Variations in Muzzle Velocity Blaser 308 Load development.

[LesC]

Following on from my previous post on a Blaser R8 load using Lapau 308 cases, Nosler 150Gr BT with N140.

I loaded 10 x 3 bullets starting at 44.7Gr in 0.2 Gr increments upto 46.5Gr, all rounds 2.8000OAL

Results were very mixed nothing more than 1.5" groups but MV was a bit wider in some loads than others.

Max fps spread I saw was 37fps (Avg 2780fps) using 46.5 Gr

Least was 6fps (Avg 2742fps) using 45.3 gr.

Fortunately the 45.3Gr was less than 1" group so will load some more and also try 45.4 to see if I can get around the 2750fps mark.

Question is could variations in the brass be the issue? I have used it all before some maybe 3 times, I do have a new box of lapau cases which I will try for my next test, will the new cases give me a diffirent result to the previooulsy fired cases?

For info the lowest across all 10 steps was 2708fps @44.7Gr max was 2817fps @ 46.5Gr not a huge variation.

 

[Stalker62]

Least was 6fps (Avg 2742fps) using 45.3 gr.

If you are getting an ES of 6 - call it good and give yourself a...

 

[LesC]

Probably a fluke..

 

[andyk]

Not wishing to be the bringer of bad news but 3 shots is not enough to test ES or SD.

It may be that 6fps ES is a really good load, but you could just be lucky.

The following are 10 shots using factory ammo in my 6.5CM:

3005
3011
3015
3018
3019
3020
3023
3031
3034
3039

That’s an ES of 34fps and SD of 11fps.

If I’d picked 3 cartridges, at random, I could have got an ES as low as 4fps or as high as 34fps.

I’m not saying that even 10 shots is great to really find the quality of a load, just trying to illustrate why 3 isn’t.

 

[LesC]

Not wishing to be the bringer of bad news but 3 shots is not enough to test ES or SD.

It may be that 6fps ES is a really good load, but you could just be lucky.

The following are 10 shots using factory ammo in my 6.5CM:

3005
3011
3015
3018
3019
3020
3023
3031
3034
3039

That’s an ES of 34fps and SD of 11fps.

If I’d picked 3 cartridges, at random, I could have got an ES as low as 4fps or as high as 34fps.

I’m not saying that even 10 shots is great to really find the quality of a load, just trying to illustrate why 3 isn’t.

Yeah thats understood, I'm not suggesting that I am selecting a load from this first test, I just want to understand what the thoughts are on what factors cause ES to vary, particularly around potentialy mixed re-use pre-fired cases, I will load more rounds from two or three of best in the 3 round test focused on grouping primarily and ES which I think go hand in hand.

 

[NullMac]

Results were very mixed nothing more than 1.5" groups but MV was a bit wider in some loads than others.

If you are trying to do a ladder test then that's what you are looking for. Sort of

Max fps spread I saw was 37fps (Avg 2780fps) using 46.5 Gr

Least was 6fps (Avg 2742fps) using 45.3 gr.

Fortunately the 45.3Gr was less than 1" group so will load some more and also try 45.4 to see if I can get around the 2750fps mark.

So your test would suggest that the 43.5gr is where you could focus. Maybe

Question is could variations in the brass be the issue?

That isn't the issue here. It will never produce variations of this size

I have used it all before some maybe 3 times, I do have a new box of lapau cases which I will try for my next test, will the new cases give me a diffirent result to the previooulsy fired cases?

Possibly. Any effects will be much smaller than what you are seeing. So don't worry about it. I have used mixed headstamped brass and they can deliver 3/4" no bother.

A few thoughts. Although it can only be speculation.

I don't know your barrel length but 2742 fps with a 150gr bullet is slow for 308. You should expect to be around 2850 fps. 150gr, N140, 2850 fps is a classic loading for 308.

Your group sizes are not purely a result of the load. 1.5" (at 100 yards ??) is really poor for a hand loaded 308 in any rifle never mind a Baser. It suggests that your test shooting still has some positional errors in it? I would be looking to build a position with supports to such an extent that the shooter has no input.

In all the years of loading 308 from 110gr to 208gr the test loads generally gave 1/2+ to ~3/4 moa just dumping powder and seating the bullet. No fancy case prep or seating depth fiddling or anything. Just be anal about an accurate powder load and using good dies to make it easy to make straight bullets. Make sure the neck is chamfered, that can have a remarkable effect if not done.

I would be looking to separate three things.
1. The shooting - get the shooter out of it as much as poss.
2. Combustion - make sure the powder loads thrown are very accurate.
3. Seating - ensure the bullets are seated straight and therefore the rounds have minimum run out. I solved this buy using decent dies rather than standard lee seating die (in particular). Having proved to myself that rounds with higher run out have wider groups.

As noted above however we don't really shoot enough rounds to be positive about the numbers we measure. So your ES of 6fps may well be invalid and you were just lucky that those 3 aligned. Or it may be THE load.

What you can be sure of though is that you ES of 37 will never get less the more rounds you fire. Same as your group will never get smaller than the first two shots. So you don't have to shoot heaps to zoom in on loads that may be of interest, but you do have to go back and shoot more rounds on particular loads to be sure that it wasn't a fluke. ES and group size though are the result of two different variables - the first is combustion the second (classically) is seating depth (in my experience only if they are seated properly in the first place)

Your Blaser will be capable of much smaller groups than that.