effect of shooting two different powders back-to-back

[Nature Boy]

I was shooting a Cortina ladder test with H4895 and 185 juggs. When done, I switched to a know load with varget. I saw a jump of 70-80 FPS off of what I had recorded for that load for the first 6-7 rounds, then it settled back down to where it was originally.

Rifle is a .308W with Bartlein 1:10 26"

What have you guys observed in similar situations?

 

[dragman]

I never shoot different powders or different bullets back to back without a complete cleaning first. The fouling is different and I have seen FPS, POI shifts and in general problems. Once it's seasoned with a load I don't change it or dabble with other stuff for the most part.

 

[Milo 2.0]

I'm a firm believer if you change powders or bullets, clean first.

 

[M-61]

When I used Varget (I no longer buy it after their great 'can not get anywhere' fiasco of a few years ago) I found it to be one of the dirtiest powders I ever used. Because of that alone I did not shoot anything else until I cleaned the barrel in which it was fired.. As it disappeared I found other powders that performed as well and did not leave a sewer pipe looking barrel. At that time it seemed to me all I read was that Varget was THE only powder to be accurate in many different cartridges.
Found that not to be so.

 

[CPorter]

In my testing, shooting different bullets, different coatings, or powders seem to produce results like what you experienced. Primers sometimes produce the effect and sometimes don't.

 

[Nature Boy]

Thanks. I've read similar experiences but this was the first time I saw a difference first hand

 

[centershot]

If I am going to change powders in a test, I always shoot one round with the new powder before shooting a group. It does make a difference. If you clean it, you have to shoot a fouler first anyway.

 

[chkunz]

When I do load development testing, I mix the test groups with a known pet load as a "control" so I have mixed groups with different bullets and powders during one testing session. I have never seen any effect from mixing bullets and powder. I have read a lot of reports that say it does but my data does not show it with the type of testing I am doing. A typical testing session for me would include two or three groups of the "control" load mixed with three or four groups of the test load. I normally shoot ten shot groups and am doing testing for the AR for XTC.

 

[mikecr]

For precision bolt action rifles, you need to expect that changes will cause change.

 

[chkunz]

For precision bolt action rifles, you need to expect that changes will cause change.

I do not disagree, I am just giving my experience with AR match rifles. I have also done some testing with "precision bolt action rifles" and use the same procedure of mixing a "control" with the test load and have not experienced any evidence that this causes change in the data. The level of accuracy I am working with is approximately X ring size groups or slightly smaller on the NRA XTC, mid range and long range targets (not F Class). If I were dealing with a higher level of accuracy it is probable that I would have to consider other factors to achieve a higher level. Again, I am not disagreeing with anyone, just giving my experience with mixing bullets and powder for my application.