Pressure signs well above max load?

[Jeffpatton00]

I could use some feedback on the pressure signs we see in this image. I'm doing a load workup for my 224 Valkyrie, with these specs:

• 30" Bartlein barrel, 5R, progressive twist to 6.5, on AR platform
• SMK 90 grain HPBT
• .020" off lands
• Federal brass, 3x fired
• Vihtavuori N140
• CCI BR4 SR primers

VV lists this load data for 90 gr bullets:

	Start	Start	Max	Max
	Grains	Velocity	Load	Velocity
N140	21.6​	2329​	23.3​	2516​

All loads show ejector marks at the arrows, and the marks at the higher loads seem no more pronounced than at the lower loads. The primers begin to flatten at 25 gr, but I'm not seeing more signs with the increased loads, maybe you'll see something.

While VV's load data shows a max at 23.3gr, the smith who built the gun settled on 25 gr as his recommended load. I want to do my own load development so I'm trying to start with pressure testing, then move to load dev, so that's where things stand so far. I understand some will note that manufacturers tend to report loads on the low side to minimize liability risk.

Now, as an engineer I do understand statistical analysis, but the groups do give the appearance of tightening as the load increases. All things being equal, I might try to find a note in the neighborhood of 25.6 gr, but given the flattened primers, is that discouraged?

What thoughts do folks have?

 

[Seabeeken]

The first thing I notice is you are using book data for a Berger bullet with a Sierra. Then I see that you are 200 fps over the max load published and we both know that pressure equates to speed. You continued to fire hotter rounds knowing there was pressure. Neither the rifle nor components were the same that VV tested. What is the difference in water capacity of VV brass as compared to yours? I tested a rifle a few years ago and found by the time I saw pressure signs I was at 74,000 PSI. I recommend backing way off and starting over. Im sure there is a node at a lower safer speed/pressure. IMO

 

[DoneNOut]

You have a gas setting problem. Meaning you are over gassed. I just went down this road on my 308 AR. Everything I shot out of it showed ejector smear/swipe. It wasn't until I adjusted the gas block to full bleed off setting that I got the ejector swipes to subside mostly. Then I discovered a heavier buffer could help with the overpressure/ejector smear. Went to a 5.3oz buffer (Up from a 3.8oz). The ejector smears completely disappeared, and I returned my gas block setting to a more balanced setting for 3:30 brass ejection pattern.

 

[lancetkenyon]

I agree with Seabeeken.

You are not comparing apples to apples, just because bullet weight in the same. Also, every single one of your rounds are over VV recommend max with a different 90gr bullet. 1.4gr OVER listed max to start.

Unfortunately, Sierra does not give bullet dimensions. Berger does.
The 190 VLD has a bearing surface of .366". I bet the SMK has more. That would mean more contact, higher friction, higher resistance, higher pressure.

Back down to middle of the road book loads and start again. Stop when you see pressure. Which ejector marks are showing you.

 

[Zen Archery]

As one who tends runs my loads hot. I agree with you most reloading manuals are playing it safe. I've found Hornady to be the most conservative manual. I test a lot of wildcat calibers. Since they are wildcat you run them to find the actual max pressure despite what Quickload and other software suggests. In testing wildcats I've gone beyond flat primers, to blown primers, to cases with mass ejection bite marks. "I" would have no issues running your favored 25.6gr. A little half moon on a case and a flat primer is probably as hot as you want to go. You will sacrificing the life of your cases in the long run. But that is your decision (one I would make all day)!

 

[Doom2]

Sierra gives 2540.fps or so with powders of the same burn rate as N140 in a 24" barrel. That probably puts a 30" barrel at about 2700 fps max. My opinion is the gunsmith had the right idea. To get the velocities you have above 25gr they use powders like 2000MR which in my opinion is too slow for a gas operated action.

 

[Jeffpatton00]

Sierra gives 2540.fps or so with powders of the same burn rate as N140 in a 24" barrel. That probably puts a 30" barrel at about 2700 fps max. My opinion is the gunsmith had the right idea. To get the velocities you have above 25gr they use powders like 2000MR which in my opinion is too slow for a gas operated action.

