The Chronograph has me scratching my head.

[LoneWolfUSMC]

OK, so I got my new Shooting Chrony F1 and out to the range I went with some loads. The GOAL is to workup a load with the same trajectory as the 168gr FGMM.

400' elevation, 79.9*F, 29.92"Hg, and lightly raining.

First up I ran 5 rounds of 168gr Federal Gold Metal Match.
2721 fps
2702 fps
2711 fps
2694 fps
2688 fps

Next up was what I was expecting to be a "clone" consisting of 168gr Nosler CC, 42.5gr of RE-15 and a CCI200 primer in Federal FL Sized brass.
2592 fps
2561 fps
2572 fps
2579 fps
2574 fps

it printed about 1" higher than the FGMM at 100 yards

Next was 168gr Nosler CC, 42.0gr of RE-15 and a CCI200 primer in Federal FL Sized brass.
2553 fps
2564 fps
2560 fps
2561 fps
2556 fps

this also printed about 1" high compared to the FGMM

I then grabbed some of my previous "accuracy load" which is 168gr SMK, Winchester neck sized brass, CCI200 primer and 45.5gr of RE-15.
2757 fps
2752 fps
2756 fps
2763 fps
2749 fps

this printed only 1/4" higher than the FGMM

Lastly for shits and grins I ran some 168gr AMAX over 42.5gr of RE-15.
2334 fps
2660 fps
2663 fps
2657 fps
2645 fps

they were still running a bit high.

to close out the session I busted out some of my 155gr Scenar loads because I knew I was at the upper end of the envelope with them, but they shoot soooo good.

155gr Lapua Scenar, 47gr of RE-15, Winchester Neck Sized brass, CCI200 primer.
2926 fps
2943 fps
2931 fps
2934 fps
2917 fps
Still no pressure signs, but they printed about 4" higher than the FGMM (no surprise there).

Now what has me scratching my head, is that the lower charges were impacting higher than the FGMM which was obviously running faster. My only guess is that the projectile was leaving the muzzle corresponding with an "up" whip on the barrel.

The next time I will be pushing testing out to 200 yards to compare the trajectory better.

From the number I got off the chrony it's looking like I need a charge of about 45.0gr of RE-15 to get the velocity I am looking for to match the FGMM. Does this sound about right?

Does anything look way off? This is my first time working with a Chronograph so I am learning as I go.

 

[USMCj]

Re: The Chronograph has me scratching my head.

Barrel warm-up caused the others to group higher maybe?

 

[Rhys]

Re: The Chronograph has me scratching my head.

I would say your right about the location in the ocilation causing the fluctuation in the POI. Looks like your chrono had a heart attack on one of those rounds with the 168 A-MAX or is it a typo? At the closer distances POI has littl if anything to do with VEL.

 

[kombar]

Re: The Chronograph has me scratching my head.

Remember that a firing gun is a dynamic system, it's not a simple case of faster shoots higher, or even what vibration node the bullet exits on. The rifle starts recoiling the instant the bullet starts down the bore. If there is any tendency for the muzzle to torque upwards on firing, the slower rounds can definitely impact higher than faster ones, since they spend more time in the bore.

Old No.4 Enfields are known to shoot slow loads significantly higher than fast ones, although in this case it is thought to be a result of the harmonics inherent in the design.

 

[LoneWolfUSMC]

Re: The Chronograph has me scratching my head.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Rhys</div><div class="ubbcode-body">Looks like your chrono had a heart attack on one of those rounds with the 168 A-MAX or is it a typo?</div></div>

It's not a typo, but I think the Chrony caught a raindrop on the window when the round passed.

 

[BLAWTON]

Re: The Chronograph has me scratching my head.

How far was it from the muzzle of the gun? Normally i would dismiss that as a false reading as well but if something like that happened you would get a way different reading. With my oehler i get the right reading or one thats WAY off.

 

[LoneWolfUSMC]

Re: The Chronograph has me scratching my head.

About 15' or so from the muzzle.

I trickle each charge, but it's always possible it got bumped on the way to seat the bullet and I didn't notice it. I don't recall it being a flyer, but I was more concerned with dinking with the Chrony than with perfect groups. When I am actually doing load development I will be recording the impact of each round and saving the target for the reloading binder.

 

[kombayotch]

Re: The Chronograph has me scratching my head.

Different powders will sometimes give different POI even at the same velocities with the same bullet. For example, from some of my OCW tests:

 

[LoneWolfUSMC]

Re: The Chronograph has me scratching my head.

I guess i need to pull down a couple FGMM rounds and check the charge. Then I can at least get an idea of what powders will give me similar velocity per charge weight.

 

[sobrbiker883]

Re: The Chronograph has me scratching my head.

If you have quickload (or a friend that does) run some numbers and find a powder that gives you a powder and charge that will put you at the same speed as FGMM that hits on an OBT accuracy node for your barrel length.
Same speed, same BC you should have the same trajectory (at least in theory). 42.4 IMR4895 does it for me with the Nosler 168's.

-I don't have QL, but I do have the excel OBT generator that gives you optimal barrel times for your barrel length. I can email you a copy if you're interested.

 

[LoneWolfUSMC]

Re: The Chronograph has me scratching my head.

Please do!

I have a fresh pound of IMR4895 sitting here, so I may load up a couple with the 42.4gr and see what we get.

I have been looking at buying Quickload. I am cringing at the $150 price tag, but the fact that I will have access to a LOT of data makes it seem like a really good deal.

 

[BLAWTON]

Re: The Chronograph has me scratching my head.

Dont they use ar2208 or 2209 in them?

There is a group buy going on right now for the new quickload LoneWolf. Check it out.

 

[MitchAlsup]

Re: The Chronograph has me scratching my head.

Inside 300 yards, barrel harmonics control th ePoI more so than velocity. 400 yards and beyond, ballistics control the PoI more than barrel harmonics.

 

[MontanaMarine]

Re: The Chronograph has me scratching my head.

Slower load, longer barrel time, more barrel rise from recoil before bullet exits. Higher impact at closer range.

Same effect only more exaggerated in short 44Mag revolver. Slow heavies always hit higher at 25 yds than faster lighter bullets.

 

[LoneWolfUSMC]

Re: The Chronograph has me scratching my head.

Wow. I just read the OBT paper and my head is spinning.