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Crimping and pressure
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Picture of Fritz Kraut
posted 24 July 2005 03:04
How much does crimping influence pressure? I shot some .308Win rounds today, and had some slight pressure signs. I have shot this load before, even in hotter weather, without any pressure signs. However, this time I used the Lee Factory Crimp after having set the bullets. Could that rise the pressure?

Regards,

Fritz


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posted 24 July 2005 07:33Hide Post
quote:
Could that rise the pressure?

Regards,

Fritz


Not without raising the velocity... have you got a chronograph?


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Posts: 4026 | Registered: 28 May 2004Reply With Quote
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posted 24 July 2005 07:56Hide Post
WinkThe answer is yes it is possible and once more probable that you could see a higher peek pressure in that before that bullet starts to move down the barrel it has to overcome a greater holding force. For the first few millisec. you can expext the curve to be parallel and a little higher than you did before.The exhaust pressures for each case will be almost the same assuming complete burning for each.The energy transfere to the bullets would also be equivalent. sofaroger


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Posts: 10226 | Location: Temple City CA | Registered: 29 April 2003Reply With Quote
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posted 24 July 2005 18:29Hide Post
quote:
Originally posted by Fritz Kraut:
How much does crimping influence pressure?

Fritz


Herr Kraut - With progressive burning smokeless powders, the peak pressure occurs long after the bullet has left the cartridge case. Therefor, whatever additional work must be performed to unfold the crimp has been done much earlier than that. So it does NOT have any significant effect on pressures.

As a matter of fact, a greatly oversize bullet can be fired through a barrel with NO ILL EFFECTS WHATSOEVER, as long as the chamber neck diameter is large enough to permit the case neck to expand and freely release the bullet. The oversize projectile will be swaged down to bore diameter long before pressure peaks. For example, .308" bullets have been fired through a 6.5 Jap barrel after some yo-yo rechambered his Arisaka to .30/'06, but did not have the barrel rebored!!

NOTE THAT WE ARE TALKING RIFLES HERE. THE RULES CHANGE SOMEWHAT WHEN FAST POWDERS ARE USED IN HANDGUNS!!


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Posts: 4386 | Location: New Woodstock, Madison County, Central NY | Registered: 04 January 2005Reply With Quote
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posted 25 July 2005 00:12Hide Post
Nobody I know crimps rifle slugs and everything I've read recommends against it.
 
Posts: 139 | Location: Oregon | Registered: 22 February 2005Reply With Quote
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posted 25 July 2005 00:20Hide Post
Bigdog2:

The crimping of rifle bullets is standard factory practice.

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Posts: 2452 | Location: Old Europe | Registered: 23 June 2001Reply With Quote
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posted 25 July 2005 01:00Hide Post
quote:
Originally posted by Bigdog2:
Nobody I know crimps rifle slugs and everything I've read recommends against it.


FYI

https://forums.accuratereloading.com/eve/forums/a/tp.../580101862#580101862


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Posts: 2750 | Location: Houston, Tx | Registered: 17 January 2005Reply With Quote
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posted 25 July 2005 01:09Hide Post
quote:
Originally posted by Bigdog2:
Nobody I know crimps rifle slugs and everything I've read recommends against it.


Well. Then, you haven't read any of the posts by people who own a Lee "Factory Crimp" die.

They all just love 'em, and swear they give BETTER ACCURACY than if the round is left uncrimped. Personally, I can't see how this can happen, since crimping into a bullet jacket where there is no crimping groove is bound to alter the relationship between ther core & jacket at that point... But one cannot argue with performance, either.


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Posts: 4386 | Location: New Woodstock, Madison County, Central NY | Registered: 04 January 2005Reply With Quote
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posted 25 July 2005 10:05Hide Post
Just for grins, I ran a standard 308 load (155 gr. Hornady over 46 grains of Varget) through Quickload, and it predicted 55,000 PSI, and 2836 fps.

Increasing the bullet start pressure (the minimum pressure required to start the bullet moving) to 7,000 PSI (from the default 3,600 PSI) increased predicted pressure to 59,600 PSI, and 2864 fps.

7,000 PSI is still less start pressure than seating a bullet into the lands.

