[Field]

i was loading mg 124g jhp with 5.9g HS-6 which in my reloading manual said would yield around 1050fps or 130pf

i chrono this ammo and find that it is SUB-Minor going around 950fps avg. or 118pf.

it is being fired out of a 4.5in barrel

1. How much is COL going to effect velocity?
2. What about crimp?

3.

i figured i should probably actually get some calipers and a chrono now, seeing as i have made an ass of myself fairly well.

when you are crimping your cartridges what diameter should you be trying to attain at the crimped area? is it going to be .355 like a normal factory cartridge?

how can you tell if there is a proper crimp?


have you ever experimented with different bullet seat depths and seen how it changed the muzzle velocity?


im thinking at least part of this problem might have come from not seating the bullet properly to thier specs. im not entirely sure about the crimping part but whatever.

thanks

[SA Friday]

Well, based on the questions and the information, I surmise you are a fairly new reloader. We all were at one time or another.

You lose velocity the longer the overall length (OAL) is. You gain velocity the shorter OAL is. Essentally, OAL should be based on how well the gun functions, and accuracy. Then you adjust the amount of powder for power factor and pressures.

HS-6 is probably a fairly slow powder for the round you are reloading. Go through the 9mm reloading section and read the various threads on 9mm minor pf loads. The only reason I can think of using HS-6 in a 9mm load is to get the extra gasses from it for an open gun or a steel gun. Titegroup is a great powder for this load, N320 or Solo 1000 would work well too. There are others, read the threads.

You MUST have calipers and a chrono to reload correctly and safely.

Crimp also should not be used to increase or decrease velocity. For a semi-auto pistol round, your crimp is nothing more than taking the bell out of the cartridge mouth and laying the case mouth next to the bullet. Friction from the case mouth is what retains the bullet in the cartridge. There is also a lot of info about this in other threads. You may want to spend some time researching crimp and undersized resizing dies.

[mlmiller1]

I agree pretty much with everything SA Friday said. Your cartridge length will affect your velocity & your pressure dramatically. One other thing to think about is whether the bullets you are loading are harder than the ones used in the book. All bullets are not the same hardness. A harder bullet will require more powder to obturate (seal) the bullet in the bore. If it doesn't seal properly, the gases will blow past the bullet as it travels down the barrel, giving up velocity rapidly. If it seals properly, you will get all the speed out of the powder that it has to offer. Does that make sense? That is why load data for lead/plated/moly coated bullets require less powder to get similar velocities. They seal with less powder, thereby making a more efficient use of the burning powder.

Keep asking questions, paying attention, reading & learning. You will be getting what you want pretty soon.

MLM

[Jman]

All of this is good info. Tons of it here too. Still, few resourses are as reliable as good manuals. Lee, Speer and Sierra are fantastic. I've been "rolliing my own" since the 70's and refer to them ALL THE TIME.


Jim

[benos]

On the relationship between OAL and velocity, I remember being surprised how many different calibers/powders shared similar relationship: Leaving the powder charge the same, seating the bullet 0.010 deeper resulted in a 10 fps increase in velocity. (And vice versa.) Or in other words, 1 fps per 0.001 OAL change.
be

(BTW, I edited the thread's title to be more specific.)

[G-ManBart]

I'll be knitpicky and make one slight correction/clarification. It's not necessarily the OAL that determines velocity increase/decrease (and subsequent matching change in pressure), it's the change in case volume that causes the increase or decrease.

Increase the case volume by seating the bullet shallower and the pressure will decrease leading to lower velocity and vice-versa. So, if you stick with the identical bullet, an increase in COAL will lower the pressure and velocity. The opposite is also true. If, however, you change bullets it's possible to increase the COAL and have no change in pressure/velocity or actually increase the pressure/velocity....it just depends on whether the new bullet takes up more or less case volume (we're assuming no change in bullet weight, jacket thickness/hardness etc).

It's because of all these factors, that they advise dropping down and carefully working up any time you change components. The ballistics experts I've known (a couple worked at Alliant) said they can usually predict what's going to happen when they change something, but even they get suprised by stuff every now and then. R,

[wide45]

You can also see raised pressure, if you start the bullet too close to the rifling.

[Field]

wide45, on Nov 9 2009, 08:34 PM, said:

You can also see raised pressure, if you start the bullet too close to the rifling.

huh?

[Aristotle]

Field, on Nov 10 2009, 11:12 AM, said:

wide45, on Nov 9 2009, 08:34 PM, said:

You can also see raised pressure, if you start the bullet too close to the rifling.

huh?

He's talking about Freebore. The distance your bullet is from the rifling of the barrel when chambered. You should know this when estimating and working out your OAL.

[G-ManBart]

Field, on Nov 10 2009, 02:12 PM, said:

wide45, on Nov 9 2009, 08:34 PM, said:

You can also see raised pressure, if you start the bullet too close to the rifling.

huh?

