Interesting chrono readings

[42769vette]

Caliber 28 Nosler
Purpose, 600 yard hunting rifle
Powder 81.9 gr H1000
Bullet 162gr ELDX
Brass Nosler
Chrono Magneto speed
Barrel Bartlein 26 inch 8.5 twist


So I'm having some odd readings, that I'm hoping someone can explain. I have had the same basic results a few times in a row now. When loading a 6 shot batch, I have a velocity jump. velocities on the last group were as follows.

Shot 1=3200
Shot 2=3198
Shot 3-3204
Shot 4=3230
Shot 5=3226
Shot 6=3232


In all 3 batch's I had a velocity jump on either side of shot 3, but the SD's were consistent. Since Ive never heard of a barrel heating up after a couple rounds, and velocity changing this drastically, I'm thinking my Chrono is shifting a little, and my real velocities are pretty constant. I'm trying a new method of load development, so I haven't put rounds on target so see what it looks like on paper.

These rounds are always shot in order of loading. Could my Acculab 123 be jumping around a bit to cause this? I do realize for this rifle's purpose it wont matter at all, It just peaked my curiosity.

What are the thoughts of the group?

 

[Willie]

You didn't mention your rate of fire, but I would suppose it is the barrel heating up. Do you have a way of monitoring barrel temp? What contour is barrel?

 

[42769vette]

You didn't mention your rate of fire, but I would suppose it is the barrel heating up. Do you have a way of monitoring barrel temp? What contour is barrel?

I have no way of measuring barrel temp. The countour is a 3B, and 5 rounds were shot in a couple minutes. It wasn't timed, but not slow, not fast. I guess Ive just never seen barrel temp jump velocity like this.

 

[Dusty Stevens]

Thru 3 shot groups on a hunting rifle. Something that big gets way way too hot on a 5 shot

 

[Rsadams]

I have no way of measuring barrel temp. The countour is a 3B, and 5 rounds were shot in a couple minutes. It wasn't timed, but not slow, not fast. I guess Ive just never seen barrel temp jump velocity like this.

Try the stick on barrel temp strips from McMaster Carr... Cheaper than most and you get like ten of them...they stay put also... You can even get their app on your phone from the play store or their online website....

 

[Bc'z]

32fps spread at 3200.how much different is poi going to be at 600 yards. Curious is all.

 

[rwj]

I’ve experienced unexpected velocities with my Magnetospeed. They were traced to the bayonet not being properly secured to the barrel and moving under recoil. A witness mark on the barrel makes detection easy.

 

[Falfan2017]

32fps spread at 3200.how much different is poi going to be at 600 yards. Curious is all.

Very little. 32 spreads is pretty good for a hunting gun. All else equal that would change your poi about .25 inches.

 

[Willie]

I have no way of measuring barrel temp. The countour is a 3B, and 5 rounds were shot in a couple minutes. It wasn't timed, but not slow, not fast. I guess Ive just never seen barrel temp jump velocity like this.

I shoot a 7stw in a 3B (fairly close to your rig) and after two shots, the temp is too hot and velocity jumps 40* on a third shot. For load testing with a hunting rifle, I always let barrel cool to ambient temperature between shots. Get the temp strips or Lazer temp gun, both are cheap.

 

[hogpatrol]

I have two 28 noslers, one a sendero contour, the other, a #5 fluted.. using rl33, they get very hot after three shots. Try two shots and let it cool. That's a lot of powder.

 

[42769vette]

I have two 28 noslers, one a sendero contour, the other, a #5 fluted.. using rl33, they get very hot after three shots. Try two shots and let it cool. That's a lot of powder.

Thanks. I loaded 5 rounds, and will shoot them periodically throughout the day tomorrow, and see what happens.

Thanks.

 

[42769vette]

32fps spread at 3200.how much different is poi going to be at 600 yards. Curious is all.

My caluculator shows 1.4 inch's, so like I said not enough to make a diffrence, the consistancy of the jump, and the amount of the jump just peaked my interest.

 

[dickn52]

I have no way of measuring barrel temp. The countour is a 3B, and 5 rounds were shot in a couple minutes. It wasn't timed, but not slow, not fast. I guess Ive just never seen barrel temp jump velocity like this.

Get one of those thermometers that works off a laser pointer. But be quick with it of have someone else actually take the temp for you.

 

[hogpatrol]

Looked up some old MS chrono data for the 28 Nosler Sendero (Brux) barrel. 87.5 gr. of RL 33 with Berger 168HVLDs.
Fired three shots, 3220, 3228, 3202, Let cool, then fired two shots 3223, 2325.

 

[Roach]

I was out testing some loads today. I'm pretty impatient with waiting. With the 6.5CM first shot was 2710 and 5th was 2754. On another string I waited about 30 seconds between shots and had the first two at 2772 and the last 3 at 2777. I guess waiting helps.

ETA: different load obv

 

[nmkid]

I’ve experienced unexpected velocities with my Magnetospeed. They were traced to the bayonet not be properly secured to the barrel and moving under recoil. A witness mark on the barrel makes detection easy.

When I started to get, "funny" readings with the my Magneto Sporter the first thing I would check is the tightness of the strap on the barrel. Now I check it after every round. Problem solved for me.

 

[Dusty Stevens]

You cant do load development waiting even 5 minutes between shots. Shoot 2-3 and see what it does. Who cares where shot 4-5 even go in a hunting situation. Even shot 3 doesnt matter

 

[Liven The Dream]

I had a 7 mag. Custom Build . After load development . Cold 200 yard 3 shoots 1/2' at 200 yards.
The more rounds the group would open.
Killed game easy. Sometimes to much Gun on Deer. it got a new Home.

 

[rayporter]

to duplicate opening day of season fire one shot per day.

velocity may vary and groups will be larger but that is what you will really be dealing with.

 

[rayporter]

since the title is about chrono readings

how many of you have watched the velocity of 2 bullets that start at the same velocity, say 3200, and at the 60 yd point one would be faster?

or one that started at 3200 be at 3050 and one that started at 3190 be going 3057 at 60yd
[ I pulled these numbers out of thin air since I have not got a 28 nos]