Slow first shots with Center-X?

[FromMyColdDeadHand]

It was 65 out and cloudy yesterday and we were under cover. Got some pretty good data out of my Labradar shooting my 40X that was re-barreled with a Douglas 24 inch. Got data for 40 shots after I had re-zeroed and got some dope, so it wasn't like it was

I've always seemed to notice that the first shot of a string would shoot slow. Looking over the data, I had four times when I had over two minutes between shots. If I include those shots, my data looks like:

max1069
min1016
Mean1055
ES53
STD Dev9.61

When I take those shots out:
max1069
min1044
Mean1057
ES25
STD Dev5.86

You can really see it when you plot the velocity versus time between shots. When the time between a shot is over two minutes, the velocity is 1040 or under.

The slowest velocity was the first shot, which would have been the coldest bore because I was setting up the Labradar. That is 1016fps.

I've attached a plot of the shot vel as time went by. You can see how a pause causes a lower, maybe even how it takes a few shots to stabilize in the 1055 range.

I also did a plot where I looked the time between shots and velocity. Not counting the initial slowest shot, the three slowest shots are the three longest time between shots. And for a linear plot "Vel= (-10485)(seconds between shots) + 1059.8"of those shots, the slope is negative with an R-square value of 0.39. Not huge, put pretty interesting. (didn't label axis', a pet peeve of mine. Vel on y, x is time for the shots min:sec)

Cold bore I get. Warmish bore surprised me. It has had probably 150ish rounds through it since my last cleaning. Like I said, I've noticed this mostly in our PD matches were we shoot at 200ish on the last string and it seemed like my first shots would be low compared to later shots in the string. It really doesn't show up in shorter ranges in accuracy, only in 125yards plus.

Is this normal?

Next time I'll set up a bunch of dots at 125 yards and shoot single shots at dots and try to correlate back hits to velocity,

 

[Va_Gentleman]

I shoot a lot of Center-X in our TSC MATCH. I really think you are on to something here, now that I look back at my log books and scoresheets of the match run.

The only variable of course is your barrel vs. the population. If that variable is not significant then this would be VERY helpful data. Very helpful indeed.

My gut feeling tells me you may have uncovered a significant find that is beneficial. Let me ponder a few days.... I think I may have a way to give a second look into this hypothesis that may confirm.

 

[FromMyColdDeadHand]

I have a 26 inch barrel. I think I have the email on the exact specs. I use the EWL brand cleaners, but I used to use CLP and thought I had the same kind of issue, but I don't have the data. I have a love-hate relationship with the Labradar. When it works, it is sweet, when it doesn't, it is infuriating. This was great data from my 40X. Shot my sons 455VPT right after and I must have changed the geometry of the gun-targets-Labradar and only half the shots registered. That is using the mic set on a green landscaping pole duct taped to the stock, and right at the muzzle.

Actually, not that I remember back, it missed a couple of shots on my 40X, so the data is a bit off, but only by a couple of shots.

I get great data out of my 308 shots. All the way out to 80 yards for most shots.

 

[SporterII]

Sounds like bullet lube temp as in barrel lube temp.

 

[Va_Gentleman]

Sounds like bullet lube temp as in barrel lube temp.

That is what I am thinking as well.... the lube is in the back of my mine as surely the viscosity will change with higher temps in the barrel... but I don't know.. that stuff is slick as snot when you are loading as it seems body heat alone from your fingers will make it "slicker".

 

[FromMyColdDeadHand]

I would think it would have to be lube related. I would think that the barrel is too big to heat up itself, in bulk, and cause that change. I was just surprised that it had that big of an effect and that it takes only 120 seconds of so to show a 30-40fps difference. I wonder if it is the Lapua Center X lube in particular? I have thought about keeping the ammo in like a close chest pocket to get it warmer and at least more consistent- if that is hot enough.

 

[djdilliodon]

How does the gun shoot? How are you cleaning the barrel? Any access to a borescope by chance?

