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Help with Ransom Rest group?

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Dr.Don
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Post by jlow Wed Jun 26, 2019 8:41 pm

First time out today doing load development with my Ransom Rest.  Testing Zero 115gr JHP at 50 yards out of my tactical pistol.  Groups were not great but I would like some help deciphering their shape.

To back up a bit.  This is my RR setup and it is attached to this block of concrete – very stable and the horizontal clamps can put down a combine pressure of around 2,000 lbs.  This setup allows easy windage adjustment and quick clamp down.

I fired the first group (ignore numbers and this dummy put the target upside down…) top right 5-rounds with my regular ammo to get the rest to settle.  As suggested by a member, the sixth round was left in the chamber and I reloaded with 6 more rounds, first five test group, one extra regular that I shot slightly over the target before I shot for group.  So five charges were tested with the same bullet/primer/same headstamp brass.  Powder increment was 0.1 grain between groups.  Brass was all trimmed to uniform length and tapered crimp applied.

The odd thing I found was group 1 (top middle), and group 3 (bottom middle).  Not much lateral dispersion but a lot of vertical stringing.  Have people seen this and know what may have caused this?

FWIW, my elevation was locked down for all groups.
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Post by zanemoseley Wed Jun 26, 2019 9:01 pm

I would ditch the Destaco toggle clamps and put something more secure. The recoil may be slightly moving your base.

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Post by jlow Wed Jun 26, 2019 9:39 pm

I would not dismiss the clamps as being a source of the problem, but a couple of points: 

·       The 4 clamps each put down 500 lb of pressure making a total of 2,000 lb total down pressure.

·       The front of the board holding the RR has a screw that goes through it and attached to the bottom board (you can see the large screw in the photo), it serve as a pivot point to adjust windage.  That screw would also make movement difficult.

·       Assuming the board holding the RR moved laterally, how would that translate to a vertical stringing group?

Again, I do not dismiss this out of hand but based on the above, a bit hard to rationalize, but I do have a plan to test it.  

In the meantime, other ideas of why the groups happen would be helpful and appreciated.


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Post by jglenn21 Wed Jun 26, 2019 10:21 pm

A. fire at least 10 rds to settle the rest before you start real testing. sometimes more.. you should check the pistol for shifting

B. recheck Nuts A, B and C for being finger tight

C develop a rhythm and method for return the rest to the starting spot each time..( watch Steve Huff of accuracy Xs videos on his ransom testing)

if you are going to only test 5 rounds groups. load with 6 rds in the mag. fire the 1st round away from the target then shoot the five for your test.
Repeat this for each test.

doesn't hurt to monitor each shot through a scope so you know which round goes where in the group.


Last edited by jglenn21 on Wed Jun 26, 2019 10:24 pm; edited 1 time in total
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Post by zanemoseley Wed Jun 26, 2019 10:23 pm

Have you tried a 22 yet? Something you know should group well. Then if that's gives good results go to a larger bore pistol again.

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Post by gregbenner Wed Jun 26, 2019 10:26 pm

Presume U R careful not to touch the gun when resetting the RR? Pulling trigger?Perhaps raise gun all the way before lowering? Someone suggested to me to put a glass of water next to the RR. Watch what happens when you fire, let water settle if disturbed. 

 Have you tried some top notch factory ammo?

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Post by S148 Thu Jun 27, 2019 7:35 am

With respect to group shape - 5 shot groups won't tell you anything. 50-shot groups, maybe. 

Imagine you shoot a 100- shot group.  Now randomly select 5 shots from that 100-shot group.  Then randomly select another 5 shots, and so on.  Some of those 5-shot group will have a vertical pattern, some will have a horizontal pattern, and so on.

Patterns happen by chance.  If there is a tendency for stringing, it requires many, many shots in one group to determine if it is real, or just a chance event. 5 shots are meaningless.

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Post by BE Mike Thu Jun 27, 2019 8:28 am

As a former outdoor master who owned and used a Ransom Rest regularly in the past, I'd say, although it is somewhat hard to determine the size of the groups by the photo only, it looks like your groups aren't too bad for a "tactical" 9mm pistol. My testing was limited to accurized 1911's, accurized Beretta 92 FS and target .22 pistols. I always attached my wooden platform (raised like yours) to a steel plate that was mounted on the concrete base using steel C clamps. You appear to have extra layers. That may or may not make any difference. I did my testing at 50 yards and fired 10 shot groups, although I disagree that "5 shot groups won't tell you anything". They still give you a trend. It is a good idea to fire some "seating" shots before recording results, but I have actually fired 10 shots without seating and gotten very good groups. Heed the advice of not touching the pistol any more than necessary. Many RR users take off the lever that pulls the trigger and prefer to use their own trigger finger. When doing so, it is advisable to still use proper trigger control. Use the "tab" on the RR to put it back into position after each shot. Basically, I don't see any problem with your RR setup, but having extra screws and bolts adds the increased chance of something getting loose. There is a good chance that your "tactical" pistol will not lock up the same and that can cause vertical stringing. Unless your pistol is custom and came with an accuracy guarantee, you really have no basis for your expectations on how it will group. This may be about as good as it gets.
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Post by jlow Thu Jun 27, 2019 8:40 am

