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one of us |
The NABs are very long for their weight. I'm not sure how far off the lands you are, but pushing deeper into the case could cause higher pressures. I shoot the 160gr/7mm in my .280 w/ the same powder charge as my 160gr partitions w/o any problems. I seat them to 3.2" vs 2.9" for the NP. | |||
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one of us |
When you increase the size of the powder chamber, (seating long,)you decrease pressure. When you decrease or reduce the size of the chamber, (seating deeply into the case,) you increase pressure. Seating into the lands causes a small and temporary spike but the usually longer cartridge length and larger powder chamber reduces it somewhat. | |||
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| <bigcountry> |
I know that holds true to "std" calibers, but I thought for the freebored calibers like Weatherby, that didn't hold true anymore. I know a guy that had a barrel rebarred to 300Weatherby but with no freebore. He now couldn't shoot factory ammo anymore, but shot reloads great. I thought that freeboring, was kinda like cheating making a medium bore chamber hold pressure like a big bore? Now I could be talking out of my ass too. So don't take this too serious. I know the 300RUM is supposed to have some freebore according to my gunsmith. Not like a weatherby, but said its supposed to have around .2" of freebore. Bob, do you think when I build up some more accubonds at the 3.6" COL spec, I should bother going up to the max 91.5gr of Re25? | ||
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| one of us |
Seating the bullets deeper will reduce the pressure. It will not increase it. The reduction comes from the fact that the bullet now has a longer run at the rifling, and the powder gases have more room in which to expand without Resistance. Resistance is the key point. quote:Turok | |||
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| one of us |
quote:I understand the basic logic behind an increased powder chamber and reduced pressure, but the problem as it is applied here lies in the throat and rifling and our inability to change this dimension via seating depth alone. First we must consider looking at the powder chamber in a different way. Powder chamber size should be seen as the overall space from the bolt face to the rifling as this would better represent the true/total chamber size, as well as the total area/space allowed for powder to burn. I chose the rifling because that is the first point where the bullet meets any real resistance and it is this resistance that it must overcome. Therefore, if you move the bullet away from the rifling, you still have not changed the overall powder chamber size (from bolt face to rifling), but you have reduced the amount of powder space readily available for the cartridge and it�s ability to contain powder. This does not increase pressure as the powder can still burn in the overall chamber size. It also gives the bullet a run at the rifling. The longer the run the lower the pressures as per the Hornady quote above. Now, if you use substantially thicker brass (i.e. military brass) not only do you reduce your available powder capacity in the case, you have physically DECREASED the powder chamber size (from bolt face to rifling). If you move up to a larger case, you will have physically increased the overall powder chamber (from bolt face to rifling) and thus pressures will go down as a result. If you move the throat/rifling closer to the bolt face, you will have decreased your overall powder chamber size (from bolt face to rifling) and will INCREASE your pressure. The opposite holds true. If you move the throat/rifling farther from the bolt face, as is the case Weatherby rifles and their freebore, you will have increased your powder chamber (from bolt face to rifling), as well as give your bullet a longer run at the rifling. Again, the longer the run the lower the pressures as per the Hornady quote above. So if you look at it this way, you simply can�t increase your chamber size by merely seating the bullet out further. That would cause the opposite affect of what you want. In order to increase the overall chamber size, you can either: A) Move the rifling further out � such as the Weatherby freebore B) Choose thinner brass, or C) Move to a larger case. Either method will reduce the pressures through an increase in the overall capacity. Turok | |||
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| <bigcountry> |
I believe your right. Last night, I got off a few shots with 200gr accubonds loaded to 3.6" COL and was able to make it to max load with no flattened primers. But I believe this to a point. [ 11-05-2003, 16:20: Message edited by: bigcountry ] | ||
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| <eldeguello> |
With slow powders in rifle cases, seating depth doesn't have too much effect on peak pressures, since these occur after the bullet has travelled four to six inches down the bore! In a pistol round using relatively fast powders, however, there is much greater effect due to differences in bullet seating depth, and crimp also! ![[Big Grin]](images/icons/grin.gif){kind=icon} What CAN potentially cause high pressures is a case which does not freely release the bullet on firing. An over-long case that jams its mouth into the leade, or one with too-thick neck walls will do this, and then there IS a problem! [ 11-05-2003, 16:28: Message edited by: eldeguello ] | ||
