Hammer Bullets Pressure Testing Results

[Veteran]

That is getting a bit nebulous and fudge-factory and well beyond the accuracy of the tool. In any case, pick a bullet in GRT which probably has a start pressure around 3k and run your load. Record the velocity and pressure. Now change the start pressure to 1000 or 0 or whatever and get your velocity and pressure. It will be lower. Now increase the charge back up until pressure equal and see velocity. I would bet few 10s of ft-second which is in the noise of velocity variation. Some folks are showing several hundred ft/s difference and showing higher velocity with same powder charge. That is not representative of lower pressures given the relatively small knob dealing with

Lou

Seems like you are on the right track to change initial pressure to 1400 or 1500 in the model, but you make no mention of accounting for friction loss in the bbl. especially say a 28 inch bbl. Its pure engineering. Lower friction loss = higher velocity. Less bullet x section contacting the lands and rifling = less friction and lower initial pressure.

It would seem youd expect more velocity gain for a given load in a longer barrel using hammers vs. standard bullets
because of friction reduction.

You consume pressure in friction loss, ie, the lower the friction loss at the end of the bbl, the higher the pressure at the muzzle. The higher the pressure at the muzzle, the higher the muzzle velocity.

Its the pressure in the whole rifle system, not just the initial pressure that matters. The whole concept of hammers is reduced x section and friction loss.

 

[Veteran]

That is getting a bit nebulous and fudge-factory and well beyond the accuracy of the tool. In any case, pick a bullet in GRT which probably has a start pressure around 3k and run your load. Record the velocity and pressure. Now change the start pressure to 1000 or 0 or whatever and get your velocity and pressure. It will be lower. Now increase the charge back up until pressure equal and see velocity. I would bet few 10s of ft-second which is in the noise of velocity variation. Some folks are showing several hundred ft/s difference and showing higher velocity with same powder charge. That is not representative of lower pressures given the relatively small knob dealing with

Lou

Seems like you are on the right track to change initial pressure to 1400 or 1500 in the model, but you make no mention of accounting for friction loss in the bbl. especially say a 28 inch bbl. Its pure engineering. Lower friction loss = higher velocity. Less bullet x section contacting the lands and rifling = less friction and lower initial pressure.

It would seem youd expect more velocity gain for a given load in a longer barrel using hammers vs. standard bullets
because of friction reduction.

You consume pressure in friction loss, ie, the lower the friction loss at the end of the bbl, the higher the pressure at the muzzle. The higher the pressure at the muzzle, the higher the muzzle velocity.

Its the pressure in the whole rifle system, not just the initial pressure that matters. The whole concept of hammers is reduced x section and friction loss.

 

[Veteran]

Physics is physics is physics.

If we can send men to the moon and model that, we can model shooting a Hammer Bullet and get correct outputs w a little work and history matching.

The real issues here have been well defined by this thread.

1) Starting pressures in the chamber are not the same as for standard construction bullets. Therefore it will be appropriate to lower them to get a history match with chrono mv.

2) Friction loss and loss of pressure in travel down the bbl
and the length of the bbl will be important to get right in the model, because of the difference in x section bearing of the bullet w lands and rifling in the hammer bullets.

So, some x section vs. length parameters and some frictional adjustment factors have to be
modeled and history matched in some experimental bbls or in some detailed physics models to derive the right friction loss per inch of bbl for these specific bullets.

If you have these parameters correct in QL or GRT, I believe one can history match the model to actual chrono data pretty accurately.

 

[Lou270]

Coeffecient of friction goes down as velocity increases. So The bore friction is pretty small part of the deal. Also as friction goes down thus does pressure (ie force pushing on bullet) so that needs accounted. Think of it as shooting a small spit ball vs a tight fitting one. Among other things lead angles and rifling types affect pressures differently with different bullets. So you are right it is a system and difficult to model. Valid pressure testing data will set you free. May not match your gun exactly but will give you a good idea of how a bullet performs with respect to another in the same system and reduce the guess work and rationalizing

Lou

 

[Veteran]

Coeffecient of friction goes down as velocity increases. So The bore friction is pretty small part of the deal. Also as friction goes down thus does pressure (ie force pushing on bullet) so that needs accounted. Think of it as shooting a small spit ball vs a tight fitting one. Among other things lead angles and rifling types affect pressures differently with different bullets. So you are right it is a system and difficult to model. Valid pressure testing data will set you free. May not match your gun exactly but will give you a good idea of how a bullet performs with respect to another in the same system and reduce the guess work and rationalizing

Lou

The coefficient of friction going down as velocity increases may not outweigh the greater c section experiencing friction in a standard bullet. I think that the magnitude of whats happening w friction loss will be far outweighed by actual x section in contact than the applicable coefficient of kinetic friction that is applied.

 

[MtPockets]

The coefficient of friction going down as velocity increases may not outweigh the greater c section experiencing friction in a standard bullet. I think that the magnitude of whats happening w friction loss will be far outweighed by actual x section in contact than the applicable coefficient of kinetic friction that is applied.

^^^^^= WAAAYYYY above my pay grade!

 

[Veteran]

Well sending a man to the moon is above my pay grade too, but if you give me the right starting pressure, and the right friction profile for a hammer bullet, I bet I can model that in QL.

