How can this be? - different wt bullets but same velocity

[Uncle Richard]

Im testing out a load for 40sw and getting the same speeds (fps) for a lighter bullet with more powder than a heavier bullet with less powder. I would think the lighter bullet would be faster with more powder, but its not.

Usually shoot 180gr RN rainer with 5.2gr WSF, chroned ~980 fps.

Due to bullet availability, Im working on a new load for 135gr RN berry's with 6.4 gr WSF... I'm getting almost the same velocity as the 180gr (980 fps).

Why? I would think smaller bullet weight and more powder should mean more fps.

Please enlighten me what I'm missing.

PS...its not the chronograph.

 

[rcmodel]

The lighter bullet is free to get out of the way faster then the powder can generate pressure..

BTW: Both your loads are very light according to Hodgdon.
They show the Start load with a 180 Hornady as 5.4 giving 946 @ 28,000 PSI.
Start load with a 135 Nosler is 7.1 giving 1,166 @ 26,000 PSI.

rc

 

[Uncle Richard]

Is there an issue shooting loads lighter than recommended published data? I havent had any cycling or feed problems in my xd.

I noticed That there are black markings on the cases at 7.1grs of wsf with the 135 bullet, but no black marks at 6.4grs wsf (which is below recommened min load).

Your thoughts?

 

[GLOOB]

In my limited experience, Rainier bullets have a thinner plating. Thus, they shoot more like cast bullets, which go faster than jacketed for the same powder charge. It might be that you can use safely use more powder with the Berry's bullet.

I have used jacketed data with all my Berry's bullets, working up to max jacketed data. So far with no issue. Trying the same with Rainier's, I've had to cut back, due to overpressure malfunctions, loss of accuracy, and massive recoil.

Indeed, Berry's suggests you start with jacketed start load data (but cautions against going above mid level loads without a work up). Rainier's suggests you use cast data. They probably know what they're talking about.

If you work up to the max load for each bullet, in your gun, a 135 gr bullet will smoke a 180 gr, regardless of manufacturer. But the Berry's might require more powder than the Rainier's, all else equal.

 

[MEHavey]

WSF is a relatively slow powder (very close to HERCO) -- and best suited for heavy bullets to get decent burn.

Your 135gr load develops enough pressure to burn 84% of the 6.4gr of the powder
Your heavier 180gr load -- even with smaller 5.2gr powder -- burns 90% .

 

[GJSchulze]

As long as your slide cycles your fine. I load my 147gr FMJ-TC 0.1gr over the lowest load that will cycle my slide to account for variations in powder drop.

I've heard a theory that a too low load can somehow cause high pressure, but I'm not sure I believe it, otherwise we'd have heard about someone with a squib exploding their barrel (without a bullet already stuck in the barrel).

 

[steve4102]

Is there an issue shooting loads lighter than recommended published data? I havent had any cycling or feed problems in my xd.

Yes, maybe, duno. Minimum(Start) means Minimum/Start, do you want to physically find out if there is "an issue" or do you want to be safe and stay withing published data? Just askin.

 

[ArchAngelCD]

There is a very good reason why published data not only lists the Max charge but the min charge too. SAFETY is why... When everyone recommends using published data you should but that goes for both ends of the pressure range.

 

[Uncle Richard]

There is a very good reason why published data not only lists the Max charge but the min charge too. SAFETY is why... When everyone recommends using published data you should but that goes for both ends of the pressure range.

I was reading my lyman manual that loads that fill at least 90% volume of the case burn more efficiently. When less than 90%, the detonation characteristics change, which could create a spike of pressure.

Does that mean when less than min recommendation of powder is used, the detonation pressure distribution through the barrel is not linear? Specifically, the maximum pressure peak occurs within the beginning of the barrel instead of equaling distributed throughout the barrel?

However, when loading at max 7.8gr, I had unspent powder on my arms. But the 6.4gr load below minimum (7.1gr) didn't have any.

Hope you guys don't mind my curiosity, I enjoy understanding this stuff in depth.

