Thread: 7saum same load different speeds

Originally Posted by kiwijames

Seating depth may be a factor to consider.

That’s a good point when I started using rl26 in my Saum seating depth made a quite a difference.

Ive been following this with interest as we have been loading the rounds for JMJWs rifle using my press, dies and chronograph.

Powder batch variation: We tested this by loading up some rounds using a batch of reloader 26 that I had been using in my 21 inch SAUM at 2940fps. This powder achieved a similar speed as the original batch in JMJWs rifle both roughly 2810fps so doesn't seem to be the powder.

Chronograph: This has been reliable for me in the past, last used in March. I was given a load for my own personal SAUM with the rifle and I chronied it to within 5fps of the old owner so I don't think the chrony is out. (Will double check on my rifle though)

Neck Tension: I did wonder if neck tension could vary based on dies? It would be interesting to load some using a differnt set of dies.

Seating depth: How much tolerance do others accept when seating projectiles? If aiming for 2.240 base to ogive would you accept cases that end up 2.238 and 2.242? This seems to be about the variance I get with my seating die and assumed this was due to variation between projectiles?

Cheers

Originally Posted by Nick.m

Ive been following this with interest as we have been loading the rounds for JMJWs rifle using my press, dies and chronograph.

Powder batch variation: We tested this by loading up some rounds using a batch of reloader 26 that I had been using in my 21 inch SAUM at 2940fps. This powder achieved a similar speed as the original batch in JMJWs rifle both roughly 2810fps so doesn't seem to be the powder.

Chronograph: This has been reliable for me in the past, last used in March. I was given a load for my own personal SAUM with the rifle and I chronied it to within 5fps of the old owner so I don't think the chrony is out. (Will double check on my rifle though)

Neck Tension: I did wonder if neck tension could vary based on dies? It would be interesting to load some using a differnt set of dies.

Seating depth: How much tolerance do others accept when seating projectiles? If aiming for 2.940 base to ogive would you accept cases that end up 2.938 and 2.942? This seems to be about the variance I get with my seating die and assumed this was due to variation between projectiles?

Cheers

You’ll easily see that variation most of the time due to brass/bullet discrepancies and also even just putting a little extra pressure on press handle at bottom of stroke will give you more depth vs just gently touching at bottom of stroke.

Minor seating depth changes don’t do jack shit.

Have you got virgin brass to try? Theirs no gst added to the speed of that load for a sale I shot the same load in my rifle and 1 other all between 2880-2920 rifle depended checking scales would be a good one my digital run .5 grain difference to my beams

Before you do anything check ACTUAL drop at distance to determine ACTUAL velocity.

Likely you will only need to adjust drop chart, or not.

You will have to do this before you shoot animals anyway, the sooner you do it the better

Originally Posted by 7mmsaum

Before you do anything check ACTUAL drop at distance to determine ACTUAL velocity.

Likely you will only need to adjust drop chart, or not.

You will have to do this before you shoot animals anyway, the sooner you do it the better

Yep that’s the plan hopefully this weekend. The load going 2810fps seems to shoot very well so will just stick with that for now and can always try some different loads later on.

Originally Posted by Kelton

Have you got virgin brass to try? Theirs no gst added to the speed of that load for a sale I shot the same load in my rifle and 1 other all between 2880-2920 rifle depended checking scales would be a good one my digital run .5 grain difference to my beams

All the rounds fired so far has been new brass

Originally Posted by McNotty

You’ll easily see that variation most of the time due to brass/bullet discrepancies and also even just putting a little extra pressure on press handle at bottom of stroke will give you more depth vs just gently touching at bottom of stroke.

Minor seating depth changes don’t do jack shit.

Agree

I found seating out further by 0.130” made a significant difference in velocity in my rifle.

It'll be slower because of throat wear, virgin brass (usually 10-30fps slower than 1x fired), I'm guessing you gave it a solid clean when you got it + barrel wear equals reduced velocities, powder lot variation, projectile lot variation, primer lot variation, possibly scale measurement variation, brass lot internal water capacity variation. So easy to see why you have reduced velocity vs original load.
All barrels slow down with use. Just ask any target shooter than wears out barrels. Usually it wont drop velocity until you give it a really good clean and then it wont get it's velocity back until you add more powder.
My 6.5prc has 1000 rounds down the tube now and has slowed down after each serious clean, which required increases in powder charge to mostly regain. It requires more powder in a now slightly looser tolerance barrel to reach the same pressure to get the same velocity again.
Also do load development with fired brass to find max load and velocities as virgin brass is softer and loses energy to expand into the chamber for the first firing.

Originally Posted by McNotty

You’ll easily see that variation most of the time due to brass/bullet discrepancies and also even just putting a little extra pressure on press handle at bottom of stroke will give you more depth vs just gently touching at bottom of stroke.

Minor seating depth changes don’t do jack shit.

Agree

I found seating out further by 0.130” made a significant difference in velocity in my rifle.

I seat mine in mm... so if 59.06mm, il seat to 59.05 or 59.07 prob way overkill, but i do it that way. also neck tension would make a difference, especially between dies, neck bushing die ? what are the 2x dies and are both sets used in his rifle and ours the same brass ?

Originally Posted by Roarless20

It'll be slower because of throat wear, virgin brass (usually 10-30fps slower than 1x fired), I'm guessing you gave it a solid clean when you got it + barrel wear equals reduced velocities, powder lot variation, projectile lot variation, primer lot variation, possibly scale measurement variation, brass lot internal water capacity variation. So easy to see why you have reduced velocity vs original load.
All barrels slow down with use. Just ask any target shooter than wears out barrels. Usually it wont drop velocity until you give it a really good clean and then it wont get it's velocity back until you add more powder.
My 6.5prc has 1000 rounds down the tube now and has slowed down after each serious clean, which required increases in powder charge to mostly regain. It requires more powder in a now slightly looser tolerance barrel to reach the same pressure to get the same velocity again.
Also do load development with fired brass to find max load and velocities as virgin brass is softer and loses energy to expand into the chamber for the first firing.

I alsways gatheres as when you give it a really good clean and remove copper etc. it slows down as its "lubrication" eg. the copper coating has gone and needs to reform again ?

My records indicate that between 0.010" jump and 0.130" jump in my 6mmGT there is only 14fps difference in mean velocity (10rd samples at each). I doubt that a small discrepancy in seating depth is causing the difference in velocity.


If you have obtained the velocity by measuring with a Garmin chrono, you've done the best you can to obtain an accurate measurement. It is correct. Obtaining velocities by shooting for drops is fraught, the system has so many other potential error sources. Chronos just work these days.


Cleaning back a barrel that has been through the initial speedup will cause a drop in velocity that will never come back without increasing powder charge. This may be the primary cause, along with some stacking tolerances of other minor differences. 90 fps is a large drop though.


I have recorded 100+ fps velocity difference with old or humid powder cf new powder of the same type.