compression

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ksbreed123
Posts: 119
Joined: Sat Mar 04, 2006 7:29 am

compression

Post by ksbreed123 »

can someone out there explain to me how to figure what is the right amount of compression to seat a bullet and how they got it. if one person says he goes .250, would that be measured from the case mouth? say for example, if the power is .250 from the case mouth after being dropped and i wanted to use a .250 compression then from the case mouth to the wad would be .500 deep.i measure my bullet and decide where i want it to be seated and compress the wad and power to that mark. to get a postell bullet right where i want it i have to compress a total of .712.thats a lot of dept.if the case buckles then i get the resizer die and a take the decapping pin out along with the stem and resize the case and it works great.but it is time comsuming but there ain't no air gap either.after being shown this method i don't want to spend time doing it. so, to make the story short to seat a 540 bullet properly how much space should there be from the top of the case to the wad.when you talk about compression,how deep does the bullet actually seat?
beltfed
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Re: compression

Post by beltfed »

If you want to compress 0.250 for that postell at total of 0.712" from the case mouth:,
you need to use the amount/wt of powder such that
0.712 minus the 0.250 = 0.462" to the top of the uncompressed powder/wad.
Then when you compress to the 0.712 for the Postell, you will have compressed the
powder 0.250". A good starting point for Goex powder.
OTOH, if you are using Swiss, I would calculate as above to compress only about 0.050 to start with.
( I really am not trying to make you out like an idiot. Please forgive me . Not intended
I just tend to walk things thru methodically)
Regards
beltfed/arnie
ksbreed123
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Re: compression

Post by ksbreed123 »

is there a book called compression 101 for dumbies because i don't get it. i'll go back to my way and be happy thanks
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Don McDowell
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Re: compression

Post by Don McDowell »

Compression isn't that hard of a deal, don't get to caught up in the numbers.
You simply put enough powder in the case to achieve the velocity/accuracy you want, figure out how far down from the case mouth to mash the powder and let the bullet and wad seat without rumpling the nose of the bullet when you seat it to the depth that your rifle/chamber decides it likes.
AKA Donny Ray Rockslinger :?
hepburn
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Re: compression

Post by hepburn »

You are confusing seating depth of the bullet--(measured from top of case to top of wad)---with compression--- which is amount the wad actually compresses the powder column. Work with case that was fired but not sized (makes easy) Drop powder as normal carefully insert wad & push down with bullet using light finger pressure until you feel it seated on powder. Remove bullet & measure distance to top of case--it is your aprox. uncompressed depth. Next by trial & error compress the wad with die until bullet is positioned to where you want it to extend into chamber (overall length) Now measure the depth of the wad to top of case--this is your compressed depth. From this measurement subtract your uncompressed measurement----the difference is how much compression you have. You will also need to subtract the thickness of your wad from this to get the true value. It really is easy once you understand what you are measuring. The unsized case makes easy to feel and insert bullet. If you ever want to tear a load apart I found easy way to remove the wad is to turn a drywall screw in wad & just pull out.
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Lumpy Grits
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Re: compression

Post by Lumpy Grits »

Each powder maker is different on the sweet spot for compression.
What powder brand are you using?
Compression, and seating depth are not the same.
Give us some details of your load-
Gary
"Hav'n you along, is like loose'n two good men"
martinibelgian
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Re: compression

Post by martinibelgian »

Do as I do - don't worry about it, compression is for me just a result from bullet seating depth and powder quantity- the more powder you load, the more compression is needed for an same cartridge OAL. It is awfully hard to change compression without changing other parameters...
monkeyboy
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Re: compression

Post by monkeyboy »

Compression and seating depth are just variables.You need to adjust each to find out what your gun likes. I usually start with the bullet touching the lands and work from there, in or out.When I find a load I like I measure the compression from the case mouth to the top of the wad with the stem on a vernier caliper.FWIW--Mike.
hepburn
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Re: compression

Post by hepburn »

Figuring compression is not difficult once you understand what you are measuring. The final distance from wad to top of case is your seating depth. Determining powder compression requires 2 measurements: 1. distance wad to top case with the wad resting on top of uncompressed powder column 2. measurement of wad to top after using die to compress powder ----the difference between (minus thickness of wad) is the amount you are actually compressing powder. Usually this distance is .060-.120" for Swiss to .250-375" for Goex or others. Swiss can shoot well with .250" & Goex little more. If you bend the case you need to reduce amount of powder.
Coltsmoke
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Re: compression

