First time using Pro chrono for rifle

[Rottenron]

Have a 300 Rum 26" barrel 1-10 twist.Use reloader 25 load used 90.grs 210 grs berger bullets and 0.005 off the lands.first shoot was 3211 ,then 3156,3180,3211,3200,3194.is this variation acceptable or should they be more closer to each other like only a couple of feet per second difference. It was a bright sunny day would that cause variation like this.Like I said its my first time shooting a rifle through the chrono.gun)

 

[blicharski1989]

That is a pretty good extreme spread.

I would confirm that the actual velocity measured is accurate within reason.

Try changing primers, make sure your COAL is consistent, back off the load a little bit? 3200 FPS is a pretty stout load. Some powders shoot best at max, some run best slightly below max from my expierience ( limited)

New Barrel? how many rds through it? signs of fouling?

What distance was the Chronograph from the muzzle? Some chronographs require 15-20 ft from magnum loads to get accurate readings

 

[Broz]

If the chrono was closer than 18 ft. move it out and reshoot.

Jeff

 

[MontanaRifleman]

Have a 300 Rum 26" barrel 1-10 twist.Use reloader 25 load used 90.grs 210 grs berger bullets and 0.005 off the lands.first shoot was 3211 ,then 3156,3180,3211,3200,3194.is this variation acceptable or should they be more closer to each other like only a couple of feet per second difference. It was a bright sunny day would that cause variation like this.Like I said its my first time shooting a rifle through the chrono.gun)

I have a Prochrono and overall it seems to be fairly accurate. It does spit out some off the wall numbers occasionally and i have seen it give averages that were different by 50 fps and more with the same load on the same day under different light conditions. I would recommend shooting your loads on overcast days. I set mine up at about 15' but Broz's recommendation of 18' is probably a good one.

You might also try 215 or 230 Hybrids in your RUM. Significantly better BC's and LR bullets than the 210's.

 

[Rottenron]

I am using Rem 9 1/2M primers.I did have the chrono 18' away and the rifle is knew .It only has 29 rounds down her.I did have 10 rounds already through it and did not clean it before i tried it through the chrono and the coal is the same on all the rounds.What primers would you recommend to uses.I appreciate all the help.Got to get all the bugs worked out before I go on my elk hunt this year. First time elk hunting

 

[jasent]

Also remember that that chrony (and most others as well) is +/- 5%. That could be 15-30 fps off. Double check by shooting at 400-500 yards and measure your vertical spred

 

[MNbogboy]

Lots of things might come into play here....Sunny days are rough on a lot of chronos...reflections off the bullet can cause premature timer starts or trips....

Another thing you mentioned is only 29 rounds down the tube....Makes me suspect that you may still be using "new" brass.....Usually it takes me 2 or three firings before the brass has stabilized.....

The list of course goes on & on....(powder charge variance, primer seating, neck tension etc.)

Your SD for the six shots was just a tad over 19....That is about 1/2 the way there already...My guess is the next time you try (on an overcast day) with two or three fired brass that your ES and SD will be a lot better.....

Good shooting,
Randy

 

[Rottenron]

Oh ya forgot to mention I was using new nosler brass.
Thanks alot guys for all the help I can use all the help I can get.