.440 PRB Consistently 1" low at 50 yards

[Hierophant]

I'm shooting a .45 caliber, .440 PRB with .015 patches and 70 grains of FFFg from a solid rest. Group size is consistent 2"-2 1/2" (good for my eyes and the open sights I think) so I'm relatively happy with that.

The problem is that the shots are consistently 1" low at 50 yards, and so would be even lower at 75-80 yards I'm thinking. I'm feeling like I may need to file down the front sight, but that makes me nervous. Would changing up ball size/patch thickness be likely to make a difference in point of impact, or just group size?

If I do have to file the front sight, what's the right/safest way to do that. Aside from slowly and carefully...

 

[Maven]

I think I'd experiment with ball diameter and/or patch thickness before filing the front sight. If you change the patch thickness, try .020" and .022" material (denim) with the .440" RB/powder charge you're now using. If that doesn't work, try a .445" RB and .015", .018" and possibly .020" patching again with 70grs. FFFg. If none of these work, you'll have to file the front sight.

 

[hanshi]

First you want to make sure you've found your accuracy load before you do anything else. After that you can start to gradually file down the front sight to raise the poi. I like my poi to be 1" to 2" high at 50 yards which puts the ball maybe 2" to 4" low at 100. That's a point blank sighting to a little over 100 yards. You powder charge and prb also figure into equation as well. I use a .440" ball and a .024" patch lubed with Hoppes or - as the first load in the woods, Natural Lube 1000 - to get between 1700 and 1800 fps.

 

[nchawkeye]

What is your load and what is it's purpose??

Once I find my load, I adjust the sights...Usually about 2 inches high at 50 yards for a deer rifle and dead on at 25 for my small game rifle...

 

[ohio ramrod]

For off hand shooting I have found that the tighter the patch and ball combination the higher the impact due to "recoil lift". But you want to get your minimum group size before adjusting the sights. Remember it is much easier to remove metal than to put it on! :idunno:

 

[rafterob]

Is 50 yards the point you are sighting in at? If so, after honing in on your load/patch/ball combo file the sight if necessary. 70 grains is a pretty hot load for a .45 so that is more than likely about the highest POI for your rifle. I would try a .445 ball and see what happens. I like to file with a slight downward angle towards the front of the barrel to give a sharper sight image. File just a tad at a time, it's easier to take it off than to put it back on.

 

[Rifleman1776]

You are on the right track, being cautious.
We need more information to really help.
What is the gun? What is you intended primary use? e.g. target or hunting? 70 gr., while not excessively hot for a .45 is a good hunting charge. And more than is needed for punching holes in paper. For serious target work I prefer a really tight ball/patch combo. I'll sometimes use an oversize (.457") ball and denim patching for competition. Same barrel for hunting it might be a .440" ball and ticking. To find yer sweet spot, try .445 and both ticking and denim, or similar cloths. It takes time. Good luck.

 

[Vaino]

Sounds like a load for deer and if it is, I'd switch to 3f and drop the powder charge to 70 grs. That's what my .45 likes. Do this before filing the sight or try some different loads as was previously said.

Irrespective of what load you decde on, when filing a front sight, I tape thin cardboard fore and aft of the sight and usually do this at the range preventing excess removal. Use a mill ******* file for smoother cutting and when the POI is achieved, lightly use some 320 grit paper around the file....Good luck.....Fred

 

[biliff]

To get some idea of how little you actually have to file you can use this formula:

D1 / R1 = D2 / R2

For front sight adjustments:
D1 is the distance between point of aim and point of impact.
R1 is range from rear sight to target.
D2 is the length the front sight must change by.
R2 is the sight radius distance between front and rear sights.

In your case, assuming your sight radius is 30" and your front sight is at 0 yds:

D1= 1"
R1=( 50yds X 36"/yd) + 30"= 1830"
R2 = 30"

Solve for D2 and you have to remove .0164" from the front sight to zero at 50 yds.

Not much.

Note: winter storm is rolling in and I'm a bit bored.

 

[Billnpatti]

Bakeoven is exactly right but let me help just a tiny bit to make the equation a little bit simpler. Using his designations, the formula is:

D2 =(D1 X R2) /R1

 

[Ron_T.]

I dunno if it's true or not since I've never checked it out with my chronograph, but I've heard that using a thin vegetable fiber over-powder wad increases muzzle velocity due to giving a better "seal" of the powder gases. A greater muzzle velocity with the same powder load should make your round ball "print" higher at any range than it would without the wad.

I've been told the velocity increase is up to 125-150 fps which might cause your rifle ball to print an inch or so higher than it does now, but this is just a thought you might try.

I'd be really careful about filing down the front sight until you're absolutely sure your load gives excellent accuracy since 70 grains of Swiss FFFg with a .490-inch ball using a 15/1000" patch mostly shoots through both sides of a deer fired from my .50 caliber Hawken. I doubt that it's too "hot" for your .45 caliber rifle, but it's not a "light" load either.

I get my vegetable fiber wads from a fella in Moore, Oklahoma... John Walters is his name and his phone number is (405) 799-0376. His email addy is: [email protected] so you might give him a call and see what he sez. He's easy to deal with and sends you the wads plus an invoice... a very trusting guy.