The one thing that puzzles me about hammer bullets is te reported diminishing returns seen on bigger than .30 calibers.

Apparently users have reported disproportionately less observed velocity increases on larger calibers than experienced below .30 caliber.

The only thing this discussion has sparked is maybe on larger calibers, the sheer length of the bullet compared to smaller calibers implies it will always experience more friction loss because its mainly the front end of the bullet that is tapered and minimized as to bearing load in contact w the barrel. Maybe on smaller calibers, there is not so much length of bullet remaining behind the tapered point, and on larger calibers, there can still be a lot of surface area to travel down the barrel behind that tapered end? I dont know, Im just trying to rationalize why the data comes out different for large calibers?

 

[cohunt]

Physics is physics is physics.

If we can send men to the moon and model that, we can model shooting a Hammer Bullet and get correct outputs w a little work and history matching.

The real issues here have been well defined by this thread.

1) Starting pressures in the chamber are not the same as for standard construction bullets. Therefore it will be appropriate to lower them to get a history match with chrono mv.

2) Friction loss and loss of pressure in travel down the bbl
and the length of the bbl will be important to get right in the model, because of the difference in x section bearing of the bullet w lands and rifling in the hammer bullets.

So, some x section vs. length parameters and some frictional adjustment factors have to be
modeled and history matched in some experimental bbls or in some detailed physics models to derive the right friction loss per inch of bbl for these specific bullets.

If you have these parameters correct in QL or GRT, I believe one can history match the model to actual chrono data pretty accurately.

Ahhhh--- but did we really send men to the moon?

 

[Veteran]

Ahhhh--- but did we really send men to the moon?

Are all the reloading tables posted herein by GL Taylor for Hammers real, or imagined?

Me says, yes, we sent men to the moon, and the posted tables are our best real world data to date on Hammer bullet loads and velocities.

In fact, there may even be enough real world data there, that Hammer Bullets could hire QL to use the verified Chrono data for each load in those tables to back into a friction profile for each of their bullets that would history match QL predictions to Hammer Actuals.

Maybe some more work by caliber and load on initial pressures too.

It could be done I think.

 

[MagnumManiac]

No and No. However if you do not view the GRT tool nor the work the gent Steve quoted is doing as credible then what is the point of this whole post to show hammers have lower start pressure.

Lou

The simple fact is, without pressure testing equipment, you have ZERO DATA to show…I have a Pressure Trace II, have done since 2010/11 and it's not just Hammer bullets that show lesser start pressure, bore rider designs, shorter bearing surfaces and HBN coating all change the outcome, as does a cold or hot primer.
Until you have proof of what you tout, really your just peeing in the wind.

Cheers.

 

[cohunt]

The simple fact is, without pressure testing equipment, you have ZERO DATA to show…I have a Pressure Trace II, have done since 2010/11 and it's not just Hammer bullets that show lesser start pressure, bore rider designs, shorter bearing surfaces and HBN coating all change the outcome, as does a cold or hot primer.
Until you have proof of what you tout, really your just peeing I the wind.

Cheers.

Even some odd ball powders will produce safe yet unbelievers velocities-- I have a pressure trace tested 6.8spcii load that would baffle most people, it uses an off the wall powder for that cartridge yet it tests safe pressures

 

[MagnumManiac]

Where in their statement do they say they make powder? I also don't see where they say they don't source their information elsewhere?

What makes their statement laughable?

Hodgdon have always IMPLIED that they MANUFACTURE powder and test it…they don't. I know where their data comes from, QL or other testing facilities like Sierra and Nosler, just to name 2.

Cheers.

 

[Veteran]

The simple fact is, without pressure testing equipment, you have ZERO DATA to show…I have a Pressure Trace II, have done since 2010/11 and it's not just Hammer bullets that show lesser start pressure, bore rider designs, shorter bearing surfaces and HBN coating all change the outcome, as does a cold or hot primer.
Until you have proof of what you tout, really your just peeing I the wind.

Cheers.

Yes, all of the things you mention which reduce friction and will logically increase velocity.

Im not sure a coating on a standard bullet will lower initial pressure measurably. It will certainly reduce friction once in the barrel. But, if you have some data, please share it. It would be interesting.

Primers are really bullet agnostic, because a hotter or less hot primer will have the same directional impact on a standard bullet, one that's coated, or a Hammer. It will provide more or less velocity in some measure to every bullet.

 

[MagnumManiac]

Even some odd ball powders will produce safe yet unbelievers velocities-- I have a pressure trace tested 6.8spcii load that would baffle most people, it uses an off the wall powder for that cartridge yet it tests safe pressures

I can attest to that. My 375 Weatherby, not factory, has a .500" freebore, as designed, it will push nearly all bullet weights at 100fps faster than a .376" freebore. Over the trace it exhibits 2 things notably different to the other chamber, a lower start pressure and a taller rise to Max pressure, which results in that faster end velocity. H4350 doesn't do this to the same level as Win 760, but it is still traceable.
All loads were maxed out at 63,000 psi as I find that the next jump in pressure is often up around 67,000-68,000psi. My rifle craters primers around that range. With it's 24" barrel, the 3,000fps it achieves with 260g Accubonds is remarkable.

Cheers.