Help me diagnose these grouping issues

[JimGnitecki]

Ok, so I finally have a good 500g 45-70 bullet mold that can produce way better 5-shot groups than the 2 earlier molds I tried! I am shooting groups at 150 meters = 164 yards, where 1 MOA = 1.72 inches, and my better groups are that small or smaller, which is good when shooting a home-cast 500g wheelweight bullet out of a Pedseroli Sharps replica, at a muzzle velocity of almost 1400 fps and no leading thanks to powder coating.

But, although some groups are great, like this one (which is in fact 1 MOA at this distance):



A number of others look like this:




or like this:



There are 3 possible causes:
- Shooter error (in sighting or hold or position)
- Load quality issue
- Cast bullet quality issue

I can see already that shooter error is an obvious contributor, since the POSITION of the groups is not consistent relative to the bullseye. So, I know I need to work on consistency of my sighting, my hold, or my position.

Notice that in all 3 of these targets, the 3 best of 5 shots are all within a group size of an inch or less (i.e. 0.58 MOA at this distance).

But in targets no. 4 and 5, 3 shots are very close together, but 2 are WAY outside of those 3.

Notice also that in Target 4, the 2 wayward shots have mostly HORIZONTAL error, while in Target 5, the 2 wayward shots have mostly VERTICAL error. Does that provide any clues as to what is going wrong with those shots?

I have not yet had time to analyze the Labradar results for this range session that was fired just this afternoon. But I plan to do that analysis later this evening, to see what SD and what ES I am getting with this batch of cartridges.

In the meantime, anyone out there experienced enough to provide some diagnostic advice?

Jim G

 

[badkarmamib]

You are obviously a better shooter than I, but one thing I (and apparently others, from my reading) often overlook, is consistent, LIGHT, cheek weld. When I tense up in anticipation of the recoil, I tend to mash my cheek harder into the comb, which changes the way the rifle recoils, while the bullet is still in the barrel. Not saying this is what is necessarily happening in your case, just what I tend to forget first when I haven't shot for a while.

 

[JimGnitecki]

You are obviously a better shooter than I, but one thing I (and apparently others, from my reading) often overlook, is consistent, LIGHT, cheek weld. When I tense up in anticipation of the recoil, I tend to mash my cheek harder into the comb, which changes the way the rifle recoils, while the bullet is still in the barrel. Not saying this is what is necessarily happening in your case, just what I tend to forget first when I haven't shot for a while.

That is a good observation. I try to be consistent, but know that I am still far from being sufficiently consistent. That COULD be one of the issues.

Jim G

 

[JimGnitecki]

I just partially analyzed the Labradar results. I do have a bullet quality issue I think, since:
SD on this batch was 11
ES was 53

This is notably worse than the first, more carefully selected bullets in the earlier test batch I made for the ladder test. Their statistics were:
SD = 8.7
ES = 20

I selected the bullets for that earlier batch very carefully out of over 160 bullets that I cast in my very first casting session with this new mold. For this 2nd batch, I drew from the remainder of the cast batch, and so the quality seems to have been lower. I'll remelt the remainder of the first cast batch and try to make my casting process more consistent. I can also add some more Tin to the wheelweight alloy I have been using, beyond the 1% that I added already. That should improve the casting consistency a bit.

Jim G

 

[troy fairweather]

Check and see if your bullets are bent, I had problems casting the lee 500, they were bending when dropped on a Towel and even when dropped into water.

 

[JimGnitecki]

The rate of velocity decay with this bullet is again rather interesting:



Looks like it will go subsonic (1120 fps at my geographic location) at about 265 yards.

Jim G

 

[Jim Watson]

Are you weighing the bullets?
A one grain spread is usual in BPCR.

 

[AJC1]

I just partially analyzed the Labradar results. I do have a bullet quality issue I think, since:
SD on this batch was 11
ES was 53

This is notably worse than the first, more carefully selected bullets in the earlier test batch I made for the ladder test. Their statistics were:
SD = 8.7
ES = 20

I selected the bullets for that earlier batch very carefully out of over 160 bullets that I cast in my very first casting session with this new mold. For this 2nd batch, I drew from the remainder of the cast batch, and so the quality seems to have been lower. I'll remelt the remainder of the first cast batch and try to make my casting process more consistent. I can also add some more Tin to the wheelweight alloy I have been using, beyond the 1% that I added already. That should improve the casting consistency a bit.

