Range Report Variables in chronographs

[krw]

I have a new 260 and ain't impressed with the velocitys I am getting. Had rifle set up for the 123 class of bullets. Have maxed out H4350, 4831SC, and Varget. Have shot SMK's and Hornady A-max's. Planned on using Lapua brass exclusively, but have loaded Rem brass also. Have hit pressure WAY before other loads listed here. 38.5 grs of Varget, Lapua brass, SMK 123, and CCI BR-2 primer yields 2865fps. When bumped to 39gr velocity only rises to 2881fps, only 16fps more with an additional 0.5gr powder. Hornady A-maxs are running 80fps slower with same load. Switched to Rem brass, 39gr Varget hit 2860fps and 39.5gr slowed down to 2846

. I really had plans on more velocity out of this rig. Could the chrono be giving false readings? Have not stretched it out to run the numbers backwards on JBM to chk velicity on it.

 

[sawgunner2001]

Re: Variables in chronographs

The only thing I can tell ya is that chronographs can give wildly different reading based solely on the position of the light hitting it (the sun). In my experience, I can shoot the same load in the morning and get a velocity reading of "x", put the rifle and ammo in the shade, come back in the afternoon and be higher or lower as much as 75 fps. That's what I can tell ya about my experience with chronographs. In order to get true velocity readings, I've chronographed the load many times and taken an average OR the better way to do it is to shoot it (the rifle...not the chronograph) at extended range (at least 500 yards) and match the drop in the ballistic calculator.

Now, when someone smarter than me comes along, they're probably gonna want to know what barrel length you're using to get those velocity readings.

 

[majohnson2]

Re: Variables in chronographs

Not sure on the chrono but I have read that Chrony tend to read slower as they age. Tried R17?

 

[leadbullet]

Re: Variables in chronographs

I have 2, beta chrony bought 3 years appart, same ammo, same time, same rifle, same distance from muzzle etc... 140 FPS dif. new batteries or not,
I feel your pain.

 

[krw]

Re: Variables in chronographs

Barrel is a 24" Kreiger 4-groove finished at 24". Reamer used is a PTG Tactical Match with the freebore shortened to 0.047", with a 0.298" neck to accomodate the Lapua brass. Also bbl is a 1-8.5 twist.

 

[majohnson2]

Re: Variables in chronographs

attherange,

Thanks verifying the Chrony the issue. It sucks that they have a problem, their product looks better Prochrono plastic case. The other nice on the Chrony is the wired remote, it gives you the ability to check your info with out waiting for others to stop shooting. Prochrono has a remote but its almost as much as the chronograph.

Last week when I got to the range there were 2 shooter with chronographs, ironically they where Prochrono Digital units. One guy and a Chrony previously but said it didn't last long and he replaced it with a Prochrono Digital unit. One guy let me shoot some rounds through the screens, why worked great. I've got Prochrono Digital on order, hopefully it makes it for the weekend since I'm going shooting.

 

[Greg Langelius *]

Re: Variables in chronographs

My experience with the .260 suggests to me that H-4350 is a better propellent for it than Varget. Varget maxes out for practical purposes at about 36-38gr with the heavier bullets. I'd suggest that H-4350 is useable at least up to 44.0gr with 140/142's (the 139 tends to peak out at a somewhat lower charge), and will probably give better velocities overall. IMHO, there is no great advantage to maxing out the .260. 2800fps is a respectable velocity for 140-ish bullets to 1000yd, and basically anything over 2650fps will work.

Very few people shoot matches over a chrono. I tend to discount chrono numbers in favor of what the target shows. Basically, a 140-ish projectile and 43.5-44gr of H-4350, with 28-32MOA of elevation above a 100yd zero will put you on, or close to on, paper at 1000yd with the 24" barrel. That load's generating enough velocity to be competitive while still taking advantage of the .260's respect for throat life. Just tune it up and down (staying below 44.5gr) for accuracy. The only thing a hotter load will do for you is make a barrel replacement come sooner.

Greg

 

[krw]

Re: Variables in chronographs

But I had this rifle set up specifically for the 123 wt bullets. Don't plan on shooting more than 600yds and wanted the flatter trajectory the 123's afford.

 

[Jedi]

Re: Variables in chronographs

lose the chrono and reverse calc fps based on actual dope used

long ago discounted chrono data as being accurate

reverse calc is way better option and costs nothing

 

[Greg Langelius *]

Re: Variables in chronographs

But, but..., there's no 'but'.

Folks who were shooting the .260 long before I started back in 2002 were doing what you're doing; 120's, 140's and Varget.

Since then, we've learned that the H-4350 is tbe powder to use, no matter whether you're shooting 142's or 85's. It just works better.

You can pay all the attention you want to your chrono, and place distance and bullet weight limits on your shooting if that's what floats your boat.

However, nothing 'real' starts happening until your switch your fixation onto what the target is telling you; and the target will akways tell you that for accuracy, what works best at the limits of the cartidge's capabilities is also what works best closer in.

The 123 is a great bullet for 600-800yd. The 139-142's work great, maybe best, at all distances. Fastest velocities and flatter trajectories have limited advantage, but they really don't buy you anything outstandingly better.

Folks also shoot shorter barrels at the limits of their capabilities, but all they are really doing is tying one arm behind their back and crowing about how well they can still do.

If folks like swimming with weights around their necks, so be it. I prefer to take full advantage of every advantage.

Greg

 

[D_TROS]

Re: Variables in chronographs

when you say you load to max then xxxx happens, what is max powder?
book max?
or pressure signs?
If pressure, what kind of pressure signs?
also having a shortened freebore will increase pressure. I would not have done that also because SMK's work very well when jumped.

also sometimes, you just get a slow barrel and that's the way the cookie crumbles.

DT

 

[244]

Re: Variables in chronographs

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: krw</div><div class="ubbcode-body">Barrel is a 24" Kreiger 4-groove finished at 24". Reamer used is a PTG Tactical Match with the freebore shortened to 0.047", with a 0.298" neck to accomodate the Lapua brass. Also bbl is a 1-8.5 twist. </div></div>

KRW- Could your shortened freebore cause the pressure to rise more quickly than "standard" freebore? If so, the small increases in velocity with added powder could possibly be an indication that you are reaching max?

 

[rmfield]

Re: Variables in chronographs

Krieger barrels tend to be a little slower and show more pressure. Don't know why, but this is the case with my current 260 (same specs as yours) as well as several other people I shoot with. Some have given up on Krieger for this reason, but there is nothing wrong with the barrel - mine is quite accurate and very happy shooting 142 MKs at 2790 fps. If you really insist on more velocity, try another barrel.

I agree 100% with Jedi above. I've spent endless hours dicking around with various chronographs (Pact, CED, Oeler) and they all fail to provide consistent results as light conditions vary. I even built a tent and used IR with one and the results were only slightly better. Use the chrono to get your velocities in the ballpark and to check ES/SD. Then go shoot at long range and reverse engineer velocities/dope charts.