 

[DanTheFarmer]

Uncle Richard,

1. There is a thing called Secondary Explosive Effect. It relates to lighter than minimum published loads having a huge pressure spike and blowing up guns. It is controversial. I recommend doing your own research on this topic.
2. The primary safety concern relating to below minimum published loads is getting a bullet stuck in the barrel. This can lead to disaster if undetected and a subsequent shot is fired. If you've got the Lyman #49 read the load data for 9mm RIFLE loads. It mentions this explicitly.
2. The Pressure vs. Time curve is never linear. The key ingredients for this curve are: a. Maximum pressure. The higher the spike means greater pressure. Too much pressure and the metal of the case/breach/barrel/etc. may give way - bad news.
b. The total area under the curve. The more area under the curve the greater force applied to the bullet. Fast powders (Titegroup, Bullseye) will have a quick spike and a quick drop off. Slow powders will have a slower rise and a slower drop off. This will lead to more area under the curve and therefore higher velocities for the bullet.
3. Smokeless powders don't detonate, they deflagrate. The difference is the speed of the reaction and the method propagation. In deflagration the reaction is subsonic and a "hot thing" causes a "cold thing" sitting next to it to combust. In detonation the reaction is supersonic and the shock wave generated at the intiation fo the explosion spreads throughout the material setting off more reactions as it (the shock wave) passes through.

Dan

 

[Uncle Richard]

Uncle Richard,

2. The Pressure vs. Time curve is never linear. The key ingredients for this curve are: a. Maximum pressure. The higher the spike means greater pressure. Too much pressure and the metal of the case/breach/barrel/etc. may give way - bad news.
b. The total area under the curve. The more area under the curve the greater force applied to the bullet. Fast powders (Titegroup, Bullseye) will have a quick spike and a quick drop off. Slow powders will have a slower rise and a slower drop off. This will lead to more area under the curve and therefore higher velocities for the bullet.

Dan

Is there a formula/calculator that will measure the pressure curve? It would be interesting to extrapolate this curve in an excel spreadsheet. I appreciate the info, find this very interesting.

 

[TfflHndn]

You are already seeing one of the signs of a too-light load - the black streaks on the outside of your casings on one load. The pressure is too light to expand the casing fully and create the proper seal with the chamber, so the gases are escaping and leaving soot on your casing. This can effect function and safety, besides sending hot gases back out the rear of the chamber which you may not like. Bump up the load on that one for sure.

 

[Uncle Richard]

You are already seeing one of the signs of a too-light load - the black streaks on the outside of your casings on one load. The pressure is too light to expand the casing fully and create the proper seal with the chamber, so the gases are escaping and leaving soot on your casing. This can effect function and safety, besides sending hot gases back out the rear of the chamber which you may not like. Bump up the load on that one for sure.

Read comment #3 again. Im getting black marks on the recommended published charges, and no black below the miniumum charge.

 

[kelbro]

The idea that minimum/start loads are there for a reason is flawed.

Check it out for yourself. Most minimums/starts listed are exactly 10% lower than the listed max. That is not a coincidence, just a recommended starting point.

There is no known method to calculate the minimum/start load short of 'keep adding powder until the bullet doesn't stick'

 

[TfflHndn]

"Read comment #3 again. Im getting black marks on the recommended published charges, and no black below the miniumum charge."

Well, you just go ahead and ignore signs that are right in front of you. At least you're in WV where I won't be shooting at the next firing point when something that's been ignored goes really wrong.

 

[DanTheFarmer]

Uncle Richard,

There isn't going to be a simple formula (or even a complicated one) that you can plug into an Excel spreadsheets to predict the Pressure vs. Time curve.

The field of Ballistics has three broad parts:
1. Terminal Ballistics - what does the projectile do when it strikes the target
2. External Ballistics - projectile behavior while flying through the air, post-muzzle and pre-target. If the type of ballistics isn't specified this is usually what is meant.
3. Internal Ballistics - Behavior of weapon, cartridge, propellants, and projectiles from primer initiation to projectile exit from muzzle.

The Pressure vs. Time curve is a central area of study in Internal Ballistics. My guess is that there were many Ph.D. thesies and several industrial fortunes made (DuPont? Nobel? Mauser? Krupp?) understanding it.

My guess is that with good test equipment, measuring the Pressure vs. Time curve and then backing into the formula to describe it wouldn't be too bad (beyond my ability but doable by many others). Predicting the behavior ahead of time? That would take some serious understanding in my opinion.

Dan

 

[MEHavey]

The "formulas" are real messy.
But here is what's going internally.



Inefficient burn of a slow powder under a light bullet (Left picture) is the problem

 

[Uncle Richard]

Thanks MEHavy for doing this....

Will need to digest these.

 

[DanTheFarmer]

MEHavey,

Thanks for welcoming me to the 21st century. Those computer things really are amazing! Those lil' electrons doin' all that calculatin'.

I don't think my statements were wrong. Internal Ballistics is some heavy duty stuff and I don't think you or I could do it on Excel but I hadn't realized how much Quickload can do! Those real smart computer guys teamed up with real smart ballistics guys and designed software to make it possible for interested laymen to do some fancy stuff.

I'll check out Quickload some more and save my pennies.

Dan

 

[DMH]

Wow!!! Thanks for a great thread.

DMH