Armory Sponsor
Posted: 5/5/2010 5:48:16 AM EDT
| I have never found a load I liked at the published min so I have never gone under it. That being said, I would be concerned about detonation rather than burning of the powder if I went under a published min. If that is not a concern, why do they publish a min? |
| If you load 10 grains of H335 in 223 or 15 grains of 4895 in .243, it is likely going to cover the bottom of the case and at no point fill the case from top to bottom when horizontal in battery. In that situation, I would expect the powder to all burn simultaneously (detonate), rather than burn from rear to front of the charge (such as with a charge of 24 grains or 45 grains respectively). In this case, would there not be concerns of going overpressure? Perhaps my exaggerated examples are too small to make it matter but you get my point? |
|
Quoted:
If you load 10 grains of H335 in 223 or 15 grains of 4895 in .243, it is likely going to cover the bottom of the case and at no point fill the case from top to bottom when horizontal in battery. In that situation, I would expect the powder to all burn simultaneously (detonate), rather than burn from rear to front of the charge (such as with a charge of 24 grains or 45 grains respectively). In this case, would there not be concerns of going overpressure? Perhaps my exaggerated examples are too small to make it matter but you get my point? Well, I've made subsonic .223 using 6 grains of H335 and a 55gr v-max bullet, no problems here. It definitely won't cycle the action on my AR which isn't surprising. Come to think of it, im not sure they're subsonic being that i dont have a crono, only assuming based on how quiet is shoots. |
|
See the Lee book for specifics, but the summary/my understanding of his opinion is:
- until you get at least 25% to 35% below max with slow powders you do not see pressure spikes. - no one has been able to re-create such spikes in a controlled environment so the cause is not known. - when reducing charges never reduce the slowest powders more than 20%. For each step up in speed on the powder chart you can reduce an additional 1%. Never reduce any powder more than 50% no matter how fast the powder. I would assume Lee has enough experience and access to pressure testing equipment that he wouldn't make the statements he does without sound testing. I can't recall what other manuals state re: reduced loads, but I happened to see this post so I reviewed my Lee manual over my lunch hour. ETA: Let me just add that I am not advocating deviating from published loads. I have not tested, nor do I intend to test Lee's opinions. I am merely posting my understanding of his opinions because they are relevant to the post at hand and because I find the discussion interesting. |
|
With some slower handgun rounds you could stick a bullet in the barrel or risk hangfires. Lots of Cowboy Action guns have been blown up lately with light loads (loaded that way to decrease recoil and increase speed of second shot for better "gaming")
In fact hangfires or faulty ignition are probably a risk with all below minimum loads - besides the odd chance of a pressure spike. I think that the primer fails to ignite all the powder, but the primer ignition blows the unburned powder to the front of the case and this forms a blockage. The bullet would not make it down the barrel in many cases. Several factors could contribute to this, including ambient temperature, primer used, powder position in the case etc. You could also have the blockage finally decide to burn and get weird hangfire and pressure issues there. This may not happen every time, but that is what makes it so dangerous - you may be lulled into complacency. While some rifle powders like 4895 can be reduced a third, most work best in the pressure range that they were engineered for. This is especially true with ball powders that need a lot of heat/pressure to burn the deterrent coatings off well. They don't take kindly to reduction. Could it be possible that you could find an accurate load between minimum and maximum rather than tread on more dangerous below minimum ground? |
|
Just to be crystal clear, I have never puposely loaded a round below the published min and I have never found a load at the published min I liked. The only reason I could ever see me loading below published mins would be for a subsonic round.
I have always been suprised at how many people do seem to load below the published min and thought this would make an interesting thread. |
|
Quoted:
I have never found a load I liked at the published min so I have never gone under it. That being said, I would be concerned about detonation rather than burning of the powder if I went under a published min. If that is not a concern, why do they publish a min? The min or starting load is the minimum safe load that will function a semi auto. (in most cases, there are always exceptions) Also for the people that want to shoot a load that uses the least amount of powder. A cheap but safe load. It is also a load that will be safe in all guns made in that caliber. Making it a "starting load" in load development. Some gun models have stronger actions than others, so the "min" load is really a "max" load for them. |
| If you're looking for reduced velocity loads, using powders appropriate to get max velocity doesn't make sense. There are several powders on the market designed especially for reduced loads like Trail Boss and AA5744. If you want a reduced load, use a powder meant for it. |
|
For what it's worth, I have had pressure spikes occur with published minimums of H4831 in a 6.5x55. After the Lee book was published, the reasons for the spikes was discovered. What happens is that the bullet starts moving at a low pressure, then meets the rifling and stops moving. At this point the powder is burning in more places than normal when the pressure builds. As the pressure builds the burn rate also goes up. In effect, the lands create a partial bore obstruction.
If the bullet is seated hard into the lands with a light charge, the problem is much less likely to occur. The problem with things like the 6.5x55 is that they are chambered to fit a very long round-nosed bullet. Thus the lands are quite a way from the end of the case mouth. In mine a 140 grain spitzer clears the case mouth before meeting the rifling. Faster powders tend to work better with light charges because they burn fast enough to keep the pressure up while the bullet engages the rifling. Also, the larger volume of excess air space helps smooth out the pressure curve, so the faster powders tend to create pressure curves similar to a slower powder. |
Armory Sponsor