Someone please help me understand these numbers!

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McAda441
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Someone please help me understand these numbers!

Post by McAda441 » Sun Jan 19, 2020 9:57 am

Got a good deal on a bunch of speer 125gr TNT rounds and so I've been working on some loads. Went to the range yesterday and had something very weird happen once I got into the hotter loads.
H110 powder, WSR primers, and once fired frontier brass for all rounds w/o crimp. Shot out of an 8.5" noveske match barrel 1:7 twist. Velocity recorded with my LabRadar chronograph
10x 17.5gr 2.060" coal -- 1864 avg fps sd 26 1.5" spread
10x 18gr 2.075" coal -- 1924 avg fps sd 29 1.2" spread
10x 18.2gr 2.075" coal -- 1931avg fps sd 18 0.8" spread
10x 18.5gr 2.075" coal -- 1944avg fps sd 22 0.75" spread
10x 18.8gr 2.075" coal -- 1978avg fps sd 14 1.2" spread
10x 18.8gr 2.100" coal -- 2054avg fps sd 25 0.6" spread
10x 19gr 2.100" coal -- 2098avg fps sd 19 0.4" spread
Zero pressure signs in any cases, obviously published load data hasn't properly tested this projectile.
Anyways, i have two questions. First, does anybody have any explanation as to why I had such a large increase in velocity with the slightly longer 18.8gr rounds?
Second, doesn't 2100fps seem pretty damn high out of an 8.5" barrel? Avg was 2098 but I had two rounds at 2112fps. Maybe someone with quick load can crunch some numbers for me but that just seems like a helluva lot of pressure. I'd like to see if I could work up to 20gr of powder but these might be close to or over max pressure. Again, no pressure signs on the case but the chrony tells a different story.

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dellet
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Re: Someone please help me understand these numbers!

Post by dellet » Sun Jan 19, 2020 10:24 am

McAda441 wrote:
Sun Jan 19, 2020 9:57 am
Got a good deal on a bunch of speer 125gr TNT rounds and so I've been working on some loads. Went to the range yesterday and had something very weird happen once I got into the hotter loads.
H110 powder, WSR primers, and once fired frontier brass for all rounds w/o crimp. Shot out of an 8.5" noveske match barrel 1:7 twist. Velocity recorded with my LabRadar chronograph
10x 17.5gr 2.060" coal -- 1864 avg fps sd 26 1.5" spread
10x 18gr 2.075" coal -- 1924 avg fps sd 29 1.2" spread
10x 18.2gr 2.075" coal -- 1931avg fps sd 18 0.8" spread
10x 18.5gr 2.075" coal -- 1944avg fps sd 22 0.75" spread
10x 18.8gr 2.075" coal -- 1978avg fps sd 14 1.2" spread
10x 18.8gr 2.100" coal -- 2054avg fps sd 25 0.6" spread
10x 19gr 2.100" coal -- 2098avg fps sd 19 0.4" spread
Zero pressure signs in any cases, obviously published load data hasn't properly tested this projectile.
Anyways, i have two questions. First, does anybody have any explanation as to why I had such a large increase in velocity with the slightly longer 18.8gr rounds?
Second, doesn't 2100fps seem pretty damn high out of an 8.5" barrel? Avg was 2098 but I had two rounds at 2112fps. Maybe someone with quick load can crunch some numbers for me but that just seems like a helluva lot of pressure. I'd like to see if I could work up to 20gr of powder but these might be close to or over max pressure. Again, no pressure signs on the case but the chrony tells a different story.
What happened that was wired?

What story did the chronograph tell that was different?
300 Blackout, not just for sub-sonics.

TRshootem
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Re: Someone please help me understand these numbers!

Post by TRshootem » Sun Jan 19, 2020 12:35 pm

I found that charges from about 18.6 to 19.5 begin to demonstrate the 'case fill/seating depth/velocity/pressure' effect that Dellet frequently mentions. I am also certain that he knows more about this particular powder and bullet combos than many credible sources. I'm sure he can help with your question.

McAda441
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Re: Someone please help me understand these numbers!

Post by McAda441 » Sun Jan 19, 2020 1:17 pm

I see how that could be confusing. It was a very long winded post. Basically I'm curious as to why there was such a velocity difference in the 18.8gr rounds with length being the only variable. Next can I keep pushing this round past 19gr or should I stop there? 2100fps seems pretty damn fast to me out of an 8.5"!

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bangbangping
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Re: Someone please help me understand these numbers!

Post by bangbangping » Sun Jan 19, 2020 2:22 pm

McAda441 wrote:
Sun Jan 19, 2020 9:57 am
First, does anybody have any explanation as to why I had such a large increase in velocity with the slightly longer 18.8gr rounds?
Yup. You were into the lands. Higher pressure.

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dellet
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Re: Someone please help me understand these numbers!

Post by dellet » Sun Jan 19, 2020 2:31 pm

bangbangping wrote:
Sun Jan 19, 2020 2:22 pm
McAda441 wrote:
Sun Jan 19, 2020 9:57 am
First, does anybody have any explanation as to why I had such a large increase in velocity with the slightly longer 18.8gr rounds?
Yup. You were into the lands. Higher pressure.
I’ve never used that bullet, does it jam that short?
300 Blackout, not just for sub-sonics.

McAda441
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Re: Someone please help me understand these numbers!

Post by McAda441 » Sun Jan 19, 2020 2:53 pm

No not at all. It cycled beautifully and was very accurate.

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bangbangping
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Re: Someone please help me understand these numbers!

Post by bangbangping » Sun Jan 19, 2020 2:57 pm

dellet wrote:
Sun Jan 19, 2020 2:31 pm
bangbangping wrote:
Sun Jan 19, 2020 2:22 pm
McAda441 wrote:
Sun Jan 19, 2020 9:57 am
First, does anybody have any explanation as to why I had such a large increase in velocity with the slightly longer 18.8gr rounds?
Yup. You were into the lands. Higher pressure.
I’ve never used that bullet, does it jam that short?
No idea. But I sounded confident, didn't I. :lol: Plus it's a Noveske.

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dellet
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Re: Someone please help me understand these numbers!

Post by dellet » Sun Jan 19, 2020 3:19 pm

bangbangping wrote:
Sun Jan 19, 2020 2:57 pm
dellet wrote:
Sun Jan 19, 2020 2:31 pm
bangbangping wrote:
Sun Jan 19, 2020 2:22 pm

Yup. You were into the lands. Higher pressure.
I’ve never used that bullet, does it jam that short?
No idea. But I sounded confident, didn't I. :lol: Plus it's a Noveske.
Jackass, you had me measuring bullets. :oops:

It’s short for weight, a bit shorter than a 110 VMax or Varmageddon.

Pretty sure the chamber issues with Noveske stopped when they went from 8.2” to 8.5”, but it’s a good reminder to always check.

Oddly Speer does not have data for that bullet, thought maybe I just learned why.
300 Blackout, not just for sub-sonics.

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dellet
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Re: Someone please help me understand these numbers!

Post by dellet » Sun Jan 19, 2020 3:23 pm

Back to the actual question.

Drop 19 grains in a fired case, rest a bullet on the powder and measure.

What’s the length?
300 Blackout, not just for sub-sonics.

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