Heavier Bullets = Same Velocity?

[coriolis7]

Hey All,

I have been reloading for a little over a year now. I spent this last weekend working up some loads for a friend's RIA 10mm.

WARNING, I am not aware of any published loads for the projectiles I'm using

The two loads I tried were:

155 Grain Plated Ranier
CCI 300 Primer
Starline Brass
IMR 800-X (8.6-9.8c grains) (hand weighed to nearest 0.05gr)
OAL - 1.275"

170 Grain Cast Hollowpoint (Modified Lee 175 TC)
25-1 Alloy
CCI 300 Primer
Starline Brass
IMR 800-x (7.0-8.6 grains) (hand weighed to nearest 0.05gr)
OAL - 1.260"

I used the Lee max load for the 155 grain XTP as the max for the 155 grain plated, and Lyman's data for the #401043 & #401638 from their 4th edition (7.0-8.2 and 7.7-8.6 respectively).

By coincidence, the max load for the cast was the same as the starting for the plated. I chronographed all of the rounds. I was surprised by what I found from the data. I plotted Charge vs Velocity, and found that the velocity was pretty much independent of bullet weight. The average velocity for both bullets at 8.6 grains was pretty much the same. The velocities for both bullets were laying on the same line.

I was expecting my cast bullets to be slower at 8.6 grains than the plated at the same charge, but staying at the same speed didn't make sense. After thinking about it overnight, here is my explanation:

*****************************************

1. Take a given lightweight bullet and charge. It will produce a given velocity and pressure [curve].

2. Now replace it with a heavier bullet. If the speed is the same, the energy is greater.

3. The only way for there to be more energy with the same charge is if the pressure is greater (Energy = Pressure x Volume).

*********************************************

But that line of thinking breaks down:

Why is the pressure greater? It can't be from increased friction because if it were, the energy overcoming that friction would rob the heavier bullet of energy, and would reduce MV. The bullet can't be in the barrel longer, or else it would be slower. Somehow, a heavier bullet is more efficient (same energy going into the gun, more energy is transferred to the bullet) than a lighter one.

Then again, bullets with lower friction (moly coated) will give lower velocities given the same charge.

Yes, I know I have only one example of the velocity not changing with bullet weight, but I wasn't expecting the speeds to remain so close. Maybe the best explanation is the longer OAL and bullet profiles offset the changes in weight.

I've have a BS in Mechanical Engineering (and took Engines as a tech elective), and this still makes my head hurt :banghead:

-Ben

 

[rchery59]

cast bullet = less friction

 

[GLOOB]

2. Now replace it with a heavier bullet. If the speed is the same, the energy is greater.

Specifically, the kinetic energy of the projectile is greater. That's the only empirical truth you can take away from this, without further disclaimers.

3. The only way for there to be more energy with the same charge is if the pressure is greater (Energy = Pressure x Volume).

No. That doesn't work on any level. First off, you are assuming that all potential energy of the compressed gas is transferred to the bullet as kinetic energy. It is not. It is also delivered to

1. the gun as recoil
2. heat from friction
3. muzzle blast and sound waves

That's just for starters. Even if you could identify and quantify all the various paths of energy transformation, you also have to realize that pressure doesn't come out of nowhere. It builds up over time, and things are moving all the while. And even if you were to further quantify it at that level, you have to also realize that regarding point #1, the amount of the initial potential energy that is transferred to the gun vs the bullet varies depending on the mass of the bullet and of the gun. So changing the bullet weight automatically skews this relationship.

 

[Toprudder]

cast bullet = less friction

+1.

Also, you seated the heavier bullet to a shorter COL, so less internal volume possibly.

The Rainier 155 I'm guessing is a truncated cone. The cast 170 is a hollowpoint. From those two facts, I would guess that the 170gn cast bullet has a significantly longer length than the 155 plated. So, the base of the bullet will be seated deeper even if the COL is the same.

What are the lengths of each projectile?

 

[coriolis7]

The cast hp is 0.590, plated is 0.503. Didn't realize the huge difference in length. Guess that makes sense. The cast bullet had an extra 0.1" of travel.