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| one of us |
I have seen an 80 fps difference in the same load by varying the seating depth in my .35 Whelen . Seating deeper raised velocity in that rifle and likely the pressure as well........... | |||
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| one of us |
I repeat, and stand by my statements made earlier. Obviously some have never seen a semi auto pistol "blow up" as a result of bullets in a magazine seating deeper into the case from recoil and insufficient crimp. Pressure INCREASES when the airspace in the cartridge is reduced. I'll even furnish the ammo and the gun just to watch someone shoot it! I've seen several. As to the area of internal ballistics mentioned by Turok, much is correct. The issue would be the definition of "powder chamber", and including the distance to the lands, it doesn't conform. In long throats, gases and pressure are already escaped or escaping before the bullet ever touches the lands. That was the whole reason Weatherby throated his rifles long originally. I too have many examples in varying seating depths where the velocity, and therefore pressures, rise as the bullet is seated deeper in the case. Read the question and the concern again. The previous answer IS correct. | |||
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Moderator |
seating depth affects VOLUME of the case, and can cause pressure to move in the opposite direction of capacity.... bullet moved in ".200 WILL cause higher pressure... out may cause lower, AEBE if you are running a hot load, and are 0.20 over book oal, then do NOT shorten that bullet without reducing powder jeffe | |||
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| one of us |
quote:The actual data does not confirm this... at least not in a rifle. It may be different in handguns, but I haven't a clue. quote:No. Seating the bullet deeper will reduce the pressure. Lets take a look at the data, which confirms Hornady's statement. The data was compiled by OKShooter with the Oehler M43. Date: 30-Nov-99 Temp: 53 F Weather: Sunny -- Moderate wind S at 14mph Barometer: 30.59 Falling Humidity: 38% Bullet 180gr Hornady SP #3070 Bullet Length: 0.662 inches to ogive 1.212 inches to tip OAL to lands: 2.744 inches (ogive) Powder: 60.0 grs. H4831SC Case: R-P Primer: R-P 9 1/2 Rifle: Winchester M 70 Classic Case Length: 2.480 Distance-----Velocity-----Std.-----Pressue---Std (inches)-------fps--------Dev.-------PSI-----Dev 0.164--------2608--------11---------50,600----600 0.059--------2620--------12---------51,300----900 0.039--------2621---------5---------51,200----700 0.019--------2624---------4---------52,100----700 -0.001-------2622---------4---------52,100----500 -0.021-------2633--------13---------53,400---1,000 edit: -0.001 and -0.021 are just touching, and jammed into the rifling. Notice that the pressures go UP as the bullet is moved OUT. It is not the other way around. To further quote the Hornady manual: quote:Conversely, you could also call some of the major bullet mfg's and ask them. They would know for sure. Let me know what they say. Turok [ 11-06-2003, 08:02: Message edited by: Turok ] | |||
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| one of us |
Turok........ What data ? That's only one example out of one rifle with one set of components. I think it's quite a stretch to conclude that every rifle will react in the same manner........in most cases throating out a chamber longer will reduce pressurea and allow you to seat out further , with maybe a gain in velicity if you increase the powder charge ......... | |||
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| one of us |
quote:Truer words were never spoken. | |||
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| one of us |
Hey Mr. Bob, Since I don't waste my time reading torucks posts, let me guess that had to be from him. If so, it is the very first thing I've ever read of his I TOTALLY agree with. If it is from one of you other guys and I missed it, you will learn if you pay attention to Bob338. | |||
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| <bigcountry> |
I was talking with Sierra's Tech support line. And he said something that made the most sense I have seen. Ok, first off I verified that by lowering my COL from 3.8" to 3.6" on my 300RUM with 200gr accubonds did lower the pressure. Duane, said its a balancing act, and I agree with him after my experiments and reading several articles. He said it can go either way. He said if I push the seating depth lower, there will be a point where pressure shoots up. And if you start at at real short seating depth like 3.53" and move the depth out, pressure should go down up to a point then start going back up closer I get to the rifling. Kinda a give and take thing. Your increasing the running go you give the bullet into the rifling, but lowering the space in the brass. | ||
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| one of us |
