Velocity Increase From Clean to Dirty Barrel.

[markymark]

Many many thanks to you all for the input. Greatly appreciated.
I was trying to run the rifle with minimal published loads in an attempt to improve how the rifle shot, as I thought that the recoil on such a light rifle was affecting how I performed behind it.
On previous posts, I mentioned that I was trying everything possible to get the bugger to shoot, recoil being one area to be addressed. With the lighter loads I did get an improvement in accuracy, but this may of been down to my better shooting technique.

I am back on it this morning. I put the rifle away without cleaning, so will see what it starts off with. The rifle is stored in an internal room, so should not be too cold, but the ammo is store in a separate area and considerably colder. Just for extra info.

The last shot of the day was a 123grn SST with 34grn of N140 that gave 2673fps. Will try a string of these today.

Will look at putting some faster rounds together, and see if I can tighten up the velocity.

Might look at purchasing a MagnetoSpeed V3, to help in my quest to get this bugger to shoot.

I’ll have a V3 for sale soon if interested.

 

[neil the plumber]

Lads, lads, lads, thank you all very much for the input. Once again you have come up with the goods.
I crunched some figures on my Quickload, and with the available powders, I opted for N150 starting at 39 grn, going up to 42grn ( which was still in the safe pressure band on the Quickload graph).
39 grn. 2785, 2775.
40 grn 2856, 2852, 2846.
41grn 2919.
The 41grn was hard to open the action and the primer looked a bit flat, so I left it at that.
So both the 39 or the 40 give very consistent velocity. These weights are very much over the ones stated on the Vit app.
I think I will go for the 40 grn.
Cheers Neil

 

[Mungo]

Lads, lads, lads, thank you all very much for the input. Once again you have come up with the goods.
I crunched some figures on my Quickload, and with the available powders, I opted for N150 starting at 39 grn, going up to 42grn ( which was still in the safe pressure band on the Quickload graph).
39 grn. 2785, 2775.
40 grn 2856, 2852, 2846.
41grn 2919.
The 41grn was hard to open the action and the primer looked a bit flat, so I left it at that.
So both the 39 or the 40 give very consistent velocity. These weights are very much over the ones stated on the Vit app.
I think I will go for the 40 grn.
Cheers Neil

What length barrel is it?

 

[HonestJohn]

I'd test over a different chrono to start with.

 

[neil the plumber]

18 INCH.

 

[Mungo]

18 INCH.

And you’re getting it that fast? Oh my.

 

[neil the plumber]

My Quickload gives speeds of 2664, but I had to input a similar but not exact bullet from their library.
What I might do is load a similar weight Hornady SST that is in my data base. To see if the speed is closer. Like many have said, I'm not too sure of my chronographs pedigree.

 

[Heym SR20]

Powder requires pressure to burn consistently. Put some powder on the ground, put a match to it and it splutters and burns inconsistently until it gets going.

Have low charges, again means inconsistency. With a clean barrel, presumably little friction to the bullet so the bullet moves quicker out of the chamber, but pressure doesn’t really build. And it’s probably a dirty burn.

Add some fouling, bullet has more resistance to overcome, meaning that pressures build more rapidly which will result in higher velocities and more complete burns. (Think how easily a patch goes down a clean compared to dirty barrel).

When developing a load its important to match powder, bullet and desired velocity.

Using data from either powder manufacturer or a good reliable source - Lee, Hornady etc the loads will have been worked up, tested and verified to work well. Yes you need to start at base load, but in any stalking rifle calibre your base starting velocity should be well above 2400 fps.

 

[trickie]

Powder requires pressure to burn consistently. Put some powder on the ground, put a match to it and it splutters and burns inconsistently until it gets going.

Have low charges, again means inconsistency. With a clean barrel, presumably little friction to the bullet so the bullet moves quicker out of the chamber, but pressure doesn’t really build. And it’s probably a dirty burn.

Add some fouling, bullet has more resistance to overcome, meaning that pressures build more rapidly which will result in higher velocities and more complete burns. (Think how easily a patch goes down a clean compared to dirty barrel).

When developing a load its important to match powder, bullet and desired velocity.

Using data from either powder manufacturer or a good reliable source - Lee, Hornady etc the loads will have been worked up, tested and verified to work well. Yes you need to start at base load, but in any stalking rifle calibre your base starting velocity should be well above 2400 fps.

Lots of great info in this thread, especially in @Heym SR20 post.

What’s not been mentioned (unless I missed it) is, with very light loads the powder doesn’t fill enough of the case for a consistent burn, on round may have most of the powder behind the primer, resulting in a better faster burn, the next round the powder may be spread evenly along the length of the round. You would then have a slower burn and significant variation in pressure performance and velocity.

 

[Kevgun]

I always aim for a powder that gives me at least a 90% case fill for the given bullet weight, with careful brass prep I can normally get the SD to single digits, not necessary for shooting Deer, but every little bit helps the confidence. as said N550 or N555 or even RS52 will do the Job, Although I have a great load for my Creedmoor using N160 and 139 Scenars, not a deer bullet, but the accuracy is great.