I am shooting a model 12-3 with a 2 inch barrel. I have 4.0 grains of Trail Boss under a Hornady 158 SWCHP, one of the swaged types out of a box of 300. OAL length is 0.150 (I really meant 1.50) inches. Velocity is running about 625 + or - a few.
I have a bundle of wet newsprint to see how far it will penetrate, and it goes through 8 inches after being shot from about 7 yards. It gets caught in a bundled towel; no HP expansion, but it does arrive at the towel base first.
Just for grins, I measure it when I get home with a digital micrometer. I get a reading of 0.342 inches in the groove and 0.350 inches on the land. I think to myself this cannot be correct so I pull an unfired bullet out of the red box. It measures 0.358 inches, just like it should.
I was expecting something close to 0.357 inches. Do any of you have any idea why my fired 38 special projectile is coming out with a reading smaller than a 9mm? I invite any comments you might have.
This message has been edited. Last edited by: Pedersoli,
Posts: 89 | Location: Port Angeles, Wa | Registered: 09 February 2005
Because you're reading your caliper wrong? Just kidding I know that is a typo. You need to slug the bore before you can say what the fired diameter is supposed to be.
OK Jellybean, you got me on that one. OAL was 1.50 inches. I did measure one of the unfired bullets to check my technique.
9mm bullet diameter is a nominal 0.355 inches and the lead bullet I am shooting is 0.358 inches so it can upset in the bore to seal and spin; thought being the barrel diameter inside is along the value of 0.357 or so.
Wouldn't you think shooting one down the bore is the same as slugging it? I know I can push a lead Hornady through the charge holes with a little pressure. It just seems odd the barrel would be that tight.
Posts: 89 | Location: Port Angeles, Wa | Registered: 09 February 2005
Pedersoli, Yes shooting one down the bore would be close to slugging it if you can catch it in your fingers without damaging the bullet. By shooting it into a medium you don't know what the bullets size was before it hit it. The wet newsprint and towel will offer resistance to the bullet and it is impossible to tell how much lead was lost due to friction or how much the diameter was affected due to the impact.
You are correct the barrel diameter is near the bullet diameter but it is smaller than the bullet. Heavy cast and jacketed bullets don't upset as easy nor do light loads. With a smaller bore diameter you don't have to try and deform the bullet bigger to fit, it's easier to squeeze the bullet smaller.
Barrels dimensions can vary and without a good test bullet/slug there is no way to tell what the diameter is. Once you have that then you can shoot into your medium and see if that has any after effects on it.
Originally posted by pinkymingeo: My S&W revolvers have 5-groove rifling. I've never been able to get a good measurement using a dial caliper.
There's your answer. If you had a barrel with even numbered rifling then you could get a good reading. When you put your caliper on the slug one side of your caliper is where a land was and the other is where a groove was. If it shoots good then don't worry about it.
To measure a bullet or bore slug from a barrel with an un-even number of grooves you need a proper guage block for the number of grooves. For a 5 groove barrel as S&W has a 72 degree block is needed.
For an example of what you are measuring think of the fct that nominal bore/groove dimensions of a .38 barrel are .350/.357. When you use caliper or micrometer without the guge block you are measuring from the bore on one side to grove on the other, or in other words you are measuring the bore diameter plus only the depth of one groove. The figure you see should be aproximately .3535" on an undamaged bullet, which one which has been fired into any expansion/penetration testing media will certainly not be (un-damaged that is).
One way to measure an odd number land/groove bullet is to wrap a piece of shim stock around the bullet, measure it then subtract the thickness of the shim X 2. This ain't exact but will be real close.
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Posts: 956 | Location: Louisiana | Registered: 04 March 2007
Hmmmm. So if anything the measurement of a bullet fired into wet newspaper should be larger and not smaller than the ideal of 0.3535, because of the action of the medium slowing the bullet down to zero FPS. How did I end up smaller?
Unless, as one person mentioned; my load is rather light as compared to some. Perhaps the upset into the barrel was not complete.
Posts: 89 | Location: Port Angeles, Wa | Registered: 09 February 2005
Or the bullet surface is being abraded away on the wet newspaper. I would think that would be the most likely cause.
The .342/350" fired bullets would practically fall through both the barrel and cylinder throats I would think. Try it.
Try some FMJ bullets into the newsprint and measure those too.
I have also read of using a squib load of about .75 to 1 grain of Bullseye and shooting into a box of loosely packed rags to get minimally damaged bullets for measuring.
"The .342/350" fired bullets would practically fall through both the barrel and cylinder throats I would think. Try it."
Nope, Rich W; they do not fall through. I know my cylinder throats are at least 0.3575 inches because I reamed them specifically for use with cast bullets. I can start the fired bullet in question at the muzzle with hand pressure.
More likely at this point, as already pointed out to me, is a mis-measurement on my part of the 5 groove rifling.
Posts: 89 | Location: Port Angeles, Wa | Registered: 09 February 2005
