I don't see where you tell us what kind of Chronograph you use. Is it a Chrony by any chance?

If it is, I have an unfolding theory.

Yes, Chrony, Master Beta model.

I think your readings are wrong. Here is my theory.

The Chrony works by detecting the shadow of the bullet as it goes over the sensor at the front. It then detects the shadow of the bullet at the back of the device. By calculating the difference in time between the front sensor detection and the back sensor detection, the Chrony knows how long it took the bullet to go from one sensor to the other.

Using that time and the distance between the front and the back sensor and it gives you a velocity in FPS. That distance is set and known to the Chrony. However, the Chrony must be unfolded in order to be set up and used and this is the critical part. If you do not unfold the Chrony completely and make sure it is flat, the distance between the front and the back sensor is reduced. However the Chrony has no way of knowing that and it will use the time difference with the total unfolded length of the Chrony, giving you a higher velocity as it takes less time to go a shorter distance.

2790fps over say 12 inches between front and back is .0043 seconds flight time. 2587fps over the same distance is .0046 seconds.

A bit of math shows that if the distance is 11.2 inches instead of 12 inches the flight time at 2587fps for those 11.2 inches is .0043 seconds, same as the flight time you showed as 2790fps.

Also if the Chrony was not completely flat, it will also point the sensor more forward and even though the distance at the bottom may only be a quarter inch, the rear sensor will be pointing further forward than that.

You want to make sure the Chrony is completely flat and parallel to the trajectory of the bullet as much as possible.

Either that, or your Chrony is bad or needs new batteries.

Interesting theory, Nikon. When I set up the chrony, I first set up my rifle and have it in the rests aimed at the target. I then set the chrony on a tripod and place it suche that I can see through the centermarks of the chrony straight through the scope. The tripod has a ball swivel head to allow it to be as close to parallel to the bullet path as I can make it (range is on a down slope). As for the batteries, that certainly may be possible, I've had this one with it (only connected when being used) for a couple years. I'll check the voltage.

quote:

Originally posted by barndg00:
Interesting theory, Nikon. When I set up the chrony, I first set up my rifle and have it in the rests aimed at the target. I then set the chrony on a tripod and place it suche that I can see through the centermarks of the chrony straight through the scope. The tripod has a ball swivel head to allow it to be as close to parallel to the bullet path as I can make it (range is on a down slope). As for the batteries, that certainly may be possible, I've had this one with it (only connected when being used) for a couple years. I'll check the voltage.

Oh, and the mounting plate for the tripod crosses the hinge, it wouldn't be able to be mounted to the tripod unless fully opened.

Have you been able to test your Chrony with known loads?

It's been a very long time since I've used mine, I switched to a Magnetospeed years ago and now a couple of team members have Labradars that we use to measure our loads.

I have tested Speer GD ammo with it, I got 1170fps for Speer GD 124gr in my P226, with Speer quoting 1150fps in a 4" barrel. I got 1155fps in a H&K P2000sk (3.7" barrel) with the 124gr +P ammo, which speer quotes as 1220fps in a 4" barrel. I've never tested it against known rifle rounds.

Thinking about it further, the fact that QL and my chrony were so consistently diffferent (just about 200fps across three different loads), I suspect there must have been some error on my part setting up the chrony. All these loads were significantly improved from before, I guess I'll teak the charges a small amount either way around the best loads for each, then try adjusting seating depth? Or is there something else to consider trying first?

It's just a difference of 200FPS is pretty significant.

So I went checking at Hodgdon and I think QL is all wrong.

For a 24inch barrel, 105gr, H4831 they get:
38.0gr 2687fps
41.0gr 2846.

I think your 39.5 @ 2790 from a 26 inch barrel is right in there.

Notice that 41.0gr is Hodgdon's max.

I would try my work up loads at 100 yards to start with and develop the tightest group. Less chance of wind and other conditions distorting the group. After an accuracy load is developed you can then try it at longer distances.

quote:

Originally posted by NikonUser:
It's just a difference of 200FPS is pretty significant.

So I went checking at Hodgdon and I think QL is all wrong.

For a 24inch barrel, 105gr, H4831 they get:
38.0gr 2687fps
41.0gr 2846.

I think your 39.5 @ 2790 from a 26 inch barrel is right in there.

Notice that 41.0gr is Hodgdon's max.

My experience has been that QL is horribly wrong at nearly everything. Velocities, Max loads, the works. My 223ai load, for example - QL says I'm 20k psi over pressure, and that I should be going 100fps slower than I am.

QL is a tool, not gospel. Believe the bullet.

I've never used Quickload. Never found a need for it and after this, I'm glad I never bothered with it.

Nikon and exx1976, thanks for your help, experience and perspective. This was the first time for me using quickload, and honestly looking back, I'm not sure how I got such high charges for some of these loads - I have never tried loading so much higher than published load data before. When I reviewed my file in Quickload, the highest charges (44 grains is clearly over max - don't know how I didn't notice it). When I try again in QL, I get about 100fps faster results for predicted velocities in QL than I did before, but I have no idea what is different. Clearly I was doing something wrong.

I did check the cases again, no pressure signs, however, I won't be using those upper end loads again. The first load for the VLD bullet was excellent, so I'll see if I can reproduce that. Otherwise, back to the drawing board, and back to basics for me with reloading - always confirm your data!

Well, with a little more digging, I figured out the issue. When I was repeating the QL calculations, I forgot to load the custom cartridge file, where I had measured the case volume - per the instructions, it was larger than the standard by 0.5gr, with the larger volume, pressures were lower and the max charge thus went up per the calculations. I will continue to go by the books going forward however.

In response to the original question it wouldn't be too hard or too expensive to try a 1pc base and bed the base to the action. Might not help at all but it would be 1 less variable to have worried about.

You didn't mention what scope you were using but I'd just say that funky parallax or other scope problems have ruined more than one longer range group. I'd at least check your scopes parallax at 200 and/or try a different scope on the rifle before I gave up on one that you've invested a good bit of time and money on already.

Otherwise an interesting thread concerning accuracy nodes etc.... ;-)

dj