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Old March 26, 2011, 08:06 PM   #1
tpcollins
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Question on compressed loads and pressure

I bought a Tikka T3 Lite in .204 for chucks and smaller varmints. It has a 20" barrel so I knew up front I won't get the maximum in velocity versus a 24"-26" or so barrel.

In my reloading manual for various calibers I see compressed loads and was wondering two things:

- how many people actually shoot compressed loads on a regular basis?

- if the hotter loads generate more pressure, is that pressure reduced in a shorter barrel or would the pressure be the same regardless of barrel length? Thanks.
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Old March 26, 2011, 08:29 PM   #2
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I shoot compressed loads on a fairly regular basis with my 45-70, 25-06, and 223 Rem.

My experience has been compressed loads are the result of slow burn rate powders skirting on the fringe of being too slow for the cartridge. Mine operate in a safe region and I get no signs of over-pressure. I like using Hodgdon powders because they give you the pressure data for their loads. It's a good guide post when selecting powder/bullet combinations.

Short barrel guns will be more efficient with quicker powders because the pressure curve for slower powders will often result in blowing unburnt powder out the end of the barrel. Some contend that barrel length will not matter and powders that produce the highest velocity in longer barrels will do the same for shorter barrels albeit somewhat reduced from the longer barrel. That doesn't make sense to me if you are blowing powder out the end of the barrel in one instance and burning it all in another.
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Old March 26, 2011, 10:10 PM   #3
chiefr
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+1 Flashhole

I too, shoot compressed loads and never had problems as long as I followed tech data.
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Old March 27, 2011, 12:04 AM   #4
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As was mentioned, compressed loads are generally with slower powders. I have some accuracy loads with IMR 4831 that the only way to get the powder in is to use a long drop tube and/or vibrate them.

You do not want to "crunch" compress them, breaking kernels. If they are not compacted before the bullet is pressed in, they may dimple out the case (as in thin Winchester cases) or the bullet will slowly be pushed back out.
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Old March 27, 2011, 12:52 AM   #5
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I've shot compressed loads in the .308, and you must crimp them in to prevent bullet creep. Chamber pressure is what they measure, so yes, they should all be the same unless you have plenty of freebore.

-7-
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Old March 27, 2011, 02:16 AM   #6
NESHOOTER
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Quote:
- if the hotter loads generate more pressure, is that pressure reduced in a shorter barrel or would the pressure be the same regardless of barrel length?
One should remember that following the reloading book will give you the max at that particular powder you maybe using and something to note is some powder are in CUP and some in PSI the pressure expressing is in the chamber area holding the round lessening as the the bullet moves down the barrel. I only matters that you will lose FPS on shorter barrels not always reflecting POI's just more footpounds on impact.
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Old March 27, 2011, 04:33 AM   #7
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My most acurate load in .221 Rem Fireball with 55 grain bullets uses a compressed load that is the starting load. Dead on acurate with no pressure sighns.
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Old March 27, 2011, 11:02 PM   #8
TGReaper
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Question on compressed loads and pressure

I have no way to measure pressure but I believe that "reasonably" compressed loads are conducive to consistent ignition.
My pet 30-06 load is compressed and has served me well in the same mod.70 for over 30 years.
TGR
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Old March 28, 2011, 09:17 PM   #9
Shoney
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DO NOT TRY THIS AT HOME OR ELSEWHERE!

I have a friend that loads his 338 WM by filling the case to overflowing with IMR XXXX, then tapping the sides to get the powder to settle, then levels it across the mouth and stuffs a bullet in. The cotton picking things are as accurate as my meticulously loaded 338's! ! ! ! ! ! ! ! !

When he hunted in the "Rain Forests" of the NW US, he did have some of the bullets pushed forward and couldn't chamber them.:
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Old March 29, 2011, 08:39 PM   #10
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Quote:
- how many people actually shoot compressed loads on a regular basis?

- if the hotter loads generate more pressure, is that pressure reduced in a shorter barrel or would the pressure be the same regardless of barrel length? Thanks.
Most of the ammunition I load for shooting Highpower matches is compressed, some more than others. As stated earlier, light compression doesn't hurt and some theorize it may lead to slightly improved ignition consistency. I will agree with the idea that in rifle cartridges compressed loads are generated by powders that are bordering too slow.

Peak pressure has nothing to do with barrel length, it is strictly measured at the chamber. That barrel could be 4" or 34", peak chamber pressure will be the same.

As for powder suitability, the slowest powders will generate the highest velocities, regardless of barrel length. The best example I have experience with is in the .44 Magnum. Winchester 296 gives me the highest velocity with either a 6" revolver or a 20" rifle. The downside is that blast and flash are more pronounced with shorter barrels and slow powders. But that's the price you pay for maximum performance.
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Old March 30, 2011, 04:39 PM   #11
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It's not an iron clad rule, but in my own observations, it seems like a lot of my best accuracy loads come when the bullet is just barely touching the powder when fully seated. Not quite compressing, but very close to it. I have shot compressed loads before where the bullet was squishing the powder a fair amount. I wasn't worried about it from a pressure standpoint, but I would be a little bit concerned about the bullet getting pushed out a little if I was carrying those rounds in my pocket over several days of hunting.
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Old March 30, 2011, 04:58 PM   #12
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I use a compressed load with certain bullets for my 7.62x39 loads. The bullets are resized JSC from, I believe, 7.62x54Rs. The length of the bullet dictates I compress the load to get OAL in tolerance, and to fit in the mag. I started out several grains below max recommended load for that caliber/ powder/bullet weight, and worked my way up to a compressed load that works really well. I can detect a slight crunch when seating the bullet. I crimp and have had no bullet creep so far.
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