Advanced Pressure-sign question

[turbo54]

I am a veteran handloader, but have recently gotten a new rifle and am scratching my head concerning some of the pressure signs I'm seeing.

The rifle: FN SPR in 284Win, 26" melonited Bartlein

So far I've been focusing on the 162 Hornady bullets, both BTHP and Amax, and also the 180 SMK. Although I did run a ladder with RE17, I've been working more with H4350.

In a nutshell, I start to get ejector marks @ 52.5gr H4350 with the 162s @ 2825fps, meanwhile, I can load 51.5gr H4350 under the 180SMK @ 2785fps before I get ejector marks.

I would really expect to see a lot more separation in chargeweight and velocity (for a max load) between a 162 and a 180 with a given powder....??

Also, I am used to seeing a rather flat primer to go along with an ejector mark. I am seeing the flattened primer with the 180SMK, but the primers in the 162 loads aren't flattening at ALL! I understand primers are NOT a good indicator of pressure, and I don't rely on them... ...but nonetheless, I find it very odd I'm seeing an ejector mark to go along with a very round, almost virgin-looking primer.

Im thinking theyre trying to tell me the wrong powder is being used. Thoughts? Should the powder be faster?

I've ever seen flat primers in weak loads, and radius'd primers in hot loads - but it's normally a rare anomaly. What I'm seeing here is totally consistent.

Would love to get a conversation going about this... thanks!

 

[Graham]

Re: Advanced Pressure-sign question

Use 4831, 4831SC, or RE17 if you want more velocity.

Try 52.0 RE17 with a 180 to the lands.

 

[SPAK]

Re: Advanced Pressure-sign question


Are the loads fired in virgin brass or fired brass?
Sometimes false pressure signs could be seen with excessive headspace. This is more pronounced with virgin brass since it tends to be smaller to start with. I don't suspect that's what's going on but it's good to keep in the back of your mind especially with a new rifle.


Regarding pressure with different bullets, sometimes the actual construction of the bullet and/or bearing surface can affect how
much pressure is generated for a given load.

For example for one of my .30-06 rifles I start to see pressure signs earlier with a 200gr accubond than I do with a 208 Amax. Given both bullets with the same brass, primer, and powder, I need to drop my charge a full grain lower for the 200gr accubond.

Granted this isn't the exact spread of bullet weights that you're using but at first glance you would think you could use the same charge weight for both the 200gr and 208gr bullets.

Again, this is just an example from my particular rifle. As I'm sure you already know everyone's particulars will be different..

 

[Graham]

Re: Advanced Pressure-sign question

Wrong powder.

 

[turbo54]

Re: Advanced Pressure-sign question

I'm seeing this phenomenon with 3 different brass conditions...

1. Virgin WW Super
2. Once fired (in my rifle), and bumped .001-.002 ( I measured)
3. Once fired in another rifle, SB sized to fit mine. My chamber is tight.

 

[turbo54]

Re: Advanced Pressure-sign question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">Wrong powder. </div></div>

I know H4831sc is by far the most popular choice in 284 for the 180s... I thought H4350 would make more sense for the 162s.

You think thats wrong, simply put?

 

[Graham]

Re: Advanced Pressure-sign question

I'm not sure, but that would appear to be the case (no pun intended). If you want to go that route, maybe try Lapua brass: Less case capacity.

The .284 will never be a magnum. Consider sticking with what works, and saving your barrel.

 

[turbo54]

Re: Advanced Pressure-sign question

Well, where to start...

The 7-08 I just set up for my buddy is seeing 2775fps with 162s under 46.5gr H4350 with no excessive pressure whatsoever. Honestly, we're limited by case capacity - just can't squeeze more in there. I'd of thought with the extra capacity of my 284, I'd be seeing 2875-2925 with H4350. Not the case!

The 2785 I'm getting with the 180smk is fairly satisfactory I think, though I'd love to see more!

I have H4831sc in inventory and will try it next. Hope to see improvement.

Assuming it works, you have essentially given a hungry man some fish to eat - I'd rather be taught to fish!