Jimmy G – yes at least my 5 round warming up group seems pretty round consistent with no flyers, but I will do some more testing to see if more is needed.  The nuts are tighten down until the mag does not drop down smoothly, then I back off one turn.  I use the lever and never touch the gun between each shot.  As mention in my post, I always fire off the first round off target that has been sitting in the hot chamber.  I am thinking of video taping the hits.

zanemoseley – have not tried my 22 yet but it will be done.


Gregbenner – yes I never touch the gun except to reload.  I do not think it is the gun vibrating has I have used a pic rail mounted accelerometer and there is no movement before I pull the trigger.

S148 – well you could be right but coming from precision rifle, I can tell you that it does not take a 50/100 round group to assess precision.  If it does, most of us would wear our barrels down in load development before we can shoot matches.

FWIW, it is not due to MV variation.  That first group for instance I measured MV with a labRadar and it had an extreme spread of 12 fps and a Sdev of 5 fps.  The other had 17 fps/7 fps for the same two values.

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Post by jlow Thu Jun 27, 2019 8:48 am

BE Mike – I agree with what you have said.  What you say about 5 shot groups is correct.  It gives you a trend that you should not take for granted but follow up on and confirm one way or the other.  Basically good loads will not give you a bad group, but bad loads may give you a good looking group.

One thing I intend to do is to shoot some high quality factory ammo to access the potential of the pistol.  Would appreciate any suggestion of brand - Atlanta Arms 115 gr JHP?

The two vertical group with low side dispersion is also interesting because they were the ones with lowest MV SDev.  At least in precision rifle, we commonly find the most precise groups most frequently (but not always) have the lowest MV SDev.

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Post by Dr.Don Thu Jun 27, 2019 8:53 am

+1 on trying a 22.  There are techniques you learn that work well on a RR, so starting out with a gun that is known to group well will help you figure out what works well and what does not with the RR.  Right now you have an unkown setup, an unknown gun, and little experience, so it's going to be difficult to clear away the smoke....
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Post by jlow Thu Jun 27, 2019 10:02 am

Good advice.

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Post by Wobbley Thu Jun 27, 2019 10:36 am

Try a 22 or Revolver in 38 Special to develop your RR technique.

That said, in these groups presented I’m not seeing significant vertical in all cases. You have 2 vertical, 3 horizontal, and one square. They are large compared to a Bullseye pistol. But this is (I presume stock) tactical pistol, probably with a polymer frame. With the exception of the two vertical groups, all of these loads are likely good enough.

I’d load fifty of the “best” load then shoot 3 15-round groups.
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Post by jlow Thu Jun 27, 2019 10:51 am

A precision 22 is a good idea but mine is not a precision 22 and of course I don't have a grip for it.

For now, I will get some Atlanta Arms ammo to evaluate the precision potential of the gun.

Another possibility is to pick one of the vertical groups with the tight SDiv and do load development by adjusting seating depth.


I also plan on evaluating the potential movement of the RR platform.

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Post by S148 Thu Jun 27, 2019 2:24 pm

What gun are you shooting?

Also, what size are those groups measuring the extreme spread? It would help to have some numbers to go with this.

And what is your load data?  Especially what powder and charge weight are you using?

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Post by Al Thu Jun 27, 2019 4:53 pm

jlow wrote:The two vertical group with low side dispersion is also interesting because they were the ones with lowest MV SDev.  At least in precision rifle, we commonly find the most precise groups most frequently (but not always) have the lowest MV SDev.

Precision rifle & bullseye are two entirely different animal.

PR we're shooting from a solid rest at ranges up to 1000 & beyond. BE we shoot with one hand @ 50 yds.


That being said, early on I extensively Ransom tested over my chronograph. I found some of my most accurate loads had the highest SD. I quit using the chronograph & went entirely on group. The paper doesn't care how much energy the bullet has when it goes through. However, long range shooting with my prairie dog rifles is a much bigger factor. Best accuracy with sufficient speed to reliably expand is extremely important.
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Post by S148 Thu Jun 27, 2019 5:05 pm

Al wrote:
jlow wrote:The two vertical group with low side dispersion is also interesting because they were the ones with lowest MV SDev.  At least in precision rifle, we commonly find the most precise groups most frequently (but not always) have the lowest MV SDev.

