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Trez 08-25-2011 03:40 PM

Too Much or Not Enough Powder?
How do I tell if my loads are too much or not enough? I was reading that not enough powder can cause over pressures...

Im developing a load for my Arisaka, Previous loads I made show that 40 grs of RL-15 were starting to bulge cases, So I made some with 36 grs. My first batch worked great, but the second batch I made with 36 grs. started to bulge cases.. (I used a 150 gr. bullet on both)
Doing some online reading Ive read that the 7.7 should be able to take between 35 and 45 grs. of RL-15... Guns & Ammo Magazine had load data for the 7.7 Arisaka between 40 and 45 grs. using a 174 gr. bullet.

Im not even close to the maximums so why are my cases bulging? The last batch that didnt work, the cases were already fire formed and I just neck sized them.... Am I loading too light?
The 7.7 case doesnt allow for a double charge, and I check all my cases anyways for double charges, so I dont think that was the culprit.

Ive read that you can use heaver data on lighter bullets, but not the other way around. Can I use the data for the 174 gr. on the 150 gr.?

Thanks for any help!!

Lindenwood 08-25-2011 04:22 PM

The only way light loads can cause overpressures is if there is a very small amount of powder such that when the cartridge is horizontal, the powder lies below the flash hole. Thus, this requires notably less than half a case full.

Could it be an out-of-spec chamber? What kind of bulging do you mean?

And yes, you can use data for a 174gr bullet under a 150gr bullet.

JonM 08-25-2011 04:24 PM

Seating bullets too deep can cause it too.

Trez 08-25-2011 04:40 PM

Ok, then the loads not too light.. the case is about 3/4 full..

Would it make a difference if I went from a boat tail to a flat based bullet? all my manuals show the same loads for both.

How do I know if I seated the bullet too much, I thought I was good as long as I stayed above the shoulder. The bullet is under OAL, so I could seat it slightly less. Can you seat a bullet to little?

I didnt crimp the bullet, should I?

I wouldnt think the chamber is outta spec. ive shot the Arisaka 3-4 times and the last time was the first time its really done it.
Ive Even shot some full power loads of 4895 in reformed 30-06 I got off a friend they were loaded to 2,800 fps. and they worked perfectly.. (they were reloaded in 1960 according to the date on the box)

noylj 08-25-2011 04:42 PM

The only way I have heard that it might be "possible" for a light charge to cause a over pressure spike is to use a powder that is slow for the cartridge and be a very light load. The hypothesis, which I have never read having been proven, is that the whole charge ignites simultaneously and causes an "instantaneous" pressure spike (the nominal or average pressure will still be low).
There is not way that this can happen within the normal range of loads likely to be shot. This applies to folks trying to shoot "gallery" loads and NOT being smart enough to move to a faster powder.
It may be a myth, since I have never seen any proof from controlled experiments, but it is still a myth that has certain limits that many people seem to ignore.
In the world of internal ballistics, your rifle and your cases will tell you. Has your rifle been checked by a 'smith to verify that there is not excess head space and the chamber is in good shape?

hiwall 08-25-2011 05:10 PM

If you only neck size that negates the effects of excess headspace, so not likely that is the problem. Pics of the bulged case next to a normal one would be very helpful. Excess oil in the chamber or case lube on the cases can cause problems. You double checked your bullets to see if they are the correct diameter? These bullets were the same ones that worked in the first batch? Check the case length(case only not with bullet) - if to long that can cause problems. Hard for the case to bulge if supported by the chamber correctly. If no pics then describe the bad cases(where is the bulge).

Trez 08-25-2011 09:59 PM


Originally Posted by JonM (Post 569661)
Seating bullets too deep can cause it too.

How do I know what the proper seating depth is? I read its the diameter of the bullet but thats longer than the neck is..

JonM 08-25-2011 10:24 PM


Originally Posted by Trez (Post 569805)
How do I know what the proper seating depth is? I read its the diameter of the bullet but thats longer than the neck is..

load manual. but the best method is an overal length gauge from hornady. if they dont offer a case for your rifle just used an empty fired case drill and tap the bottom of the case to fit the gauge

BillM 08-25-2011 11:35 PM

Are you trimming the brass to length? It's possible that too long brass
can get into the leade and get "trapped" between the bullet and barrel.
This can impede bullet release and cause a pressure spike even with light loads.

Trez 08-25-2011 11:41 PM

I finally figured it out!! I was way over seating the bullet... :eek:
Man, you guys are good! THANK YOU!!
Im glad it was a Arisaka... Its strong enough let me learn from my mistake..... :o

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