I thought I'd add a little more info, and thanks to all who've commented so far. Here's a shot of the primers, labeled by charge weight. I did note a slight decrease in depriming force required between the lowest to highest charge weights, but contrary my expectation, the highest charge weights showed acceptable tension with no loose primer pockets. Also, I was in error, these were Hornady brass, not Federal. I wish Lapua or Peterson, etc., would make 224V brass but no dice.

 

[Doom2]

The first thing I notice is you are using book data for a Berger bullet with a Sierra. Then I see that you are 200 fps over the max load published and we both know that pressure equates to speed. You continued to fire hotter rounds knowing there was pressure. Neither the rifle nor components were the same that VV tested. What is the difference in water capacity of VV brass as compared to yours? I tested a rifle a few years ago and found by the time I saw pressure signs I was at 74,000 PSI. I recommend backing way off and starting over. Im sure there is a node at a lower safer speed/pressure. IMO

While the onset of pressure signs varies with cartridge and specific components, it is a good approximation that swipe marks and hard bolt lift occur around 70k psi. Primers are much harder to gauge. A full pressure load in one cartridge will look different in another cartridge if the max pressures are different.

 

[cohunt]

While the onset of pressure signs varies with cartridge and specific components, it is a good approximation that swipe marks and hard bolt lift occur around 70k psi. Primers are much harder to gauge. A full pressure load in one cartridge will look different in another cartridge if the max pressures are different.

It's not a bolt gun.

I have experienced what bfg has said--- when you handload for a gas gun you will probably need to tune the gas system.
I don't like bleed off gas blocks or heavy buffers but I'm a huge believer in adjustable gas blocks in general.
If you close off the gas you delay the start of the ejection process and may very well loose your pressure signs and quite possibly even gain a touch more velocity.
The first question is always "where is your brass ejecting?"--- if you are throwing brass forward of 3 o'clock then try limiting the gas--- if you still have the pressure signs then you may be too high.

The only real way to know is a pressure trace system. But pressure signs plus tuning of gas system componants is a valuable skill to learn in gas guns as different powders act differently with different length gas systems.

 

[Jeffpatton00]

It's not a bolt gun.

I have experienced what bfg has said--- when you handload for a gas gun you will probably need to tune the gas system.
I don't like bleed off gas blocks or heavy buffers but I'm a huge believer in adjustable gas blocks in general.
If you close off the gas you delay the start of the ejection process and may very well loose your pressure signs and quite possibly even gain a touch more velocity.
The first question is always "where is your brass ejecting?"--- if you are throwing brass forward of 3 o'clock then try limiting the gas--- if you still have the pressure signs then you may be too high.

The only real way to know is a pressure trace system. But pressure signs plus tuning of gas system componants is a valuable skill to learn in gas guns as different powders act differently with different length gas systems.

This is throwing brass at 3 or 3:30, but I'll see what tuning the gas block does, that's interesting.

 

[DoneNOut]

I don't like bleed off gas blocks or heavy buffers

I'm genuinely interested to know why on both.

 

[cohunt]

That's about right, but you could turn it down just a bit more to eject around 4 o'clock and still have reliable functioning.

The gas pushes back through the gas tube to the key and pushes the bolt back until it "unlocks" and turns the bolt, then it continues back against the buffer and spring to slow it down so as not to bottom or have too much bounce before returning forward to load another round.

Basically the extra buffer weight helps control bolt bounce, the spring controls bcg rebound and ability to strip rounds from the mag, the gas hole opening and gas length control the pressure and volume of gas back to the gas key/bolt .

If your powder/bullet combo is creating a higher pressure at your gas hole then it will try to unlock the bolt before it should be therefore it can create false pressure signs.

If you stick with that same bullet/powder combo, the only way to reduce the "energy" back to the bolt is to reduce the gas hole size ( this is what adjustable gas blocks do)

A heavy buffer will slow the unlock time slightly but it takes more gas to make all your loads cycle reliably, i feel you are better off limiting gas to the bolt and keeping it behind the bullet pushing it down the barrel.

I'm not a huge fan of "venting/bleed off" gas blocks because you are wasting a small amount of your gas pressure by venting it to the air and not keeping it behind the bullet.

