The 22UM

[Formidilosus]

No doubt I’m running over pressure but I don’t see anything that would indicate 80k psi.

The only thing I have is primer flow but it’s an unbushed R700 so that’s pretty typical.

Velocity is pressure. A 24” barrel will be around 3,050fps MV for a 90gr bullet at 65k. By the time like are seeing “pressure” most of the time those loads are way over 65,000.

 

[Mike D Texas]

Velocity is pressure. A 24” barrel will be around 3,050fps MV for a 90gr bullet at 65k. By the time like are seeing “pressure” most of the time those loads are way over 65,000.

I don’t disagree and I have no doubts I’m probably 70k+ but I’m getting 5-7 firings on Lapua brass and no “traditional” pressure signs like sticky bolt, clickers, swipes, etc…

This is running RL26 powder which tends to produce higher velocities than the Hodgdon extreme powders. I’m aware of the quirky characteristics of it at higher temps. I develop most of my loads here in the summer so winter loads are typically safe, I just have to adjust for velocity loss at lower temps.


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[Stocky]

I don’t disagree and I have no doubts I’m probably 70k+ but I’m getting 5-7 firings on Lapua brass and no “traditional” pressure signs like sticky bolt, clickers, swipes, etc…

This is running RL26 powder which tends to produce higher velocities than the Hodgdon extreme powders. I’m aware of the quirky characteristics of it at higher temps. I develop most of my loads here in the summer so winter loads are typically safe, I just have to adjust for velocity loss at lower temps.


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For a reference point GRT puts an 88 eld at 22-250AI at 68kspi to hit 3400 in a 25" barrel with RL26 and 70k by 3430.

In a 20" it puts you around 3170fps at 65kpsi.

@Formidilosus What do you think the UM is running at pressurewise? Whilst GRT is a guide only it does suggest that the 22UM doing doing 3612 out of a 20" barrel with H1000 puts it well into the 80+kpsi pressure range assuming 75.5grain case capacity. I dont know GRTs accuracy is regards to extreme overbore but I have closer to a 180fps difference in say a creed to a UM at 65kpsi.

Obviously the Retumbo load was a bit hot. GRT has 67 grains of retumbo at 73kpsi but at only 3390fps. For 3700 its at 92kpsi which would make sense loosing primer pockets in quality brass.

GRT suggests that N570 followed by N565 are your best options I take it that these are on your too try list.

 

[HighUintas]

GRT and quickload both require highly accurate measurements of the chamber, cartridge, and bore to get those pressure predictions close.

 

[Formidilosus]

For a reference point GRT puts an 88 eld at 22-250AI at 68kspi to hit 3400 in a 25" barrel with RL26 and 70k by 3430.

In a 20" it puts you around 3170fps at 65kpsi.

@Formidilosus What do you think the UM is running at pressurewise?

Oh I’m Running it hot. 65k pressure should end up at around 3,400’ish with a 20” barrel and an 80gr bullet.

 

[Stocky]

GRT and quickload both require highly accurate measurements of the chamber, cartridge, and bore to get those pressure predictions close.

For predicted results from powder charge yes absolutely for correlating velocity and pressure no it takes a large change in powder capacity or presuure to make a seriously different velocity.

 

[Stocky]

Oh I’m Running it hot. 65k pressure should end up at around 3,400’ish with a 20” barrel and an 80gr bullet.

OK that's exactly where get puts its or there abouts powder choice dependent. I run hot loads not calling it out. Any high quality brass except nosler or peterson I've been able to run 70-75kpsi long term and no loose any cases prematurely. The sig hybrid brass interests me when you see how much Performance is gained with pressure with minimal recoil increase vs bigger cases. Obviously it may have other effects but I'm don't know enough about them to say.

 

[HighUintas]

For predicted results from powder charge yes absolutely for correlating velocity and pressure no it takes a large change in powder capacity or presuure to make a seriously different velocity.

What you are saying doesn't make sense. You have to start with a few knowns in the program. Without having any actual numbers you could be off by l 5000psi or more

 

[Stocky]

What you are saying doesn't make sense. You have to start with a few knowns in the program. Without having any actual numbers you could be off by l 5000psi or more

What knowns don't I have that would give a significant change in the velocity to pressure ratio? Case capacity and chamber dimensions make minimal pressure differences. If the 22 creed chambers are within saami spec and the 22um is just a necked down 6um which I used the reamer spec for modeling in GRT. I can adjust the case capacity or even any of the specs 10%either direction and still have a velocity difference under 5% if I match up pressures in GRT. No one claimed its perfect but it's allows comparison and ±5000psi at 80kpsi is still hot. I'm using it as an indicator of pressure via velocity whilst comparing to published load data where available.
Are you saying GRT/quickload are useless for their or not perfect? As I'm just saying they allow comparisons