.270 WSM Velocity

[juice]

Finally put the chronograph to work last night on the wife's 270WSM. I loaded up 60gr of IMR 7828 with 140gr accubonds. The book was telling me velocity should have been around 3100fps. When we starting charting it all we could get was 2840. Anbody have any ideas why the big disparity?

Thanks!

 

[sageadvice]

Several factors but some of the most common is the test gun in the book may have had a different twist rate or a longer barrel.

As standard reference, you can't ever depend on the "books" numbers to be dead nuts accurate. 160 FPS off is a bunch though, was there any signs of too much pressure?

Joey

 

[juice]

No signs of pressure. It was accurate but that velocity is much closer to what I'd expect from a standard .270. Looks like the barrel length was the same between test book and ours. It is a Tikka T3 Lite.

 

[cbeard]

?????

Can't explain that.Should be faster.

 

[Cahunter805]

That does seem a bit slow. Lots of factors to consider. I think 7828 is a bit slow for the 270. Have you tried other powders such as rl17 or rl19. Even h4831.

 

[juice]

Haven't tried any other powders yet. I had a lot of 7828 laying around for my 7 STW so I put it to use. Only thing I can think of is the primer but would that have a 300 fps impact?

 

[ELKOHOLIC]

Maybe the numbers in the manual are stretched a little to make it look more appealing than the 270.

 

[Pre64]

You'll need to try some different loads to get a picture of what's going on. Could be the powder, could be the twist. Could be the barrel, could be the chamber. Could be all of the above. If it were easy I'd only have one kind of powder in the closet.

 

[deadibob]

Have you tried running factory ammo through the chrono to compare. Magpro gets some of the better velocities with the 270wsm.

 

[Boskee]

Things like this can be a head scratcher. Things I'd look at...1) Did you weigh your charges or just drop them? 2) Were the powder and primers old? 3) Primers can make a difference in the burn in a case but usually not that much. 4) 7828 usually works better in larger capacity cases like your STW etc. 5) sometimes a different powder with a faster burn rate may work better in a smaller capacity case. That case was designed to work in 22-24 inch barrel guns and to create a good burn in a smaller area and they usually shoot pretty close to velocity with mid to light bullets and a faster burning powder. I would suspect powder as being the culprit not your barrel or bullet.

 

[NoDoe]

Just read a article on the 300 WSM road test. It said that the 300 WSM would not shoot heavy bullets as fast as the 300 WM with the same barrel lengths. They tried 20, 22, and 24 inch. Mabey it is the same thing with the 270 WSM.
Don

 

[deadibob]

NoDoe it's not the same thing. The reason the 300 wsm won't shoot heavy bullets as fast as the 300 win mag is reduced case capacity and the larger bullets 180+ take up too much room in the case, thus reducing the amount of propellant in the 300wsm.

That would not be the case with the 270 wsm and 140 grain bullet. He's simply using the wrong powder.

 

[NoDoe]

Point taken Deadibob.
Don

 

[juice]

Thanks everyone. I'll try some RL 19. Someone mentioned old powder.........what is the shelf life on powder? Would this have that big of an impact? I still don't really have a good answer as to the big discrepancy between the book and the graph. I have a digital scale so every load was measured. The graph didn't suggest varying charges as it was consistent every shot. I'm going to pull a bullet and weight the charge on the old scale to be sure.

 

[deadibob]

As long as the powder has been stored properly I wouldn't worry about age. The only powder I've had start to go bad was some 4350 that spent 3 years in a St. George steel-roofed storage shed. Plus that powder was at least 18 years old. When powder goes bad it will smell bad and start to have a red dust on it.

I have ammo from world war 2 that shoots great (over 60 years old) and lots of other ammo that's 30+ years old. Just keep it cool and dry, it will last indefinetely under those conditions.

 

[REDDOG]

LAST EDITED ON Jul-23-10 AT 09:36PM (MST)[p]For the love...7828 is fine in WSM's..PRESSURE=VELOCITY, you gotta go to the top to find where the top is in that particular rifle...reloading manuals are a good source for suggestions, but not the final word.

If you aren't comfortable working up, then enjoy sub 270 win velocitys..

I'm sure this will send most of you into a tizzy, but its the truth.

edit...I just looked at a bit of data, and ~2800 fps is about right for 60 grains of 7828.

 

[mtmuley]

I'd even set up and re-test before I got too exited. Chronographs have been wrong before. mtmuley

 

[Boskee]

Most guys are getting around 3000ft/sec with 60 grains in that powder. Given that most current manuals seem to cutoff around 62 grain or below that seems reasonable to arrive at 3100+/- ft/sec in that load. Reddog has a good point and is 100% correct in that many guns show no signs of pressure above that maximum but we suggested powder that may get him where he wants to be within max published data. Reloading manuals today are a bit more conservative in nature and if you look at some older manuals they recommended a heavier charge in many of the same powders we use today for the same cartridges.

I didn't say 7828 wouldn't work but there are other alternatives many were recommended by others, out there that will get him up the pressure curve within spec that may make him more comfortable. Some guys just don't feel comfortable going above the published loads and if that's the case find a powder that will work. Some of us learned that it's a guide and know that as Reddog pointed out a little over max can really make a difference but if you can't identify the signs of over pressure it may cause you some issues. Speed and accuracy don't always go hand in hand, but in some guns they are the magical elixir of tiny groups. We all need to find that blend that suits our needs but be aware that in some guns loads well below the published max may be at max in the gun in your hands or a little over max can be fine in others.

 

[Pre64]

We all need to find that blend that suits our needs but be aware that in some guns loads well below the published max may be at max in the gun in your hands or a little over max can be fine in others.


Well said.


Fun part of reloading is that there is no end to the combinations you can choose from.

 

[elkchaserreturns]

Hello All,
It never ceases to amaze me when I hear about someone just picking a load out of the book and expecting to get the same results!
Just cuz its a "published load" don't mean it will be safe in your gun.
Alway, Always, Always start below max published (around 10% works well for me!)& "work up" your load. Even when you do "work up" a load, some wierd things can happen.
I was working up a load for a friends .308 Win some years back and, if memory serves, we were using:

1) Winchester cases (once fired, F.L sized & trimmed)
2) CCI 200 primers (new)
3) Winchester 748 Ball Powder (new)
4) 165 gr Sierra Spitzer Boatails

I like to shoot five shot groups and increase the load by one grain increments per batch as I work up.

Long story short, first group showed flattened primers.
Second group, second shot, had complete case rupture and primer fell out of the case when extacting case from the rifle.
WTF!!!!
This was still four grains BELOW max load as published in the Sierra Manual.

Stopped shooting (duh!), went home & pulled the bullets to double check load weight. All was as expected but the results spoke for themselves.

Never have figured that one out but I'm sure glad I didn't just pick the load one grain below max and trust them to be safe.

I have been reloading for forty years now and I still go back & re-read the instructions printed in every one of my loading manuals from time to time.(Alzhiemers kicking in I guess!)