Jim G

Are you weight sorting? I separate bullets by weight for group shooting and disguard bullets out of weight range. The tuff part in our small batch casting that number moves every session. I pc each batch a different color to help keep them separate. The guys making monster batches of alloy are starting off better than us because it's the same metal every time, just mold temperature variations their after. It's fun, challenging and frustrating all at once

 

[JimGnitecki]

Check and see if your bullets are bent, I had problems casting the lee 500, they were bending when dropped on a Towel and even when dropped into water.

This too is a very good point. This is a TWO-cavity mold. In the first batch, I noticed a number of the bullets had tiny "chips" on the perimeter of the base and had to be remmelted of course. I correctly diagnosed that problem as being caused by the bullets hitting either the mold or each other when they dropped out of the mold. Holding the mold differently so that they could not hit either the mold halves or each other solved that problem.

I AM dropping them onto 6 layers of cotton washcloth, and not allowing later-cast bullets to land anywhere near previously cast bullets. But it is still perhaps possible that they are being deformed slightly on landing. I can try to let them cool a bit longer in the mold. Right now, I am giving them 5 seconds after pour to harden before I open the mold. Extending the time I keep the mold closed before opening it MAY affect their ability to drop out though. I'll have to try it and see.

Jim G

 

[JimGnitecki]

Are you weight sorting? I separate bullets by weight for group shooting and disguard bullets out of weight range. The tuff part in our small batch casting that number moves every session. I pc each batch a different color to help keep them separate. The guys making monster batches of alloy are starting off better than us because it's the same metal every time, just mold temperature variations their after. It's fun, challenging and frustrating all at once

Jim Watson and AJC1: The weight observation is a good one. I am finding that right now ny ES on weight is 0.9%, which is pretty much exactly the same ES I was getting on bullets I was buying before I started casting. But, it sounds like I need to tighten that ES. Do you tighten it by weight SORTING only, or can I also somehow improve the weight consistency by doing something different in casting? For example, would upping the percentage of Tin added to the wheelweight alloy, from 1% to 2% help with weight uniformity?

Jim G

 

[AJC1]

Jim Watson and AJC1: The weight observation is a good one. I am finding that right now ny ES on weight is 0.9%, which is pretty much exactly the same ES I was getting on bullets I was buying before I started casting. But, it sounds like I need to tighten that ES. Do you tighten it by weight SORTING only, or can I also somehow improve the weight consistency by doing something different in casting? For example, would upping the percentage of Tin added to the wheelweight alloy, from 1% to 2% help with weight uniformity?

Jim G

If I rember correctly as the mold warmed I got more weight and a little bigger bullets. Not enough to measure but I could feel a little more resistance in the sizer. Your rythem of casting comes into play. More material doesn't change that, but the volume in the pot does. I cast from full to half and stop. I'm not making Saturn 5 rockets like you though.

 

[troy fairweather]

Ya I had a few that looked like bananas, I was dropping in a coffee can full of water and now use a five gallon bucket. Even with the bucket they can bend when they hit the bottom. So now I slow way down usually pore another mold before I drop them and hold the mold close to the water, even then some bend. I size them that help to see if there bent when I roll them and check the tips of they wobble. Make sure your stem for the sizer is long enough to size one at a time.

 

[JimGnitecki]

Ya I had a few that looked like bananas, I was dropping in a coffee can full of water and now use a five gallon bucket. Even with the bucket they can bend when they hit the bottom. So now I slow way down usually pore another mold before I drop them and hold the mold close to the water, even then some bend. I size them that help to see if there bent when I roll them and check the tips of they wobble. Make sure your stem for the sizer is long enough to size one at a time.

I just checked the length of the bearing surface in the Lee sizing insert I am using. It is about .976". The shank of the bullet is only about 0.731". So, the sizing surface IS almost 1/4" longer than the shank, so yes, it does each bullet one at a time. But thanks for drawing my attention to this.

Jim G

 

[eddiememphis]

How are you measuring your powder? How often do you clean the barrel? When do the fliers occur- always first, always last or random? Has the rifle shot tighter groups than this in the past?

 

[JimGnitecki]

How are you measuring your powder? How often do you clean the barrel? When do the fliers occur- always first, always last or random? Has the rifle shot tighter groups than this in the past?

