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Bullet Jam Increasing Pressure?

 
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  #1  
Old 10-28-2012, 07:22 PM
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Bullet Jam Increasing Pressure?

I was just out loading a couple reduced loads for the 338 Lapua and i jamed one round of each at .040 into lands, .025 into lands, and .010 into lands.

I was wondering if there is a point in which an increased jam wont create anymore pressure than a jam that is slightly less? What i mean is lets say you jam a bullet .080 and another at .060, since the bullet is already jammed so much that an increase or decrease in jam length wont make much of a difference on velocity or pressure, but may make a difference in accuracy. Am i correct in my thinking?

I know i didnt explain it very well but if someone understands what im saying and can explain it better please do.
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Old 10-28-2012, 08:27 PM
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Re: Bullet Jam Increasing Pressure?

Quote:
Originally Posted by barnesuser28 View Post
I was just out loading a couple reduced loads for the 338 Lapua and i jamed one round of each at .040 into lands, .025 into lands, and .010 into lands.

I was wondering if there is a point in which an increased jam wont create anymore pressure than a jam that is slightly less? What i mean is lets say you jam a bullet .080 and another at .060, since the bullet is already jammed so much that an increase or decrease in jam length wont make much of a difference on velocity or pressure, but may make a difference in accuracy. Am i correct in my thinking?

I know i didnt explain it very well but if someone understands what im saying and can explain it better please do.
I've seen some rounds in 7mm actually push the bullets back they were jambed hard enough. I guess it depends on the situation but you would conceivably do casing damage jambing the round from extraction if pulled unfired, slip the bullet in more, engrave the bullet more, or jamb the action from closing because of the bullet engraving force being to hard to overcome closing the bolt.
I'd guess once firmly jambed letting the bullet have no run it wouldn't matter as much for pressure as for usability with the gun.
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Old 10-29-2012, 09:45 AM
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Re: Bullet Jam Increasing Pressure?

I don't know what you expect such jamming to accomplish but as said above there's a point after which the bore/lands will simply push the bullets deeper when the cartridges are chambered. The diameter/caliber of the bore, as such, won't make any difference. If you want to obtain good bullet-to-bore alignment just load straight ammo to start with.

Seating long does delays initial bullet movement and you can be sure that WILL increase starting pressure but with no normal benefit to anything good.
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Old 10-29-2012, 12:46 PM
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Re: Bullet Jam Increasing Pressure?

I'm not sure exactly what your asking but its all in what your gun likes if your looking for accuracy . I think theres also a point where you can jam the lands and nothing will change other than the bullet will be pushed back into the case to close the bolt . I shoot my .338 lapua 300SMK's with a zero freebore chamber so I can get them into the factory magazine an I jam them into the lands .003 as it seemed that after .005 Jam nothing changed. Hope that helps.
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Old 10-29-2012, 03:09 PM
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Re: Bullet Jam Increasing Pressure?

Riley,

I made two reloading goofs w/my 338 RUM.

First one was that I didn't realize that I had adjusted the seater die to a greatly increased overall length. Then packed up and went to the range. Couldn't close the bolt on the loaded cartridge.

Not being one to give up easily I applied enough pressure with my palm to get it closed.

I shot 5 shots that way. Right around 1/4 MOA @ 200. Pretty sweet!!!

Except that upon unfired case extraction left the Berger 300 in the bore. Took a pretty good drop with a 27" brass rod to dislodge the bullet. Note I'm too much of a tight wad to simply fire that last round.

That deep seating kept under 1/4 MOA for a long time till I get to thinkin' that it's simply bad deal to have that condition in a sporting rifle.

I backed the COL off until it "just" doesn't stick. 1/4 MOA consistency remained. I'll settle for that.

However, COL is long enough that I need to click the bold release to removed an unfired round. I'll settle for that too.

The other goof was loading that load w/102 gr of 50 BMG. Only moving @ 2735 MV but I'll settle for that too.

I notice no change in apparent pressure with either seating method.

Velocity remained the same for both seating lengths. . . Wondered about that but it is what it is.

FWIW
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Old 10-29-2012, 05:10 PM
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Re: Bullet Jam Increasing Pressure?

The reason i want to jam the bullets so far is i can only fit about 37 grains of trail boss in the case and that doesnt give me the velocities i need so i thought by jamming them into the lands it will increase pressure and velocity si i can reach the velocities im after. Also i varied the powder charge in the cases so im not expecting an extra .015 bullet jump to give me another 100 fps in velocity. I will go out right now and see if the bullet is set back at all when chambered.
__________________

I'm 16
"Firearms are second only to the Constitution in importance; they are the peoples' liberty's teeth."
~George Washington

"The only advantage a light rifle has is weight, all other advantages go to the heavy rifle."
~ JE Custom

Biggest fail of 2014 so far... http://www.longrangehunting.com/foru...ea-ftf-128972/

My guess on W3P .308 230 Grain Bullet: G1 .740-.755
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  #7  
Old 10-29-2012, 05:38 PM
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Re: Bullet Jam Increasing Pressure?

So after taking a look at my data book i realized that 2 loads gave me the velocity i needed so i pulled the rounds i already had loaded and put less powder and seated them to the lands, and i just seated the other round .015 into the lands so i think i should be good now.
__________________

I'm 16
"Firearms are second only to the Constitution in importance; they are the peoples' liberty's teeth."
~George Washington

"The only advantage a light rifle has is weight, all other advantages go to the heavy rifle."
~ JE Custom

Biggest fail of 2014 so far... http://www.longrangehunting.com/foru...ea-ftf-128972/

My guess on W3P .308 230 Grain Bullet: G1 .740-.755
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