hERE'S MY OPINION: PUshing a bullet further into the cartridge definately increases pressure--BUT--in a rifle not very much. From experimenting with quickload the amount the average guy might change pressure with several adjustments might be 2,000psi. NOW-it would be my opinion that freebore probably would more than make up for 2,000 psi. If you go to IMR's website they have some interesting charts on weatherby calibers where they list pressure. On one chart they show weatherby cartridges shot with weatherby guns. Then at another place they show some weatherby loads with 24" barrrels (and I assume) these are loads NOT with weatherby rifles. These loads are making strong pressure at about 3-4 grains less than the weatherby loads. For all practical purposes I would say seating depths don't affect pressure (in a rifle) enough to make a difference UNTIL you start getting right next to the lands and then I believe every gun will be an individual at how much pressure might go up. | |||
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| one of us |
It does depend on the powder/bullet/cartridge combo. As bigcountry said, it's a balancing act. With slow powders, probably not an issue, w/ faster pwoders, I'ld be more carefull. | |||
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| Moderator |
okay, friends... ASSUMING the bullet is NOT jammed into the lands (this is another issue) or, said another way, there is enough freebore (quickload data... doens't matter WHAT the number is, it matter what the DIRECTION is) 300 rum at 3.6, with X amount of 7828 60,000psi make that 3.8 drops to 56,000 (55,986) make it 3.4 JUMPS to 65,000 (64,933) to let you in on the "secret" at 3.8, there 105.9 gr of water capacity at 3.6, there 102.09 gr of water capacity at 3.4, there 98.4 gr of water capacity now, someone please tell me again how a shorter round, all else being EQUAL has less pressure, UNLESS you are jammed into the lands jeffe | |||
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| <bigcountry> |
Cool data. But does that account for any freebore? I thought freebore is there to let relieve that pressure spike associated with being close to the lands? I thought that was Roy W whole bag of tricks. | ||
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| one of us |
I'm afraid I don't understand, Jeffe. I understood the 3.8 etc is the distance between the contact points of ogive and rifling, and not the seating depth?? This (I mean seating the depth/pressue question) would be a nice test for the PressureTrace device - maybe a PT owner wants to elaborate on this ? [ 11-07-2003, 02:58: Message edited by: waitaminit ] | |||
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| one of us |
the balancing act you speak of, is it the fact that you are between the "airspace" both behind and in front of the bullet? i was always taught that the closer to the lands the higher the pressure but i guess that would depend on your starting point. by compressing the charge you would increase pressure but move away from the lands. if you seat out to close to the lands you also increase pressure. "between" is the key then. got it i think.. woofer | |||
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| one of us |
quote:It does appear that both sides of the oppinion were at least half right. Except, only one side is big enought to admit it ![[Wink]](images/icons/wink.gif){kind=icon} .The Sierra tech put it best, it is a balancing act. An extreme either way of the happy medium WILL cause higher pressure. If you jam the bullet into the lands, you WILL cause higher pressure. If you seat the bullet too deep, it WILL cause higher pressure. quote:In this case, the oppinion of moving the bullet closer to the lands would almost assuredly caused higher pressure. That is a bad thing and I am surprised that HotCor would have reccommended you go that route. He should know better. quote:Bigcountry hit a very good point and is correct. As I understand it, QuickLoad does NOT take the bullet jump (distance to the lands and grooves) into account. In doing so, it calculates the powder chamber as being bigger than it actually is. Obviously this would reduce pressures. Can QuickLoad compute bullet jump? That would provide a better example of what happens with the pressure. Of all the manuals I have, only the Nosler Reloading Manual #4 makes mention of such an effect. Perhaps there is mention of this in other manuals I don't have? Turok | |||
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| Moderator |
quote:No, 3.8 is the overall cart length. if you make it LONGER, and it has the SAME (or enough) throar, the case is effectively longer. let me put this in other words.. Ever open a bottle of CORKED wine? With the cork barely hanging out of the neck, is there more free space IN the bottle? YES with the cork jammed nearly into the bottle (falling in) is there less free space? YES As for toruk, i have stated, at least twice, ALL ELSE BEING EQUAL... and Toruk, if the guy has freebore left (no radical spike) and he puts the bullet back IN the case, he will raise pressure... If he doesn't, then he would have a pressure spike. so, the ONLY instance where I am incorrect in this matter is a round right up against the rifling. big country's QUESTION was quote:jeffe | |||
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| one of us |
