Velocity drop

[2skeet]

I have a seasoned 700 Remington in 260 caliber. My current load of 47grs of R-19, Federal Match primer, 120gr BT Nosler that is showing 2970FPS. It's very accurate and does well on whitetails, but I decided that I would try to work up a load with a heavier bullet. I settled on Hornaday 129gr SP Interlock and was working with R-19 Remington 9.5 primers. Starting loads of 42grs to 45grs with 1gr jumps. I'm running these across a Caldwell G2chronograph. The velocity's have been very constant to published data from the Hornaday manual. Until I shot the load of 44grs. It produced the one of the tightest groups in the test but really throwed me a loop when FPS reading came back almost 700FPS slower then published. This was a four-shoot grp and the deviation was less than 20FPS. The next load of 45grs of R-19 the velocity came back up to mirror book spec. The powder drops where scaled, powder is from the same lot, same with primers and bullets. I know the chronograph is not a high-end unit, but it has been constant. This has me scratching my head. Any and all thought appreciated as to why this particular load dropped off so badly. Thanks

 

[Eagle Six]

Setup your Caldwell and shoot it again.

And, Welcome to the forum.

 

[Kurz]

Any number of variables could be causing a significant change.

Always check significant variations by shooting the same load again and even possibly a third time to see any justification. I'd shoot that same load as developed as many as 10 times to prove repeatability.

700 FPS on one shot could indicate a chronograph failure. Or a failed powder drop. Nearly dead primer...

More testing.

 

[Chuckhunter]

To me it sounds like a chrono error more than a load error but this is just an educated guess. If the cases didn't have smoked shoulders and the primers looked like the rest of the loads, I think you're all right. 700 fps is a hugh error, that's what makes me think it's a chrono error. Let us know if you get it figured out.

 

[Coyotefurharvester]

How many loads in the 44 gr group? Did you restart the chronograph after seeing the 44 gr group readings?

 

[2skeet]

Thanks for the responses. I usually shoot three shot test group loads, but this one had four in it. The three-shot group before and the three-shot group after, all were within 40fps of Hornaday's manual. No, I did not turn the chronograph on or off during the test. Before I start each new load, I enter the load information in the app on my phone fire and then save the group. My plan is to retry the load again to see if anything changes. I'm still in the learning curve on using a chronograph.

 

[MrK.]

My Caldwell gets wonky when the battery gets low. I change it about every 3rd or 4th session. Recently I was shooting 6 ARC groups with a load doing about 2900. I had two consecutive shots that were both around 1250. I changed the battery and no further issues.

 

[2skeet]

Had a chance to get to the range today to retry the loads that were way low on velocity across my G2 Caldwell last week. The results were good. Velocities all duplicated or were within published reloading manuals. Don't know what may have happened, but again I'm guessing the hobby grade chronograph just laid an egg that day. I believe that I'm going to settle on the load of 44grs of Reloader-19 with the 129 Hornaday SP Interlock Remington 9.5 primers. FPS avg. 2743 with a 9.0 deviation. Had three touching. Going to load back and see if I can get a repeat. Again, Thanks for all the input and ideas.

 

[fkimble@charter.net]

Sounds like the crono picked up 3 shots and then you divided by 4!

Frank

 

[Zero333]

Or you accidentally charged 34 gr instead of 44 ?

But what Frank just said makes more sense