Pressure signs in lower charges?

[joneb]

I've been trying Hodgdon's Lil-Gun in 22 Hornet with 50-52gr bullets for a 1:9 twist 22" Handirifle. I found that 11.8gr of LG shows signs of over pressure with a 50gr Speer tnt and 12.4-12.7gr does not, both with SRP I've seen the same thing in .357 mag with Accurate #9 with 158gr jacketed using SPP 13.5-13.8gr works well, but below 11.8gr shows over pressure signs.
So whats the cause of this? In both cases the load with more powder produced better numbers and accuracy and no signs of over pressure.

 

[BigBore45]

Pics of overpressure cases?

 

[joneb]

Pics of overpressure cases?

In the hornet, shell extraction was sticky and the primers were quite flat along with difficult resizing. In the the 357 mag fired from a Ruger security six, sticky shell extraction and flattened primers. Sorry no pics.

 

[Andrew Leigh]

Morning,

I see you are slightly under the recommended Hodgdons start load which is good. What you do not give is your COL which would be useful and the primers being used. The most useful data of all would be to know your average speed at this load.

Pressure signs are not always what they seem to be. Excessive headspace can lead to flattened primers however hard to lift bolt is a dead give away.

If I simulate your load in QuickLOAD; with your 50gr. Speer HP TNT #1030over the 11.8gr of Hodgdons Lil-Gun and a COL of 1.850", a case length of 1.393" then your velocity is estimated to be 2 825fps at a pressure of 59 539psi which is way over the SAAMI limit of 43 511psi.

One thing I can tell you is that all things being the same in the loading components and dimensions, is that an increase in charge will NEVER lead to a reduction in pressure. This would defy all pressure laws.

The only place to look at now is the case capacity. Its would be useful if you could provide the H2O case capacity in grains. i.e. take 5 fire formed cases weigh each, now fill with water to the top of the neck (use a drop of dishwash to reduce the surface tension and meniscus) and weigh again. Weight 2 - Weight 1 will give the case capacity. Now average these out and let me know.

Do you have access to a chrony?

 

[GooseGestapo]

Lil'Gun does some strange things.
I've seen several articles including one in the Hodgdon "Annual Manual" when Lil'Gun first came out, where it was mentioned that going below a certain point was contraindicated as well as above a certain point (ie: with 158gr JHP in .357mag above 18.0gr listed max) that velocities will DECREASE, rather than increase.
ie: 19.0gr of Lil'Gun is about 100fps SLOWER from a Ruger Sec.6, 4" I had, than 17.8gr!
I did some extensive chronographing and accuracy testing with 158gr and H110 and 2400 (as well as Lil'Gun) from a 20" bbl Winchester M94 back about '06. It (Lil'Gun) gave highest velocity and accuracy of ANY powder I tested, and pressure was "ok"... Velocity was over 2,100fps! but 18.4 (next larger powder measure cavity) would drop to around 1,980-2,000fps.

Personally, I think that your 11.8gr with 52gr bullet is a bit heavy, as I only use 12.5 with a 40gr bullet in mine. And with small PISTOL primers, at that.
Also, there are significant differences in bore bearing surfaces between different bullets, (length of bore diameter shank) that increases or alternatively decreases bore friction, hence pressure curve differences.
Also, the Handi-Rifle in general, and Hornet case in particular aren't very good in handling pressures.
I've had several Handi-Rifles over the years to include one in .22Hornet back in the '70's. It "ate" Hornet brass due to brass "flowing" into the extractor/ejector slot. It also had such poor metal in the trigger assembly, it wouldn't "hold" a trigger job. Metal galled and good trigger ended up after 2-300 shots being "hard". Three different gunsmiths couldn't "fix" it. Barrel was "rough", and it never gave acceptable accuracy (4" at 50yds). It went down the road !!! (As did a .22wmr, .243win, and .45/70 Handi-rifle).
My current "Hornet", has been the only "keeper"; a Ruger M77/22KBZ (heavy bbl, stainless steel, laminated stock circa 1996). It still has "issues", but most have been resolved.
It won't tolerate a lot of the maximum loads published through the years. Another Ruger M77/22 I had, had such a large, sloppy chamber it would shoot "OK" with 13.2gr of H110 over a 35gr V-max, the best load I ever found for it. My current rifle will "lock-up" with that load, and wouldn't even chamber loads using neck-sized brass from that rifle.

 

[fguffey]

In both cases the load with more powder produced better numbers and accuracy and no signs of over pressure.

It is possible the bullet is being launched into the rifling before the powder has a chance to get started. Meaning the barrel is plugged when the powder builds pressure. It is said it is not that difficult to get the bullet moving the problem is time.

F. Guffey

 

[Drail]

Chamber pressure really needs to be measured. Looking for "signs" of overpressure on a case is not the way to go - by the time you can "see" it - you're already over the limit.

 

[joneb]

What you do not give is your COL which would be useful and the primers being used.

I used a COL 1.9" for the 50gr#1030 Speer TNT , I'm using WSR, CCI 400 and 500 primers.
The cases I have are Winchester, Hornady and PPU, the Winchester cases have noticeably more volume than the other two.
11.8gr of Lil-gun gave a average velocity of 2,781 fps and a ES of 74 fps. brass Winchester, CCI 500.
12.0gr of Lil-gun, av 2,706 fps ES 39 fps. brass Win. CCI 500
12.2gr of Lil-gun, av 2,704 fps ES 66 fps. brass Win. CCI 500
12.6gr of Lil-gun, av 2,723 fps ES 64.5 fps brass Win. WSR

I'm using the Lee Pacesetter 3 piece die set, the dies use a O-ring in the lock ring I may switch the lock rings of the sizing and FCD die to RCBS lock rings. I don't think I'm getting the same crimp with different batches.

