FMJ bullet variations

[RM]

Reloading manuals give reloading data with many different FMJ bullets- RN, hollow point, JSP, TMJ, Speer GDHP, Hornady XTP, FMJ Match, etc. What do you do when the bullets you are using are different from those use in the Reloading Manual? For example, you have RN FMJ, and the load described is for GDHP's? Or you have Montana Gold TMJ and the Load data is for Hornady XTP bullets? To what extent are FMJ bullets different or the same in deciding on a correct powder charge? Thank you.

 

[1SOW]

I'm fairly new to reloading, but have switched between Win 124 FMJRN, Precision Delta 124 FMJRN, and Montana Gold 124 CMJRN.

These three will run very close to the same over N320 powder. I'm using very light comp loads, so I'm not pushing the envelope on any of my loads. I've found "forum threads" that say the HPs in these and others also shoot close to the same.

Where I couldn't get a referenced load , I started low with 'similar' bullet data and worked up using a chrono. When different brand bullet length differed, I shortened or added the difference to my oal. I also asked for load data in the forums to get a feel for the trend. I wouldn't be confident, even with published load data without the chrono to confirm it.

 

[moooose102]

maybe i am just niaeve, but i interchange all jacketed bullet data (within the same weight). the barrel has no idea whether the bullet has a round nose or a spitzer point. of course i do not just pick a load, and load it at max either. i work up to what i feel is max (or hot enough) within the load specs. group size is more important than an extra 100-300 fps.

 

[rcmodel]

the barrel has no idea whether the bullet has a round nose or a spitzer point.

Yes, it actually does.

Changing bullet shapes of the same weight changes the amount of bearing surface engraved by the rifling, (Bore friction) as well as how much of the shank is seated inside the case to get the same OAL. (Internal case capacity)

Both can have a large effect on chamber pressure.

You will get by with it on low to medium charges, but can quickly get over-pressure when approaching maximum loads.

Jacketed bullets are generally harder then plated bullets like the Berry, Speer Gold-Dot / TMJ and others and they use different data.

Hollow points are longer and have more bearing surface / seating depth for the same weight then JSP or FMJ, Encapsulated, etc.

To answer the question?
You can substitute data to some extent, until you get to near maximum loads.
Then it pays to have the correct tested data for the bullet you are using.

rc

 

[Ol` Joe]

rc is steering you right. There can be a big difference. Work up your load from starting and expect to find your max varies from the books if you sub bullets.

 

[Shoney]

RM
You should take some time and learn what the abbreviations stand for. Most loading manuals have a discussion of this. If your manuals do not have this information, go to:
http://www.saami.org/Glossary/display.cfm?letter=C
http://www.snipercountry.com/Comp.htm

And Midway has a small compendium http://www.midwayusa.com/guntecdictionary.exe/home

You should also be aware that many "hollow point" bullets are designed for target shooting only (as RC stated, the engraving surface being longer & therefore theoretically more accurate), not for rapid expansion in hunting or PD use.