Burn Rate Question
Anyone know how many inches of barrel it takes to completely consume the powder in a 17 HMR.
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We would need to know exactly what powder and how much. 0 -
Being as it is a rimfire and not reloadable and as the factroy will not divulge the exact powder they use in their loads all we have to go on are what we do know. The weight of the projectile, and the volumn of the case and the assumption that it is a fast burning powder, and the velocity. 0 -
Wouldn't you rather know the point at which the pressure was no longer enough to overcome the drag, even if the powder burned out several inches ago? You gotta figure, even if you loaded it with Bullseye so that the powder got done burning before the bullet was fully engraved, there would still be enough pressure after two or three inches to keep building velocity. 0 -
quote:Originally posted by SoreShoulder
Wouldn't you rather know the point at which the pressure was no longer enough to overcome the drag, even if the powder burned out several inches ago? You gotta figure, even if you loaded it with Bullseye so that the powder got done burning before the bullet was fully engraved, there would still be enough pressure after two or three inches to keep building velocity.
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The question isn't "when does the powder stop burning", because the bullet should still be accelerating after that happens. The real question is "at what point does more barrel length not yield any more velocity".
My understanding is that with an ordinary .22LR velocity tops out at about 18 inches. Obviously that will depend on exact powder type, primer, and bullet weight. After that, bullet speed actually starts to slow down (because of barrel drag/friction), though there may still be other valid reasons to have a longer barrel (eg longer sight radius, quieter operation, etc).
I don't know for sure, but my guess is that with a .17 HMR, which is based on a .22 magnum, I bet you could probably add another 2-4 inches and still extract out more velocity. So my guess is maybe 20-22 inches.
The only way to know for sure is to take your favorite load, and a test barrel, then chop down the barrel an inch at a time, chronographing in between.0 -
Beantown, my thoughts as well. Perhaps I should have asked if anyone knows the pressure curve of a 17 HMR. As you said once the pressure starts to decrease, drag takes over and the round slows down. Maybe I should call Hornady. I have a conversion for a customer and the barrel has already been cut to 18" and he was concerned about velocity. 0 -
If the question is "What barrel length gives the highest velocity for a .17 HMR?" the answer seems to be 19 inches- but 18" is only a tad slower. See chrono tests here: http://www.bullberry.com/HMRdata.html
Beantown- I seem to remember max 22LR velocity at 12 inches- but have seen others claim 16 inches. Would like to see chronos before I claimed certainty.0 -
Well...for both the 22WMR, and 17HMR there are center fire versions of each. Why not look over the loading data for that? The internal combustion chamber is smaller, and you have the added boost of a small rifle primer too. I am sure because of this that the pressures, and velocities are substantially higher. I am talking about the 17, and 22 CCM cartridges. I know they like AA 1680 powder, if memory serves me.
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Talked to Hornady. Without giving me specific velocities the Balistition said that down to 21" there was no velocity loss. That shorter than 16 velocity started to drop off fast and that he would not go below 18" and that 20" seemed about right. Doing a a conversion on a Remington 580 and the barrel had been cut to 18" but I looked around and found a 24" so the point becomes moot unless he now wants it cut to 20 or 21. 0
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