It's not the easiest concept to describe, and I only have a basic understanding of it, but imagine a situation where the cartridge is in the chamber and the bullet is .001" from touching the rifling. You fire the gun and the instant the primer detonates, the bullet moves that .001" and is now providing significant resistance to the exanding hot gases as the powder burns. Now compare that with a situation where the bullet is .010 from the rifling when chambered. The primer detonates, the bullet starts to move, the powder burns and the gases expand and start to move the bullet faster before the bullet meets the resistance of the rifiling. It's normally only a problem if you're near the pressure limits and you happen to stumble on a situation where the pressure peak happens right as the bullet starts to move....but there's no real way to tell any of that stuff remotely. R,

[GentlemanJim]

In my old days building major 9mm guns in the 1980s

.010 free bore was the difference between unsafe and safe pressures.
Jim

[tooslo]

I'm wondering...Are there known optimum OAL for certain guns? Like, for instance a G17?

[Aristotle]

tooslo, on Nov 10 2009, 08:56 PM, said:

I'm wondering...Are there known optimum OAL for certain guns? Like, for instance a G17?

no, not all G17's are set up the same. And by "optimum", do you mean performance or reliability, cause there "can" be a difference between the two.

[Field]

oh what do ya know...i get my calipers (2 day free shipping from amazon) and i had those bullets seated almost EXACTLY to the recommended depth

one odd thing though i notice with looking at a few of my cartridges is with these 9mm cases they seem to never be factory spec diamter, alot of them are closer to .380 rather than .35. but i dont think ive had any problems in that respect. it would be good to know what kind of deviation is acceptable

i think most of my issues would be from having undercharged cases not working the action all the way because i was using charge numbers from that stinky hornady manual and not verifying the actual velocity out of my gun with a chrono. (which i will have tommorrow i hope)

because yeah i was using some ammo before that was working fine at a higher pf and i figured something might have been kind of fishy when the powder charge i was using was way higher than what the manual even listed.

This post has been edited by Field: 11 November 2009 - 12:57 PM

[JeffWard]

Crimp and 9mm...

I've always heard, and practiced simply removing the bell with the crimp die for 9mm Minor. No real tight crimp needed.

Is this true across the board?

Jeff

[tooslo]

Aristotle, on Nov 10 2009, 11:03 PM, said:

tooslo, on Nov 10 2009, 08:56 PM, said:

I'm wondering...Are there known optimum OAL for certain guns? Like, for instance a G17?

no, not all G17's are set up the same. And by "optimum", do you mean performance or reliability, cause there "can" be a difference between the two.

Set up the same?? Aren't G17 barrels (at least Glock factory) all the same? Wouldn't the distance from the end of the case relief to the rifling be the same? AND, wouldn't there be an ideal OAL that would take all this into account?

Just asking, you understand.

[Field]

how much can you deviate from the recommended COL?

[FullRace]

Field, on Nov 12 2009, 04:33 PM, said:

how much can you deviate from the recommended COL?

Several factors affect deviation from COL, Bullet OAL, Barrel, Bullet design, COL restricted by magazine, powder and bullet combination. Probably missed a factor or two.

[Sarge]

To make this more confusing to the OP keep in mind that in my experience lot's of things change when you change oal. Aside from what has been mentioned here you will find that standard deviations will fluctuate and group sizes will change. I tend to try to load as long as I can because in my gun my groups are tighter. But if I reduce the charge and shorten the oal my groups grow a little but my standard deviation drops alot. So for me the trick is to settle on what works best for me to be comfortable across the board. I like accurate loads because I want to KNOW that if I play my part I should shoot A's or hit long range steel.

There is actually quite a bit to this reloading thing. It is fun and sometimes frustrating to find the best loads.

[Field]

im assuming here that as temperature and humidity drop, your muzzle velocity increases. But for anyone that has experience with this what kind of changes do you see when going from 100f down to around 20-30f?

[G-ManBart]

Field, on Nov 14 2009, 12:54 PM, said:

im assuming here that as temperature and humidity drop, your muzzle velocity increases. But for anyone that has experience with this what kind of changes do you see when going from 100f down to around 20-30f?

The answer to that question could nearly fill a book! The short, short version is that in most cases, as the temperature goes up, the velocity goes up. At our common pistol distances air density doesn't make any difference to speak of, but hotter air is less dense, so you should see an increase in velocity based on that. As humidity rises, air density decreases, so that would also cause an increase in velocity. In reality, it's mostly based on the way the temperature influences the gunpowder in the cartridge. Powders can be positively temperature sensitive, meaning pressures and velocity will increase with increased temperatures or negatively temperature sensitive where pressures and velocity drop with raised temperatures, or neutral temp sensitive. There are also a lot of powders that are pretty neutral, but do show a slight change with temperature, but not enough to really factor in when picking a load.

The short, short, short answer is that there are very few true rules when it comes to this stuff, you'll have to see what your gun and your load do under different conditions before you really know anything, and even then you'll only sort of know since most folks don't have the time to do really exhaustive testing (say a couple of 100 round strings per day/time/temp etc) to rule out normal variation. R,

[fritzthemoose]

tooslo, on Nov 11 2009, 05:56 AM, said:

I'm wondering...Are there known optimum OAL for certain guns? Like, for instance a G17?

the OAL with Glock is determined by the magazine as this is rather short. so you could use a higher OAL chamberwise but not fit it into the mag. there are some bullet shapes that are better than others. you should be able to get 29,5 mm in all magazines but might be able to fit 29,7 with a different bullet shape.

if available in the US try Ares bullets. The polygone profile of the Glock together with the high velocity cover of the ares can give amazing results.

Also consider that some powders like the SP 2 require a light pressure load to work to full potential in a 9 mm. If you are not comfortable with it use SPM or SR primers.