help with 375 h&h mag reloads

T

tklau000

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Hoping for some advice here reloading 375 h&h mag with 66.5 gr. Of 4064 an 300 gr. Sierra first 20 shot great then stuck bolt flat primers an stuck cases in chamber oh yah an using cci 250 primers some people said cci 250 isn't igniting it but I do not know was gunna try wlrm primers cases are trimmed exact an no where near the land all is sierra hand book specifications just curious what direction to go
 
66.5 of IMR4064 is 1.5 over max according to Hodgdon. Manuals do vary though.
CCI 250s are magnum primers. Magnum primers are about the powder used, NOT the cartridge name. IMR4064 doesn't need 'em.
"...stuck bolt, flat primers and stuck cases in chamber..." Indicates seriously excessive pressure. Kind of hard to imagine just 1.5 over max is the cause though. You may be seeing high pressures caused by the magnum primer. Try a regular LR primer.
 
If this is 375 Holland & Holland and IMR 4064, several sources I checked show 66.5 as close to max but certainly below it, and magnum rifle primers are correct. This also agrees with my own personal experiences. I never used 4064 in 375 but I have used other stick powders that appear in the data. In fact, most data on this cartridge allows for old British rifles; modern rifles should be good for more. Do you use a digital scale? I've had mental malfunctions where a different number looks right for a second. I really suspect some kind of never-happen-again fluke. I would fix up a few more, starting lower and working up to 66.5.
 
Yah all my books say magnum primer as well I think hornady is one that doesn't.I was thinking of the wlrm primers just in case my cci 250 were acting strange but it shot em good an then not so good hodgdon said there max is less than my load but hodgdon is a little more light than most books
 
An sorry about Grammer not much of a computer person I got on this forum today because I have heard people on here have good knowledge when it comes to reloading.....
 
The first 20 rounds were fine. Was the next round that overloaded from a subsequent loading session or part of the same session? Especially if from the next session, It sounds like an overload managed to sneak in some way. Perhaps if measuring each round by scale, the scale adjustment became offset in error by an additional 5 grains or something along that order. Did you disassemble any of the remaining rounds and check the charges? I assume that no more were fired after the overload. With the balance beam scale that I use to set the powder measure, I can guess that something like that could happen. Perhaps thinking that the scale is still set to 66.5 grains, it may have been bumped up unintentionally to 71.5 grains or so.
 
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I've come closer to making mistakes since I left the old balance scale and went digital. I write the number down now and put the piece of paper beside the scale. Of course you still have to remember to look at them. The 21st round thing might be important too. Was it a fresh loading session, or maybe a fresh shooting session? A lot of people would think 20 rds of 375 was enough for one sitting. Something about the rifle might have changed and run pressure up. Elmer Kieth told a story how a dauber wasp puttied-up one of his chambers and blew his sixgun up. Could be a lot of things. I would just check everything real good and work the load up again. You may never know.
 
All loads were done at one session of reloading 10 rounds.the beam scale is still sitting at 66.5 I looked when I got home an I pulled bullets to re weigh all was perfect could it be primers???pretty frustrating to get a hole shooter an this pop up.I was gunna work back up from 65 to my 66.5 load with wlrm primers gun is clean iv checked nearly everything but haven't tried a new primer could this possibly help?thanks for all the responses an help with this
 
You might dump some powder onto a piece of paper under good light and make sure the kernels are all the same. Ages ago I had a kernel of IMR something-else land in my pan. I got excited and mailed it back and they said once in a while when they change product a bit might stick in the equipment. One kernel wouldn't matter but if a clump came through it could cause serious contamination. I just can't see how one primer from the same lot could make that much difference. If you figure anything out let us know.
 
I am going to work load up from 65,65.5,66,66.5 with same powder an wlrm primers an see if anything changes again I use cci primers for everything so I doubt that's it an I bought a new pound of 4064 I might use on this go around.imr 4064 is not temp sensitive is it I didn't think it was anyways?
 
It would be so slight you could only measure it with sophisticated equipment. Something really dramatic happened with yours. Did you decide to try another bullet?
 
I am still using sierra.Is it possible to push the case neck to far back an cause pressure issues like over size it an still would chamber?
 
Not quite sure what you are asking but you could be aluding to possibly over crimping during bullet seating and pushing the shoulder back excessively. However when that happens the case body immediately below the shoulder is usually bulged and the round would probably not chamber. But since the round did chamber, and as far as you know it chambered normally, that probably is not a consideration in this incident but just something to be familiar with in the future. Bulging can happen with excessive crimping since the case is not supported by the inside of the die at that point. But on the other hand, if the bolt was closed over a bulge but with excessive force, could that raise pressure? That question remains unanswered but I wouldn't think so.

If your question relates to pushing the shoulder back excessively during sizing, I wouldn't think the pressure would increase as much as what you experienced. The case would just fireform with some stretching.
 
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I did a ladder test from min to almost max an am still getting ejector marks on cases an pretty excessive kick with the imr 4064 an 300 gr. Sierra GK any thoughts
 
It appears you may have to settle for the load that fails to display excessive pressure rather than trying to push to the limit. The brass you are using could make some difference. I suppose Remington and Winchester cases are the most commonly used for the .375. I just weighed one of each. With spent primers still intact the Winchester case weighed 246.5 grains and the Remington 10 grains higher at 256.5. It is common for Remington cases to outweigh Winchester cases per given caliber. So if you are using Remingtons or even Federals that would probably be heavier yet, you might want to try Winchesters for perhaps slightly more velocity before pressure becomes noticeable. But the 10 grain difference between the two is not all that much considering the size of the case.
 
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Have you considered going with a different bullet like a 270 grain Hornady? One of the most consistently accurate .375 bullet I have come across is the 235 grain Speer, not for elephants of course but for light game, those having been used with a Model 70 Win. Is your preference for the 300 grain Sierra for accuracy purposes? I just checked my notes on the 300 Sierra fired from a Remington 700 and I just indicated the accuracy as "OK", with the Hornadies and Speers superior. I guess the just "OK" notation accounts for having almost a full box of the Sierra 300 bullets remaining (for sale cheaply).
 
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I am getting a weird like kinda groove all the way around the case were the neck meets the shoulder is this normal
 
I agree with Condor Bravo's suggestion about the bullets. I use the 270 gr Hornady with an almost max load of RL15 in my Model 70. It will usually print all holes touching about the size of a quarter or a little more. The 260 gr Nosler AB or Partition will do about the same. Great bullets for plains game but I would likely use the 300 gr Partition or A Frame for large bears or buffalo.
 
No a groove at the shoulder/neck junction is not at all normal. Does this occur after sizing, or after bullet seating, or after firing? And are you crimping the bullet? If still using the 300 grain Sierra, it does not have a crimping cannelure and normally crimping should not be done. Note from post #14 that over crimping can create a bulge around the case body just below the shoulder and this would become apparent during chambering. Lube dents can occur on the shoulder if excessive lube is applied to that area and not removed prior to sizing. But a groove around the shoulder/neck junction appears to be something usually not encountered.
 
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