Make good smoke... :v


Strength & Honor...

Ron T.

 

[Wes/Tex]

Think our two Bills need the T-shirt, "Another day with no plans to use calculus" :rotf: :thumbsup:

To Ron: I'm not sure I'd accept the "sealing bore" theory at face-value. Years ago, when I worked at NASA and we had access to some pretty neat equipment between contracts & missions, we spent an entire weekend using a really 'high speed' camera to check the theory out. Too many years have gone by to recall the exact shutter speed, but we didn't find a single load that showed the patched ball ahead of the smoke from the powder ignition. This included loads with such tight PRB to bore fit they almost required a 16 pound sledge to get down on the powder...and we made sure they were down against the powder! I'll admit it's not in the 'scientific' category, but I've never really believed the theory of sealing the bore is really possible since then. Yes, patching helps seal and provides the ball's grip to the rifling but it doesn't appear anything can completely seal against those kind of pressures.

 

[hanshi]

I've chronographed loads in my rifles with wads and without. OP wads do seen to lower the standard deviation (sd) but the velocity increases were insignificant being in the 15-20fps range.

 

[Hierophant]

Wow, lots of good info and lots of things to try out. I bought some .445 balls and .018 and .020 lubed patches today, and so will try the different combinations of balls/patches as suggested and see how it goes.

Some wanted to know more about the rifle. It's an early Pennsylvania style long rifle, custom build. The barrel is inscribed B Turner and that is the only marking on it (I bought it used). Barrel is 38", I'm not sure what type of lock, but it sparks very nicely.

I intend to use it mostly as hunting rifle, I don't see any formal competition shooting in my near future. Ideally I'd like to have 2 loads for it, a 40-50 grain load for small game and range plinking and a 60-70 grain load for deer. If it can only be one, then the deer load has to be the one.

I was surprised that some consider the 70 grain charge to be a little hot for a .45 and that there doesn't seem to be a hard and fast rule. Some say 60 grains is enough, others that you can go as high as 90. 70 grains seems to be the consensus for a "hunting load" for a .45 though so that's what I went with.

 

[Hierophant]

To get some idea of how little you actually have to file you can use this formula:

D1 / R1 = D2 / R2

For front sight adjustments:
D1 is the distance between point of aim and point of impact.
R1 is range from rear sight to target.
D2 is the length the front sight must change by.
R2 is the sight radius distance between front and rear sights.

In your case, assuming your sight radius is 30" and your front sight is at 0 yds:

D1= 1"
R1=( 50yds X 36"/yd) + 30"= 1830"
R2 = 30"

Solve for D2 and you have to remove .0164" from the front sight to zero at 50 yds.

Not much.

Note: winter storm is rolling in and I'm a bit bored.

I'm not in this for the math! :rotf:

However, that's great info and was going to be my next question...if I do have to file, then how much.

 

[Rifleman1776]

we didn't find a single load that showed the patched ball ahead of the smoke from the powder ignition. This included loads with such tight PRB to bore fit they almost required a 16 pound sledge to get down on the powder...and we made sure they were down against the powder! I'll admit it's not in the 'scientific' category, but I've never really believed the theory of sealing the bore is really possible since then. Yes, patching helps seal and provides the ball's grip to the rifling but it doesn't appear anything can completely seal against those kind of pressures.

That is indeed interesting. I never would have believed such a statement correct. But since you went to such great lengths to waste gub'mnt time and money, I know it has to be correct. I'm still very surprised at your findings.

 

[hanshi]

70 grains of 3F is the load (deer) for my .45 flintlock. It gives me around 1800fps. I do think 60 grains is a perfectly fine deer load and just use 70grns because it shoots so well. My percussion .45 is perfectly fine with 60grns.

 

[Wes/Tex]

That is indeed interesting. I never would have believed such a statement correct. But since you went to such great lengths to waste gub'mnt time and money, I know it has to be correct. I'm still very surprised at your findings.

No more surprised than we were! I, personally, couldn't image it was possible but we tried every kind of ball size and patch material you could think of. It became sort of a challenge to beat the camera at it's own game.

I ought to note that we paid for the film since we didn't consider it kosher to use NASA film to play with. Kind of an expensive weekend but no end of fun and frustration!

 

[biliff]

Some wanted to know more about the rifle. It's an early Pennsylvania style long rifle, custom build. The barrel is inscribed B Turner and that is the only marking on it (I bought it used).

Interesting, My squirrel rifle was built by a B ~ Turner out of Mississippi.

 

[Rifleman1776]

That is indeed interesting. I never would have believed such a statement correct. But since you went to such great lengths to waste gub'mnt time and money, I know it has to be correct. I'm still very surprised at your findings.

No more surprised than we were! I, personally, couldn't image it was possible but we tried every kind of ball size and patch material you could think of. It became sort of a challenge to beat the camera at it's own game.

I ought to note that we paid for the film since we didn't consider it kosher to use NASA film to play with. Kind of an expensive weekend but no end of fun and frustration!

I should have put a :wink: in there. Just joshing about the gum'mnt thing.
Another thought :hmm: Is it possible/likely you were seeing detrius or vapor being forced out ahead of the ball from the rapid compression and not powder and gasses from the ignition? Just a thought.