Does seating depth and crimping affect velocity?

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elmerdeer

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I have a few questions for you guys to answer,
1) Does seating the bullet .005 off the lands change velocity as opposed to seating .020 off the lands?
2)Does a light crimp make velocity slower as oppossed to no crimp?
3)I shot some reloads with my 7mm rem the other day, it was -15c or a 5f (cold) my loads were
RL22 66.5gr with 140 accubonds out of a 26" barrel,Sauer 202, my average speed with these loads was 2975fps.The Nosler book list that laod at 3240fps with a 24' tube, WHY THE BIG DIFFERENCE does the cold affect the velocity that much or is my barrel a bit slow? It is a new gun this was the 2nd time at the range with it.
Sorry for all the questions guys
Thanks
Elmer
 
1) - Likely little effect on velocity - I'd be careful about going so close to the lands.
2) Slower - crimp consumes energy
3) Temperature has an effect on velocity - likely the principal cause of your results. So do other variables such as bore dia, roughness, bullet dia material, etc
 
elmerdeer said:
I have a few questions for you guys to answer,
1) Does seating the bullet .005 off the lands change velocity as opposed to seating .020 off the lands?
2)Does a light crimp make velocity slower as oppossed to no crimp?
3)I shot some reloads with my 7mm rem the other day, it was -15c or a 5f (cold) my loads were
RL22 66.5gr with 140 accubonds out of a 26" barrel,Sauer 202, my average speed with these loads was 2975fps.The Nosler book list that laod at 3240fps with a 24' tube, WHY THE BIG DIFFERENCE does the cold affect the velocity that much or is my barrel a bit slow? It is a new gun this was the 2nd time at the range with it.
Sorry for all the questions guys
Thanks
Elmer
Click to expand...

1. Yes the velocity will change when adjusting the OAL, you are in effect creating freebore which lowers your pressure and speed.
2. Crimping will give you better consistency if your necks thicknesses are not all the same.
3. All rifles are different and the load may not achieve published velocities under the best of conditions but one thing is for shure cold weather shooting always lowers velocities, that's why you have to adjust your loads for the weather.
bigbull
 
I think the variation could be a result of the cold weather. I know that hot weather can result in unusually high pressures and colder weather the opposite.
 
elmerdeer said:
The Nosler book list that laod at 3240fps with a 24' tube, WHY THE BIG DIFFERENCE
Click to expand...

The Nosler data is a bit suspect in this case... Alliant lists a charge of 70.0 grains of RL22 to get the same velocity Nosler somehow attained with just 66.5 grains...

That doesn't mean Nosler are a bunch of horse-stealing liars--I've seen it suggested that overbore cartridges at 'smaller' bore sizes (7mm and smaller; the .264 Win Mag is infamous for this) are susceptible to wide pressure spikes and pressure variations, even with identical components, on different rifles. A tighter chamber could be all the difference. Of course, Nosler could also be a bunch of lawyer-kissing wieners. YMMV.

I'd suggest you try the Alliant data, and see what you get. If velocity still doesn't cooperate, try some other powders. RL19 is a crowd favorite at this bullet weight, and I bet IMR4350 and IMR4831 would do OK too.
 
Lefty #### said:
I doubt that you'd see much more than 50fps variation from +20 to -20 degrees.
Click to expand...

that depends on the powder. IMR 3031 and Olin 760 both lose almost 10% of velocity over that aprox. tempature range. 7MM magnums are usually a big disapointment to owners that have cronographs. Think of a 7mm magnum as a heavy loud .280!
 
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