I am using an RCBS Chargemaster Lite, with claimed accuracy of 0.1g. I leave it on for a coulle of hours before using it to let the elctronics get fully warm. Occasionally, it finishes dispensing to the 27.5g target, but then the digital reading changees slightly seconds later due to electronic scale drift. When that happens, I recycle that powder load into the hopper and have the machine drop a replacement load.

My available time slots for going to and from the range, setting up and tearing down, and doing the actual shooting, enable only 40 to 50 rounds fired each range session. Then, the barrel gets cleaned.

The flyers do not have a "pattern" as to when they occur. Random.

There is no meaningful past with this bullet. This is only the second time I have taken this bullet to the range. The first time DID produce some groups that were smaller, and there were more of them as a percentage of total groups fired during the session. That is probably because I selected the cats bullets carefully and from a larger available batch to choose from.

 

[JimGnitecki]

I analyzed the statistics further. I discovered that if I eliminated TWO shots from the Labradar - the absolute lowest velocity shot and the absolute highest velocity shot, the statistics improve notably to:

Stattistics after eliminating 1 hi and 1 lo:
Average	1371​
SD	8.8​
Hi	1387​
Lo	1353​
ES	34​

The absolute lowest velocity shot was the very first shot of the day, and many shooters say to always disregard that first shot.

The absolute highest velocity shot was the 21st shot fired today, and was 27 fps above the average, and 10 fps above the next fastest shot. I have no idea why that happened. I know that I checked the pwoder weight displayed on the digital display of the scaale/dispenser, for each and every shot, and NONE of them were off the 27.5g target at all. So, no idea what happened with that one shot.

Jim G

 

[troy fairweather]

What is your rest, with those long barrels it can be important to make sure where the forend is resting is the same each shot.

 

[Milt1]

My diagnosis is just from eyeballing the targets. Target # 3, I see no problem at all as you probably can't group them much better than that. Target # 4 is very similar to # 3 with the exception of a pulled shot in the lower left, shooter error. On target # 5 for some reason you're shooting most of them low. If you raised the three shots that are almost touching up into the black, it would be practically the same groupings as you have in # 3 and # 4. Again in # 5, there's another pulled shot at the bottom of the target, shooter error.

 

[JimGnitecki]

What is your rest, with those long barrels it can be important to make sure where the forend is resting is the same each shot.

Yes. For load testing (not regular shooting), I use a Rempel bipod with a small bag that has a "u" shaped channel, the right width for the Pedersoli barrel, fastened to the Rempel via Picatinny rail.



The bag is always positioned just behind the front "flair" of the wood Schnabel forend, which makes "indexing" the position of the small bag very easy. The Rempel is adjustable for height via a fine capstan wheel, and it is VERY wide - about 18 inches wide, and has metal fore-aft runners that rest on the concrete shooting station bench.

I adjust the Rempel height so that the crosshairs in the 6x Leatherwood Hi-Lux semi-authentic "buffalo rifle" telescopic sight are just a bit above the POA, and then raise the butt of the rifle just enough with my LEFT hand to place the crosshairs exactly on the POA.

I have a very low resting heart rate (very low 50s) which is good, but I can usually SEE the heart pulses in the crosshairs. I am trying to get more relaxed to eliminate that.

Jim G

 

[JimGnitecki]

My diagnosis is just from eyeballing the targets. Target # 3, I see no problem at all as you probably can't group them much better than that. Target # 4 is very similar to # 3 with the exception of a pulled shot in the lower left, shooter error. On target # 5 for some reason you're shooting most of them low. If you raised the three shots that are almost touching up into the black, it would be practically the same groupings as you have in # 3 and # 4. Again in # 5, there's another pulled shot at the bottom of the target, shooter error.

The way I see it, Targets 4 and 5 each have TWO bad shots outside the 3-shot cluster of good shots. I need to figure out exactly why and how those 2 shots are outside the tight 3-shot clusters.

I THINK the variance in the location of the 3-shot clusters is the result of a shooter hold or positioning error that I need to find the cause of.

Jim G

 

[ms6852]

What is the rifle twist on your rifle. If it is a slower than the 1:18 found on Pedersoli rifles like a 1:20 for example you could try dropping velocity down to about 1200 fps since it is a 500 grain bullet I think it will give you more consistent groups. Also agree with the suggestions recommended above.