I'm certain the primers are telling me something here... perhaps ~50gr H4350 is maximum for a 162 bullet in a 7mm bore, and thats why the 7-08 gets 2775 with 46.5 and I get 2825 with 52.5?? Meanwhile the 284 can actually use it's capacity advantage over the 7-08 to send a heavier bullet nearly the same speed with the same powder?

I'm open to theories or knowledge here - I'm reaching!

 

[Guest]

Re: Advanced Pressure-sign question

Issue is peak pressure vs peak pressure time.
I've ran H-4350 an H-380(20" drop tube installed)in .308's pushing 190 vlds that after one firing, the pockets were to large to hold a primer, with no marks on the case at all.
I've marked cases an had flat primers, w/o a pocket issue.
All the totals at the time the primer goes off can stack, an the brass takes on the same ability, as a 1st term Senator, looking for a 2rd.

 

[Valere]

Re: Advanced Pressure-sign question

How does your kanooder valve look? A pretty smart guy who helped me with trigger control at the range last week told me a clogged kanooder valve can cause the conditions you are describing.

(hehehe) Good luck with the new stick, hope you find the answer.

 

[Killswitch Engage]

Re: Advanced Pressure-sign question

Different cartridge. But I'm running 42.9 gr of 4350 on my creedmoor and have light ejector marks but nice radius primers and easy bolt lift etc. This is the only pressure sign I have and it surprises me that I have some brass with
6 firings and still tight pockets.

 

[SPAK]

Re: Advanced Pressure-sign question

Turbo

I think your on to something regarding the bore size... I would think given the same powder charge, the cartridge with a smaller neck diameter would generate more chamber pressure than the cartridge with a larger neck diameter..

Also given the same powder charge and same neck diameter a smaller case should generate more chamber pressure than a larger case.

peak pressure also happens quicker with the faster powder as Greg alluded to above..

Perhaps this is common knowledge, I wouldn't know...
I'm definitely no expert in internal ballistics so anyone else feel free to chime in..

I would think a slower powder would work better.. You won't hit peak pressure as quickly and you'll probably get more velocity..

 

[turbo54]

Re: Advanced Pressure-sign question

Well, H4831sc works much, much better than H4350 with both 162amax and 180smk...

Though I have to compress the shit out of it to get enough in there, while maintaining a max COAL of 2.950", the practical maximum for Alpha type 3s and type 4s.

57.5gr H4831sc, 162amax seems to go 2975 or close to it, and 56gr H4831sc and 180smk goes close to 2850. Casehead/primers look "right" to me, and acted like I'm used to seeing. I got zero ejector marks, no heavy bolt lift at any charge.

Seems to me, the faster powder (H4350), slams the case into the boltface, causing the ejector mark, but never develops enough pressure to squeeze/flatten the primer up against the boltface...???

My theory is pressure over a length of time flattens primers, and rapid pressure spikes tend to cause ejector marks.

 

[RTodd]

Re: Advanced Pressure-sign question

I'm not sure I agree with your theory of primer flattening versus pressure/time curve, but I'm not willing to argue the point either. Do you really think you have enough headspace for the brass's momentum to play a significant role in generating case head marks?

I do think you are wise to pay attention to ejector marks on the case head. Short of improperly annealed brass, ejector marks are not likely to lie. We have some awfully strong actions, but why set out to use the safety margins? Seldom can we use the extra 50 or 100 fps anyway. Those are some impressive velocities you're turning.

Randy

 

[turbo54]

Re: Advanced Pressure-sign question

After more consideration, maybe the ejector marks, with no primer flattening, has something to do with imoroper pressure rise, not allowing the case to "bite" into the chamber...

We've all seen serious ejector marks from known "ok" pressure cartridges when the chamber is lubricated by something, be it water, solvent or oil.

The velocities I back-calculated seem high to me. With H4831sc, I would expect ~2900 from the 162 and ~2800 from the 180. Maybe melonite has something to do with it...maybe compressed charge is more efficient... I don't know.

But... I have a goid zero, and a goid scope I know tracks. I even used conservative BCs... Hornady advertises .625 for the 162, I used .610. I forget Sierra's claim on the 180, but other folks here say .650 works great...

Anyway, I intend to pursue the extremely obvious node @ ~57gr/162amax and then run it over the chrony. I'll be happy at 2900+. 2975 would be amazing.