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New cartridge design

 
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  #8  
Old 06-05-2007, 10:30 AM
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Re: New cartridge design


Less powder equals longer barrel life,also less velocity.....

There 5000 fps is with a 20 grain bullet,who shoots 20 grains bullets in this caliber?.......
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  #9  
Old 06-05-2007, 11:47 AM
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Re: New cartridge design

Forward ignition was tried at Williamsport by several back a ways...no one uses it.

Till you get the primer tube in there you REALLY cut your case capacity...

YMMV,
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  #10  
Old 06-05-2007, 02:39 PM
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Re: New cartridge design

jwp & 1000br,

Here's what I've learned so far. All tests in 338 Win Mag. REM 700 Sporter.

For equal amounts of powder velocity and pressure is lower with FI.

If the load is MAX for FI, don't shoot it w/out the flash tube.

For equal average velocities SDs and ESs are smaller with FI.

Pressure curves w/FI did not show the small pressure spike just prior to the bullet exiting the muzzle. W/o the FI it almost always appeared.

Temperature test(feable attempt w/poor sensor(s): Heat appeared to concentrate at or just ahead of the chamber then flow forward. With conventional ignition, the whole barrel length heated up fast.

Felt recoil was definitely less w/FI but not enough to make it a real feature.

Powder capacity taken up by the flash tube can be compensated for by using appropriate. For example in my 270 AM and conventional ignition using US869 give about 90% or so load density (if I correctly understand what LD is?). 90% LD leaves just enough room to make 100% LD with the flash tube installed.

Having said all of that, here's where I am. I was excited to rebarrel the 338 Win w/a 338 RUM and go to the next level. I got the 338 RUM shooting 300 SMKs @ 2735 +/1 FPS and clover leafs @ 200 yds. So why mess with the FI [img]/ubbthreads/images/graemlins/confused.gif[/img]

FI may be an advanted IF all the powder could be made to burn in the case and gases only entering the throat and barrel. Maybe throats would last a bit longer.
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  #11  
Old 06-05-2007, 03:19 PM
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Re: New cartridge design

Front ignition is as old as Gibbs, and each of your findings match his.
It simply comes down to more powder burning in the case, rather than following the bullet down the barrel.. Less pushed with the bullet, contributing to recoil, and burning off.. Less powder blasting of the leade.

The powder column of a WSM/WSSM is too wide to follow the bullet well. This causes similar(but less) gains as that of front ignition.

I'd be interested in your application method.
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  #12  
Old 06-05-2007, 04:56 PM
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Re: New cartridge design

This is interesting stuff, certainly not new, it has been done over and over for the last 50 yeards and the military does it with large artilary shells, at least they used to.

I tested Front ignition in my 7mm AM and a bit in my 270 AM. Standard performance with both is a 200 gr ULD RBBT loaded to around 3300 fps with around 105.0 gr WC872 in the 7mm and for the 270 AM average velocity is generally in the 3375 fps range with around 102.0 gr WC872.

These are average numbers with 30" barrels.

When I tested these two rounds, same rifles, with front ignition, I found several interesting things.

First lets talk about the 7mm.

I found with the 7mm AM based off the 338 Lapua case that this worked best if the cases were fired once with full pressure loads before using installing the ignition tube. Why? Well, on the first firing of any case the case head is going to expand more then it will from that point on given we are using comfortable working pressures.

I found that if I installed a flash tube in the virgin cases and fired them, in nealy every instance, the tube would be extremely loose after this firing and several were flat out gone.

When I tested with once fired cases, this did not happen nearly as often. Some were loose but only 1/2 rotation was needed to snug them up again.

Performance was very similiar to what I was getting with standard ignition. I would say top end loads using FI were 50 fps faster at most. It did however take up to 5 grains more powder to reach this top end velocity. The reason is simply, when you are using a standard ignition system, the bullet and powder charge weight need to be combined to determine the resulting chamber pressure because the powder is being forced down the bore to some degree along with the bullet.

With the forward ignition, this is not the case. I would estimate 90% of the powder never leaved the case as it burns. So with standard ignition you have a 200 gr bullet plus 105 grains of powder for a total payload of 305 grains. Over 30% more then with front ignition.

I also found that barrel temps were FAR lower using forward ignition then with standard ignition. To that same point, fired cases with forward ignition were much hotter to the touch then standard ignition rounds, again, the reason is obvious, the powder is burning in the case, not in the bore.

This is the reason the throat lasts so much longer.

With the 270 AM, I had some problems getting the sold Rem cases to hold the threads on the flashtubes. I tried some permanent thread locker and that helped quite a bit but personally, I do not care for this ignition method using these cases. Results however were nearly identical to the 7mm AM results.

I personally feel that forward ignition is best suited to larger case capacity rounds then most of us deal with on a regular basis. I think rounds such as my 338 Allen Magnum would get a huge boost in barrel life using this method of ignition and I hope to test that theory out here soon.

For smaller chamberings, the benefits are certainly there but practicality issues come into play in my opinion and in most instances, front ignition is not practical for many conventional chamberings.

Just my experience.

Kirby Allen(50)
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