Why don't they.....

[fieldwanderer]

Why aren't .17HMR bullets heavier but more or less the same speed (works out about 290 ft/lbs@25gns)?

 

AND, why not lead? I take it they'd melt or be notably less accurate?

 

 

Not being funny about it or anything, just curious really.

[casts_by_fly]

because to go with a heavier bullet at the same speed as the 17 gr, you'd have to increase the pressure inside the round. Rimfires are limited in pressure because the rims will burst. They are the weak point in the cartridge. I think the pressure limit on the 22mag/HMR is limited at 20-25K psi. The 5mm mag rimfire was designed to be better than the 22 mag and work at a higher pressure (thicker rim) somewhere around 30-35K psi. You can get the 38 gr 20 cal bullet up to 2100 in the 5 mag, which is quite a bit more energy than the HMR.

 

Lead can't handle speeds much more than 16-1800 or so. It is too soft and the bullets would not take in the rifling. They would slide down the bore (fouling like non other) and be pretty inaccurate. Some of the cast bullet shooters are using some high antimony hard cast bullets up around 2K I think, but that is pushing the limits.

 

Thanks

Rick

Edited April 2, 2009 by casts_by_fly

[Beardo]

is there such as thing as subsonic .17? in theory it would be much flatter flying than a .22lr and just as quiet

[Billy.]

is there such as thing as subsonic .17? in theory it would be much flatter flying than a .22lr and just as quiet

 

Nope, becuase the bullet wouldn't expand on impact. Secondly it'd completely ruin the point of a .17

 

I just want a 10grn .17 bullet, so it's more explosive. *evil laugh*

[Guest topshot_2k]

Why the need for a heavier bullet? the 20gr bullets are heavy enough. The .17hmr is a fast, accurate round for vermin control and it does the job very well. also the light bullets don't ricochet like heavier rimfire bullets do

[Guest topshot_2k]

is there such as thing as subsonic .17? in theory it would be much flatter flying than a .22lr and just as quiet

 

it wouldnt due to the smaller bullet going much faster than the 22lr, so you would still get a loud 'crack'

[bennyblanco]

is there such as thing as subsonic .17? in theory it would be much flatter flying than a .22lr and just as quiet

 

 

Why do you think it would be flatter flying?

 

At 1050fps it would be making 41ftlbs at the muzzle and with a 50 zero you would be looking at an 8" drop at 100yds, basically an expensive to run FAC air gun :unsure:

 

ben

[fieldwanderer]

Why the need for a heavier bullet? the 20gr bullets are heavy enough. The .17hmr is a fast, accurate round for vermin control and it does the job very well. also the light bullets don't ricochet like heavier rimfire bullets do :unsure:

 

I just wondered if there was any more power that could be squeezed out of 'em abd if there was, why it wasn't being done. I just like to ponder things like this to be honest

[casts_by_fly]

it wouldnt due to the smaller bullet going much faster than the 22lr, so you would still get a loud 'crack'

 

 

no, the bullet would still be doing ~1020 fps, and the BC's are close enough to not matter. So trajectory wise it would be nearly identical to a 22 subsonic. Then energy wise it would suck because it has less than half the weight.

 

There would be no crack. The crack is from the speed, and a subsonic bullet doesn't have the speed.

 

thanks

rick

[casts_by_fly]

I just wondered if there was any more power that could be squeezed out of 'em abd if there was, why it wasn't being done. I just like to ponder things like this to be honest :unsure:

 

 

wanderer,

 

Have a read through the internal ballistics page on Hornady's website. It describes what goes on inside of a cartridge.

 

Long story short, you have a given volume (which is the volume of the cartridge plus the volume of the barrel) and a given energy content (the internal energy of the powder). The maximum amount of energy in the system is set once you determine the charge. You then loose energy (i.e. not imparted into the bullet) to heating the barrel (friction). You loose a little more in any unburnt powder that comes out of the barrel. You then also loose some to the gasses in the barrel that escape with the bullet. You can add more energy by adding more powder (and increasing pressure), changing the powder (which changes the energy density of the system), by burning more powder (longer barrel with slower powder), or decreasing friction in the barrel (moly coating).

 

In the case of the HMR you can't add more powder as that would increase the pressure above safe levels. You can't increase barrel length as the powder is pretty well set. Moly coating might help a little by decreasing the pressure, thus allwoing you to add more powder. That would require a longer barrel to burn it all.

 

All that said, take the HMR for what it is. It is a rimfire cartridge with excellent out of the box accuracy across a broad range of guns with minimal ammo tuning. It has a great trajectory out to 125 yards or so and is build for vermin sized game. If you want more out of a 17, then you need to go with a bigger one.

 

Thanks

Rick

[Billy.]

Sorry, I did read the thread whilst I was at work so I missed the beginning bit about this.

 

Basically, you don't want a heavier bullet to get more thump, you want lighter.

 

If you imagine a bullet that weighs 150 grn and the same calibre, with a 90 grn bullet. The bullet is still travelling with the same force (say 2000 ft/lbs) This bullet has to exert all this energy upon its target on impact.

 

If you picture it the other way and have the object you're shooting heading towards the bullet (floating in mid air) at a speed that would equal the bullet impacting at 2000ft/lbs. The smaller lighter bullet would be affected more because there is less mass. If you can't picture a deer doing 3,000mph, think about something like a wrecking ball hitting a bullet and then it doing the same with a smaller one.

 

Hopefully this makes sense and that is the reason I use 100grn bullets in my .270, not 150 grn.

[casts_by_fly]

harford,

 

The reason behind your reasoning is based on momentum. A heavier bullet of the same diameter and construction will penetrate deeper than a lighter bullet of the same given both have the same energy, i.e. the 100 gr 243 bullet and the 75 gr 243 bullet will have similar energies coming from the same gun. However the 100 gr will penetrate much deeper. The difference is momentum.

 

Momentum is mass times velocity (compare to energy which is mass x velocity x velocity). Momentum determines the penetration of an object. An object that derives its momentum from mass will penetrate more than an object that derives its momentum from velocity. That is because velocity will be lost as an object penetrates a medium while mass will not. Velocity loss is a function of the current velocity. The faster the object is going, the faster it sheds velocity to drag. So a very light, fast object will shed its velocity as it penetrates a medium and thus the energy and momentum will drop quickly whereas a heavier object at a slower speed will not shed its velocity as fast (and it can't shed mass) so it will maintain momentum further. This is an important concept for archery. It is well known that slow, heavy arrows will penetrate deeper than light, fast ones. This is why.

 

In the case of lighter bullets, the velocity loss corresponds to the object loosing energy. Conservation of energy says that it has to go somewhere. The somewhere is the animal. A light bullet that goes from 2500 to zero (stops just under the skin on the far side) has shed all of its energy into the animal, while a heavier bullet (of the same construction) with the same energy would have penetrated further and gone entirely though, thus transferring less energy to the animal (it took some energy with it after it exited)

 

However, all of this assumes the same construction for both bullets AND that both bullets remain intact. This is great for nosler partitions, Sierra GK's, and big heavy roundnose bullets from slow guns. The fact that there are so many different constructions of bullets can render the penetration argument moot for most everything we shoot. For pretty much any cartridge you can pick a bullet style and a weight to your liking. If you want to penetrate just into the body and blow up (such as for people shooting to keep furs) than there are bullets to do that. If you want maximum penetration you have that. There are plenty of options between. If you want more 'thump' then go with a bigger gun. We certainly aren't spoiled for choice.

 

Thanks,

Rick