6mm Creedmoor 115 DTACS 40grs of H4350 ,were having a hot summer and I'm getting pressure signs in NV Desert . These loads did fine in cooler weather. So question is rather than pull the bullets,what about seating them deeper ? They nearly touching the lands now ....
H4350 Temperature what ?
- Thread starter Ironworker
- Start date
For each i degree increase in temperature H4350 gains 0.29 FPS in velocity. Shouldn't make much difference.
Seating bullets into the lands will increase pressures, but it doesn't sound like that where you're at. Seating them deeper will reduce volume and increase pressure, so I doubt that approach is going to be of much help to you. Here is AZ, when shooting at higher temperatures (like from 95°- 110°), I've reduce my powder charge a little for the cases I use this time of year.
ive seen just the opposite a few times... where seating a little deeper will actually decrease pressure... i dont know if a little of the gases escape around the bullet before it seals up in the bore or what... i would seat a hand full of them a little deeper and see if i still had pressure signs... if not find a seating node a little deeper than where your at now... my .02 cents...
I'm with ngb1787; I have a soft side 6 pack cooler that's perfect for this, and I have been known to refrigerate the gel pack a bit for loads develop
Very interesting
It is generally accepted that with rifles and loads in the normal range the effect of a running start at the lands greatly exceeds the effect of decreased capacity. This means seating deeper will reduce peak pressure levels. See anything from Brownell's Pressure Factors from Wolfe to John Barsness with current writings on the subject.
This does not apply to bullet setback in semiautomatic pistol cartridges.
However pressure signs as most people use the term do not appear until a load is significantly over SAAMI pressures. It follows that minimal reduction from a load showing pressure signs results in loads that are still over SAAMI pressures. I question that loads so near over-pressure signs that the difference between summer and winter makes the signs show up are in fact all that fine in cooler weather. That is the loads may actually be in the gap between SAAMI pressures and the level of actually showing pressure signs. FREX look at the historical record of load development for the Shooting Times Westerner when new; loads were developed with classic pressure signs for a guide and later found to be overpressure with instrumented tests. For this reason I doubt keeping the loads cooler will give SAAMI pressures but rather will give over SAAMI pressures but without pressure signs. Of course for historical reasons with some cartridges SAAMI pressures are so low as to be safely exceeded.
Depending on the number of loads prepared I wouldn't hesitate to try deeper seating for a few loads. But for any quantity and in general I would develop loads de novo comparing measured speeds with book speeds for a sense of powder charge at top SAAMI pressures. Then I would compare my new maximum with the existing loads. If close enough I would be happy with deeper seating. If not very close I would pull the bullets and reduce the loads.
This does not apply to bullet setback in semiautomatic pistol cartridges.
However pressure signs as most people use the term do not appear until a load is significantly over SAAMI pressures. It follows that minimal reduction from a load showing pressure signs results in loads that are still over SAAMI pressures. I question that loads so near over-pressure signs that the difference between summer and winter makes the signs show up are in fact all that fine in cooler weather. That is the loads may actually be in the gap between SAAMI pressures and the level of actually showing pressure signs. FREX look at the historical record of load development for the Shooting Times Westerner when new; loads were developed with classic pressure signs for a guide and later found to be overpressure with instrumented tests. For this reason I doubt keeping the loads cooler will give SAAMI pressures but rather will give over SAAMI pressures but without pressure signs. Of course for historical reasons with some cartridges SAAMI pressures are so low as to be safely exceeded.
Depending on the number of loads prepared I wouldn't hesitate to try deeper seating for a few loads. But for any quantity and in general I would develop loads de novo comparing measured speeds with book speeds for a sense of powder charge at top SAAMI pressures. Then I would compare my new maximum with the existing loads. If close enough I would be happy with deeper seating. If not very close I would pull the bullets and reduce the loads.
The belief that deeper seating increases pressures is a myth, one that has been much strengthened by misunderstanding the COAL effect in QuickLOAD.
At one time, some reloading manuals and pamphlets/booklets (printed in their tens of thousands in pre-Internet days) would have little tables showing the actual effects of deeper seating. Vihtavuori's fold-up loading data pamphlet (at a time when it had fewer than half of today's powder grades and a lot less cartridges) had all sorts of little goodies like this including one on COAL effect on chamber pressure / MV. The company took a standard 7.62 M180-type military load loaded with Viht extruded powder and using the Nato-spec COAL as a base gave the readings for four or five steps deeper seating. At this remove in time, I can't remember how big those steps were, but the first three or four showed no change at all, then the final (deepest seating) produced a pretty big drop in both metrics.
