Time between strings on randsom rest

I already load an extra sacrifice round that sits in the chamber and is fired over the target before testing each group.  That way I do not have to touch the gun i.e. rack the slide but only change magazines.

My question is assuming you are testing multiple groups of 5 or 10 rounds, do you allow the barrel to cool between shooting groups and how long do you wait?

The reason I ask is I am trying to figure out if a hot barrel will affect groups size and shape.

I'm not a ransom rest expert or anything. I just test my guns the way they would be shot in a match. 5 rounds in each magazine that I would be using. I don't disregard a 1st round flyer. Honestly, I don't use the "random rest" that much. Mainly I'll test off sandbags, and if I can call the shots within an inch or so, the gun or the load is good enough.

The point is not to make an artificial condition which does not relate to matches.  The point is to create a controlled condition to properly evaluate loads.  They are two separate different things, both important but should be evaluated independently.

I set a glass of water next to the  rest. When the water completely settles I fire again.

I understand you do this and it is for the vibrations.  I can tell you that using a set of electronic accelerometers, the vibrations in my setup is gone faster than I can follow.

The point of my question is not vibration, but heat in the barrel i.e. how much does a hot barrel affect group size and shape.

Hot barrel doesn't do squat in a 1911. Rifle boys are concerned, pistol shooters should have no concern. I used to RR a lot back in the day.....it doesn't matter.
Jon

I can understand your desire to know the effect of barrel  heat on group size and shape, for its own sake.  However, I am sorry to say I am trying to understand how this might be actionable to our sport of Bullseye shooting. We get 10 or 20 seconds for a five shot string, and we get to wait between strings only for as long as the tower talker allows.  How will you use the info you generate?

The possibility of the first shot impact differing from the remaining four is also an interesting one, but again, if there is a problem, how can it be addressed?  The command "...with five rounds, load..." is pretty specific.  Nor do we get to "burn" a first shot before we shoot a string, whether slow or sustained, and I don't hold off on the first shot to compensate for any differences - perhaps others do.

Please understand I am looking forward to your results and encourage your testing efforts, but I also am trying to understand how the results you might generate can be used to increase our scores.

Good luck to you, and I look forward to your results.

First of all, I am not a bullseye shooter.  My background is a research scientist and as such, I was taught that when testing, you test if possible one parameter at a time - this is what I was doing.  Testing under conditions where more than one variable could affect your results means that you never know what is responsible for what you see and thus impossible to address and modify.

My goal was never to find a load that I could shoot bullseye but to test the inherent precision of my barrel.

Get a barrel tester and have at it! RR will never give a research scientist data worth having. We BE shooters commonly refer to RR as Random Rest.
Jon

For a measly price of $2,855.00 I can get one as Sams Custom Gunworks - going for it right now - right...

Get real folks, this is a hobby not work....

jlow wrote:For a measly price of $2,855.00 I can get one as Sams Custom Gunworks - going for it right now - right...

Get real folks, this is a hobby not work....

If you are already using accelerometers for your testing what's a few more measly kilobucks  ?

The accelerometers are on a MantisX which sits on the pic rail of my gun.  It cost about $160 and I use it normally for training.

https://mantisx.com/products/mantisx

Thanks for the info - looks like an interesting training device.   Since you've written previously of seeking/finding nodes for your barrels and your precision rifle background, I was assuming you were using equipment capable of micrometer and microsecond resolution that one might find only in a research lab.  That technology applied to barrels would be of interest to a lot of benchrest shooters.

The MantisX is not a toy and is fully capable of measuring movement in micrometers and time in milliseconds (not microseconds).

jlow wrote:My goal was never to find a load that I could shoot bullseye but to test the inherent precision of my barrel.

The ONLY way to do that is with a barrel tester, as soon as you add the gun WAY too many variables enter into play.  I don't want to even get into ammo variation.  Send the barrel out for testing with several different loads.  If you put a verified 1" barrel in a poorly built gun you will have a 3" gun or worse that could on a rare occasion shoot a 1.5" group.  Put that same barrel in a well built gun and you have a gun that consistently shoots <1.5" with an occasional near 1" group. 
===================
Ransom Rest
I used a Ransom rest for some time and got very consistent results from session to session.  It took a lot of work to do so.  I never wasted a first shot, never waited for a barrel to cool down even after 10 mags.  I always tested a known load at the start and end of testing to make sure the set up was good. Now I test new loads shooting from sandbags using a 1-4X scope.  It took a while to develop my technique and I knew I was there when my results were approaching 90% of my RR results.