A heavier buffer/spring combo will be more forgiving over multiple loads, but a lighter buffer/spring with the right size gas hole is better for gun longevity but it is more finicky and needs more adjustment for multiple loads.

I feel an adjustable gas block should be adjusted for individual loads and it's not a set it/forget it tool.

Just my 2c

 

[cohunt]

I'm genuinely interested to know why on both.

It's just the way I was taught--- use the lightest buffer you can without having bolt bounce and the smallest gas hole to have reliable functioning --- this puts the least amount of stress/wear and tear on the gun and keeps the most amount of gas pressure/volume behind the bullet where it does the most work for you-- pushing the bullet faster

I typically run buffers lighter than "standard"-- even as light as a 1 Oz plastic buffer with a light weight titanium carrier in my 308, and I always run an adjustable gas block tuned for each of my hand loads. I have never had to run a H, H2, or H3 buffer in any of my guns ( I have 7 different cartridges in ar chassis rifles)-- I was told a heavy buffer was to stop bolt bounce when firing in full auto, and is just a "band-aid' for too large of a gas hole in a gun fired semi auto.

I honestly don't understand the idea of a "venting" gas block-- why would you want to vent gas off to the air? The gas should only serve 2 purposes: 1 push the bullet down the barrel, and 2 operate the bolt system. Why put gas in the air?

 

[Coldfinger]

Look

I could use some feedback on the pressure signs we see in this image. I'm doing a load workup for my 224 Valkyrie, with these specs:

• 30" Bartlein barrel, 5R, progressive twist to 6.5, on AR platform
• SMK 90 grain HPBT
• .020" off lands
• Federal brass, 3x fired
• Vihtavuori N140
• CCI BR4 SR primers

VV lists this load data for 90 gr bullets:

	Start	Start	Max	Max
	Grains	Velocity	Load	Velocity
N140	21.6​	2329​	23.3​	2516​

All loads show ejector marks at the arrows, and the marks at the higher loads seem no more pronounced than at the lower loads. The primers begin to flatten at 25 gr, but I'm not seeing more signs with the increased loads, maybe you'll see something.

While VV's load data shows a max at 23.3gr, the smith who built the gun settled on 25 gr as his recommended load. I want to do my own load development so I'm trying to start with pressure testing, then move to load dev, so that's where things stand so far. I understand some will note that manufacturers tend to report loads on the low side to minimize liability risk.

Now, as an engineer I do understand statistical analysis, but the groups do give the appearance of tightening as the load increases. All things being equal, I might try to find a note in the neighborhood of 25.6 gr, but given the flattened primers, is that discouraged?

What thoughts do folks have?

View attachment 309933

I could use some feedback on the pressure signs we see in this image. I'm doing a load workup for my 224 Valkyrie, with these specs:

• 30" Bartlein barrel, 5R, progressive twist to 6.5, on AR platform
• SMK 90 grain HPBT
• .020" off lands
• Federal brass, 3x fired
• Vihtavuori N140
• CCI BR4 SR primers

VV lists this load data for 90 gr bullets:

	Start	Start	Max	Max
	Grains	Velocity	Load	Velocity
N140	21.6​	2329​	23.3​	2516​

All loads show ejector marks at the arrows, and the marks at the higher loads seem no more pronounced than at the lower loads. The primers begin to flatten at 25 gr, but I'm not seeing more signs with the increased loads, maybe you'll see something.

While VV's load data shows a max at 23.3gr, the smith who built the gun settled on 25 gr as his recommended load. I want to do my own load development so I'm trying to start with pressure testing, then move to load dev, so that's where things stand so far. I understand some will note that manufacturers tend to report loads on the low side to minimize liability risk.

Now, as an engineer I do understand statistical analysis, but the groups do give the appearance of tightening as the load increases. All things being equal, I might try to find a note in the neighborhood of 25.6 gr, but given the flattened primers, is that discouraged?

What thoughts do folks have?

Looks like your pressure is at 25.6 judging by the primers but groups the best so far. Me personally as long as the primer pockets are still secure that's the load for me.