 

[Va_Gentleman]

I am pretty sure the Biathlon lube is different due to the colder temps in Biathlon. @armorpl8chikn would use Biathlon when our competitions were chilly..... His input would be good on this too.... I am interested, as this impacts the scores and could help me strategize our next match... A lot of misses that we see on the targets are high and in shots 4 -10... PAR time is 180 seconds for 10 shots.. so they warm up quick.

 

[4sfed]

I see Eley increasing in velocity from 1060 to 1090 within the first 3 or 4 shots.

 

[armorpl8chikn]

It seems I have Ben summoned...

Well...all I can say is this correlates with our long standing trend accross 10-15 well known rifles in our circle. The general understanding is this:
Long range results can be very sporadic in temps under ~80deg.
When our southern delightful summer arrives, if you have a stellar lot of 922A, CenterX, or Midas, the planets seem to align.
If memory serves ALL our (that our is not me but several shooters) record scores have been logged in 90+deg weather. Apache has the score cards going back to 2010. My best scores were ALWAYS shot in very hot humid weather....always.
There is a correlation between ambient temperature and higher or lower scores. I'd say those score cards would tell an incredible story.

As far as Crono numbers, I don't know of anyone in our circle that does that, we always put lead on steel. We have some impressive lead smudge pics.

It can be a lube thing, but that isn't all of it. The waxy lube of 922A definitely isn't performing until at least 80deg, but eel snot is a bit more forgiving, but not much.

As to the BiPolar....I've backed that horse a time or two. I think it's mostly a dead end street for our purposes. Yes the lube is very waxy....almost hard even, which scrambles my brain a bit for cold weather ammo.

I been at it 8 years now in a "semi pro" capacity (chuckle). Chasing the magic in a white coat is exhausting.
Just have fun with it, most folks will spend a very long time achieving the ability to outshoot their ammo.

 

[armorpl8chikn]

Also to add:
We were only at it a short time when we discovered this temperature anomoly.
I was trying to come up with a way to make a barrel cozy from battery powered socks.
The juice isn't worth the squeeze. The lowly but impressive little rimfire has a ceiling. No amount of money is going to crack that ceiling.

 

[SporterII]

To the OP
Temp Andthe cover you are shooting under.
Sunshine on your barrel and ammo.

 

[Va_Gentleman]

(On cool competition days with sun, I would leave my magazines in the dashboard of my truck!!)

 

[natdscott]

Rimfire BR guys have noted this, and accompanying impact shifts, for years. Their solution has largely been to try to keep the time between shots to 45 seconds or so.

...and there ain't NOBODY as crazy as rimfire BR crazy.

 

[FromMyColdDeadHand]

How does the gun shoot? How are you cleaning the barrel? Any access to a borescope by chance?

I'm using the Slip2000 family of cleaner and lube. Clean, lube, run a dry patch. These shots were probably 100 shots in, so I would think not much would be left. Gun shoots good. 10 shots touching at 50yards. One thing I did notice, before I was running the chrono, was a string where the rounds hit my POA, then then the POI climbed 1/2 a bullet diameter for about 6 shots.

To the OP
Temp Andthe cover you are shooting under.
Sunshine on your barrel and ammo.

Cloudy day, under cover, 65F when we left and these shots were taken. Pretty stable conditions. Wind was about 10 from 1-3 oclock.

Rimfire BR guys have noted this, and accompanying impact shifts, for years. Their solution has largely been to try to keep the time between shots to 45 seconds or so.

...and there ain't NOBODY as crazy as rimfire BR crazy.

I've felt that the gun/ammo temp was more important than air temp. I remember leaving some rounds out in the sun on a hot day in a loaded mag and those round FLEW. Also if the gun rack was in the sun between rounds seemed to have an effect.

I'm just looking for predictability, or at least consistency. We get a lot of cold to start and 90 degree days out here in CO. I think I'll get a big old battery pack for the Labradar and camp out early on the 200 yard range and shoot single dots that I can correlate to MVs and cross reference to ammo and gun temp.

 

[natdscott]

I think I'll get a big old battery pack for the Labradar and camp out early on the 200 yard range and shoot single dots that I can correlate to MVs and cross reference to ammo and gun temp.

