Odd condition...

[nikonNUT]

Good morning and happy Labor Day all! IF this is in the wrong section I apologize. I think I finally have my load dialed in but I'm getting an odd condition. Loaded up 31 (whipped up a fowler) rounds yesterday and hit the range. I shot a fouler and then a 5 shot group to check accuracy then strapped on the Magnetospeed V3. I was shooting 5 rounds and then cooling the barrel for 7 minutes with a Magnetospeed Rifle Kuhl (the suppressor and the barrel get warm). The part that's throwing me is this. The first shot was always 20 to 30 FPS slower than the rest. Culling those shots resulted in an ES of 8 and a SD of 3.1 (pretty OK in my book) over 24 shots. Not culling? UGH! Not great... So am I over cooling (seems unlikely?) my barrel between strings or is something else going on? The result is crazy consistent and I'm at a loss!

 

[Supersubes]

Not unusual at all. Sometimes they start faster than the average. I have a proof barrel doing that now. But you know what, that first round always go into the group, evan at distance. If your first round goes into the group, move on, you’re done. If yours doesn’t go in the group, map it out for consistency, and work the deviation into your cold bore shot setup.

 

[Milo 2.5]

Good morning and happy Labor Day all! IF this is in the wrong section I apologize. I think I finally have my load dialed in but I'm getting an odd condition. Loaded up 31 (whipped up a fowler) rounds yesterday and hit the range. I shot a fowler and then a 5 shot group to check accuracy then strapped on the Magnetospeed V3. I was shooting 5 rounds and then cooling the barrel for 7 minutes with a Magnetospeed Rifle Kuhl (the suppressor and the barrel get warm). The part that's throwing me is this. The first shot was always 20 to 30 FPS slower than the rest. Culling those shots resulted in an ES of 8 and a SD of 3.1 (pretty OK in my book) over 24 shots. Not culling? UGH! Not great... So am I over cooling (seems unlikely?) my barrel between strings or is something else going on? The result is crazy consistent and I'm at a loss!

I have seen funky things with barrel coolers, though never have a chrono in play. Lately with a friends thinner barrel Bergera, we run a rifle kuhl because he has one rifle. Never letting the barrel completely cool, his first shot is always erratic, and I think it is because the inside is cooler than the outside, one shot and good to go. I guess we need to get the whole barrel to ambient and try a couple.
Barrels coolers are sweet, but nothing beats standing them in a corner and letting nature work.

 

[Threadcutter308]

I've resisted the temptation for a barrel cooler. Introduces too much temp variation between cold barrel and hottest barrel. I shoot off the bench and give a 60 second break between shots.

For me, pretty common that the first shot is slower, 30 FPS sounds similar to what I've seen.

 

[nikonNUT]

Thanks guys! It's an MTU profile (I think? 1.125" at the action and .930" at the muzzle.) so there maybe a funky thermal "transfer" thing going on. I was mainly running the Rifle Kuhl to keep suppressor temps in check. I'll try letting nature handle it and see what comes of it. I actually had the though cross my mind that first round pop and velocity might be interconnected. Weird right?

 

[Bandit320]

Ate you letting the rounds set in the barrel for an extended period before you fire them? A hot chamber could be heating the powder in rounds 2+ of the string and increase the velocity, depending on the powders you’re using.

Mike

 

[nikonNUT]

Ate you letting the rounds set in the barrel for an extended period before you fire them? A hot chamber could be heating the powder in rounds 2+ of the string and increase the velocity, depending on the powders you’re using.

Mike

Single feeding and a chambered round is sitting for maybe 15 to 20 seconds...

 

[nn8734]

Good morning and happy Labor Day all! IF this is in the wrong section I apologize. I think I finally have my load dialed in but I'm getting an odd condition. Loaded up 31 (whipped up a fowler) rounds yesterday and hit the range. I shot a fouler and then a 5 shot group to check accuracy then strapped on the Magnetospeed V3. I was shooting 5 rounds and then cooling the barrel for 7 minutes with a Magnetospeed Rifle Kuhl (the suppressor and the barrel get warm). The part that's throwing me is this. The first shot was always 20 to 30 FPS slower than the rest. Culling those shots resulted in an ES of 8 and a SD of 3.1 (pretty OK in my book) over 24 shots. Not culling? UGH! Not great... So am I over cooling (seems unlikely?) my barrel between strings or is something else going on? The result is crazy consistent and I'm at a loss!

With the suppressor on, what is your cold bore elevation hold over at 600 (or any significant distance) with that load and how does it compare to your warm bore hold over?

 

[nikonNUT]

With the suppressor on, what is your cold bore elevation hold over at 600 (or any significant distance) with that load and how does it compare to your warm bore hold over?

I have not checked hold over yet as I was just chronoing my loads. I only have 200 yards ATM but I will get a number and report back. I would say it is prett minimal at that close range.

 

[Ledzep]

Try it once without the suppressor. Just look at velocity and see if the 1st round still drops low.

 

[nikonNUT]

Try it once without the suppressor. Just look at velocity and see if the 1st round still drops low.

So loaded up a handful of rounds (Nothing super critical as far as process control ) and hit the range sans suppressor as suggested. Shot a fouler and a 5-shot string for grouping and then slapped the chrono on and checked MV. Time between shots was 1 minute plus time to switch from my readers to my shooting glasses chamber a round. It went like this...
#1 2743 FPS
#2 2737 FPS
#3 2749 FPS
#4 2743 FPS
#5 2749 FPS
SD of 17 and an SD of 6.4 (not great but I think I fell off the node a bit). All in all shot to shot seems a lot more consistent without the can and shoots much softer. I'm going to re-tweek my load and save the can for the 6.5CM.

 

[Ledzep]

ES/SD numbers look fine for a 5-shot. A friend of mine also noticed his first shot 30-40fps slower than the rest of his string. Removing the suppressor straightened it out.

What caliber are you shooting? My friend was experiencing it in a 6mm ARC bolt gun. We don't have a good explanation for it yet. Same suppressor with his 6.5 Creedmoor behaves normally. Can is a 30 cal Dead Air Nomad.

 

[nikonNUT]

ES/SD numbers look fine for a 5-shot. A friend of mine also noticed his first shot 30-40fps slower than the rest of his string. Removing the suppressor straightened it out.

What caliber are you shooting? My friend was experiencing it in a 6mm ARC bolt gun. We don't have a good explanation for it yet. Same suppressor with his 6.5 Creedmoor behaves normally. Can is a 30 cal Dead Air Nomad.

I'm shooting a .338LM bolt gun and the can is a Hybrid 46 with a 9MM bravo cap. I'm in the same boat in that my 6.5CM gas gun runs perfectly fine. I have no expiation either. Is your friends 6.5 a bolt gun or a gas gun?

 

[Ledzep]

His 6.5 is a bolt action, also.

 

[nikonNUT]

His 6.5 is a bolt action, also.

Well my theory is out the window then. I was hoping you were going to say gas gun so we could have an "Ah ha!" moment. So weird!