Here's the whole friction thing. I've heard lower friction means higher velocity (cast bullets) and that lower friction means lower velocity (see moly bullet proponants).

I understand that it's not just pressure x volume, but the area under the pressure/distance curve. All of the energy in the sustem comes from the powder. The rest is lost as friction, heat transfer through the barrel (very small, since heat transfer takes time to happen), exhaust through the muzzle, and in recoil.

It sounds like a coincidence that the two bullets ended up going the same speed, not some deeper fundamental reason.

 

[steve4102]

Your shorter 155gr bullet seated .015 longer than your longer 170gr Lead bullet is going to cause a major change in pressure.

Why did you seat the 155gr bullet .015 longer than Max OAL? I'm surprised it fit the mag and chambered.

 

[coriolis7]

I seated the 155 farther out to see if it would still chamber, and because I didnt have data for that bullet/powder combo, so I wanted some room. Figured I could go back and do another workup with a shorter oal.

I pluncked both in the chamber, and fed a couple in the mag. However, the mag didnt want more than 4 of either. Lesson learned.

 

[Toprudder]

It sounds like a coincidence that the two bullets ended up going the same speed, not some deeper fundamental reason.

I agree.

 

[blarby]

Ok, so let me see if I understand the premise :

You actually "made up" from scratch loads -both in charge weight and length- and are wondering why the numbers don't track ?

Forgive me for being pointed, but.....

Your understanding of how pressure relates to velocity is meddling at best.
You are containing a controlled explosion, not erecting a structure.
This is further compounded by the fact that your understanding of how internal case dimensions are altered by seating depth of given bullets, drastically changing ( for better, or more likely worse ) published pressures you are basing your guesses off of, is being solely determined by velocity. You cannot roughly interpret the pressure curves of published loads against your madeup data in any meaningful way.

By coincidence, the max load for the cast was the same as the starting for the plated.

Thats not a coincidence, and only further supports my belief that your skill level is not sufficient to generate load data from a hat.

I seated the 155 farther out to see if it would still chamber, and because I didnt have data for that bullet/powder combo, so I wanted some room. Figured I could go back and do another workup with a shorter oal.

Guessing again ?

The cast hp is 0.590, plated is 0.503. Didn't realize the huge difference in length. Guess that makes sense. The cast bullet had an extra 0.1" of travel.

Didn't realize ? Didn't measure ? Or couldn't see ? All are bad.

The way you are extrapolating data is going to get you in serious trouble in short order.


STOP.

PLEASE, STOP.

You are literally toying with one of the highest pressure autoloading cartridges, with very narrow windows of safe operation, in a firearm without a fully supported chamber in a factory barrel. STOP, STOP STOP STOP.

I'm an experimental type of guy, and I'm glad you made it out safe. Count that blessing for what it is, grab a load book, suitable components, and go back to square one.

Reason: added red

I concur. For what thats worth !

 

[TimSr]

cast bullet = less friction

x3


When a cast bullet of similar design and weight is fired over the same charge as a jacketed, plated, coated bullet, it will ususally be traveling faster.

 

[Haxby]

The same thing happens all the time with jacketed bullets. Flip through a reloading manual, and you can find dozens of entries where a light charge with a lighter bullet will be about the same as the max charge with a heavier bullet, at about the same velocity. The difference is pressure. It takes more force to accelerate the more massive bullet.

 

[Zendude]

I've have a BS in Mechanical Engineering (and took Engines as a tech elective), and this still makes my head hurt :banghead:

-Ben

When I was in engineering school, I was always skeptical of the assumptions in the engineering problems the professors used. In a problem such as a bullet velocity in a gun, they would set up the problem and instruct us to ignore friction, wind resistance, temperature, burn rate, etc. When I graduated I didn't think I could really solve any real world problems with any degree of confidence.

 

[Toprudder]

When I was in engineering school, I was always skeptical of the assumptions in the engineering problems the professors used. In a problem such as a bullet velocity in a gun, they would set up the problem and instruct us to ignore friction, wind resistance, temperature, burn rate, etc. When I graduated I didn't think I could really solve any real world problems with any degree of confidence.

I always say that I will take empirical data over theoretical hypothesis.