 

[JimGnitecki]

What is the rifle twist on your rifle. If it is a slower than the 1:18 found on Pedersoli rifles like a 1:20 for example you could try dropping velocity down to about 1200 fps since it is a 500 grain bullet I think it will give you more consistent groups. Also agree with the suggestions recommended above.

The twist rate is 1:18. I also do not want to drop the velocity, as I am trying to keep the bullet supersonic to avoid transonic effects as long as possible on longer range shots. Also, I HAVE during ladder testing tried velocities encompassing about 1060 fps through 1400 fps, and the lower velocities did not improve accuracy with my specific rifle even at short ranges, let alone at longer ranges. The rifle seems to prefer higher velocities. In fact, the really low velocities tried gave pretty disappointing results. Unfortunately, this makes the recoil issues with a 500g bullet even more significant, but I am finding that if I hold the rifle properly, the shoulder bruising goes away.

Jim G

 

[JimGnitecki]

Hmm. I am wondering if the Schnabel forend might be an issue:



Note how the Schnabel (tapered and then flared) forend has 2 features that I now see MIGHT be problematic:

1. The "slope" of the underside of the forend will cause the rifle barrel to "fall" as the rifle moves rearward during recoil. The exact AMOUNT of fall will vary unless the rifle is placed in EXACTLY the same fore/aft position each time.

2. The "flare" at the very front of the Schnabel forend will cause a "an upward jump" in the rifle barrel IF the recoil movement is sufficiently large to reach the flair.

Looking at point 2 above more closely, I see that this IS a good possibility. Here's why: The Leatherwood Hi-Lux scope, with its EXTERNAL elevation and windage adjustments, is designed to mitigate the effects of heavy recoil by allowing the scope tube to "slide" within its front and rear mounts. As a result, during each shot, as the rifle moves rearward, the scope tube does not. It "stays in place" while the rifle and scope MOUNTS move rearward. So, after each shot, the front end of the scope tube is seen to be about 1.13" forward of where it was before the shot, relative to the muzzle. The shooter simply slides it back "into battery" in the mounts as part of preparing for the next shot.

But, this means that the rifle is indeed moving rearward about 1.18" when fired. So, if the small bag / rempel bipod assembly is located at LEAST 1.13" rearward of the flare, the small bag / rempel bipod assembly will not encounter the flare during recoil. BUT, if the assembly is located less than 1.13" from the flare, it WILL encounter the flare. As a result, the barrel would jump upward when it does so.

So, controlling the POSITIONING of the forend upon the rest assembly is much more critical than I assumed. I need to move the point of contact bewteen the rest assembly and the rifle forend far enough rearward to ENSURE that the forend flare is NOT encountered during recoil. AND, I have to ensure that I do not move the point of contact far enough rearward to get to the point where the TAPER in the forend changes slope and transitions into the FLAT underside of the forend!

In other words, posiitoning the rifle forward / rearward on the Schnabel forend has to be absolutely consistent! I need to put a piece of tape on the underside of the forend and consistently place the rest assembly to just touch it.

Since I have NOT been THAT closely controlling fore-aft positioning of the rifle on the rest assembly, that COULD explain some of the out-of-group shots on the targets.


Jim G

 

[Jim Watson]

Maybe things are different with nitro but BPCR shooters rest the barrel, not the foreend. It is usual to mark the barrel at the location most accurate or maybe by the talcum powder and mallet exercise.

 

[DustyRusty]

I am using an RCBS Chargemaster Lite, with claimed accuracy of 0.1g. I leave it on for a coulle of hours before using it to let the elctronics get fully warm. Occasionally, it finishes dispensing to the 27.5g target, but then the digital reading changees slightly seconds later due to electronic scale drift. When that happens, I recycle that powder load into the hopper and have the machine drop a replacement load.

I read your post with great interest. The only 2 cents I can pitch in are tips for the RCBS scale.

Warm up as you are doing, wipe down with a dryer sheet.
Check under the platen where the pressure measuring cell is and be sure there is no powder granule in there.
I block off the HVAC vent to stop any drafts.
I level the scale.
I check it against a beam scale for accuracy.
Blow out the measure before changing powders.
Explanations on request.
But you knew all that, right?