Strange POI Vertical Stringing Problem

[Doc_Stihl]

I'll start out by saying, I just got back from shooting and I haven't tried anything yet. I'm going to slug the bore, cast the chamber asap.

The problem. I have a new TC Contender 10" 44 Mag bull barrel. Shooting 310gr GC Lee slugs, sized .430, cast in WW and air cooled over 20Gr of H110 lit up by a CCI LPM.

The 310's shoot great. (Snappy, but great) NO problem there, the problem is with my Trailboss plinking loads. They hit 4' high!!!

All in a nice little group, but 4' at 35 yards.
3 other 44's tonight shot point of impact within inches between the 310 magnums and the plinking loads in varying weights and styles. Plinking loads were 230gr RN and SWC-GC and 240gr Swaged hornadys. ALL the loads had little to no POI change in the revolvers, but every single plinking load hit high with the contender.

Anyone care to take a guess at the cause or reason?

[stubshaft]

Bullets loaded with Trail Boss are going out alot slower.

In my 500 S&W the differencce between my regular loads and plinking loads are about 18"@25yds. I went as far as hetting another front sight for my Encore to use for the different loads.

[oneokie]

As stubshaft said, the velocity. Boolit is in the barrel longer. Dwell time.

[lylejb]

did i read that right? 4 FEET high?

does this contender have any porting / muzzle brake? If so, maybe the lower gas volume of the light loads isn't working evenly with the ports??

just a thought.

LB

[Linstrum]

The answer very likely lies where stubshaft and oneokie said - dwell time. That is a good observation! So is lylejb's point about porting, that could be something to consider if a gun has porting.

To enlarge a bit on what they are getting at, most guns are built so that they are held onto below the center line of the barrel bore. The farther below the center line, the greater the leverage factor is and the tendancy for the gun to pivot around the point where the gun is held onto. Accelerating a projectile follows the particular one of Newton's Laws of Motion that states: "For every action there is an equal and opposite reaction". As we already know, a very heavy projectile getting accelerated will cause the muzzle to climb more than a light projectile. Also, the greater the rate of acceleration, the more the reaction and hence the greater the muzzle climb.

Another factor in muzzle climb not often mentioned is the burn rate of the powder. When the powder initially burns slowly and then picks up in burn rate just as the projectile nears the muzzle it will cause the muzzle to climb more than when the powder burns quickly at first and then drops off as the projectile nears the muzzle. The reason why the muzzle climb is greater with powders that increase in burn rate when the projectile nears the muzzle is from the leverage factor created by projectile acceleration being greater the farther away the acceleration takes place from the point where the gun is held onto.

And then there is another factor often overlooked, which is that the mass of the powder charge is a significant factor in recoil "kick" and muzzle climb, although for pistols with a comparatively small powder charge the recoil and muzzle climb are not as pronounced as a magnum rifle with ~ 75 grains of powder pushing a 300 grain projectile.

I hope this helps shed some light on the rather mysterious goings-on, I find it a bit bizarre myself! Jeez! FOUR FEET? I have a 9mm Walther P1 that is just as bad, though, so you are not alone!


rl563

[Doc_Stihl]

did i read that right? 4 FEET high?

does this contender have any porting / muzzle brake? If so, maybe the lower gas volume of the light loads isn't working evenly with the ports??

just a thought.

LB

No porting or break. It's a bull barrel. 10" Blue.

I cleaned it up real well this morning. I'm going to cast the chamber and slug the bore at lunch. I suspect that it might be a throat issue. The 310Gr WFN lee were crimped in the 1st groove, making them substantially longer.


As far as the velocity, My puma 92, 2 different redhawks and a blackhawk ALL with different barrel lengths shot at the same POI.
I think it's more than velocity and dwell. (Opinion based on ignorance and guessing :-D )

[Blackhawk]

Doc - I thought that contender was 12"... My 10.5" blackhawk shot the plinkers into nearly the same hole as the hot 310's. Nearly the same barrel length as his contender, but feet off on POI only with the plinkers.

[Doc_Stihl]

I cast the chamber at lunch and the throat looks mighty long to me. I'm going to put the casting on an optical comparator to meaure it. (unless anyone else has a method)

Completely forgot to measure the barrel, but I think it is 12". I'll slug it tonight and see what that shows.

I think the real test will come when I load up some 310 Plink (Trail Boss) loads at the far crimp and see what that gets me.

[lylejb]

do you have access to a ransom rest? Or can you sandbag the pistol to eliminate as much movement as possible? my thought is: if possible to eliminate movement for testing, fire both types of load, and recheck the POI's. this would greatly reduce or eliminate the dwell time / gun movement.

if the rounds then group close, you know it IS the pistol / dwell time / gun's reaction under recoil.

If, however, the rounds still group feet apart, then it is NOT a dwell / movement issue, and your correct to investigate throat / chamber.

bottom line: need to check if this happening because of INTERNAL concerns , or external forces.