It seems that crimping a bullet does increase pressure slightly, and loads should be worked up from below.

Incidentally, I believe you can use a milder primer with a firm bullet crimp, which should off-set the increase in pressure. FWIW, Dutch.


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Posts: 4564 | Location: Idaho Falls, ID, USA | Registered: 21 September 2000Reply With Quote
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posted 25 July 2005 10:40Hide Post
quote:
Nobody I know crimps rifle slugs and everything I've read recommends against it.


Bull!

http://www.accuratereloading.com/crimping.html
 
Posts: 1205 | Location: Minnesota | Registered: 07 February 2004Reply With Quote
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posted 25 July 2005 20:08Hide Post
I have experienced greater velocities by crimping the bullets tighter. I have only done this a few times but the velocity always was 15-30 fps faster when the bullet was crimped tight.

I usually only turn my Lee FCDs in 1/4 turn once it contacts the shell holder on my Bolt rifle loads, just enough crimp to hold the bullet snug.

I have occasionally crimped them w/ more crimp (about 1/2 turn or so) and the Crimp die indents the bullets like a cannelure (i've pulled them and seen the rings). I do believe that this increased start pressure causes the charge to burn in a different manner than if no tention is present. A bullet w/o a crimp doesn't have to have much pressure at all to engage the bullet into the lands but, a bullet that has a strong crimp sort of has two starting pressures (the one from the crimp and the one as the bullet is forced into the lands).

I personally have had much better accuracy when crimping w/ a Lee FCD, I find the crimped rounds to be much more consistent and Hey, it works, so I sure ain't changing it any time soon.

Good Luck!

Reloader
 
Posts: 4146 | Location: North Louisiana | Registered: 18 February 2004Reply With Quote
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Picture of El Deguello
posted 25 July 2005 22:13Hide Post
quote:
Originally posted by steve4102:
quote:
Nobody I know crimps rifle slugs and everything I've read recommends against it.


Bull!

http://www.accuratereloading.com/crimping.html


quote:
Well, when I went into this project, I must admit that I was a bit skeptical about finding any improvements. Now if we look at the groups, we find that the crimped ammo shot approximately 10% better. Also, the standard deviation seems to be lower with the crimped ammo. I think this needs looking into further.


It certainly seems like a good subject for further examination. (I wonder if the benchrest boys are crimping their loads??)


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Posts: 4386 | Location: New Woodstock, Madison County, Central NY | Registered: 04 January 2005Reply With Quote
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posted 25 July 2005 22:47Hide Post
El, the 100, 200, 300 yd BR shooters use no crimp. Neck size bushings are normally .004" below neck dia.
 
Posts: 868 | Location: maryland | Registered: 25 July 2004Reply With Quote
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posted 26 July 2005 02:03Hide Post
Evidently, "Fritz Kraut" has helped me reopen an ongoing arguement about Crimping. The nice article referred to by "Steve4102" is less than compelling as to the advantage or disadvantage of crimping the standard rifle cartridge, and even it ends by saying "I think this needs looking into further."
A quick survey in another reloading forum shows far less certainty in the benefits of crimping except for in pistols, lever guns and big bore rifles. Kraut's 308 Winchester doesn't seem to fit in these catagories. Though if he did put a solid crimp on his 308 Win., it certainly could be expected to raise case pressure.

It might be best to say that the question of whether or not to crimp standard bottleneck rifle cartridges, ranks alongside such topics as "neck turning", "distance from lands", or the use of flat base or boat tail bullets, all of which may or may not make any difference to a particular round or rifle or usage of such.

To each his own---I elect not to
 
Posts: 139 | Location: Oregon | Registered: 22 February 2005Reply With Quote
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posted 26 July 2005 03:13Hide Post
If you work up a load without crimping and then crimp it (or increase the neck tension is a better way of putting it) then you certainly run the risk of increased pressure as the case neck holds onto the bullet a bit longer allowing more of the powder to be consumed (incrasing the pressure inside the case) before the bullet starts into the barrel.

If your original load was near max pressure then the additional neck tension will probably show over-pressure signs. If it was a milder load it may or may not show pressure signs.