Unless your matches are shot at chronographs, you'd be better to spend your time finding out WHERE the bullets are going rather than how fast they get there.

-Nate

 

[Tiger_Shilone]

Interesting data for sure FMCDH.

Went and looked up my chrono data using Center-X on the Vudoo, Martini MKII and CZ455 and I don't have that trend, but I also do not have time between shots so I can only go off the first shot of the string. Most of my data strings are around 25 shots on average. 2 of those barrels are 16" and the martini is 28"

I'll start keeping times for the ARA benchrest shoots later in the year

 

[FromMyColdDeadHand]

I'm a data nerd. Give me a couple hundred or more data points to play with and I enjoy slicing and dicing. Figuring out vertical POI from velocity data and then looking at shot time and ambient, ammo and gun temp sounds like a fun morning. My guess is that I'll get to a point of what a cool bore offset will be. Right now it seems about 1mil elevation difference at 200yards. Cold to hot. But that is anecdotal.

To me, getting the velocities and shot placements will take the 'what happened' out of the mix.

 

[armorpl8chikn]

Give me a couple hundred or more data points to play with and I enjoy slicing and dicing. Figuring out vertical POI from velocity data and then looking at shot time and ambient, ammo and gun temp sounds like a fun morning. My guess is that I'll get to a point of what a cool bore offset will be. Right now it seems about 1mil elevation difference at 200yards. Cold to hot. But that is anecdotal.

That sounds like a root canal to me.

To me, getting the velocities and shot placements will take the 'what happened' out of the mix.

It won't.

 

[Va_Gentleman]

Need to have a covered 200 yard indoor range... and a big 4x8 sheet of white foam board. 2 boxes of Center-X, a chrono, a vice that slides horizontally and a data points of FPS and Impact...

 

[FromMyColdDeadHand]

As I was putting away my gear, I was thinking about how to take the monkey out of the equation with some kind of rig....

Armor- Why not? I know it won't take everything out. But it should be the major driver of the vertical dispersion. I think Tubbs is looking at chrono data for his extreme long range shooting as another tool to divine out the entrails of each shots the feedback from the ballistics gods.

I love parsing out the signal from the noise. Systems always seem chaotic when you look at them and then you start to tease the information out of the data- and all of a sudden all you can see is the signal and you wonder how you ever missed it in the first place. Make a theory, test the theory, break it, and start over a bit smarter, or wiser- definitely poorer.

 

[JG26_Irish]

A few years ago, I was shooting a Rem540XR that had a few miles on it. It shoots great but it always took 5-10 rds to warm up and settle down. Also, if I paused for more than 60sec between shots I could expect the groups to expand until it warmed up again (~5 shots). If I stops for say 5 or 10 minutes due to the range going cold for tgt placement or any other reason, I had to shoot 10 more shots to warm it up and get it to group at its best. Anytime the bbl was cold or cooling, it would disperse the POI more than usual. I failed to record any data which indicates if the dispersion was more or less in the vertical vs horizontal. I thought this was normal until I purchased a 2nd Rem 540XR which was in near unfired condition. This gun had a tighter bore and would warm up and settle down much faster and was far less temperature sensitive than the older, well worn model. My recollection is that cold bore shots were usually high-right at 50y. I did not shoot either out past 200y. The old worn out 540 still recorded my best 100y groups and some of my best 200y groups. These were with both Eley and Lapua ammo.

Speed of sound is lower at colder temps. It is about 1086 fps, at freezing which means that the typical tgt ammo may be hovering close to going supersonic in very cold temps. I think the most of your biathlon ammo including the Polar Bi-match Lapua stuff is dialed back a little to insure that it is not going ballistic since that would upset the accuracy. The lubes are different too.

If you have a way to slug your bbl you might be able to mic the slugs and see if it is slightly loose? or not when compared to a rifle that is less heat sensitive? Guessing now. You said it was a Douglas 24"? Is it cut rifling or button rifled? Are you using any kind of muzzle dampener?

Irish