I have been shooting a Marlin 357 lever gun for a couple years. Have a very accurate load...4.7g Unigue behind a cast 158 rnfp loaded into a 38 special. Always been a good combo. I have loaded the same into a 357 mag case for better cycle in the lever action. This load now is no where close to the same in the 38 sp. I have stepped it up to 5.2g and just back from the range, and still not satisfied. How can there be such a difference in the 2 cases with the same powder and bullet?
Need some help with this bullet please...
- Thread starter MGRAY
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shootstraight57
Member
I might be wrong and correct me if I am but I looked into all my Lyman Reloading Handbooks and they show a lower FPS on the 357 than the 38 with a 158 rnfp with that powder charge.
beatledog7
Member
The .357 case has significantly more internal volume and thus requires more powder to build to the same pressure. Exactly how much more is a matter of consulting the manuals.
Vec
Member
Along those same lines if you seat the bullet deeper (0.125" deeper) to have the same volume you should get the same performance.
Of course the bullet might not be really suitable to do that with (crimping and all), but it's workable in some instances.
Of course the bullet might not be really suitable to do that with (crimping and all), but it's workable in some instances.
beatledog7
Member
Same volume, more bearing surface. Sounds like a recipe for overpressure.
Steve2md
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If you seat the bullet deeper, it negates the point of using the .357 casings. Using the .38sp load in a .357 case is asking for an over pressure incident. look up the data for your .38sp load, then cross check the bullet weight and velocity for a .357 load. you should get the same performance using the .357 data at the .38 velocity.
Vec
Member
The problem is if you're trying to use the same amount of powder and you seat to a far longer OAL, you'll push the bullet slower as your experiment showed.
Keep in mind we are talking about the same bullet weight and design in both cases seated to the same volume under the projectile with the same type and amount of powder. The bearing surface is the same -- that is determined by the bullet design. Remember, you're not trying to swage the bullet down to a smaller size with the .357 than a .38, mainly trying to get by the crimp just like a .38 case which doesn't take much. The powder has the almost same volume to work with and it's working to push the same mass bullet down the barrel. The internal ballistics in the first few moments as far as the powder is concerned (max pressure happens here) is almost identical (see #2 below).
Will there be higher pressure with the .357 case? Yes, marginally. Why? Two reasons: 1) Because there will be less blow-by around the bullet since the chamber is more filled than a .38 case in a .357 chamber. (the .38 is 1/8" shorter; firing a .38 cartridge in a .357 chamber will leave at least 1/8" of leade before constricting a bit. 2) The case web has a tiny bit of extra material typically taking up a tiny bit of space. Here's a thread for that: http://www.thehighroad.org/archive/index.php/t-515233.html&& If you could seat the bullet such that the same amount of volume was under the bullet, then you'd have damn near exactly the same internal ballistics.
You also have another big thing working in your favor: Max pressure for a .38+P is 20K psi while a .357 is rated to 35K psi. This will overcome any possible pressure increases handily making the round safe to fire in the .357.
Keep in mind we are talking about the same bullet weight and design in both cases seated to the same volume under the projectile with the same type and amount of powder. The bearing surface is the same -- that is determined by the bullet design. Remember, you're not trying to swage the bullet down to a smaller size with the .357 than a .38, mainly trying to get by the crimp just like a .38 case which doesn't take much. The powder has the almost same volume to work with and it's working to push the same mass bullet down the barrel. The internal ballistics in the first few moments as far as the powder is concerned (max pressure happens here) is almost identical (see #2 below).
Will there be higher pressure with the .357 case? Yes, marginally. Why? Two reasons: 1) Because there will be less blow-by around the bullet since the chamber is more filled than a .38 case in a .357 chamber. (the .38 is 1/8" shorter; firing a .38 cartridge in a .357 chamber will leave at least 1/8" of leade before constricting a bit. 2) The case web has a tiny bit of extra material typically taking up a tiny bit of space. Here's a thread for that: http://www.thehighroad.org/archive/index.php/t-515233.html&& If you could seat the bullet such that the same amount of volume was under the bullet, then you'd have damn near exactly the same internal ballistics.
You also have another big thing working in your favor: Max pressure for a .38+P is 20K psi while a .357 is rated to 35K psi. This will overcome any possible pressure increases handily making the round safe to fire in the .357.
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