have been .5 inches. But at the time I had called them as flubbed shots so its something for me to work on.

Thanks for all the help guys, especially roberti11 and H4831.