300y ladder with 223/80.5 Berger/N540

[kyotekiller25]

Took my R700 223 Wylde with Bartlein HV 28" 8T and .080" FB out this morning and did a quick 9 shot ladder at 300 yards. Get an idea of pressure/velocity and find the upper node.

80.5g Bergers, approx .020 off, COAL 2.485", N540, Rem 7.5 and 2x fired Lapua brass. Shoulders bumped .002" and neck tension also .002"

It left me with more questions than answers, and didn't really show anything definitive in my opinion. The overall group wasn't bad, about 1 MOA for all 9 shots, but no real correlation to velocity/impacts either. Also, the jump in velocity of 70fps from 24.1 (2876) to 24.3 (2946) had me thinking I was around max, but there were no obvious signs of pressure anywhere. The jump from 24.3 to 24.5 was pretty normal again at 35fps. Not sure if I should creep up in .1g increments to find max with the velocity I'm already at, but I have a feeling there might be a node at that 24.5 (2980) area.

I also had something super odd happen and I can't explain it or figure it out. While trying to get my seating depths figured out, I had 3 extra rounds all loaded at 23.5 Only difference was 1 was really short at 2.4" and the other 2 were pretty dang close to where they were suppose to be at around 2.480". I figured I'd use the shortest one for a cold bore and see where it impacted at 300 and get a good zero to go off. Velocity read 2811fps. Ok no problems there. So I shoot the 9 shot ladder and the 23.5 charge showed 2829fps. OK still doing fine. Finished up the ladder and still had those extra 2 cartridges loaded at I decided to use them up on the 500 yard gong and get some more numbers from the garmin. I was shocked when the 1st read 3063fps. No hard bolt lift, cases look fine, primer looked fine, so I shot the last one and it was 3053fps. Again, no obvious signs of pressure. But my main concern and question here is how on earth was there a 225fps discrepancy in velocity with those 2 shots at 23.5 from the previous 2 at 23.5? I individually weighed each charge on a balance beam and I'm certain the Garmin is ok.

I was shooting for 2950fps with no pressure, as that seems about right for an 80g bullet and 28" barrel. I'm thinking 3050fps is definitely over pressure, even though I'm not seeing the tall tale signs. And I'm not even totally sure what to think of those 2 rounds that hit 3050fps at that low charge weight anyway.

Anyway I'd love to hear your guys thoughts and where you would go from here? Still better than a good day at work, but still a little frustrated also...

Target dot is 2"

 

[mark5pt56]

My only suggestion is on shot count, I like to have 2, usually 3 of each to have a better sample. Call shots and while it's not the "Bro 5" 3 gives you more data, group and chrono data.

 

[kyotekiller25]

That's true. I think I'll load 3 each from 23.8-24.8 in .2g increments and shoot them on a horizontal line at 100 yards and go from there.

Don't want to go lower than 2850 as this is a 1K trainer rifle. Tough to beat the 75 ELDMs at 3000, but figured I'd give the 80.5 Bergers a shot. I would expect them to shoot better and be less fussy.

 

[mark5pt56]

I would go at least 200, depending on mirage, etc, 300 starts to get tricky, maybe hit it early in the day. Do one each low to high, then reverse, finishing with low to high. Try to give a minute in between shots on each run and 5 between each run.

 

[Doom]

The problem with a Ladder shot at 300 yds is that it mixes the factors that affect the Point of impact. By that I mean the the path the bullet leaves the barrel and the velocity variation that is affecting the drop which also affects the POI. The environmental also begin to come into play including mirage.

When shooting a Ladder on Target at 100yds you have to dissect what variables will be affecting the point of impact (POI) and consider the effect those variables on the POI. Velocity as it affects the built drop due to gravity is almost nothing. A 100 fps variation in most centerfire cartridges is going to affect the POI by less than a caliber. The largest variable in terms of impact at that range is the line of sight/flight path that the bullet leaves the barrel. This is primarily determined by where the barrel is pointing in its vibration cycle and velocity of the barrel that is perpendicular to the bullets velocity. This is a function of the barrel vibration frequency and the barrel time which is a function of velocity. When the powder charge is burning uniformly and the barrel is moving slowly in the cycle then small change in the velocity will not cause a large variation in point of impact. As for seating depth, it has a very small effect on the POI but due to the behavior of the bullet and its orientation in the rifling will affect the dispersion around the POI. When shot at longer distances the inherent variations in velocity (SD and ES) begin to have greater influence on the POI and can confuse the results.

