Seating depth question - Same OAL between FMJ & JHP of same weight?


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bg84fs
March 20, 2010, 09:59 PM
Good evening,
I'm new to reloading and this forum and have done a good bit of reading on the subject in preparation before I actually start doing it. I have almost everything I need to begin. (Still need to buy a scale and powder thrower)

At the gun show today I picked up a bag of 100 bullets: 95gr JHP from Montana Gold. My 2 reloading books (Lyman 49th and a one Cal - one book) don't have data for a 95 grain JHP, but they do list 95gr FMJ.

My main concern is seating depth as the OAL listed for the equivalent weight bullet in the same caliber of a different type (FMJ vs the JHPs I bought), might take up a different amount of space inside the cartridge when seated to the same OAL, and develop different (potentially unsafe) pressures inside the cartridge.

I searched the internet for a good 90 minutes trying to find load data specifically for the 95 grain JHP in .380, regardless of brand, and haven't had much luck determining if I can use a different bullet type of the same weight with the load data. It seems 90 grain is more popular and data on the 95gr JHP for .380 isn't readily available.

My Lyman book lists .900" OAL for the 95 grain FMJ. Will this OAL length work for a JHP or is there likely too much difference in the length of the bullet? They don't list the length of the bullet used in their data, though they do specify it as a Sierra FMJ #8105

Any suggestions on either finding/extrapolating load data for the 95gr JHP?

Thank you!

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ranger335v
March 20, 2010, 10:09 PM
"My main concern is seating depth as the OAL listed for the equivalent weight bullet in the same caliber of a different type (FMJ vs the JHPs I bought), might take up a different amount of space inside the cartridge when seated to the same OAL, and develop different (potentially unsafe) pressures inside the cartridge."

No rational OAL change will make a safe load unsafe. Find an OAL that feeds and chambers in your weapon and use it.

Years back few loading data sources bothered to even suggest an OAL, they knew we would seat as needed for best results anyway. And they were correct in that assumption. I've been reloading for some 45 years and have never paid even the slightest attention to any book OAL.

ranger335v
March 20, 2010, 10:13 PM
Duplicate

Walkalong
March 20, 2010, 10:33 PM
A JHP of the same weight will generally have a shorter O.A.L. than a FMJ (RN) of the same weight due to the shape up front. Due to its length, it may or may not actually seat any deeper though.

ranger335v posted
No rational OAL change will make a safe load unsafe. Find an OAL that feeds and chambers in your weapon and use it.

I agree.

Welcome to THR bg84fs

Walkalong
March 20, 2010, 10:36 PM
Oh yea.

Speer #13 will list the same charges for 2 or 3 bullet styles of the same weight. JHP, JSP, FMJ etc.

1SOW
March 21, 2010, 12:09 AM
My main concern is seating depth as the OAL listed for the equivalent weight bullet in the same caliber of a different type (FMJ vs the JHPs I bought), might take up a different amount of space inside the cartridge when seated to the same OAL, and develop different (potentially unsafe) pressures inside the cartridge.

I don't reload .380, but the same formula will work to 'know' the seating depth.

Case length + bullet length - OAL =Seating Depth

9mm.... MG124.... OAL
.7473 + .5925 - 1.134 =Seating Depth

1.3398 - 1.134 = .2058" seating depth

918v
March 21, 2010, 02:02 AM
My Lyman book lists .900" OAL for the 95 grain FMJ. Will this OAL length work for a JHP or is there likely too much difference in the length of the bullet? They don't list the length of the bullet used in their data, though they do specify it as a Sierra FMJ #8105

How long is your MG bullet? Keep in mind that OAL is critical in short, low capacity cases filled with quick-burning powders. A JHP is longer than a similar weight FMJ and is usually seated deeper to fit in the magazine. Deeper means less internal capacity and more pressure. Plus, you prolly have a blowback pistol and they're intolerant of excessive pressures. Be careful.