When I start going down the testing rabbit hole,  I try to remember what a High Master told me, this a sport where lubed rocks will hold the 10 ring at 25 yards.
- Dave

When I first started RR testing I weighed & measured all my cases and trickle dropped the charges same as I did when testing rifle. - what a waste of time!!

I think it is correct that the most clear way to test a barrel is to test it by itself – that makes sense.  However, a firearm is a system and in any system, its effectiveness is only as good as its weakest point.  I could test the barrel but even if it is a “one holer”, what good would that do me if the gun as a system will not shoot?  I guess one could eliminate each part of the gun one at a time until the culprit is found, but that really is not something that your regular shooter can do as we cannot always find or construct replacements.  This is why it is reasonable to evaluate the gun and not just the barrel.

Thank you for your feedback on the RR.  I think running an evaluation group at the start and at the end is a good idea.  Scopes are great and was the way I did load development for my PCC, but my pistol is not set up for scopes.  This whole thing of course is an adventure for me and I am enjoying the learnings.

I was interested in the technology of barrel testers and so was looking at what Sams Custom Gunworks LLC had to offer.

I came away with some concerns.  If you look at this photo of the tester, the barrel is clamped tight in their jig using their custom inserts for specific barrels.  The way the barrel is held of course helps to prevent movement but is unfortunately very artificial compared to how it is held in the firearm.

The reason this is important is because anytime something touches a barrel, it affects the harmonics and precision of the barrel.  This is the whole reason why rifle barrels are best free floated i.e. not touching anything.

Would the way the barrel tester hold the barrel affect precision?  Very likely.  Would the results translates to what one would see in the firearm, not likely.

Personally, I believe that you have completely overlooked the differences between an auto-loading polymer pistol and a precision rifle.


https://www.youtube.com/watch?v=7Fr5ccyriJI

I am of course fully aware of the difference and the fact that an auto-loading polymer pistol is not a rifle, but the fact is still clamping a barrel down tight and not letting it free float is very different than it's normal function and can affect precision.  Are you 100% sure that it won't?

Greetings,

Interesting comment about "harmonics".

Back in the late '70's we built our first barrel tester.

It held the barrel by the breech and the muzzle was 'free floating'.

With match ammo, the groups were dismal.

An Engineer friend suggested putting a support at the muzzle end.

This worked wonders.

X-ring groups were now produced.

We discovered that the groups fired via the 'barrel tester' and compared to groups fired via the 'Random Rest' were about 1/2" larger with a fresh build 1911 at 50 yards. The 1/2" we attributed to tolerance buildup within the pistol build.

Today, I still use the muzzle support on the tester I built.

My test results repeat.

Ballistics is a subject that is not well discussed. The closest I came to any scientific results is when I machined a barrel for an FBI Special Agent. He had access to the FBI Ballistic lab and he almost got them to test the 32 ACP for us.

Still, barrel testing keeps me out of the bars and well amused in my old age.

Cheers,

Dave

having built quite a few rifles for myself and family, free floating "most" rifle barrels works fine.. the exception are the thin lightweight barrels such as you find on the Remington 700 mountain rifles.. everyone I ever owned wouldn't shoot for anything with a free floated barrel. Always had to put a pressure point on the end of the forestock..   Think how thin our pistol barrels are.. What Dave described  happening to a tester with no barrel support makes perfect sense..

There is another barrel tester out there that does not support the barrel.. wouldn't own it.

An exception is the Model 70 extreme weather stainless in .270 WSM. At 100 yds with factory Win ammo, that little spaghetti-noodle barrel would cloverleaf 5 shots off of a cheap rifle rest. I could not believe it. I guess the node was right where it should be (perhaps Winchester's design?). I had a muzzle brake custom fitted (my Dad's rifle...wanting a little less recoil) and as expected the groups opened up a bit, but still no problem putting them into a 1" circle at 200 yds. Nice flat shooter out to 400 yds. 

I also started RR testing this past Spring, getting into this new pistol hobby. I tested my 1911, clamped via its frame, and a Sig P210 (clamped via the wood grips). I came to the conclusion that the RR suffers in two respects. First, the pivot friction material varies in static (breakaway) friction. When I tested on cool dry days, I noticed variation in pivot resistance torque vs. on hot humid days. Even though the pivot stop (the adjustable thumb screw) contact is steel-on-steel, this sets up the possibility that with a static torque in the pivot that can vary from shot to shot, you can experience a varying "bouncing" effect since steel-on-steel has a relatively high coefficient of restitution. So I just focused on reducing side-to-side variation at 50 yds and accepted a certain amount of vertical stringing. Some day I might experiment...I would replace the friction material with an (unlubricated) ball or roller thrust bearing, and use a static weight to resist rotation after ignition, suspended below the bench. A simple air cylinder damper would then cushion return to battery and follow-up shots. Second, the panels do flex somewhat, so clamping method really matters, particularly with wood grips in place. Overtightening is a problem. I'm happy with the results I got, and will likely experiment some more this Fall.