I've seen the same a few times with modern match handloads in initial coarse COAL tests. 284 Win with the very long 183gn Sierra MK didn't perform in or near the lands so I went considerably deeper in ten thou' steps. At 40 thou' jump not only did the vertical start to tune out, what had been a remarkably consistent MV throughout all previous steps (five round strings with ES of only one or two fps as well!) took a 10 fps drop. Not vast, but big enough to be significant. In totally non-scientific terms, this is explained as the bullet getting a 'run at the lands' and therefore engraving more quickly and producing less of a check / pressure build-up as it hits the lands. Where there is a great deal of wear increasing the effective freebore as in very well-used military surplus rifles you can end up going way over maximum book charges in order to attain standard pressures / MVs - as long as the worn throat is smooth. (Over-bore capacity cartridges that wear throats out rapidly often roughen them considerably too and that increases pressures, sometimes disastrously.)
This note seems to have disappeared from recent loading manuals, the sole exception being both Norma editions which mention it in a single sentence.
But, surely QuickLOAD shows the very opposite? The point about COAL in QL is that it assumes that the COAL you input has the bullet either in the lands (when a shot-start pressure increase has to manually applied) or just outside, so the COAL is a measure of the chamber which affects the fireformed case's / combustion chamber's volume and from that pressure. In a long freebore / large-jump scenario, the bullet leaves the case mouth before peak pressure is produced and when it reaches / is checked by hitting the lands the combustion chamber volume is greater than in a short-freebore situation. So a short COAL with a big jump (whether from the chamber or from the bullet seated position) produces less pressure than the same COAL just off the lands as the former's combustion chamber volume is that of the fireformed case + the volume of the space between the bullet base's unfired position and that of where it is checked in the lands. That's without any beneficial 'run at the lands' effect.
Going back to the OP, if the loads are over-pressure for current ambient temperatures then redo them. If over-pressure signs show (hard bolt-lift, marked case-heads never mind worse signs), then a significant change is needed. Seating bullets deeper may reduce pressures a little, but unless the bullets are in the lands, the odds are that the change won't be enough. It needs a significant charge reduction, the simplest and by far the most effective/reliable remedy.
As @cem says, this issue only applies to rifle cartridges and not to small capacity straight-wall pistol cartridges. Over-deep bullet seating has wrecked more than a few fine 9mm Para pistols over the years.
There is one possible exception to this 'rule' in rifle cartridges - very high fill-ratio loads with ball powders. It used to be said in manuals, don't use ball types in compressed loads as it could increase pressure, but again this homily has disappeared except for the Norma manual. There it says don't do this as it risks affecting ignition and burn consistency by removing gaps completely between the already closely packed kernels affecting primer flash penetration. That makes more sense to me than the former reason, and there is a well-known if extreme example. Early factory production of 458 Win Magnum dangerous game ammo with very heavily compressed loads and a heavy case-mouth crimp to hold the round together often saw kernels 'clump' into impenetrable lumps that wouldn't ignite at all producing squib loads. (It didn't happen to factory fresh or newly loaded test rounds so the factory couldn't figure what was causing the bad user feedback. It was eventually discovered that the problem arose when the ammo was a year or two old.)
Thanks members for excellent information . 40grs of H4350 now,how much should I drop the charge,2 grs ? Also I styotre am in a ice chest ,plus deeper seating
OP....we cant tell you how much to reduce the load because we dont know how much "over"you are ,,,,and you didnt tell us the charge wt, to start with,,,everyone in guessing,,,bottom line ,,,what works in cool weather can be too much in hot,,,this is part of the learning curve for you,,,,Roger
PS,,,Laurie knows his stuff ,,,he has lots of range/trigger time,,,
PS,,,Laurie knows his stuff ,,,he has lots of range/trigger time,,,
How much has your bullet velocity changed since you adopted the load? Adjusting seating depth may not be necessary if you back off the load a bit. I would pull the bullets after checking your velocity, if it's safe to do so.
Im from Las Vegas, NV and it get hot here too.
I'm inclined to suggest that you pull the bulletts and start over.
I would like to see it explained and demonstrated scientifically that setting back a projectile from the lands in a handgun produces inverse results from the same procedure in a rifle.
The mechanical process is identical, we have handguns and rifles that do not fully enclosed the case head and some handguns and rifles that do fully enclose the case head. The chemical/mechanical process vary in proportions and pressures but otherwise are identical.
LVLAaron
Gold $$ Contributor
Saw this with my own two eyes at the range this week. Goes against conventional wisdom but increasing seating depth from the lands did in fact reduce velocity.
It makes sense that both rifles and handguns would have the same responce.
I wonder if the program uses case capacity in its calculations but omits the freebore area?
We've not had handguns in the UK for over 20 years now so material on loading their cartridges is thin since we don't use them much, 357, 45 Colt, and the 44s in leverguns aside.