Consistent neck tension together with consistent case-length trimming are two of the more important things when it comes to accuracy.


DB Bill aka Bill George
 
Posts: 4360 | Location: Sunny Southern California | Registered: 22 May 2002Reply With Quote
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Picture of bartsche
posted 26 July 2005 07:11Hide Post
quote:
Originally posted by Dutch:
Just for grins, I ran a standard 308 load (155 gr. Hornady over 46 grains of Varget) through Quickload, and it predicted 55,000 PSI, and 2836 fps.

Increasing the bullet start pressure (the minimum pressure required to start the bullet moving) to 7,000 PSI (from the default 3,600 PSI) increased predicted pressure to 59,600 PSI, and 2864 fps.

7,000 PSI is still less start pressure than seating a bullet into the lands.

It seems that crimping a bullet does increase pressure slightly, and loads should be worked up from below.

Incidentally, I believe you can use a milder primer with a firm bullet crimp, which should off-set the increase in pressure. FWIW, Dutch.


Thanks for the co-oberating info ,Dutch beerroger


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Posts: 10226 | Location: Temple City CA | Registered: 29 April 2003Reply With Quote
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Picture of Fritz Kraut
posted 26 July 2005 13:53Hide Post
Thanks for all friendly replies - they have been very informative. beer

I'll back the load a grain and go on crimping. At least it could mean a cartridge or two more from a canister of powder. Wink

I think I'll also consider to get factory Crimp dies for my .22 H and .222R, as I can't operate with seating depth, because of the magasine length. Perhaps the crimping could compensate that limitation and enable better accuracy.

Regards,

Fritz


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Posts: 846 | Location: Sweden | Registered: 19 April 2001Reply With Quote
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posted 26 July 2005 17:59Hide Post
For my 22 Hornet, that had accuracy problems, one of the several things I did to improve accuracy was to crimp the bullet. It helped.
I now crimp all of my Hornet loads.
Don




 
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posted 27 July 2005 01:15Hide Post
quote:
Originally posted by eddieharren:
El, the 100, 200, 300 yd BR shooters use no crimp. Neck size bushings are normally .004" below neck dia.


Thanks! It has beeen years since I was up to snuff on benchrest loading techniques....


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Posts: 4386 | Location: New Woodstock, Madison County, Central NY | Registered: 04 January 2005Reply With Quote
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posted 27 July 2005 03:25Hide Post
This is what Lee has to say about the crimp die and pressure. This is from their web site.

A firm crimp improves accuracy because pressure must build to a higher level before the bullet begins to move. This higher start pressure insures a more uniform pressure curve and less velocity variation. Even powder selection is less critical.
 
Posts: 1205 | Location: Minnesota | Registered: 07 February 2004Reply With Quote
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posted 28 July 2005 02:39Hide Post
When ever a Lee factory crimp die is used, you need to go back to the minimun starting load and work up. Remember, whenever you make a change in your load, you should start over for safety.
 
Posts: 116 | Location: Eastport Maine | Registered: 24 April 2005Reply With Quote
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posted 28 July 2005 09:57Hide Post
On my straight long belted big bores I crimp.If bullets have no cannelure, I put one on
if using medium to slow powders.In big bores where some bullets may start easy with slow powders we want to get
the initial pressure up good so bullet won't hesitate when it enters rifling, and crimping
does help to do that with consistancy.Ed.


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posted 28 July 2005 20:51Hide Post
quote:
Originally posted by steve4102:
This is what Lee has to say about the crimp die and pressure. This is from their web site.

A firm crimp improves accuracy because pressure must build to a higher level before the bullet begins to move. This higher start pressure insures a more uniform pressure curve and less velocity variation. Even powder selection is less critical.


Please note that this info from Lee does NOT state that PEAK pressures will be raised by crimping, and does NOT contain any instructions to consider reducing the powder charge because you are crimping the bullets.


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Posts: 4386 | Location: New Woodstock, Madison County, Central NY | Registered: 04 January 2005Reply With Quote
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posted 28 July 2005 21:17Hide Post
chronograph, chronograph, chronograph...

All components being equal, if the pressure goes up with crimping, so will the velocity.

