Is Oal Different Fmj Vs Jhp For Open Gun

[redwoods]

I am setting up my reloads for a new (used) open gun I am purchasing. The previous owner gave me reloading data for what is working well in the gun. The only difference I made to the loading components was that he was using fmj, I am using jhp. How should I load the OAL? I am guessing that the jhp is shorter than the fmj. Should I just drop a few tenths of a grain....from 9.0 to 8.6 grains and load my jhp a little longer?

Thanks,

Redwoods

IMR4756

Fed SRP

Zero 125 Jhp

Rem+p 38super brass

9grains powder

1.235-1.240 Oal (for fmj)

[lcs]

I am setting up my reloads for a new (used) open gun I am purchasing. The previous owner gave me reloading data for what is working well in the gun. The only difference I made to the loading components was that he was using fmj, I am using jhp. How should I load the OAL? I am guessing that the jhp is shorter than the fmj. Should I just drop a few tenths of a grain....from 9.0 to 8.6 grains and load my jhp a little longer?

Thanks,

Redwoods

IMR4756

Fed SRP

Zero 125 Jhp

Rem+p 38super brass

9grains powder

1.235-1.240 Oal (for fmj)

(1) Was the FMJ the same 125gn weight?

(2) Was the FMJ .355 or .356?

(3) FMJ are typically a little longer than JHP

You can probably use the same OAL. You would be smart to back off the load a little as you suggested and then see how the gun feels and what the chrono says. Work up slowly till you reach major PF and the gun feels good.

If he was using 115 grain FMJs you need to start your load around 8.2 and work up.

There is a lot of information on OPEN gun powders and load data here on be.com. Hope I helped you some.

[redwoods]

The previous owner was using 125gr. .356 fmj

I am using 125gr .356 jhp

I made up a load of 8.1gr. with 1.245 oal

He was loading 9.1gr with 1.240 oal

I am also at 8150 feet elevation, he shot it in KY, I am in CO.

Now all I need to do is wait for the gun to be shipped so I can try my loads. I just don't want to blow it up from my negligence in reloading.

Thanks for the help,

Redwoods

[n2ipsc]

...The only difference I made to the loading components was that he was using fmj, I am using jhp. How should I load the OAL? I am guessing that the jhp is shorter than the fmj. Should I just drop a few tenths of a grain....from 9.0 to 8.6 grains and load my jhp a little longer?

Your best bet for starters will likely be to measure the difference between the JHP and the FMJ, subtract this difference from the OAL (that is, load the JHP's to a shorter OAL), and keep the powder charge the same. This will keep the cartridge length as measured to the ogive closest to the load you know works (FMJ) and thus provide reliable feeding.

By way of example, MT Gold JHP's are 0.015" shorter than their FMJ's (since they don't have the "nose" the FMJ's do). So, for my LimCat BelchFire, I load FMJ's to 1.255" and JHP's to 1.240" over the same powder charge - velocities are exactly the same, and they all feed 100%.

[Bluemax29]

I switched from FMJ to JHP and now I'm back to FMJ. I loaded my FMJ to 1.240 OAL 125 gr zero bullet. When I switched to JHP I tried to load the JHP to the same OAL and exprienced alot of problems. To make a long story short, when I set my machine back up to load FMJ 1.240, then ran the JHP through, I had no problems. The OAL on the JHP was 1.200 but ran without any issues.

[itchy]

I would think that there are two issues you need to look at. One is overall length, which can affect feeding. The other is the actual space for powder, when loaded to a certain length. Changing the volume of the case will affect pressure. I guess the two are really related and will affect each other. Like it was stated in a previous post, if both bullets are the same length, then you can load to the same OAL, and theoretically you should get same pressure, and feeding characteristics, and velocities.

Good luck,

Itchy

[ipscbob]

UHMMMM.....How about working up a new load using a chronograph? Any time you change a load you should always run some over a chronograph. You do have a chronograph, don't you?