In need of some edjumication ;)

[Wagon Box Willy]

Howdy pards.

So I bought some PRS45's in. 454 to use in my '66 to try to reduce blowback.  I matched the boolit up against the JP200's I normally load and  looked close so I loaded them up with the same charge as the JP200's.

Went out in the back yard and shot at a 8" target from about 75' and first shot...missed. fired 4 more and nary a hit.  So I put the target on some foam board and tried again....hit, but it was a foot and a half to the right...4 more in about the same place.

Not knowing any better I chalked it up to bullet diameter.  Tried it again with some more reloads the next chance I got and the same thing. 
So after a match where Driftwood said "shouldn't do that" I decided to reload again but this time use DJ's dowel marking to set the amount of charge.  Well I dropped the load down to about 31gr and loaded 10.  Back to the backyard and all 10 hit just where they were supposed to.

So apparently it was the load, but why?  This is where I need a little education.  I assume I was over compressing the BP but why did it have that effect on the accuracy?

Thanks
  Willy

[wildman1]

Bullet weight, shape, twist rate, speed all will effect bullet flight, accuracy. WM

[Mossyrock]

You're not holding your mouth right...hold your tongue to the other side...seriously.   

[Wagon Box Willy]

You're not holding your mouth right...hold your tongue to the other side...seriously.   

Ahh, I thought that if you shot to the right you held your tongue to the right...I should have known my tongue was closer to the rear sight so of course I should've held it to the left   

[Wagon Box Willy]

Bullet weight, shape, twist, rate, speed all will effect bullet flight, accuracy. WM

thanks, I got that.  But I wouldn't have thunk that the increased pressure caused by the powder compression would have affected the accuracy like that.  OR, am I wrong in thinking that the compression increased bullet speed?
Willy

[Driftwood Johnson]

Howdy Willy

I shot some trap last night. I'm suffering from a cold right now, so I am sucking on a lot of throat lozenges. I found I was shooting better with the lozenge in my left cheek rather than the right. Go figure.

I can't really answer your question. By reducing the powder charge you clearly reduced the amount of compression and therefor also reduced the velocity. To tell you the truth, I do very little actual precision shooting with Black Powder. If I buy a new (or new to me) gun I usually take it to the range once and run my favorite loads through it to see where it prints. I have so many guns that I only put Black Powder through these days that I don't do any special load development for each one. I just shoot it once, see where it is printing, do any sight adjustment necessary, and leave it at that. I seldom shoot a rifle at more than 50 yards these days because my eyesight is so bad that I have a lot of trouble seeing the sights and the target any further out than that. Whatever group size I get is what I am gonna get.

I know I often talk about compressing the powder between 1/16" and 1/8". To tell you the truth, I suspect that my 44-40 and 45 Colt loads are probably a lot closer to the 1/16" end of things. That's probably mostly coincidence resulting from the particular Lee dipper I used when I first started creating my loads. Whether or not it makes much difference I really don't know because I don't do any side by side comparisons of different loads from the same gun.

I do know the BPCR guys do a lot of load development. Most of them will tweak their loads by changing all the parameters around. Bullet weight, card thickness, and amount of compression. Probably which side they keep their wad of gum in too. Most of those guys will eventually settle on what particular combination works best for a particular gun. It may be a lot of compression, it may not. Each gun is going to like a particular combination best, and exactly why is often a mystery. But for those guys, the adventure is tweaking the load until they get it just right. For me, its just blasting ten rounds as fast as I can and hearing the targets ring. And the targets are usually pretty close.

I will say that we were all very impressed with your loads, you had a whole lot of boom in them. Maybe more than some of the rest of us. Probably more compression leads to more boom.

[Mako]

thanks, I got that.  But I wouldn't have thunk that the increased pressure caused by the powder compression would have affected the accuracy like that.  OR, am I wrong in thinking that the compression increased bullet speed?
Willy

Willy,
Compression will increase the efficiency of burn rate of BP.  It burns faster which means more pressure and a faster pressure curve rate, so yes, it will increase the velocity.  What you need is consistent pressure which will render consistent velocity.

That is part of the equation, another part is being in the right frequency for that particular barrel.  Barrel harmonics play a role in the accuracy equation, but at the range and relatively crude accuracies we are talking about velocity will play the bigger role.

Crimp is probably as important or more important than the compression once you have any compression.  Are you using the same cases for your loads?  Have you checked your case lengths?  If they are different they will have totally different crimps.  Crimps play a major role in pressure building and the resulting velocities.

Regards,
Mako

[Wagon Box Willy]

Thanks for the replies.

Willy

[Blackpowder Burn]

If you are using a relatively soft bullet, perhaps the heavier load (more compression) requires enough force to compress the powder and seat the bullet that you are deforming the bullet nose and causing the shift in point of impact?

[fourfingersofdeath]

Perhaps the hotter load will help the boolit to obturiate better, promoting a good burn, sealing off bore nicely and develop decent, usable pressure (just a shot in the dark). I was using commercial bullets in 38cases in my 357 and getting pretty reasonable accuracy. I think I used 2.8Gns Bullseye, which was retrieved from my memory from many years previous. I ran out of ammo one Sunday morning at the range and Frank, my mate who is a bit of a power fiend, gave me some of his. I can't remember but they used the same bullet and primer, but a fair bit more powder. I was a bit sceptical, but didn't want to go home yet. They made a bit more noise and kicked a bit more, but were scary accurate and the POI was a tad lower. I thought about it afterwards and realised that the load I was using was initially for HBWCs and these were SWC commercial cast polymer coated hard lead bullets. Frank's loads were obturiating properly and mine were failing to do so it seems. Swallowed my pride and used Frank's load after that, 

[Wagon Box Willy]

The hotter load moved the POI so much at 75' that in order to bring it on target I had to move the front bead over to the right centered on the angle of the octagonal barrel transition....or about a quarter inch so in my mind that was not good and not a load I wanted to keep.  I wish I had a Chronograph to play with but I'm thinking I increased the speed beyond what the 20" barrel, rifling and bullet aerodynamics could handle and still be accurate.
Willy

[Springfield Slim]

The PRS is quite a bit longer than the J/P so you were compressing the load more than I would think reasonable. Might have been damageing the bases of the bullet also. They are also 50 grains heavier. So now you have a heavier bullet with a compressed load. I'm not surprised the POI changed. As far as accuracy, you said they all hit in the same place, which is what accuracy is. They just aren't regulated to where your sights are set with the heavier charge.