Precision rifle & bullseye are two entirely different animal.

PR we're shooting from a solid rest at ranges up to 1000 & beyond. BE we shoot with one hand @ 50 yds.


That being said, early on I extensively Ransom tested over my chronograph. I found some of my most accurate loads had the highest SD. I quit using the chronograph & went entirely on group. The paper doesn't care how much energy the bullet has when it goes through. However, long range shooting with my prairie dog rifles is a much bigger factor. Best accuracy with sufficient speed to reliably expand is extremely important.
Al

Just to add to this, an article at the link below found no correlation between velocity variation and group size in the typical handgun at 25 yards fired from a Ransom Rest.

https://americanhandgunner.com/handguns/exclusive-consistent-velocity-accuracy/

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Post by jlow Thu Jun 27, 2019 5:41 pm

Like I said in my post “but not always”.  However, even though I too have seen precise goups with not so good SDiv, almost all precise groups I have found do indeed have excellent SDiv, thus the comment.  The point is when I see tight side dispersion groups with tight SDiv, I think it is worthwhile exploring.  In the end, load development is always an experiment and one follow one’s ideas and theories.  I don’t think your evidence is strong enough for me to not worth testing.  Nothing in reloading is guaranteed except if one is not willing to try stuff, one would certainly fail.

I do not think velocity difference has anything to do with my vertical stringing – the distance is too short for it to have any significant effect.  I think velocity consistency is a reflection of the fact that the rounds are being fired at or close to an accuracy node where the barrels are at rest (vs. vibrating which produces what we called a scattered node)

FWIW, I do think rifles and handguns are the same, the only difference is the length of the barrel.  There is no rational reason I can come up with to say they are different.  Different in how we shoot them certainly but not the physics which affect their precision.

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Post by S148 Thu Jun 27, 2019 5:51 pm

Were all those groups with the same load? Or were there 6 different loads?

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Post by jlow Thu Jun 27, 2019 8:46 pm

As per the OP "So five charges were tested with the same bullet/primer/same headstamp brass.  Powder increment was 0.1 grain between groups.  Brass was all trimmed to uniform length and tapered crimp applied."

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Post by S148 Thu Jun 27, 2019 8:58 pm

Sorry I missed that. 

Any information on the gun, gunpowder, charge weight, group size measurements?

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Post by willnewton Fri Jun 28, 2019 5:23 am

When you say a tactical pistol, do you mean one with a plastic frame?  What is the pistol?  Plastic frames can be harder to mount properly in the rest.

Also, a torque wrench helps get even tension on the grips.

Mounting system looks fine.

As for diagnosing your groups, not much to say.  It looks like what you would expect from a 9mm tactical pistol, which is 5-6” groups that are not all that consistent.  I didn't have to see a million shot group to decipher that from your targets.

A high level accurized pistol can tell you a lot with just five shots.

5-shots on a dinner plate will look randomly dispersed and inconsistent.  5- shots on a $0.50 piece will look tight and beautiful, no matter how randomly they are dispersed in that group.  Wink
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Post by jlow Fri Jun 28, 2019 7:38 pm

Took a little time to report back as I want to run my second test.  Basically repeat the first group with the low lateral dispersion but had the vertical stringing, and low SDEV.  Ran the same charge but with different seating depth.

The gun is a SA XDm 5.25 Competition with factory barrel.  Bullet is Zero 115gr JHP, FC brass trimmed, Titegroup, and Rem 1 ½ primer.

For those who thinks the rest is not rock steady, I attached a Mitotomo digital caliper against the base the RR was attached to and with the end of the caliper against the base but attached to the baseboard.  Zero caliper prior to firing and record deflection afterwards.  There was of course deflection from the recoil but movement was between 2 to 7 thousands of an inch so basically no movement.

Fired 5 rounds to settle the rest (group 0, labelled 6, top right), and then 5 different 5 round groups with sacrifice round in between to avoid cooking the round.  Sacrifice round was fired over the target so not recorded.  Groups goes from top middle (group 1, labelled 7), to top right (group 2, labelled 8 ), then bottom left (group 3, labelled 9), and so forth.  MV was monitored with LabRadar.  Computer group evaluation done with On Target software.

Best group was group 4 with group size of 3.1” which as per before had the lowest SDEV of 11.  (COAL/ES, SDEV, MV avg, MOA for all groups are in insert).  Did not see the vertical stringing this time.  Perhaps it was because I did not lock down the elevation nut which I did this time.

Pretty happy with the results but will go back to confirm.
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Post by james r chapman Fri Jun 28, 2019 7:44 pm

if those are 115's crank up the velocity to the 1100-1150 range and report back...
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Post by jlow Fri Jun 28, 2019 8:42 pm

Did you find a good accuracy node up here?

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