 

[Andrew Leigh]

At 2 781fps you are at 55 600psi vs. SAAMI of 49 000psi.

 

[Grumulkin]

I've been trying Hodgdon's Lil-Gun in 22 Hornet with 50-52gr bullets for a 1:9 twist 22" Handirifle. I found that 11.8gr of LG shows signs of over pressure with a 50gr Speer tnt and 12.4-12.7gr does not, both with SRP I've seen the same thing in .357 mag with Accurate #9 with 158gr jacketed using SPP 13.5-13.8gr works well, but below 11.8gr shows over pressure signs.
So whats the cause of this? In both cases the load with more powder produced better numbers and accuracy and no signs of over pressure.

This has also happened to me AND I know the cause. You can ignore the other statments about excess headspace, excess velocity which you didn't measure and is assumed from Quickload theorization, etc. It is a well known fact and published in reputable manuals that too low a powder charge CAN cause excess pressure even to the point of splintered stocks.

In my particular case, I was cautiously working up a 454 Casull load for a Freedom Arms Model 83. Said lower load locked the cylinder up and when the load was increased, no further problems were encountered.

What is happening is this. It's a well known fact that jamming a bullet into the lands will give a higher pressure than if the bullet is allowed to jump a little. That's why loads for Weatherbys with freebore can be too hot for guns without freebore. It's also known that smokless powder is not an explosive unlike black powder which is. What this means is that for smokless powder to burn VERY fast, it has to be under pressure. If you burn smokless powder in an open space, it will burn fast but doesn't explode per se.

So, with too low a powder charge the bullet moves out of the case and hits the lands and because the pressure is too low starts to get stuck. Several things could happen depending on the particular circumstances. It could be a squib resulting in a bullet stuck in the barrel or if conditions are right there could be faster burning of the powder due to the bullet not exiting quite fast enough and hence even markedly increased pressure that successfully pushes the almost stuck bullet out of the barrel. Another thing that can happen is a hang fire which is another potential part of the continuum.

 

[joneb]

Thanks Grumulkin,
I worked with Accurate 1680, 300MP and H-110 in the Hornet and I have not noticed this issue.
I will look for 40gr bullets for the Hornet these with a shorter OAL may work better with Lil-gun? The Speer TNT #1030 has a short bearing surface seated at 1.9" I am at the start of the ogive.
One of my favorite powders for .357 Mag. is 2400, it does well in a wide range of charges.

 

[Andrew Leigh]

@Grumulkin.

Morning, are you describing the pre-detonation phenomenon? From my understanding this only appears at greatly reduced loads and not at minimum loads where the OP is at.

QL does not factor in the proximity of the bullet to the lands and will give a generic Shot Initialisation Pressure for each type of bullet, in this case the pressure used is 3 626psi to overcome the lands with a running start. QL would have one manually intervene when the bullet is seated on the lands and in so doing the loader must add an additional 7 200psi to the 3 626psi.

I have done independent tests which prove that the QL factors are very close to correct, at least for a .308 that is. What is not clear is if the OP is on the lands.

 

[Grumulkin]

Morning, are you describing the pre-detonation phenomenon? From my understanding this only appears at greatly reduced loads and not at minimum loads where the OP is at.

I've heard it described as detonation but not as pre-detonation. Maybe someone has called it pre-detonation or you may be thinking of pre-ignition, detonation or dieseling that sometimes occurs in gasoline powered cars where it keeps running after the ignition is turned off.

I don't thing the loads have to be "greatly reduced" either. What many may not think of is that barrels may not be uniform. The bore can be a little smaller than advertised or a little bigger and the twist may not be exactly what you thought. So, a load may effectively be lighter than it appears to be on paper.

There was one who operates a firearms business who tested 10 "identical" rifles with "identical" loads. There was about a 200 fps difference between the highest and lowest velocities in that test. What this illustrates is that firearms can be different despite being supposedly identical and that depending on velocity to determine how high pressure is can be misleading.

 

[joneb]

Thanks Andrew,

What is not clear is if the OP is on the lands.

I seated a Speer#1030 at 1.943" and it chambered fine, so I assumed 1.9" would be ok?

 

[Sunray]

11.8 gr of LG is under minimum, according to Hodgdon, but only by .2. There really shouldn't be pressure signs. However, below minimum loads can be detonating vs burning. Causes weird pressures. And powder either burns or it detonates. There's no pre-detonating.
How'd you come up with 1.9" as the OAL? Hodgdon shows 1.850" as max. My old Lyman book gives 1.723". Even at 1.943" sitting on the lands is not going to raise pressures to dangerous levels. Max 55 grain bullet load runs at 42,900 CUP. Not exactly low pressure.
"...I have done independent tests..." In a proper ballistics lab? No other tests are valid.
QuickLoad is not a ballistics lab. QuickLoad is a computer program invented by people who very likely have never seen a real firearm.

 

[joneb]

How'd you come up with 1.9" as the OAL?

the Speer 50gr TNT #1030 is a strange bird with a short bearing surface, at 1.9" the .224" bullet measures .2235" at the case mouth. So I am just seating on the ogive at this length.

 

[Andrew Leigh]

"...I have done independent tests..." In a proper ballistics lab? No other tests are valid.

That's a little harsh, by implication then all load development is invalid when not conducted under lab conditions?

QuickLoad is not a ballistics lab. QuickLoad is a computer program invented by people who very likely have never seen a real firearm.

You know this for a fact or are you merely speculating? QL is not the final authority on ballistics but it is a remarkably accurate and powerful tool for the handloader.