In the days when there was a good range of printed magazines here and many excellent articles on specialist handloading, this issue would arise every now and then. One I particularly remember was about the big-bore lead bullet numbers for the WW1 and earlier British service revolvers. .455, 476 Enfield and so on. (Despite the name, the 476 is also a 45.)
They had much shorter cases than the US 45 Colt with very limited capacity left after bullet seating and used tiny chopped cordite charges. They are very easy to overload and with the Webley MkI through MkVI service revolvers being relatively weak hinged frame types, need a fair bit of knowledge and guidance to load safely with modern solid head brass (reduces internal capacity over the original balloon head).
The issue that always came up on articles on these cartridges was to avoid the use of some modern design wadcutter type and/or modern versions of the original 'manstopper' bullet a plain hollow-based lead cylinder. Modern plain-base versions reduced the space under the bullet and pressures went through the roof. Everything else (weight, diameter etc was the same as other designs), there was just less powder space. The usual powder is Bullseye and it was posited that such very fast burners don't detonate but aren't far off it, so peak pressures are reached before the bullet has moved much, or even at all. Change the usable volume below the bullet and an out of proportion pressure change occurs.
There was a guy called Clive Stevens who tested and wrote up vast numbers of handgun cartridge handloading features in a long-gone British shooting magazine and one of his loves was the strange and masochist discipline of long-range service pistol in which the British Army 9mm Browning GP35 design was used in issue form, not even the magazine safety removed to improve trigger pull, in 100, 200 and 300 yard stages. This involved loading jacketed 130, 140 (maybe 150gn too?) 0.357" bullets designed for the 38s / 357 Mag. Because magazine operation / feed was mandatory, COAL was critical for the round to feed, so bullets couldn't be seated out. Bullet pull had to be very heavy to stop bullets being pushed back into the case and IIRC part of the handloading process involved rolling a new cannelure into the bullet jacket to suit the 9mmP case with a part roll-crimp and mucho taper crimp. (Even super-gluing bullets into the case was tried IIRC!) This was a very dangerous process for the inexperienced or careless and a few pistols were wrecked. Much of this was said to be down to the already small charge space in 9mmP being further reduced by the longer shank bullets making powder selection and load super-critical, as well as instances where insufficiently secured bullets were pushed back further into the case. The effects were said to be much greater than were calculated purely for the increased pressure effects of a heavier 0.002" fatter bullet.
In the days when there was a good range of printed magazines here and many excellent articles on specialist handloading, this issue would arise every now and then. One I particularly remember was about the big-bore lead bullet numbers for the WW1 and earlier British service revolvers. .455, 476 Enfield and so on. (Despite the name, the 476 is also a 45.)
They had much shorter cases than the US 45 Colt with very limited capacity left after bullet seating and used tiny chopped cordite charges. They are very easy to overload and with the Webley MkI through MkVI service revolvers being relatively weak hinged frame types, need a fair bit of knowledge and guidance to load safely with modern solid head brass (reduces internal capacity over the original balloon head).
The issue that always came up on articles on these cartridges was to avoid the use of some modern design wadcutter type and/or modern versions of the original 'manstopper' bullet a plain hollow-based lead cylinder. Modern plain-base versions reduced the space under the bullet and pressures went through the roof. Everything else (weight, diameter etc was the same as other designs), there was just less powder space. The usual powder is Bullseye and it was posited that such very fast burners don't detonate but aren't far off it, so peak pressures are reached before the bullet has moved much, or even at all. Change the usable volume below the bullet and an out of proportion pressure change occurs.
There was a guy called Clive Stevens who tested and wrote up vast numbers of handgun cartridge handloading features in a long-gone British shooting magazine and one of his loves was the strange and masochist discipline of long-range service pistol in which the British Army 9mm Browning GP35 design was used in issue form, not even the magazine safety removed to improve trigger pull, in 100, 200 and 300 yard stages. This involved loading jacketed 130, 140 (maybe 150gn too?) 0.357" bullets designed for the 38s / 357 Mag. Because magazine operation / feed was mandatory, COAL was critical for the round to feed, so bullets couldn't be seated out. Bullet pull had to be very heavy to stop bullets being pushed back into the case and IIRC part of the handloading process involved rolling a new cannelure into the bullet jacket to suit the 9mmP case with a part roll-crimp and mucho taper crimp. (Even super-gluing bullets into the case was tried IIRC!) This was a very dangerous process for the inexperienced or careless and a few pistols were wrecked. Much of this was said to be down to the already small charge space in 9mmP being further reduced by the longer shank bullets making powder selection and load super-critical, as well as instances where insufficiently secured bullets were pushed back further into the case. The effects were said to be much greater than were calculated purely for the increased pressure effects of a heavier 0.002" fatter bullet.
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