Post by Coltsmoke »

I'll give this a shot. Let's start at the beginning of your Over All Length that you want. Figure out how much powder it takes to touch the bottom of your bullet with the bullet sitting directly on top of the powder and have your OAL that you want. Now if you use a .030 wad under your bullet you will have to compress that down .030 to have your OAL at the same length. Now you have .030 compression, if you use a .060 wad and compress it down to maintain the OAL, now you have .060 compression. So now you have your compression die set. Let's say your OAL is 2.930, you have 60gr. of power in the case and you are going to add a .030 wad so you will have .030 compression with 60gr. of powder. I'm assuming you are loading a .45 round. On average adding a grain of powder in a .45 case will raise the powder column height .020. If you dump 61gr. of powder in your case and sit your bullet on top of the powder your OAL will change to 2.950, so now you will have .050 compression on that load. 62gr. with the bullet sitting on top will change the OAL to 2.970 now you will have .070 compression on that load and so on. Just add powder, then sit the bullet on top and measure what the new OAL is and subtract the OAL you want and that will tell you how much compression you are going to have. Dat iz how I duz minz.
Normal isn't coming back, but Jesus is.
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kenny s
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Re: compression

Post by kenny s »

what compression does everyone use for OD 1 1/2?
As for compression..
do the same thing every time. don't vary, and use a compression die...
don't compress with the bullet and seating die.

simplistic I know, but bears repeating
Ken
hepburn
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Re: compression

Post by hepburn »

If you mean Old E----all Goex requires 2x of usual amount for Swiss----1/4" --3/8". I have found OE 1 1/2 works well starting around .200"up to .325" ----you just have to try till gun says it works. From experience I find as you go from coarse to fine granulation you can use little less as powder gets finer. Still have to start somewhere & keep trying till it works.
Trigger1212
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Re: compression

Post by Trigger1212 »

Hepburn,

Might be mis-understanding your explaination, or just picking the flyshit out of the pepper, but! In your original explaination you state add the powder your want, then seat wad of your choice down on powder. Measure from mouth to wad. Then compress powder to desired depth (using compression die) which will allow you to seat bullet to desired depth in case. Pull bullet from case then measure from mouth to wad. Then you subtract the uncompressed measurement from the compressed measurement giving you your "amount of compression" for that load.

Then you state you must subtract the thickness of the wad to get the true compression amount. This is not accurate, the wad is in the first measurement and is in the second measurement so there is no need to subtract the thickness of the wad from the calculation.

I'm with the guys that say keep it simple, put in the amount of powder you think you will need for the velocity you desire, then add wad and compress with the die until you can seat the bullet to the desired depth for your chamber. To fine tune the load keep the compression die set to the same depth just add/subtract the amount of power you put in the case. Just remember, no air gaps between wad and powder (too little powder) and that you can only stuff so much powder in a case before it's over compressed and you will bulge the case walls.

I used to drive myself batty over this kind of stuff then just said it don't matter, use proper loading methodology to find the load your rifle likes, then measure your compression/power weight and record it for future use rather that the other way around.

My .02!

Cheers!

Wade
bruce m
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Re: compression

Post by bruce m »

i often wonder what compression really does and how it works.
a particular question that keeps arising is relative to case length/
how hard the powder is compressed, say 1/4" in a 2 1/10"case must be more than how hard the powder is compressed in a 2 7/8" case for the same 1/4".
do you need to compress a longer charge a greater measurement than a shorter one for the same tightness of powder packing?
is this what we aim for, or something else?
is it about powder ignition, powder burning, or something else?
just to add mud to the water, droptubed charges work best when breech seating with an airgap.
keep safe,
bruce.
ventum est amicus meus
Kurt
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Re: compression

Post by Kurt »

I was going to put my .02 cents in but it would just create more confusion :roll: :D

Compression changes from case to case by inside volume even from the same manufacturer especially adding cases from different runs and manufactures as well how the powder is dropped into the case and how much neck tension the bullet gets when seating it from different case neck thickness. It all plays hell with vertical.
This were breach seating GG or PP excels :D
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