Chronograph the loads before and after the crimp, that's the easiest way to see an increase (or not) in pressure.

All else is speculation without that information.


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Posts: 4026 | Registered: 28 May 2004Reply With Quote
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posted 28 July 2005 21:29Hide Post
New guy, usually I am a big proponent of chronographs, but when you are moving bullets into lands or crimping, you can actually decrease velocity while increasing pressure.

As far as the Lee statement, Richard Lee also suggest it is a good idea to load shells without a scale, by dipping powder, and by beating on his handloader gizmo with a hammer. I'm going to take what he says there with a fair amount of salt..... JMO, Dutch.


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Posts: 4564 | Location: Idaho Falls, ID, USA | Registered: 21 September 2000Reply With Quote
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posted 29 July 2005 09:42Hide Post
quote:
Originally posted by Dutch:
New guy, usually I am a big proponent of chronographs, but when you are moving bullets into lands or crimping, you can actually decrease velocity while increasing pressure.

As far as the Lee statement, Richard Lee also suggest it is a good idea to load shells without a scale, by dipping powder, and by beating on his handloader gizmo with a hammer. I'm going to take what he says there with a fair amount of salt..... JMO, Dutch.


With all due respect Dutch and, again, assuming all components are the same... please explain to me how pressure and velocity (within the laws of physics as we understand them) are not directly correlated.

I'd argue that if it takes X-amount of pressure to drive a bullet a certain speed, and that assuming a change is made which results in an increase in velocity, then clearly there was an increase in the amount of pressure required to push the bullet to the resulting faster speed.

Decreasing pressure can't possibly make a bullet go faster, can it?

More pressure drives the bullet faster, and less pressure slows it down.


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Posts: 4026 | Registered: 28 May 2004Reply With Quote
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posted 29 July 2005 10:14Hide Post
The pressure moving the bullet, we are talking about average pressure over the length of the barrel or the area under the pressure curve.
Initial pressure may be up due to crimping,
and may increase overall pressure under curve,
or due to many factors pressure under the
curve may be close to the same as
uncrimped load. So velocity may be up or close to the same in comparison.Powder type, barrel length, case type, etc are all affecting factors.Ed


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posted 29 July 2005 18:16Hide Post
quote:
With all due respect Dutch and, again, assuming all components are the same... please explain to me how pressure and velocity (within the laws of physics as we understand them) are not directly correlated.

I'd argue that if it takes X-amount of pressure to drive a bullet a certain speed, and that assuming a change is made which results in an increase in velocity, then clearly there was an increase in the amount of pressure required to push the bullet to the resulting faster speed.


New Guy, The velocity is related to time under pressure. Not nessacarily the peak pressure. The faster the rise time, the longer the powder holds peak pressure, longer barrels cause the bullet to travel under pressure longer, all cause velocity variations. Crimping or jamming the bullet in the lands can cause the pressure to rise to peak faster and allow the bullet more barrel time under higher pressure then a slow climb from a unhindered bullet start would.


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Posts: 2535 | Location: Michigan | Registered: 20 January 2001Reply With Quote
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posted 29 July 2005 19:50Hide Post
Clearly we could right a book on the subject and differing opinions. I understand the realitive time spent in the bore under a pressure curve as it relates to velocity.

I guess the pracitcal question for Fritz is how does he identify any differences of pressure from crimping? right?

Without the labratory pressure guages needed to identify that, I have to say that velocity variations as obtained with a chronograph are his most readily available tool.


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Posts: 4026 | Registered: 28 May 2004Reply With Quote
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posted 29 July 2005 20:24Hide Post
New guy, be my guest and write a book about your opinions. I suggest you first try the experiment and see what the facts are.

My loading book has several of observations where hard jams decrease velocity, while increasing peak pressure signs.

The other gentlemen have made good observations regarding total pressure. There is one more factor that should be considered.

Energy is used for several things inside a rifle barrel: one of which is engraving the bullet. If we make an analogy to pushing a car up onto a curb, with a engraving a bullet: it takes much less effort to push a car onto that curb if you take a little run at it. As a matter of fact, it takes very little, and it hardly slows the car down. Then again, put the wheels against the concrete before starting to push, and effort increase very substantially.