 

[Toprudder]

Thats not a coincidence

I believe it is a coincidence that several variables all stacked together to cause the similar velocity.

In looking at his max charges, and comparing it to the data at Hodgdon, I believe he was conservative in his workups, as long as the velocity for the plated was kept under 1250fps.

I think he was just questioning the results when comparing the bullets.

I've had to work up loads before when I did not have published data for the exact bullet I am using. Unfortunately, there doesn't seem to be a good database available for the dimensions of bullets. They list the COL, but that is only useful if the bullet you are using is identical or at least the same length, and often we don't have any way of finding that info.

 

[coriolis7]

Barlby,

I understand your concern, but I was using the best load data I could find, not making up loads out of thin air. I altered the loads in order to be as conservative as I could. I used load data for similar weight bullets (using load data for heavier bullets as needed), checked several sources to confirm that I didn't happen to pick uncharacteristically "hot" data, loaded to longer OAL than the published loads called for, and worked up my loads from the lowest starting charge I could find by increments as small as 0.1 grain at the top.

My load development process is to work up to max charge with as long an OAL as will chamber. Every time I set up the seat and crimp dies, I push the first 3 rounds nose first onto a scale at 50 pounds for 30 seconds. If any of the 3 rounds have any setback, I adjust crimp. If I see pressure signs, unexpected chrono results, excessive recoil or muzzle blask, I stop. Once I have established the max at that length, I start the work-up at a shorter length closer to published loads. Again, working up from start charge at increments as small as 0.1 grain near max (yes, hand weighed). The reason I load to max charge during work up is so I can see how close I am to the "edge". If 0.4 grains will take me over what I have established as a safe load, and my powder charger can't be trusted to throw that accurately with that powder, I either back off on charge or hand weigh each case.

The only problem I had was I had never had a problem with rounds not feeding in a magazine. In my guns, if a round would plunk, it would fit in a magazine. With this 10mm, the problem only manifested itself at the 4th or 5th round, but every round plunked.

Yes, I'm guessing with these loads, but I am starting as conservatively as I can, and slowly working up.

 

[blarby]

Given the many, many, MANY well documented cases of case failure using improper handloading techniques ( and some even proper ! ) combined with unsupported chambers in 40s/w and 10mm, all I can advise you to do safely is to follow published load data to the letter.

If you're going to get experimental, at least...least... and I say that begrudgingly... get a fully supported aftermarket barrel.

I'm not attempting to be alarmingly prudish for no reason. You are walking down a road that has ended in absolute disaster for a large swath of folks, using the same methodology a lot of them used- and will either admit to, or have found out as a matter of course in investigating the ka-boom.

I don't raise the alarm bell often, because folks raise it on me often enough...usually in relation to much more lower pressure rounds. Feel free to "look me up", and you'll see that both of these are true statements.

With and for that reason, I don't "cry wolf".

The first time you set-back one of those 170gr cast bullets at maximum charge (due to the over-long HP catching on the feedramp during cycling), you're going to found out exactly what happens when overpressure meets unsupported chamber.

I'm not trying to be a *insert censored* im trying to save your gun , hands, and eyes.

Your barrel may be tested at +50% pressure to be sold in Europe- trust me, your brass isn't.

 

[coriolis7]

The RIA 10mm has a fully supported chamber, and my hollowpoints have the same length as the lee 175 tc, which is what I'm using for comparison purposes. I check against setback both at the loading bench and by cycling rounds several times to make sure there is no set back. I even brought my micometer to the range and measured the rim and case diameters to check for any bulges (using virgin starline brass).

I would not be doing any load development in an unsupported barrel, or in used brass. There is always a risk in hand loading / reloading. I have done much riskier things with much graver consequences if I messed up, and I accept this level of risk.

I thank you for your concern.

 

[murf]

Welcome to the high road, coriolis7. I hope the frankness and honesty here don't scare you away.

murf

 

[Dudedog]

Don't own or load for a 10, but I would like to say welcome coriolis7.
Great people here.

 

[Potatohead]

Yah, Agree with above, welcome Coriolis, sounds like you might fit right in. Don't let the Blarb barbs bother you, I bet he's just trying to make sure you're keeping it safe.