JDGray
March 21, 2010, 08:24 AM
Calling the bullet manufacturer, always helps. They will tell you the suggested oal for that bullet. Using fmj oal data on hps, will result in possible out of battery condition. Taking the barrel out of your gun, and using it for a case gauge works. Long seat the hp bullet in the case, and keep checking it and seating it deeper, untill it just goes in flush. Record the measurement, subtract .030" or so, and see if it fits in your magazine. If it fits, use this as your max oal for that bullet profile.

Or just call the bullet maker:neener:

And Welcome!!

bg84fs
March 21, 2010, 12:27 PM
I'm measuring the Montana Gold bullet as .443" long. This is being loaded for use in an Beretta 84FS Cheetah if that helps any.

918v
March 21, 2010, 01:35 PM
My QuickLoad program calculated a 3000 PSI difference between the MG bullet and the Sierra at a .900" OAL when using 231 powder. The MG bullet is .030" longer and takes up more space in the case. I'd reduce Sierra's starting load by 10% for the MG bullet.

rfwobbly
March 21, 2010, 03:17 PM
No rational OAL change will make a safe load unsafe. Find an OAL that feeds and chambers in your weapon and use it.

I agree in principal with that statement, but as 918V found, it will make a difference. The problem is this: we reloaders talk about OAL, which is an outside tip-to-tip measurement. But what reloaders are thinking and also concerned about is where the base of the bullet is being placed.

The following diagram shows what happens to internal volumes when equal OALs are applied to different shaped bullets.

http://lh6.ggpht.com/_E3bV2jGIaSg/S3Y1scveqpI/AAAAAAAAAw8/azIMQl8gFlQ/s720/SeatingDepth.jpg

Now, some autos (especially 45ACP) are very sensitive to OAL because it affects feed reliability. So what you have is a situation where you may need to be aware of where BOTH ends of the bullet end up.

bg84fs
March 22, 2010, 12:29 AM
I e-mailed Montana Gold, the manufacturer of the bullet, to see if they could point me in the right direction for finding load data for this specific bullet. I'll post my results when they reply.

bg84fs
March 23, 2010, 03:51 PM
No reply to my e-mail so I called. The woman who answered said they don't have any load data and I needed to check a generic loading manual. No help at all.

I might look into some software that can calculate the seating depth based on the bullet length to attain the same PSI as the load data specified for a similar round of a different bullet type.

dcbridgwater
March 23, 2010, 04:14 PM
That is pretty much the same responce I got out of them when I sent them an Email awhile back. Here is the responce I got "check the reloading manuals or brianenos.com for other guys loads.thanks,jo". They may sell decent bullets but their customer service kinda stinks. So have have put the Montana Gold bullets on the back burner untill I have gained enough knowledge to consider my self an experienced reloader.

Peter_S
March 23, 2010, 04:23 PM
JDGray's advice is worth following. For every new round I develop this is what I do. There are so many bullet makers with different dimensions and shapes that it's almost impossible to find the EXACT information in a publication.

Once you have figured out the OAL make a few dummy rounds and see that they cycle properly.

From there go to the minimum powder load recommended for that weight and style bullet. (I always go minimum less 10% and work up from there.)

Cloudpeak
March 23, 2010, 06:11 PM
When setting up to load a new bullet, I always make a dummy round or two and use the removed barrel to check for fit. If the case head is not flush with the barrel hood, I seat the bullet deeper until it is. I set the bullet just a few thousandths deeper to assure the odd round won't have a bullet that jams into the leade due to manufacturing tolerances. (I shoot my own cast bullets and there are minor differences in bullets. I want to have a loaded round that I can eject easily if needed and not have a round that is jammed into the leade/rifling.) I then start with a reduced load and work up until I get the accuracy I'm looking for. I don't load my cast bullets to maximum loads, IOW.

Bullets of the same weight are not created equal even though they may be, for instance, round nose and neither are barrel chambers. I don't depend on OAL recommendations in manuals but fit the OAL to the chamber.

If you enjoyed reading about "Seating depth question - Same OAL between FMJ & JHP of same weight?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!