If you make powder space smaller by shortening the COL, and move the rifling back the same amount,IE keep same bullet travel to the lands, the pressure will go up with same bullet and powder charge.If you keep rifling in same place, as you shorten COL, you might drop pressure,due to more freebore; until you make powder space substantially smaller then it will go back up.Ed. | |||
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| one of us |
quote:I am assuming that you are not moving the rifling. If this is actually the case, you will have to contend with the happy medium. The data you posted generated by QuickLoad assumes you haven't reached the rifling yet. Unless I am mistaken (I don't have QL) it will assume that you haven't reached the lands regardless of how far you set it out. So, could you run QL again with the same perameters as you originally posted, but continue to move the bullet out until it is seated with a mm or so in the case. The data also assumes that you haven't reached the happy medium yet either. The happy medium (as per the Sierra Tech) is explained below. quote:I agree, BUT only if he is on the negative side of the HAPPY MEDIUM. If he is on the positive side of the happy medium, then the pressure will be reduced (As was the case with bigcountry, and the data I posted). If we think of the happy medium (the seating depth between seating too deep and too long in comparison to the rifling), as the �zero� point that produces �normal� pressure, we can say that pressure will RISE at +/- 5 of either side of the happy medium. I.e. -------------Happy Medium------------- Too Deep -------------------- Too Long -5, -4, -3, -2, -1, 0, +1, +2, +3, +4, +5 Pressure -----------------------Pressure Rise ------------------------------ Rise ----------------Normal--------------- ---------------Pressure--------------- If this is so, then we could see pressure RISE as the bullet is seated �1, -2, -3, -4, -5 deeper into the case. At the same time, you could see pressure FALL as you moved the bullet out (�5, -4, -3, -2, -1,), UNTILL you reach the happy medium. After the happy medium has been reached, then we could see pressures RISE as we move the bullet out past the happy medium 0, +1, +2, +3, +4, +5. At the same time, we should see the pressures fall as we seat the bullet deeper into the case UNTIL we reach the happy medium (+5, +4, +3, +2, +1, 0) The HAPPY MEDIUM is the key. You will see pressure rise on either side of it, and thus all of us were only half correct ![[Smile]](images/icons/smile.gif){kind=icon} Turok | |||
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| Moderator |
fair enough jeffe | |||
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| one of us |
What Turok has stated is true. Bob338 is right on some account and so is Jeffe, but Ed wrote: If you keep rifling in same place, as you shorten COL, you might drop pressure,due to more freebore; until you make powder space substantially smaller then it will go back up.Ed. This is correct, and I have pressure data to support it. Pressure can rise from either going too deep or too long. It can happen on Both. I also have a 300 Ultra Mag and have shot plenty of 200gr Accubonds to specifically know what happened with them too. Mine contacts the lands at long 2.835" and I believe Bigcountry's contacts a bit earlier, maybe near the same thou, I can't remember for sure. Seating "at" the lands results in higher PSI than seating them back to 3.660" where it dropped PSI and MV substantially, about 70 FPS and 5K PSI. I've not seated them deeper than 3.660" to see when PSI starts to come back up again, but it surely will at some point, these just fit in the mag at 3.660" so I never checked it shorter as it was already a substantial jump. The short factory OAL's didn't shoot for $hit anyway. Some data on three different lots of RL25 at 3.835" OAL that I collected: 84, 86, 88gr tested to find peak PSI. Lot # 25057 84gr = 63,0K PSI = 3057 FPS 86gr = 67,0K PSI = 3116 FPS 88gr = 68,3K PSI = ---- Lot # 25180 84gr = 65,0K PSI = 3076 FPS 86gr = 67,3K PSI = 3121 FPS 88gr = 70,5K PSI = 3201 FPS Lot # 25108 84gr = 61,7K PSI = 3009 FPS 86gr = 65,0K PSI = 3108 FPS 88gr = 67,0K PSI = 3150 FPS Remington Factory 180gr Partitions: 62,9K PSI = 3244 FPS Remington Factory 180gr Sciroccos: 60,3K PSI = 3180 FPS I always start well below max load and work up the load with the bullet at the lands first, backing off almost always results in lower PSI and MV, so I'm in the safe zone when playing with OAL... to a point. I don't think this will always hold true for chambers that allow bullets to be seated at normal magazine lengths and still contact the lands, you may start to run UP pressure as soon as you start to seat them deeper than they were designed to be. Here's one such case where PSI rises back up again as we go too deep: 308 WIN M70 Classic Compact 20" barrel 165gr SGK SPBT (land contact = 2.900") WW case IMR 4064 BR2 OAL 2.845" 1.) 41.5gr = 40,6K PSI = 2346 FPS = 0.4 MOA 2.) 42.0gr = 42,0K PSI = 2383 FPS = 1.15 MOA 3.) 43.5gr = 47,7K PSI = 2505 FPS = 0.8 MOA OAL 2.775" 1.) 41.5gr = 43,0K PSI = 2379 FPS = 1.0 MOA 2.) 42.0gr = 46,1K PSI = 2441 FPS = 1.0 MOA 3.) 43.5gr = 53,6K PSI = 2578 FPS = 0.9 MOA PSI and MV were tested using Oehler's M43 PBL. [ 11-07-2003, 08:12: Message edited by: Brent Moffitt ] | |||
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