Extremely low muzzle velocity (1350fps)...

Smith.denverlee

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May 10, 2018
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I could use a little help trying to figure out a problem. I picked up a Savage prefit barrel from Carbon Six in 6.5 Creedmoor. I loaded up some rounds and noticed the chamber had less throat than I expected. I was using 140 gr Hornady SSTs and had to keep the OAL under 2.800” otherwise I was jammed and had a tough time lifting the bolt and removing the round.

I went to the range today to do my barrel break in and my first round came in at 1350 fps with 41.2 gr of H4350. I initially thought it had to be an issue with my chronograph and it just got a bad read. I took another shot and it came in right at 1350 too. I still wasn’t sure I trusted the chrono to be right and hoped it was just a low battery type issue. I took another shot with a slightly higher load (.2 gr) and it came in at 1380. I had another shooter with me and we decided to test the chrono on his rifle. With factory ammo he was at 2750 and with my handloads he was at 2550. This leads me to believe I was actually getting those low speeds. I have never seen or heard of this before. I knew barrels could fluctuate in speed some, but this is way beyond anything I expected. Has anyone seen this before?

My initial thought is that maybe the bore is two small. I am thinking that generally a slightly smaller bore would allow you to build more pressure and maybe get a bit more speed but if the bore is too small it may be restricting the bullet so much that it is killing the speed. The only other thought I had was that the chamber was too loose limiting the pressure build. I didn’t have any overpressure signs on the brass and checked my go/nogo gauges when I got home and everything still checked out. I am at a bit of a loss.
 

lariat

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I would think it would be too big rather than too small if you are not seeing any overpressure signs. That energy has to go somewhere and if it was staying in the chamber it should be hammering your brass.
 

lariat

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Another way to confirm the chrono would be to do a modified ladder test. The drop would tell you an approximate velocity for a given bullet weight.
 

ma smith

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Shoot it at some distance X on paper
and do the ballistics...

1350 isn't far off 22LR ballistics
2700 is exactly 2x (double),

drop ... should be way off
even @ 100yds
 
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Jef-in-AZ

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Jan 19, 2021
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What chrono? Some that require you to supply your own beam for the sensors to sit on have a switch to select different lengths. For example if a 18” bar is used for a 36” sensor setting it will read double velocity, and vise versa.
 
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308sako

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If it's a 6.5 the outside of the fired neck portion of your cases should measure approximately .297" as mentioned above it just might be a barrel blank of a larger caliber was mistakenly chambered as your 6.5 dream rifle.
 

DairyDictator

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Either your bore is massive, or that chrono is fucked. If the bullet drops right down in the muzzle, they used the wrong blank. Funny, I would think they would have caught that when they went to use the chamber reamer. Without support from the bore, it had to have been wobbling around pretty good.

Also, check to make sure it actually has rifling while you're at it. I've only ever seen it once, but it's a possibility.

If neither of those things are the problem, that chrono is definitely broken.

If the bore was too small, your velocity would be through the roof if it made it out of the barrel and you'd be blowing primers at a minimum.
 

redbullitt

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I'd think chrono first unless your have verified it works well, maybe shooting something of known speed through it?

Could have missed it, but I didn't see what chronograph is being used?
 

WhiteDingo

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Also, check to make sure it actually has rifling while you're at it. I've only ever seen it once, but it's a possibility.

That's interesting. I actually had a rifle come in the other day that someone had purchased from a shop across town. Lower end AR, wasn't grouping (actually tumbling) at 50 yards. The bore was as bright and shiny (and smooth) as an off the rack Benelli. Oops.

If OP's chrono is measuring his buddy's projectile velocity as correct (which I think he stated), I would lean towards the wrong caliber blank being used.
 

sgtmack

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Just thinking out load, but if the bore was oversize enough to cause that much velocity loss, would you notice the short throat? A larger bore should allow the bullet farther into the bore before it hit the rifling.
I would check how tight a bullet fits in to the muzzle. If it disappears they used the wrong blank. Of course if they did, you will need to have it replaced, and then they can rechamber this one in the proper caliber so you you can use it to build another rifle.
 
