What are the problems associated with loading a bullet past the manufacturers specs?

[Tamarac]

My Rifle:
260 Remington
VZ24 98 Mauser action
27" 1-9" twist Shillen barrel
Timney Featherweight, 1 1/2#

My load:
Cal: 260 Remington
Powder: IMR 4064, 39.0 gr
Primer: Standard Winchester Large Rifle
Bullet: 123 gr Lapua Scenar

Story:
I got a last minute call to do some shooting at 600-900 yards. The only ammo I had available was the load above. I chronographed this load at 2987 fps and had absolutely no pressure signs. It performed beautifully for me at 600, ringing a 12" plate every time.

This morning I found Lapua's online data listing their max load for the 123 gr Scenar / gr 44.6 gr N160 at 2759 fps. That's 228 fps slower than my load.

My Question:
What are the issues/problems of pushing a bullet past the max speed listed in the manufacturers listed loads? Since I only shoot this at 600, would there potentially be problems that would manifest itself if I took the load to 900 or further?

 

[g0rd0]

you have no problem with that load. The only issue that you have is compareing it to another powder.
Just remember to always confirm your load data with a different published source, start low and work up.
One idea you may want to try is to use the same load data and play with your seating depth a bit. Load a dummy (no primer or powder with the inside of the neck lubed seat a bullet just enough to hold it in place), now chamber it as the bullet contacts the rifleing it will seat to its absolute max OAL for your rifle using that bullet, it will change with different bullets.
Using this as a start set your seat stem on top of this dummy twist it down 10 tho" do 5 loads then screw it down another 5 thou, then another 5 tho then another 5 tho. Keep them all separate and see wich group of 5 is best. You will find that depth matters.
The worst part of this is you may find that the most accuate OAL may not cycle through your mag and bolt feed. This is rare but, sometimes occurs.

 

[Tamarac]

g0rd0;
Thanks for the tip.

My question//confusion/concern really arises from the fact that Lapua lists their fastest load for this bullet at 2759. My load (yes, with a different powder) is 228 fps faster. So, in a nutshell is going that much faster over the manufacturers load an issue or am I over analyzing this?

 

[pods8]

You title sounds like COAL but the post is clearly taking powder charge it seems.

Powder charge alone is a guideline since brass/primers/etc. and component lots can all vary things. Velocity is a good tip off though and if you don't have a published match you may have to iterate between some loads. You said laupa is listing with N160 ~2760fps. And hodgdon lists 37gr 4064 at 2800fps with a speer 120gr. Yes a different bullet but you're running quite a bit more powder and velocity, even with 3" extra barrel, you are very likely running over pressure. Remember pressure signs don't start showing up till you are OVER pressure.

I can't state anything from a safety aspect definitively but you would be exceeding the published rating of things. Now the ratings are based on making sure there aren't failures so the majority of time there is margin BUT if you get the combo of factors at play that remove that margin then you may have an issue of varying seriousness on your hands...

Personally I'd consider looking for a load that is backed off a bit.

 

[g0rd0]

g0rd0;
Thanks for the tip.

My question//confusion/concern really arises from the fact that Lapua lists their fastest load for this bullet at 2759. My load (yes, with a different powder) is 228 fps faster. So, in a nutshell is going that much faster over the manufacturers load an issue or am I over analyzing this?

in a word no.
what size barrel did they use? was the development done in a lab? are their loads calculated or proven? what brass did they use? was the brass neck sized, full sized, fire formed? way too many questions.
You will find that if you are to open the Nosler, Lee, Lyman and Speer books find a common load say 3006 180 grn sp XX.X grn IMR4064 you may get 4 different velosities from your rifle and not 1 of those 4 may list the same vel. Go figure.
Always go with published data, confirm with another source, start low and work up.
Never be afraid to ask questions, use common sense and most of all enjoy what you do to the fullest

 

[HARPERC]

I'm hearing your question a bit differently, are you asking about the integrity of the bullet itself traveling faster?

If so, I would answer if there was a problem it would show up well before 600 yards, and one source using the Lapua 123 in a 6.5-.284 is well over 3100 fps. So yes the bullet itself should be OK in flight.

Sorry if I'm reading it wrong.

 

[Tamarac]

Some background information for everyone.

Lapua's gun lists an 18 3/4" barrel, 1-9" twist.

My gun is a 27" barrel with a 1-9" twist, so I know it won't even be close to apples to apples.

I started out using the 123 gr SMK, since that was the closest weight/profile I could find. As always, start low and work up. And finally (not dropping nearly this much powder), but I'm only dropping 39.0 and Sierra is saying up to 42.0 is max (IMR4064). I know the 123 SMK is not a direct comparison to the 123 Lapua Scenar but its the closest published out there.

Common sense says to me since its not a direct comparison to try and stay away from max. Was I wrong in my approach?

 

[pods8]

What velocity does sierra publish? For some reason I read 42grs earlier, 39gr doesn't seem too high in that realm.

 

[Tamarac]

For a 120 gr SMK Sierra lists 42.0 gr IMR4064 3000 fps.
http://www.northfloridashooting.com/Misc/Reloading_260remington.pdf

I'm pushing max velocity for a similar bullet, less powder to do it though...

 

[pods8]

Well you have 37gr with a Speer at 2800 per hodgdon and 42gr with a sierra at 3000 both from a 24" tube. My speer manual calls 39gr at 2822 for their 120. Re looking at things you likely are in a good zone.

 

[DocDoc]

Your barrel is 8" longer than the Lapua reference. At 25 fps per inch it should be 200 fps faster - roughly. Individual barrels from the same manufacturer can be faster by a 100 fps or so. You are getting no high pressure signs, not unreasonable charge compared to some other listings, you are good to go.

 

[Tamarac]

Thanks for the validation guys.