Point of impact change with summer weather?

[tddeangelo]

Shot my rifle for the first time today since mid-February. I had been shooting 120gr 2f and it was hitting 2"-3" high at 50. Today it was 6". I worked the charged down to 95gr and got same 50 yard point of impact and groups were similar in size.

It was in the 30's last time I shot and today it was in the 80's. That's about the biggest variable. Didn't change lube, patching, or ball. Not even prime powder or flint was changed.

Just the heat?

[hanshi]

Heat and moisture can cause a stock to swell and put more pressure on certain parts of the barrel.  This can have the effect of a slight bending of the barrel.  It can also mess with the barrel vibration process.  Screws can loosen as the stock swells.

[rhbrink]

Black powder is temperature sensitive but that does seem like a lot of vertical. Add in the stuff hanshi mentioned and YEP it can happen!

RB

[LRB]

  The most common cause, in my experience, is un-slotted barrel lugs. Especially when the changes are vertical. If the lugs are not slotted for the pins to be able to move, swelling or shrinking of the stock pressures the barrel. The lug mortices should also have fore and aft room to allow the stock to move a little.

[smylee grouch]

Would there be any chance that you were wearing a heavey coat back then and the gun is recoiling different now thus causing some point of impact differences?

[tddeangelo]

  The most common cause, in my experience, is un-slotted barrel lugs. Especially when the changes are vertical. If the lugs are not slotted for the pins to be able to move, swelling or shrinking of the stock pressures the barrel. The lug mortices should also have fore and aft room to allow the stock to move a little.

The lugs are slotted.

smylee, you may be on to something there, as I've not shot it in summer weight clothes till yesterday. I was shooting off a bench rest though, so I'd hoped that would mitigate such things a bit.

Once I found the charge to get back on the mark, I was shooting offhand and keeping them on a 6" dot at 50 as I did in the past. Seemed like it just wanted the lighter charge.

Guess I'll just have to keep shooting and see what it does.

[bob in the woods]

What lube are you using ?   Some are "thinner" in the summer, which means that they are more "slick" which can cause a shift in POI

[Daryl]

If the gun (forend) is sitting on a sand bag, or (heaven forbid) a block of wood and allowed to bounce on the rest when it's fired, the elevation most certainly can be different than when hand held. 
Even a good sand bag will or can cause elevation changes if the forend is rested there - and changes if rested in different locations on the forend.

When I shoot from a rest and am concerned over the 'precision' of the shot (exact shot placement) I hold the forend as if I am offhand shooting, and rest the back of my had on the bag or rest. that way, the ball impact is exactly the same as when I am shooting offhand.

How you see and hold the sights in different lighting conditions also can play a part in ball impact location.  Of course different clothing can also effect ball impact, just as different loads, powder, patches and ball diameter can effect the shot. 'consistency, though art a jewel'.

[tddeangelo]

I was using Hoppes for lube. I had the rifle rested on a tripod rest with a bag on top. I usually have it placed with the rest about right under the rear sight. The range I use doesn't have deep enough benches to rest the muzzle.

I'm thinking it may be recoil/clothing related. I have to mind my form in winter clothes offhand or it shoots about the same amount high at 50 when I shoot offhand, but I didn't have that issue off the bench. I guess it makes sense, though, that without the thicker winter clothes to soak up some recoil it would react more to the recoil just off my shoulder without any "padding".

I'll have to take another crack at it soon and see what I come up with.

On a side note, a guy I know through work was also at the range. I do IT work and he works for one of the contractors I hire for work beyond my internal staff's capacity. Anyway, he'd brought hard drives slated for destruction and was using his AR15 to do that job. He asked me to shoot one with the flintlock as he was curious if it would go through it. I chuckled and said, "without any problem, but if you want to see it for yourself, go ahead and put one out there."

He hung a drive on the 50-yard mark. Drives are roughly 6" tall by 3-4" wide. I caught it about an inch from the top (remember things were hitting higher than I was accustomed). That drive was sure destroyed! My rifle is a 62-cal, and I'm running a 600 ball and 120gr 2F. It made about a 1" clean hole and blew a bunch of shrapnel out the back (we picked it all up).  He had a new found respect for a flintlock and round ball.

[hanshi]

Back when I use to shoot a lot of smokeless centerfire, I'd rest the forearm on a sand bag and rest the toe of the rifle butt on one.  I'd change elevation by squeezing the rear bag but did have the butt firmly against my shoulder with my opposite arm wrapped around with my left hand on my right shoulder.  Shooting that way let me shoot 100 yard groups and easily tell which load was a 7/8" load or a 1/2" load, or smaller.  That simply does not work with a muzzleloader (for me) and gives me shotgun patterns rather than groups.  My best ML shooting comes by resting the way Daryl described.

[Natureboy]

  Warm weather also affects air density.  Just like in baseball, the ball travels farther and higher when the air is warm.

[Daryl]

Changing lubes can easily make elevation AND windage changes.

[tddeangelo]

No change in lube.

I thought about all the ideas in this thread and realized something that DID change.

I forgot my rear sandbag and there weren't any in the bin at the range as usual. So I had no rear bag. I used my left hand under the toe instead.

Normally I hold the rifle as Daryl described.

Bet that's the culprit.

I'll shoot again and report back. It's a hard chore, but I'll take it on.

[bob in the woods]

Here's another "variable" that I forgot to take into account myself. Just this past weekend I shot in a match [ primitive ]
and decided I'd take my .54 flint rifle to the rendezvous, rather than my .40
I had cast these balls [ .54 ] last year.  They were a little more resistant to loading, and shot a tad different than my range notes indicated.  When I got home I miked them, and they had "grown" I'm not sure how that's possible; but they did.
They also seemed harder than I remember, so probably not pure lead.  I still have lots of stuff I cast up years ago, so will have to be more careful what I pack next time.

[Pete G.]

A tighter fitting ball MAY contribute to better powder combustion, contributing to slightly higher pressure and a higher impact. All conjecture of course, but if you have access to a chronograph it might be interesting to find out.

[Osprey]

One factor may be like what I have around here.  During the summer my guns always shoot high - from deflection off all the mosquitoes between me and the target!   

[Daryl]

Must bee shooting a big bore, Osprey - or the balls would be shooting low due to the drag on penetrating all those bugs, unless of course, they are ground hovering mosquitoes.