A poser for the day

[clowdis]

After going through a bit of vertical dispersion in a team match last weekend and having the coach twisting the elevation knob on my Palma rifle what I thought was too much, I got to thinking. The temperature was hot here in NC and my barrel got extremely hot during my string of fire which was 22 shots in about 10 minutes. So when I got home I drug out the old Machinists Handbook and looked up the coefficient of thermal expansion of steel and applied that to the bore diameter ASSuming a delta temperature 250 degrees. running through the numbers I came up with a bore diameter increase of .0005 or a hot bore diameter of .3085. Now I wonder what effect, if any, that diameter increase would have on muzzle velocity and the trajectory of a 155 grain bullet at 1,000 yards?

 

[kelbro]

running through the numbers I came up with a bore diameter increase of .0005 or a hot bore diameter of .3085. Now I wonder what effect, if any, that diameter increase would have on muzzle velocity and the trajectory of a 155 grain bullet at 1,000 yards?

Easily determined by QuickLoad. I don't have it installed on this PC.

 

[Mr. Ten-X]

If you are absolutely confident that you are holding hard and are using a thermally stabile powder like Varget, look to your ignition first. Firing pin shape, firing pin protrusion and firing pin strength. Known lot of primers stored properly?

Action screws at proper torque?

Bedding issue?

Those would be the first things that I would look.

We fired in 117 degree temps in Kimberly SA with highly tuned Palma rifles/ammo. Any verticals were operator malfunction.

 

[clowdis]

I'm almost 100% sure that any vertical was operator induced But was just curious if the increase in bore diameter would have any effect on muzzle velocity. When I get back from Perry I think I'll shoot some over the chrono (hot barrel and cold barrel) just to see if there is any difference in the numbers.

 

[Mr. Ten-X]

Personal opinion (with no data to support it mind you), but I would think that the rate the powder burns at, given a specific ambient temp, will have a greater effect than any possible bore dimensional change in a string.

 

[broncman]

Has anyone chrono'd a 20 shot string at the same pace as a fast match? Would be interested to see this.

 

[M14AMU]

Has anyone chrono'd a 20 shot string at the same pace as a fast match? Would be interested to see this.

" fast match?"

What the hades is a 'fast match'??

 

[rminut]

Blair,
it seems to me that if the metal expanded due to heat the outside diameter would get larger but the inside diameter would get smaller. My assumption would be if the barrel was frozen the inside diameter would increase in dimensional size. explain to me how it could be any other way.
Thanks,
Robert

 

[butchlambert]

After going through a bit of vertical dispersion in a team match last weekend and having the coach twisting the elevation knob on my Palma rifle what I thought was too much, I got to thinking. The temperature was hot here in NC and my barrel got extremely hot during my string of fire which was 22 shots in about 10 minutes. So when I got home I drug out the old Machinists Handbook and looked up the coefficient of thermal expansion of steel and applied that to the bore diameter ASSuming a delta temperature 250 degrees. running through the numbers I came up with a bore diameter increase of .0005 or a hot bore diameter of .3085. Now I wonder what effect, if any, that diameter increase would have on muzzle velocity and the trajectory of a 155 grain bullet at 1,000 yards?
[/quote

Did you mean groove diameter? I think so.

 

[Old Navy]

Blair,
it seems to me that if the metal expanded due to heat the outside diameter would get larger but the inside diameter would get smaller. My assumption would be if the barrel was frozen the inside diameter would increase in dimensional size. explain to me how it could be any other way.
Thanks,
Robert

The ID will increase also. Later! Frank

 

[DOGCAPPER]

+1 for Frank!! I have seen it in physic lab..LT

 

[Steve Blair]

+1 for Frank!! I have seen it in physic lab..LT

[br]
I agree, but you don't even need a physics lab. How does a mechanic get a tight sleeve or gear to fit over a shaft? He heats it. As the metal expands, both ID and OD will increase.

 

[Immike]

I have to use this trick often to get parts together and have put the inner components in the deep freeze to gain more or reduce the use of heat. Heat can effect things and a barrel has plenty. Since the bore is not perfect and it rises, then the expansion serve as a bending or warping. A barrel will move with just the heat of a shop light passed down the side. I have heard as much as.005 on a heavy barrel. It makes me wonder how much the sun moves it. Most movement on the targets I believe come from ammo temperature and mirage. I keep my ammo shaded to eliminate one of them.

 

[Pres100]

Has anyone chrono'd a 20 shot string at the same pace as a fast match? Would be interested to see this.

" fast match?"

What the hades is a 'fast match'??

I would assume the same as rapid fire (opposed to slow fire). Wouldn't be too hard to do with a magneto speed chrono.

 

[REastman]

Blair...holler at James Crofrs or Phil Kelley...I think they shot the 1000 yard matches that day with a magneto speed attached. They would probably share some numbers from speeds at the start vs. end.

 

[clowdis]

Blair...holler at James Crofrs or Phil Kelley...I think they shot the 1000 yard matches that day with a magneto speed attached. They would probably share some numbers from speeds at the start vs. end.

I did see Jim and Phil over there with the magneto speed. I have some IMR 4320 that I need to run through my Palma rifle now that I'm back from Perry and I'll run some numbers off that.

 

[hogpatrol]

If you are absolutely confident that you are holding hard and are using a thermally stabile powder like Varget, look to your ignition first. Firing pin shape, firing pin protrusion and firing pin strength. Known lot of primers stored properly?

Action screws at proper torque?

Bedding issue?

Those would be the first things that I would look.

We fired in 117 degree temps in Kimberly SA with highly tuned Palma rifles/ammo. Any verticals were operator malfunction.

You weren't shooting across the Big Hole, were you? It's got to be cooler there down by the water. ;D Hog, recently returned from Petrusville/Jakkalskuil Safaris.

 

[Rustystud]

Blair

I just shot 200 rounds of 7mm/08 in 94 degree weather shooting over a magneto speed. The velocities increased with each firing until the barrels were well over 300*F. Then they stabilized out. This was a brand new barrel. I found when the barrel cooled and was cleaned the first three firings shot low. The velocities did not stabilize until after shots 5 or 6. Then extreme spreads went to 9 fps or less.
Nat Lambeth

 

[clowdis]

Have rounds loaded for testing with Palma rifle and 6BRX but looks like rain all day. A little better tomorrow but not much. Might have to wait until next weekend.