Home Forums Hunting & Shooting Ask The Gunwriters Very erratic velocities?

Guys I have a strange one, never seen or heard anything like this.

I have a KS 700 in 280 Rem and was just working up some 140 grain loads and am experiencing widely ranging velocities. These are Win cases in nickel which I picked up somewhere as once fired. I resized them just till I felt resitance when chambering and then bumped them back .004. Trimmed to length and seated Federal 210 primers from a lot that has given me no troubles. I started out with AA4350 powder of which I have a very good supply of and started working up loads over the chronograph.

Crazy stuff! Would get velocities that changed 200-300 fps from the same loads! Tried 3-4 different powder charges, no change. Thought well bad powder, so I got a fresh can of R-19 out, same deal. Figured I got some crazy bullets, checked weights, all good but got another brand anyway. Same deal.

Figured my chrono was wacky maybe. Put fresh battery in and no change. So I ran some 243 loads I had done a couple days ago. Perfect. So not the chronograph.

I built some 162 grain loads for the 280 a couple weeks ago and had no issues, using a different batch of cases.

Could the cases cause this? They look fine and I ran into no issues sizing etc. It was some I had never used before. Never saw or heard of anything like this! Looking for some ideas.

I'd try sizing the "now fired in your rifle" nickel cases and see how they work out. In fact, if it were me, I'd only partially neck size those fired cases to give a light crush-fit on a false-shoulder on the neck.

1. "Once-Fired" sometimes isn't, depending upon your source. So, you could be dealing with work-hardened necks.

2. Commercial "once-fired" might not have been fired from the same bbl/chamber.

I've bought a fair amount of commercial once-fired brass. Everything except 223's get's fire-formed to whatever rifle I intend to use it with prior to actual load workup with it. If I already have a load, I still "fire-form" the once-fired to my chamber.

223's all get small-base re-sized then loaded on a Dillon 550 or 650 and used in a multitude of different rifles.

Does it do the same thing with NON-nickled cases????......

Neck tension variance..................assuming your powder charge variation is not the problem. Thrown with powder measure or weighed individually.

MM

Did not notice anything erratic prior with brass cases but have not shot this gun a lot. Had a bunch of factory loads I had picked up at a very good price and shot those mostly. Just recently started loading for it.

I use a Pact electronic powder dispenser and it has always thrown accurate charges. I do check it with my manual scale after it goes through the calibration when first turning it on or changing powders.

I had cleaned the rifle about midway through this ordeal and as I think about it the pressure on the cleaning rod seemed to change just a bit, it was slight and I did not think much of it at the time but after going over everything I am wondering if there is something going on in the bore.

I do not have a borescope but do have some JB bore paste, maybe I should try giving yhe bore a good scrubbing with that,

This^^^^^^

How close is the Chrono? Muzzle blast can cause bad readings (high) and the .280 may have more than your .243.

You'd have to be a terrible hand at the powder measure to get 300 fps swings like the OP mentioned.

About 15 feet.

Are the readings showing faster than expected or both high and low? Muzzle blast gives fast readings.

Or, it's just a bad KS and you should sell it to me for further evaluation 😃

No the highs seem about right, the lows are way off. For example a 56.5 grain charge of R-19 will show just over 3100 fps which is right in line, the next shot may be 2750. This is using a 140 Nosler PT.

Are you a southpaw? This is a lefty.

Was the sun shining directly on the slits of the light sensors? Even with the diffusers, I used to see weird velocities with my old Pact chronograph and its skycreens especially around noon to 3:00 or so. I guess the sensors were essentially “blinded” or overpowered by direct light shining into the slits. I taped pieces of cardboard alongside the skyscreens to keep the slits in shade.

Sometimes using a black Sharpie to darken the bullet can help too.

Nevermind....☹️

Overcast

Lol!!

Ok guys. I just got done scrubbing the bore thoroughly with a brush wrapped with a patch and bore paste. I got a LOT of black junk out of the barrel and I have no more "rough" spots. Carbon fouling? It is soaking now with Marvel Mystery oil which is an excellent penetrating oil. I am going to let it set overnight with the MM oil and will clean again tomorrow and see what I have.

So could an excessive amount of carbon cause these erratic velocities?

The factory loads were Federal HE loads with the Trophy Bonded bullets. I still have 3-4 boxes of these.

Just for schidts & giggles, as a quick test I'd swap primers to something a bit warmer... WLRs or magnums of whatever sort you may have & shoot 5 or 10 shots to see if that fixes it. Fed 210s are fairly mild & AA4350 is closer to IMR 4831 than the other 4350s.

I have used Fed 210 primers in my 270 and 30 06 with AA 4350, H 4831 etc with no issues.

I am wondering if the Fed HE loads caused this as that is mostly what was fired previously in this gun. Probably had 2 boxes fired since last cleaning. I have not used this gun a lot.