In other words, energy used to engrave is not available to accellerate the bullet. The energy the bullet gets during the running start is taken from the energy budget in the hard jam situation. FWIW, Dutch.


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Posts: 4564 | Location: Idaho Falls, ID, USA | Registered: 21 September 2000Reply With Quote
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posted 29 July 2005 21:27Hide Post
Yes, Dutch, you are right... there are lots of theoretical variables in each gun and vary from gun to gun, and energy is used in different forms, etc...

But the question remains as to how Fritz is supposed to practically identify pressure rises from his crimping.

What practical tools can he use?


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Posts: 4026 | Registered: 28 May 2004Reply With Quote
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Picture of Fritz Kraut
posted 29 July 2005 21:37Hide Post
quote:
Originally posted by new_guy:
But the question remains as to how Fritz is supposed to practically identify pressure rises from his crimping.

What practical tools can he use?


Fritz the Kraut will go to the shooting range with new loaded cartridges. There will be three several loads with the same bullet, with 1 grain difference, and one half of them crimped and the other half uncrimped. Smiler

I will make these test as soon as possible and than come back to tell the result.

Regards,

Fritz


The true and only Fritz Kraut
 
Posts: 846 | Location: Sweden | Registered: 19 April 2001Reply With Quote
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posted 29 July 2005 21:43Hide Post
A poster in the past, Stan Watson, that went by the name of OKshooter did a lot of pressure testing on a 30-06 with a Oehler pressure ballistic lab and offered a book of his findings sometime back.
I checked my copy the manual of his and found he did a single test on crimping vs no crimp useing the 180 gr Hornady over WMR powder. He found the crimped cartridge gave 15 fps more vel and 1,300 psi more pressure then the uncrimped cartridge.
The main differance in the two in his opinion was the appearent greater consistancy in the pressure & vel of the crimped load. He does note however that switching to a faster or slower powder may give different result, and the difference wasn`t concidered enough to cause him to worry about adding a crimp raising a safe load to dangerous pressure levels in otherwise reasonable loads.


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Posts: 2535 | Location: Michigan | Registered: 20 January 2001Reply With Quote
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posted 30 July 2005 02:08Hide Post
quote:
Originally posted by new_guy:
chronograph, chronograph, chronograph...

All components being equal, if the pressure goes up with crimping, so will the velocity.

Chronograph the loads before and after the crimp, that's the easiest way to see an increase (or not) in pressure.

All else is speculation without that information.
Hey new-guy, Do the terms "dv/dt and area-moment" mean anything to you?
---

quote:
Originally posted by new_guy:
But the question remains as to how Fritz is supposed to practically identify pressure rises from his crimping.

What practical tools can he use?
Just the very best Pressure Detection method OF-ALL-TIME, good old Pressure Ring Expansion(PRE).
 
Posts: 9920 | Location: Carolinas, USA | Registered: 22 April 2001Reply With Quote
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posted 30 July 2005 02:15Hide Post
quote:
Originally posted by Ol` Joe:
A poster in the past, Stan Watson, that went by the name of OKshooter ...
Hey Ol' Joe, Do you remember any of stanley's posts from the old "Shooters" web site where he was inclined to post Loads for the Beginners to see which he claimed exceeded 100,000psi(M43)?

Are you aware that stanley can not comprehend "why" a person either needs to P-FLR or FLR a case in order for PRE to work properly?

Are you aware his M43 is non-calibrated?
 
Posts: 9920 | Location: Carolinas, USA | Registered: 22 April 2001Reply With Quote
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posted 30 July 2005 17:07Hide Post
quote:
Originally posted by Fritz Kraut:
quote:
Originally posted by new_guy:
But the question remains as to how Fritz is supposed to practically identify pressure rises from his crimping.

What practical tools can he use?


Fritz the Kraut will go to the shooting range with new loaded cartridges. There will be three several loads with the same bullet, with 1 grain difference, and one half of them crimped and the other half uncrimped. Smiler

I will make these test as soon as possible and than come back to tell the result.

Regards,

Fritz


Ganz Gutt, Herr Kraut! The imperical approach is always the best. We'll be awaiting your report!!

Danke!


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