 

[KYAggie]

The problem with a Ladder shot at 300 yds is that it mixes the factors that affect the Point of impact. By that I mean the the path the bullet leaves the barrel and the velocity variation that is affecting the drop which also affects the POI. The environmental also begin to come into play including mirage.

When shooting a Ladder on Target at 100yds you have to dissect what variables will be affecting the point of impact (POI) and consider the effect those variables on the POI. Velocity as it affects the built drop due to gravity is almost nothing. A 100 fps variation in most centerfire cartridges is going to affect the POI by less than a caliber. The largest variable in terms of impact at that range is the line of sight/flight path that the bullet leaves the barrel. This is primarily determined by where the barrel is pointing in its vibration cycle and velocity of the barrel that is perpendicular to the bullets velocity. This is a function of the barrel vibration frequency and the barrel time which is a function of velocity. When the powder charge is burning uniformly and the barrel is moving slowly in the cycle then small change in the velocity will not cause a large variation in point of impact. As for seating depth, it has a very small effect on the POI but due to the behavior of the bullet and its orientation in the rifling will affect the dispersion around the POI. When shot at longer distances the inherent variations in velocity (SD and ES) begin to have greater influence on the POI and can confuse the results.

I’m confused, but it I haven’t had breakfast yet…..

So, ladder test at 300 yards, 100 yards, and longer distances all bad……so stop doing ladder test??

 

[diggler1833]

.223 is probably one of the more difficult cartridges to get tight ES/SD on (which still seems to defy logic). With a sample size of (1) and no idea what your ES/SD are going to be... it is going to be really difficult to accurately explain your velocity phenomenon for the first nine shots.

People are going to argue the merits of the ladder tests for the rest of time. If I were forced to do one - for any reason other than to find pressure limits - I'd probably do it at 600 yards, where the environmental factors really begin to come into play... and you'll really start to see the effects of velocity spreads in your vertical on target.

At this point, I'd probably suggest just picking a velocity that you're comfortable with (no pressure), and messing with seating depth until the accuracy occurs that you're after.

 

[RegionRat]

The vertical component of the middle seven steps is normal, but that horizontal for 300 yards is a problem.

Your test distance was way too close for this style of test yet the horizontal spread is not lining up with the vertical performance.

For example, if we assume a perfect trajectory the vertical difference from a shot at your slowest speed of 2752 to your fastest at 2981, would only be a difference of 2.66" at 300 yards.

Your results match that pretty well, but the point is that if we shot that test at 600 yards, the spread would be 16.27" and much easier to see if there was any evidence of positive compensation worth investigating.

At this point, we would say that anything in the middle of that ladder test is acceptable based on the vertical. The real question is what went wrong with the horizontal?

It all points at needing to answer the questions with more shots but if you were the cause of the horizontal then you have to do better.

It has been said, but I will still say it again.... when you shoot an Audette Ladder test, it has to be far enough away to allow the shot-fall to spread out vertically such that you could detect any evidence of positive compensation. If you cannot shoot enough distance, then one of the other test methods would be better. Good Luck and in for the range resports.

 

[Aftermath]

At this point, I'd probably suggest just picking a velocity that you're comfortable with (no pressure), and messing with seating depth until the accuracy occurs that you're after.

This is pretty much what I do.

I decide what bullet I want to shoot and see if it will fit the magazine (external or internal) with an appropriate seating of the bullet so it's not too deep in the case. I have the chamber cut so at that max magazine seating depth, the bullet is kissing the lands. I load varying powder charges (sometimes with varying powders) with the bullets touching the lands and look for pressure while measuring velocity. I choose a velocity I like below pressure signs and start seating depth tests.