Regarding the OP and a hot barrel, I guess heat could increase the diameter and length. It could bend the barrel if it had a residual stress after machining. Length (0.00X") and diameter (0.000X") changes would be immaterial, IMHO. Bending would decrease accuracy, but it would be hard to quantify. It seems to me that a "bad" barrel would have internal flaws from the machining/finishing processes, perhaps also due to material flaws. A borescope could pick that up, but rifle guys have used a borescope and seen absolute crap inside a barrel that still held 1/2 MOA at 600 yards.

First thing is I want to thank people for writing and sharing their learnings.  I have an advanced degree in science and have worked in the research area for many years until my retirement.  What that means is I know a lot about something but nothing about a lot of other stuff – Bullseye shooting being one.  I do ask a lot of questions, but I only do this because I know it is an effective way to learn.  Of course, being a novice, some of my assumptions are inevitably incorrect but that is OK because I also inevitably learn something new as I am CLEARLY learning here.

Jon Eulette - As stated previously, I am not in the “BE game”, but why does my question “mean nothing at all in the BE game”?  If you are talking about my polymer-based pistol – I would agree, but if you are talking about striving to evaluation precision with a RR – I disagree.

As stated, I have concern as it relates to the barrel tester, Dave’s input (thank you for your input as the builder!) tells me that the same concerns also occur to you, but I do understand that supporting the muzzel end paradoxically made it work better.  In science, we understand that sometimes theories works, but other times it does not.  The reason is simple – we do not have full grasp of all the variables which sometimes is not possible.  However, results from testing like this gives us useful answers.  We call this the empirical approach – it is also very effective.  Great job Dave!

Jglenn21 – I think the problem with thin lightweight barrels is by virtue of their thin nature, it bends when it gets hot and so the pressure point helps support it.  It is a workable solution even though it is not an ideal solution.  I don’t think this relates to pistol barrels as they are very short so much stiffer and so bending is not likely an issue.  But there are sometimes rare anomalies like trovaert’s example that we cannot explain – all that means is we do not have a total grasp of all the variables.

Trovaert – some interesting observations from your RR testing!  I wonder if that is what was responsible for my vertical stringing?  Please tell me if you find a fix!  Appreciate you input on the hot barrel.  Your insight as to what it may do is why I pose my question initially.

To continue to ask questions, what exactly is the correct way to clamp a pistol with a ransoms rest?  I understand that the pressure should be equal and so one tighten the screws a little with each of them at a time.  Certainly, as tight as possible without affecting function which in my case mean the magazine will be released normally.  Other than that, what else can someone do?

I did say I want to “test the inherent precision of my barrel”, what I meant is to test the inherent precision of my handgun.  Yes, I understand that most folks here thinks that it is impossible for a polymer gun to shoot as well as a precision crafted handgun, and you are most probably correct, but there could of course be exceptions.  Here is a specific case posted on this board where a shooter was able to obtain 10 shot groups with a polymer pistiol with under the 1.5” groups mentioned as accepted precision for a HM pistol.

https://www.bullseyeforum.net/t11883-cz-p-09-ransom-rest-results?highlight=ransome+rest

So yes it can be done, can it be done with all polymer pistols, not likely.  Can it be done with mine, don’t know.  But I won’t know until I look.

On free floating barrels (from my basic understanding):
Harmonics might be a thing for long rifle barrels, but even if it applies to pistol barrels they need to be tested as they are in the pistol.
A 1911 and all Browning short action recoil support the barrel at the muzzle. A testing jig should eliminate all possible variables. Not add an unsupported muzzle and the questions of how the supported lock up changes things.
So if testing a barrel for a short action recoil, the muzzle bets supported. If it's a barrel from a fixed barrel such as a Korth you secure it only at the chamber end or you add the compensator and support it solidly at both ends.
Avoiding adding new variables is one of the issues I've had in understanding the value of using a RR. It doesn't hold the pistol still and seems to have so many variables of it's own that aren't necessarily equivalent to actually shooting the pistol unsupported and many variables that aren't measurable to guarantee repeat-ability.