LB

[stubshaft]

If the problem was attributed to the chamber/throat he would/should not be getting groups of around 3". The only problem as I see it is that the position of the groups is in question.

[Linstrum]

Ignorance and guessing = intuition! :drinks:


rl565

[Doc_Stihl]

A dozen 310Gr loads seated to the long crimp over trail boss and a dozen move over unique with the same results, about 4 feet high.

And after those were shot, another string of H110 hot loads still hit point of aim.

I'm going to run some jacketed stuff through it and see how those print.

[oneokie]

If you have access to a chronograph, check the speed of the different loads. My WAG is that there is a very substantial difference in speed. Back to the dwell time.

[Doc_Stihl]

There is definetly a substantial difference in speed. The H110's are in the 1250FPS range. The TrailBoss plinking loads are in the 800FPS range.

As an added note, it appears that I have some fouling/leading at the muzzle.(Just forward of throat looks clean) Just the last inch or so looks like I have some build up. The barrel was scrubbed well before this last test. And I shot around 20 rounds. I'll clean it up and see what it is.

[oneokie]

There is definetly a substantial difference in speed. The H110's are in the 1250FPS range. The TrailBoss plinking loads are in the 800FPS range.

Depending on how one does the math, and I am not a math whiz, the plinker load boolit is taking from 36% to 56% longer to exit the muzzle.


As an added note, it appears that I have some fouling/leading at the muzzle.(Just forward of throat looks clean)

Sounds like a lube problem. My 2 ¢


Just the last inch or so looks like I have some build up. The barrel was scrubbed well before this last test. And I shot around 20 rounds. I'll clean it up and see what it is.

[Doc_Stihl]

I'm lubing up a selection of bullets with LLA and giving it another go.

[NHlever]

I would agree with most of what has been said above including the OP's observations. I would also look closely at how the gun is being rested during the tests. Sometimes things like resting the butt on the sandbags, etc. can make quite a difference. I've gotten several inches of difference between the 300 gr loads, and 250 gr loads in both the .45 Colt, and the .44 Mag, but haven't seen 4' luckily!

[badgeredd]

There is definetly a substantial difference in speed. The H110's are in the 1250FPS range. The TrailBoss plinking loads are in the 800FPS range.

As an added note, it appears that I have some fouling/leading at the muzzle.(Just forward of throat looks clean) Just the last inch or so looks like I have some build up. The barrel was scrubbed well before this last test. And I shot around 20 rounds. I'll clean it up and see what it is.

My opinion is that your dwell time is the biggest cause of the change in POI.

You definitely have a lube problem, assuming your fit is good. If you can't lube using a sizer/luber, you might want to try a more substantial lube using a pan lube method. Personally, I haven't had much good luck with LLA beyond use for plinking loads in short barreled guns, which could be just me. I prefer a lube with some substance to it so it doesn't run out before it exits the barrel.

Edd

[Doc_Stihl]

Ive rested on a bench resting on the barrel and the frame, the barrel alone, the frame alone, free hand, and supported wrists, no real change.

I was using Carnuba on everything. My thinking is my plinking loads aren't making enough speed to get the lube viscous and working.

I have had great luck with LLA for use in plinking loads in short barreled guns, that's why I'm going to try it with this one.

If the LLA shows any sort of promise to fixing the POI, I'll pan lube up some with lyman moly, or maybe get a couple sticks of something dedicated to slow speed.

[cajun shooter]

Try BAC on a few rounds and see what you get. I would also give speed green a trial. It's counter part NASA is the best BP lube I've tried.

[Linstrum]

Hi, Doc_Stihl,

Leading can definitely take the fun out of shooting!

Lee Liquid Alox is darned good stuff, and so are several others that are sold commercially or ho'made from recipes (like Felix's World Famous Lube recipe). I have used several of them and have no complaints with the ones I've tried, but stick to using two in particular because of their availability and ease of use.

For my Lee 500-grain x 0.515" boolits that I use for .50 BMG "plinker" loads cast from wheel weights and do not have gas checks, I use either Lee Liquid Alox or Johnson's paste wax (which is mainly carnauba wax and Stoddard solvent/kerosene). After sufficient time to let them dry, I have not had any leading problems at ~ 1500 feet per second in a 30-inch barrel.

Let us know what you find that works best for your particular situation.


rl571

[Doc_Stihl]

DWELL seems to be the culprit.

I shot a variety of rounds from a rest. When the forend is held down, impact is on target. When allowed to recoil (even though it's almost nonexistant) the rounds hit high. And the muzzle velocity dictates the POI up until about 1200fps and then they all seem to hit the same pie plate.

Very disapointing. I had hopes of making this a light plinker/trail boss shooter.

FWIW, I picked up a 357 that behaves in the SAME manner. POI is about 2.5' high with a 38WC vs a 357mag 158gc at speed.

I'm going to try a set of "very light" crimps and also going to play with mag primers and upping the tb load to max before I give up.