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whatsupdoc

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    Take a bullet and stick it into the muzzle end of the barrel.
    Does the rifling contact the bullet ogive?

    Dis you shoot another rifle over the crono to check the results?
     

    minn_wild1

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    What scale are you using? Calibrated? Are you sure you didn't have 31 grains?
     

    Smith.denverlee

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    May 10, 2018
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    The chrono is just the Caldwell optical one. I measured the lands and grooves at the muzzle today and they were within .001" of what McGowen specs on their website and consistent with my other barrels.

    I was able to get my hands on a Magnetospeed this afternoon and get to the range for a few shots. I was seeing typical speeds for my charge weight but I was also seeing some pressure signs. The drop also seemed consistent out to 300 yards with the speed readings I was getting.

    Right now I am hoping to just blame the chrono but I am a little bothered that it gave me bad data for my rifle yesterday and then gave decent data for the guy next to me. I am hoping to make it out later this week with the Caldwell and the Magnetospeed to try some more testing to put my mind at ease.
     

    lariat

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    The chrono is just the Caldwell optical one. I measured the lands and grooves at the muzzle today and they were within .001" of what McGowen specs on their website and consistent with my other barrels.

    I was able to get my hands on a Magnetospeed this afternoon and get to the range for a few shots. I was seeing typical speeds for my charge weight but I was also seeing some pressure signs. The drop also seemed consistent out to 300 yards with the speed readings I was getting.

    Right now I am hoping to just blame the chrono but I am a little bothered that it gave me bad data for my rifle yesterday and then gave decent data for the guy next to me. I am hoping to make it out later this week with the Caldwell and the Magnetospeed to try some more testing to put my mind at ease.
    A few have given good advice here with the bore size and the drop. Now that the bore is confirmed, Back into the speed with the drop data at various distances (bastardized ladder). Any ballistics app can get you there, and it will tell you if your Chrony is shit.

    The only other thing I can think of it that you batch of H4350 is bad, but that’s seriously doubtful.
     

    chevy_man

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    A few have given good advice here with the bore size and the drop. Now that the bore is confirmed, Back into the speed with the drop data at various distances (bastardized ladder). Any ballistics app can get you there, and it will tell you if your Chrony is shit.

    The only other thing I can think of it that you batch of H4350 is bad, but that’s seriously doubtful.
    I've got one super slow lot of h4350, but it was only 2grns to bump the velocity back up.


    I'd say you were shooting through a bad spot in the chrono. I've been using a cheap caldwell and will occasionally get silly readings until I square and level it again, always have to shoot through the upper 1/3 to get decent readings.
     

    Wiillk

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    May 18, 2020
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    First call the barrel maker. Then

    Do a chamber cast. Make sure you get a good casting of the throat as well. From there you can tell what your chamber looks like. Then, slug the barrel. An old school way of telling you exactly what your barrel is. Finally check for any barrel anomalies like a slightly budged barrel that might not be obvious looking at it externally (never heard of this last one but I would check everything).
     
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    Lesloan

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    Mar 22, 2014
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    The OP said that the other guy's gun shot normal velocities with the OP's hand loads. I assume these loads came from the same batch that were delivering 1350 fps in his (the OP's) own gun. If that's true, then the problem is definitely with the new barrel, or so it seems to me. You could slug the barrel to at least eliminate the bore diameter as an issue, but I really think that's overkill. I'd return the barrel & be done with it.
     

    rottenruger

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    May 31, 2020
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    How'd the brass look? Pressure signs, soot around the neck?
    What does the soot around the neck signify? I was shooting some 6.5 CM in my old Savage, ammo I use regularly in my RPR, and it was acting difficult and sooting the neck....but no further down. Hornady, Lapua and Norma brass, 140 ELDX bullets, now with Superperformance powder.

    I did some research and came on the concept of small base sizing, something I was not familiar with, but providence had me with the die so I tried it right off and it solved the problem........

    But I still don't understand the problem or the solution, really. Has this something to do with formfitting to the chamber, and I went awry by switching rifles?

    And do you think I should load separate ammo for each rifle, so the brass can be form fitted to each chamber?

    Thanks for any feedback!
     

    Snuby642

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    It would cost nothing to pull down a round and check the charge weight.