Decreasing velocities

[Confederate rifleman]

Here's a wierd one. took my Chrono to the range to see what weighed T7 charges( 2f)were giving me in my Black Diamond XR .50 cal. The load was CCI musket caps on a single vent Ampco nipple a 250 gr .45 Hornady XTP in Harvester crush rib sabots.The weighed charges were 45 and 50 grains. The first up was the 45 gr load. Group size was 2 5/16 for 3 at 100 velocities were shot 1521, 1528 ,1562 fps. Group2 ,50 gr 2 3/16" velocities 1669 ,1617 ,1533 fps Group3 3 15/16" velocities 1523,1583,1517 fpsThese are the 50 grain charges! Group 4 45 gr 2" group , 1548,1490,1521 fps.Interesting that by the 5th shot velocity takes a dive.The barrel is swabbed between each shot thoroughy too. I'm going to try a flamethrower nipple to see if the effect is repeated. Point of impact is not effected by the change. The shot to shot variation is also larger than I like. Group 1 41 fps ,2 63 fps 3 136 fps and 4 66 fps. I am careful not to have the patch saturated to the point where it dampens the breech and effects the powder.I also thoroughly dry the bore as well.These loads are alittle larger , and in the case of 3 , significantly larger than this rifle usually gives. I'm confused as to why this is happening. Anyone else out there see this effect? I got into the habit , when I chrono loads , of shooting every round I brought with me. Glad I did! Any ideas?

 

[Okie Hog]

It could be due to inconsistent seating of the sabot/bullet on the powder. Some TC guns like a tight fitting sabot that is seated hard on the powder. My Encore does not like the crush rib sabots at all.

 

[cayuga]

While we swab after each shot, we don't really clean them. I am sure there is some fouling building up. But why that makes the velocities change.. who knows. I don't have a chronograph, but I do have a black diamond..

 

[Confederate rifleman]

seat and swab

My Black Diamond XR is rather tight. Bore .499 groove .511 to be exact and crush ribs are pretty hard to ram. I swab until the patches come clean. Its kinda interesting though. Maybe its the buildup of klinker in the recess of the breechplug. One thing that also gives concern is that I can clean her completely and then patch her with Hoppes and get nothing on a patch.But if I scrub her with a bore brush after a cleaning the patches are black as night. This makes me think that perhaps T7 doesn't completely clean out with water. I JB the bore every couple hundred rounds, this barrel has 508 through it, so no gremlins start making a mess.Perhaps its plastic fouling ,but I doubt it as I've never seen any in this barrel and ramming, though tight, is quite smooth. One of the really challenging and fun aspects of frontstuffers is that there is always more to learn. More to figure out, you never stop learning...

 

[Lee 9]

How old is the powder? Have you ever had it out when the humidity was real high or it was raining?

 

[cayuga]

I do believe a brass bore brush and a solvent will bring those black tracks because of a chemical reaction. I can not prove it. But I have rifles that are clean and if I brush them, I get black on the patch...

 

[CarlV]

Any ideas?

Yes. Your gun and loads are shooting just dandy for such a light load. That amount of disparity in velocity between shots is really pretty good. The bench rest guys don't even pay attention to what you show until they get WAY out there.

It surely sounds as if you know what you're doing with a ML so I'm thinking your loading technique is fine.

Maybe try upping the load to somewhere around 100 grains where the powder (2F) can get some real pressure behind it might make it burn more consistantly?

 

[Confederate rifleman]

Reactions

I thought about some reaction to the bore brush as a source of the black on the patches ,but, I get the same black stuff on patches when I use JB paste or Iosso bore paste so its still a mystery. I'm afraid 100 grain charges are not an option for me. 5 years ago I got rear ended and one of the lingering effects is I am rather sensative to recoil. The powder is about a year old and is kept in its original container. I've actually found T7 to remain pretty consistent over time.I used to make paper cartridges for field loads and recently fired some that were 5 years old and they shot fine and were right on for velocity. At this point , the variations are more of a curiosity than a problem. This rifle has done everything I've asked of it (and then some). I will report if the switch back to the flamethrower nipple has any effect. With the single port nipple being very short compared to a flamethrower, it leaves a tunnel in the breechplug for the powder to fill before it hits the face of the nipple. Perhaps the powder doesn't fill it evenly and effects the load density.The flame thrower nipple fills the area right up to the bottom of the plug recess. granted the difference between the loads is probably in the range that you'd get from one box of ammo to another, its just odd. I like shooting loads that are in the big bore magnum handgun range as they are ( usually) quite accurate and extremely effective on deer without being expensive,loud or hard kicking.A really nice thing is that even at short range you can hear the bullet strike.When that smoke cloud blocks your vision, that crack ,splat, plop or thump lets you know you connected and ,generally,where.Its a nice little plus...

 

[cayuga]

JB Bore paste always brings up a black patch. I think that has an oxidation quality to the metal to really bring out all the nasty stuff in the bore. I use that stuff as well about every three months.

 

[Confederate rifleman]

flamethrowers

Went out with the flamethrower nipple and got a surprise.The velocities remained more consistent compared to the single port Ampco, BUT,I lost 100fps with the same load.I really shouldn't be surprised due to the 3 vents in the flamethrower and the amount of blowback it creates.100 fps does seem alittle much though.I havent measured them , but the flamethrower holes are significantly larger than typically seen in a single port nipple, even when new.Accuracy was very good so that isn't a problem.One thing about single vs. flamethrowers is the flamethrowers leave the cap on the nipple while the conventional nipple has the cap sticking in the striker face.Also, I tried field type swabing and found for each shot after the initial one velocities crept up. A thorough cleaning and the cycle repeats.1st round is always the slowest.Thoroughly cleaning between shots gives very good consistency.I think I am on to something regarding the fouling that builds up in the breech plug channel when using a conventional nipple.I think I'll try popping a cap between groups to blow out the fouling and see if I get any improvement in consistency past 10 shots. This is fun! Thanks for indulging me!